|Appropriate Technology for Sewage Pollution Control in the Wider Caribbean Region|
|Caribbean Environment Programme Technical Report #40 1998||All CEP Technical Reports|
Papers, textbooks, manuals, and handbooks that contributed to sections of this report are summarised below. Some of the texts and articles cited address issues in parts of the world other than the WCR, but they are included for their usefulness in explaining technologies or procedures. The structure of this literature review follows the section outline of the report. Abstracts on some of the works discussed in this section are provided in Appendix C.
BACKGROUND ON SEWAGE POLLUTION IN THE WCR
A key source of current information on sewage pollution issues for the Caribbean region is the series of conference proceedings published since 1992 by the Caribbean Water and Wastewater Association (CWWA). The proceedings provide a convenient handbook of papers of current topical interest. Included in the 1994 proceedings, for example, were a number of papers of interest to the reader of this report. "Near Zero Discharge Systems : As Low Cost, Advance Technology For Caribbean Water And Wastewater" by Donald Bullock (Bullock 1994) presents a concept for on-site systems including "underwater reversing sand filters" for sink and washing drainage followed by aeration and reverse osmosis. The intended use of this system is to treat household grey water for return to potable use. A separate, smaller system would be used for toilet water to prepare it for soil absorption or discharge to a receiving water. "Coral Reefs, Sewage and Water Quality Standards " by Thomas J. Goreau (Goreau 1994) presents summary data on the damage done to coral reefs by eutrophication of the coastal zone, soil erosion, high temperatures, sport divers, and overfishing. The author reports from a perspective of 35 years of study of the ecology of coral reefs in Jamaica. The author finds that eutrophication (excess nutrient fertilisation) of coastal waters has caused a dramatic withdrawal of coral reefs. Reefs which formally had more than 95 percent live coral are now more than 95 percent covered by algae. The author reports that rising nitrate and phosphate concentrations in the coastal waters have had a direct effect in this conversion to a less desirable ecology. "Impacts of Wastewater on Caribbean Coastal and Marine Areas" by Arthur B. Archer (Archer, A. B. 1994) presents an overview of sewage pollution problems faced by the Caribbean region including algae deposition on sea-grass beds, coral reef damage, and reduction in fisheries. The potential for amelioration of these problems by nutrient removal from sewage effluent and installation of long marine outfalls is discussed. "Sandfiltration Treatment of Domestic Wastewater A Viable Option in Complex Areas" by Desmond Munroe (Monroe 1994) presents a discussion of potential solutions to the pressing problem of nitrate contamination of ground water supplies by septic tank effluent. A series of alternatives are considered including:
Intermittent sand filters
Total retention, and
Overland flow system
The author presents background examples from Jamaica where pollution of groundwater by latrines and septic tanks connected to leach fields or percolation/absorption pits has led to serious public. Three articles discussed numerical modelling, environmental condition, and water quality modelling for Kingston Harbour in Jamaica (Gay and Burgess 1994, Hamman 1994, Tarbotton 1994.) Several articles (Chaulk, et al. 1994, Suite 1994, Pemberton 1994, and Hunter 1994) discuss management issues directly pertinent to building wastewater utility infrastructure in the region. Several others present strategies for design of wastewater treatment lagoons (McTaggart and Barnard 1994, Marococchio 1994, and Pearson 1994.)
"Wastewater Disposal in the Caribbean: Status and Strategies" (Archer, A. 1989) and "Developing Alternative Approaches to Urban Wastewater Disposal in Latin America and the Caribbean" (Bartone 1984) are good overviews to wastewater disposal in the Caribbean. The authors mention such possible waste treatment technologies in the WCR as submarine outfalls with minimal pre-treatment, treated effluent reuse for irrigation and other "unconventional" technologies for urban slum sanitation. They also mention current problems in setting water quality standards. Too often, the regulatory agencies in Latin America and the Caribbean attempt to define a set standard based on water usage or classification. This approach has not worked well because of its inflexibility, its failure to correlate water quality with discharges, and its disregard of economic issues.
Regional Overview of Land-Based Sources of Pollution in the Wider Caribbean Region (UNEP 1994) provides an overview of the volume and types of pollution generated in various regions of the Caribbean. The report identifies sewage as one of the major pollution sources. Waste loads from each region in the WCR are provided, along with a breakdown of existing sewage plants and the industries that are predominant in the different regions.
The Report on a Rapid Assessment of Liquid Effluents from Land Based Sources in Trinidad and Tobago (Institute of Marine Affairs 1992) is a detailed survey of pollutant loads and sources in Trinidad and Tobagos coastal waters. The report identifies oil refineries, livestock farms, food and chemical processing industries, and domestic sewage as the main BOD sources in coastal waters.
"History and Application of Microbiological Water Quality Standards in the Marine Environment" (UNEP 1994) provides a history of the development of water quality standards in the United States and the effect of this development on water quality standards in other countries. Water quality guidelines for the United States and a few Central American countries are listed. The author points out that most WCR countries with national water quality standards adopted them from U.S. standards, with minimal consideration given to the economic situation and priorities of the adopting country. The author feels that planners must "conduct a thorough review of the prevailing local water quality guidelines/standards (if any exist) to ensure that local economic development priorities are reasonably accounted for." Also, "the decision to design the system for other than minimum water quality standards should be supported by demonstrated need, or a state local/national policy decision." The author also introduces the controversy of whether swimming in water that is moderately contaminated with coliforms is a public health issue or one of aesthetics. Studies correlating sickness upon contact with water to quality of the water (in terms of coliform count) are reviewed.
"Review on the Present State of Marine Pollution by Sewage and Present Monitoring and Control Practices in the Wider Caribbean" (CEPPOL 1991) is a draft report written for an April 1991 CEPPOL Seminar in Kingston, Jamaica. The report was meant to be amended after the meeting, and may have some incorrect information. However, it is an excellent review on existing wastewater treatment practices used in different countries in the region. The overwhelming trend is that most of the Caribbean is not served by wastewater collection systems with centralised treatment. For example, in the Eastern Caribbean and the Bahamas, approximately 40 percent of the population is using pit privies, 40 percent is using septic tanks, 11 percent use connected disposal systems with centralised treatment, and 9 percent have no waste disposal facilities at all. In the WCR, many of the existing collection systems and treatment facilities are in poor repair. This review includes current monitoring programs for different countries.
ENVIRONMENTAL PLANNING AND MANAGEMENT
The, Appropriate Sanitation Alternatives (Kalbermatten, J.M. 1982; World Bank Studies in Water Supply and Sanitation No. 1) is a comprehensive paper on the steps and questions a planner in a developing country needs to address to improve sanitation associated with excreta disposal. It includes information on technology options. The authors argue that developing countries are better served by being provided with lists of inappropriate technology they should avoid than by being told that a single, particular technology is most suitable. Site-specific conditions, social and economic considerations, and local preference are difficult to account for in selecting "appropriate" or "correct" technology for developing nations.
Management of Industrial Wastewater (High Institute of Public Health 1981) is a compilation of the Proceedings of the 1981 International Symposium in Alexandria, Egypt. It includes case studies and papers on planning, management and control of industrial pollution, as well as on specific treatment technologies. The case studies are not very current, but the book serves as a good reference for some of the treatment technologies available to the industrial wastewater industry.
"Industrial Pollution Control in Developing Nations" (Miller, J.P 1981) discusses the conflict of encouraging economic growth in a developing country, while at the same time imposing environmental restrictions that discourage industrial development. However, "experience shows that reasonably effective pollution control facilities cost from one to five percent of the installed capital cost of a new industry. Clean up programs needed in the future to clean up industrially polluted areas, however, can cost a hundred or even a thousand times as much as the original industrial development." Other topics such as funding, governmental involvement, and subsidies for pollution prevention are also discussed.
Planning for Small Community Wastewater Treatment Systems (U.S. State Department et al. 1994), sponsored by the U.S. EPA, is taken from "The Middle East Peace Process Multilateral Working Groups on Environment and Water Resources" which was held in Cairo, Egypt in June 1994. This document touches on planning, management, water reuse, collection and treatment technologies, and information resources available in the Middle East and United States.
The manual Wastewater Treatment/Disposal for Small Communities (U.S. EPA 1992) includes a chapter on planning, and management, yet is not an appropriate source for planning in the Wider Caribbean Region. This manual assumes that the user will be planning in the well-defined regulatory framework of the United States.
Guidelines for Improving Wastewater and Solid Waste Management (Andrews, R.N. 1993) was written with developing countries in mind. Many industrialised countries manage waste through advanced technology and stringent regulatory requirements. However, some developing countries do not have institutions or regulatory agencies strong enough to enforce stringent requirements or the resources to pay for advanced technology. This manual offers guidance in determining the best technologies, policy instruments, and institutions for a particular country or community.
The following EPA manuals also discuss planning of treatment facilities or processes:
Alternative Wastewater Collection Systems (U.S. EPA 1991)
Municipal Wastewater Stabilisation Ponds (U.S. EPA 1983)
Onsite Wastewater Treatment and Disposal Systems (U.S. EPA 1980)
Rapid Infiltration and Overland Flow (U.S. EPA 1984)
Sludge Treatment and Disposal (U.S. EPA 1979)
"Planning Replicable Small Flow Wastewater Treatment Facilities in Developing Nations", (Gaber, A. 1993) describes the steps required to plan for a small community treatment plant in a developing nation. The author indicates that two responses have historically been given to the question, "How can wastewater development best occur in the complex environment of a developing country?" One response has been that innovative external technology and components can always solve wastewater problems. The other is that technology is useless unless the local system can adequately sustain the required infrastructure. This paper focuses on the latter response.
"Evaluation of Innovative Wastewater Treatment Technology" (Qasim, S.R. 1993), "How Appropriate are Appropriate Waste Management Technologies" (Bhamidimarri, R. 1996), and "Appropriate Wastewater Treatment Technology for Small Communities" (Kreissl, J.F. 1996) all attempt to define the terms "innovative" and "appropriate." Most seem to agree that appropriate technology must be:
Affordable in capital cost and operation and maintenance
Operable at a reasonable cost and with locally available labour
Reliable enough to consistently meet effluent quality requirements.
"Control of Pollution in Organised Industrial Districts: A Case Study from Turkey" (Filibeli, A. 1996) discusses planning strategies in Turkey for controlling industrial wastewater pollution. In 1993 there were 100 "Organised Industrial Districts" (OIDs) in Turkey, and much growth is anticipated. The idea of the OID is to provide to industrial investors parcels with suitable infrastructure (roads, power, water supply, wastewater collection and disposal, technical consulting, communication, etc.) at a low enough cost to encourage development. Each OID has a central wastewater treatment plant. Some of the industries must pre-treat their wastewater before discharging to the central collection system. The authors emphasise waste minimisation and strategic zoning of the industrial sectors so that similar industries can be near each other and share pre-treatment facilities and costs.
"Wastewater Treatment Meets Third World Needs," (Nichols, A.B. 1987) addresses some of the sanitary and health-related needs of developing nations, as well as the World Banks financial assistance in various projects. The impact of coliform-polluted waters is discussed. According to the World Bank, "acute water shortages combined with pollution now cause 25,000 deaths a day." The Bank notes that "the appropriate reuse wastewater treatment system must be able to remove helminths, reduce bacterial and viral pathogens, and be free from odour and appearance nuisances." Also, "Latin America should not adopt a priori official policies which advocate secondary treatment, unless there appears to be clear justification." For developing countries, it is very important to determine the cost of wastewater treatment, and what degree of treatment is necessary. Bacterial and pathogen removal in wastewater has been directly correlated with health, but questions remain about the health impacts of BOD and TSS.
COLLECTION SYSTEM ALTERNATIVES
The EPA manual, Alternative Wastewater Collection Systems (U.S. EPA 1991) discusses pressure sewers, vacuum sewers, conventional gravity sewers and small diameter sewers. Potential applications are discussed for all kinds of geographical and hydrogeologic conditions, quantities of flow, economic constraints and distribution of wastewater sources. This is a comprehensive manual on collection systems.
Guidelines for Improving Wastewater and Solid Waste Management (Andrews, R.N. 1993) provides a brief list of wastewater collection systems. It also lists factors that must be considered in determining whether a collection system is needed or an on-site treatment system will be adequate. The choice is influenced by lot size, population density, topography, groundwater elevation, and soil characteristics. "On-site disposal is appropriate for low-density areas with nearly flat topography, good percolating soils, and a water table at least one meter below the surface. For households, the on-site choices are latrines or septic tanks that combine collection with treatment. Off-site treatment is appropriate in high-density areas with gently sloping topography, high water tables, clay soils or rock with poor percolation, and where space for off-site treatment and disposal is available."
Planning for Small Community Wastewater Treatment Systems (U.S. State Department et al. 1994) provides examples of "simplified sewers." The basic principles behind simplified sewers are: determining the tractive force necessary for movement of particles versus minimum velocity; reduced sewer depth; and consideration of improved materials, construction and cleaning equipment. Example layouts and plans are included
A presentation by Charles Vanderlyn on "Small Diameter Sewers" (Inter-American Development Bank 1992) at The Seminar on Appropriate and Innovative Wastewater Technologies for Latin American Countries discusses traditional collection system technologies with an emphasis on small diameter sewers. For small communities, the cost of installing a conventional gravity sewer is prohibitively large. These systems need costly, large-diameter pipes to ensure that sewage flows freely, with manholes every 100 meters or at any change of direction. By pre-treating sewage from households or small clusters with septic tanks, most of the solids can be retained, thus allowing smaller diameter pipes to be used for sewer construction. Since most of the solids are removed, there is no need to maintain minimum velocity to prevent solids build-up. Another option is to use a grinder pump instead of a septic tank, to break down any solids that could cause clogging. The author stresses that even though these systems are cost-effective in the United States, more evaluation or pilot studies need to be performed in other countries to determine their cost-effectiveness there, due to the difference in the relative cost of power and materials.
"The Feasibility Studies and Design of a Public Sewage Collection, Treatment and Outfall Scheme for the South Coast of Barbados" (Fries, H. 1992) discusses the methodology and process of designing a wastewater collection system for the southern part of the island of Barbados. Forty kilometres of sanitary sewer and 80 kilometres of service connections are to be installed, pending funding from the Inter-American Development Bank. Trenchless construction methods are being investigated due to utility line congestion. Direct and indirect social costs are expected to be high. These include:
Compensating businesses for construction disturbances
Property damage claims
Reduction of pavement life through installations
Cost in traffic diversions and delays.
"Alteration in Sewage Characteristics Upon Aging" (Kaijun, W. 1995) discusses how the performance and efficiency of a treatment system depends on the characteristics of the wastewater when it arrives at a treatment facility. The main points are that most odorous components from sewage in transport lines are from the formation of sulphate reduction products. The author maintains that the odour can be controlled by imposing aerobic conditions on the sewage. He also states that the sewer systems could contribute a lot more to pre-treatment from anaerobic microbial reactions than is presently the case in many systems. One possibility recommended for further investigation is "seeding" sewage lines with an active microbial population to increase COD reduction during transport. Another possibility is recycling the sludge build-up in the lower part of the sewer line back to the upper region, to increase the bacterial concentration. The authors proposed "seeding" or aeration is very expensive and does not seem feasible or cost-effective.
"The Option of Appropriate System for Wastewater Treatment in Low-Density Areas" (Ukita, M. 1993) is a statistical review of when collection systems in lieu of on-site treatment become economical in Japan. The authors determined that collection systems are advantageous when housing density exceeds 9.5 houses/hectare. Curves are given for collection system costs per household versus house density in Japan. Emphasis is also given to choosing the appropriate treatment system by considering economic factors, receiving-water quality, and the overall environmental impact of the discharged effluent.
Domestic Sewage Treatment Options for household systems
Appropriate Sanitation Alternatives (Kalbermatten, J.M. 1982) has information on household sanitation systems that can be employed by developing countries when collection systems are not available. Pit latrines are essentially a hole in the ground where excreta fall. The excreta decompose anaerobically, yet the pit eventually fills up. When it is three-quarters full, it must be decommissioned (sealed up) or pumped out. There are many variations on the pit latrine, such as a pour-flush toilet, where the excreta falls down a curved chute into a separate compartment. Water or sullage is used to flush the waste. An advantage to a pour-flush toilet is that it can be inside since it does not smell. Composting toilets are another alternative, yet require more maintenance and operational skill. In addition to the mixing and occasional heating requirements, grass, ash, sawdust or other organic material must be added to maintain the necessary balance of organic material and nutrient. There are some complications in wet climates as well.
The Innovative and Alternative Technology Assessment Manual (U.S. EPA 1980) has a fact sheet on three different types of non-water carriage toilets: incinerating toilets; composting toilets; and oil recirculating toilets. These options may be viable where water is scarce or other wastewater treatment options are not available. Incinerating and composting toilets have potential as an economical option, but the oil-recirculating toilet is not recommended as it generates oily residuals and requires solid-oil separation.
"Wastewater Treatment Technologies: Pit Latrines." (Kaltwasser, B.J. 1995) is a comprehensive discussion of the theory of pit latrines, design considerations, variations on pit latrine design, maintenance requirements, and applications. Some important considerations are: size needed; groundwater contamination (lining or no?); ventilation; proper measures to prevent problems with pests (flies, rodents); and not using the latrine when it is at capacity. Another consideration is that wet latrines can decompose solids faster than dry latrines because the microbiology can migrate faster to more food sources in water. Designing a wet latrine can minimise the required maintenance of solids removal or decommissioning.
Domestic Sewage Treatment Options for on-site systems
The Innovative and Alternative Technology Assessment Manual (U.S. EPA 1980) includes a few fact sheets on septic tanks with different effluent disposal options. Septic tanks can be used with soil absorption fields for effluent disposal if the soil permeability is at least 25 mm/hour. Sandy soils are the most permeable. At least 660 mm is needed between the infiltrative surface and the highest potential groundwater level to minimise groundwater contamination. If effluent application rates are not excessive, the soil effectively removes BOD, TSS, bacteria, viruses, and metals. If groundwater levels are typically high, mound or at-grade systems can be used to dispose of septic tank effluent. Mound systems are elevated absorption beds which provide treatment for the effluent before ultimate disposal into the groundwater. The Municipal Wastewater Technology Facts Sheets (U.S. Department of Commerce 1991) includes the same facts sheets on septic tanks with absorption beds and mound systems.
The EPA manual, Onsite Wastewater Treatment and Disposal (U.S. EPA 1980) discusses the same information in greater detail. Information is provided on determining whether the soils are appropriate for absorption fields, on what size and shape the septic tank needs to be for proper treatment, on how to ensure proper hydraulics in the tank, on proper maintenance procedures and time intervals, and on the options for effluent disposal. In addition to absorption field or mound disposal, disposal possibilities include sand filters, surface water discharge, and evaporation ponds. This is a comprehensive reference book on soil treatment systems.
The manual, Wastewater Treatment/Disposal for Small Communities (U.S. EPA 1992) does not discuss septic tanks in great detail, but mentions that holding or containment tanks can be used to store wastewater until it can be collected for off-site treatment or disposal. Although this option eliminates the need for treatment, it has many drawbacks. Pumping may have to be frequent (depending on tank size) and it can be prohibitively expensive if the community is in a remote area. The holding tank must be of very high construction quality to prevent liquid, solid, or odour leakage.
"Wastewater Treatment TechnologiesSeptic Tanks" (Kaltwasser, B.J. 1995) provides an academic explanation of how septic tanks work, as well as some important design considerations. If properly sized, septic tanks need to be emptied only once every five to seven years, although an emptying period of two to three years is more typical. One option for effluent disposal is using small-diameter gravity sewers to carry the effluent to another treatment facility or process. This may not be appropriate in very rural areas, but it may be economical if the population density is high enough.
Domestic Sewage Treatment Options for low-technology, land-intensive treatment
Each of the following manuals provides important design, operation, maintenance, and other applicable information about lagoons/ponds, fixed film processes, infiltration/percolation, wetlands, overland flow, and sand filtration:
Innovative and Alternative Technology Assessment Manual (U.S. EPA 1980)
Municipal Wastewater Treatment Technology Fact Sheets (U.S. Department of Commerce 1991)
- Design Manual: Constructed Wetlands for Municipal Wastewater Treatment (U.S. EPA 1975)
Onsite Wastewater Treatment and Disposal Systems (U.S. EPA 1980)
Wastewater Treatment and Disposal for Small Communities (U.S. EPA 1992)
Manual of Appropriate Wastewater Treatment Technologies for the Caribbean Including Relevant Technologies in Operation Worldwide (Millette, E. 1992)
The Process Design Manual of Land Treatment of Municipal Wastewater (U.S. EPA 1984) is a useful resource for infiltration/percolation and overland flow treatment processes.
The following manuals provide design information on lagoons or stabilisation ponds; each contains excellent resource data for a design engineer in the planning or design stages of a project.:
Manual of Appropriate Wastewater Treatment Technologies for the Caribbean Including Relevant Technologies in Operation Worldwide (Millette, E.M. 1992),
Municipal Wastewater Stabilization Ponds (U.S. EPA 1983), and
Notes on the Design and Operation of Waste Stabilisation Ponds in Warm Climates of Developing Countries (Arthur, J.P. 1983)
"BOD 5 Removal in Facultative Ponds: Experience in Tanzania" (Mayo, A.W. 1996) provides data from nine facultative ponds in operation under tropical conditions. The authors feel that improper operation is due to incorrect design. For example, designs must take into account the appropriate reaction rate for microbiology in tropical climates. The BOD removal versus detention time and the BOD removal rate constant versus BOD loading rate are some topics explored here. An optimal loading rate of 450 kilograms/hectare/day is given.
"Comparison of the Purifying Efficiency of High Rate Algal Pond with Stabilisation Pond" (Picot, B. 1992) discusses the pros and cons of two types of pond system for use in coastal areas with "Mediterranean" climates. In high rate algal ponds (HRAPs), algal growth is encouraged (thus increasing nutrient removal), depths are shallower, mechanical mixing is introduced, and detention times are shorter (4 to 10 days). This reduces the surface area needed. This study found that HRAP lagoons could provide the same level of treatment as stabilisation ponds in one fifth the area. Although stabilisation ponds require more area, their long detention times promote sedimentation and bacterial and pathogen die-off or removal.
The trend of low pathogen concentration in HRAPs and stabilisation ponds suggests that temperature elevation or sunlight on the pond can remove pathogens. "The Effect of Sunlight on Faecal Coliforms in Ponds: Implications for Research and Design" (Curtis, T.P. 1992) tackles the complex problem of modelling faecal coliform removal in stabilisation ponds. Sunlight intensity, dissolved oxygen of the water, and pH of the lagoon affect coliform removal rates. The authors found in their research that "1) light can only have an impact on faecal coliforms if complemented by a high dissolved oxygen (DO) concentrations (sic) and a high pH; 2) the tendency of algae to impede light penetration is offset by their ability to raise the pH and DO; and 3) that visible light is more important than UV." A history of previous work on the topic is provided in this report.
"Efficiency of Faecal Bacterial Removal in Waste Stabilisation Ponds in Kenya" (Mills, S.W. 1992) presents faecal coliform die-off rates for seven waste stabilisation ponds in Africa. The results were lower than predicted by traditional design equations based on temperature. Good correlation was found between faecal coliform first-order removal rate constants and temperature and influent faecal coliform concentration. The authors note that higher removal rates have been recorded before, but may reflect removals by sedimentation also. The pH values rarely exceeded 9, and the authors speculated that much better removal could be achieved if the pH could be maintained near 10.
In "Influence of Climate on Stabilisation Ponds" (Mendes, B.S. 1995), a correlation was developed for BOD removal and BOD loading rate for five different climates in Portugal.
"Sustainabililty and Wastewater Treatment" (Panetta, 1992) looks at wastewater treatment with a focus on environmental and cost appropriateness. The paper describes an alternative to conventional wastewater treatment technology in the form of the Advanced Integrated Pond System (AIPS). AIPS is a lagoon treatment system developed by William J. Oswald of the University of California that attempts to optimise features of anaerobic, facultative, high rate algae, and settling ponds for integrated wastewater management. The raw wastewater flows through the ponds in series. The first cell in the treatment train is the anaerobic or primary pond. This pond is designed for 5-10 days of hydraulic residence time and is relatively deep (4-5 meters.) Wastewater is directed to the centre of the anaerobic cell at the bottom of the pond to trap most solids, including helminth ova and parasite cysts. The second cell in the series is a more shallow (2-3 meters) facultative pond in which algae growth and sedimentation both take place. The third cell in the series is the high rate algae pond which is shallow (1-2 meters) to encourage full penetration of sunlight throughout the water column to maximise photosynthetic growth, and which may contain paddle wheel or axial flow mixers to prevent sedimentation. A portion of the oxygen-rich effluent from this cell may be recirculated by pumping to the anaerobic cell to provide an aerobic cap for odour control. The fourth cell in the pond series is relatively deep (2-3 meters) and unmixed to encourage sedimentation of algae. More cells in the pond series may be provided for further sedimentation and exposure of effluent to ultraviolet light and elevated pH for disinfection. The author provides brief descriptions of AIPS facilities in St. Helens, Ridgemark, Santee, and Arcata, California.
"Experimental Plants for Very Small Communities" (Boutin, C. 1993) evaluates five existing small-community wastewater treatment processes in France with wastewater flow equivalents from 50 to 400 people. The author states that one of the two most used treatment processes for this flow range in Francethe lagoon or stabilisation pond processis not satisfactory for communities so small. If the pond is oversized or if the connection rate remains low in the first few years, the pond fills to a very low level. This causes an increasing concentration of pollutant in the pond due to lack of effluent. Also, when a strong storm occurs, due to the small capacity of the pond, hydraulic overload can flush the pond, causing a discharge with high organic content.
"Rotavirus Removal in Experimental Waste Stabilisation Pond Systems" (Oragui, J. 1995) reviews rotavirus removal in different pond configurations. The authors found that rotavirus removal is a very slow process, requiring a lot of detention time in several ponds in series. In one configuration, the rotavirus removal was not related to pH, chlorophyll, ammonia or sulphide levels. In the "innovative" configuration, the combination of shallow depth and long retention times permitted development of a high pH in the pond, which encouraged rotavirus die-off.
"Treatment of Wastewater by Stabilisation PondsApplication to Tunisian Conditions" (Ghrabi, A. 1993) concludes from studies of stabilisation ponds in France that warm climates greatly improve the efficiency of ponds due to increased microbial reaction rate. This can allow for a higher loading rate or decreased area. Also, sediment accumulation occurred mainly in the first in a series of ponds. The deposition rate was high (5 cm/year in the first pond and 1.3 to 1.6 cm/year in the maturation pond). In contrast to Boutin, (Boutin, C. 1993), the author feels that stabilisation ponds offer many advantages for small communities (with wastewater flows less than 0.25 million gallons per day (mgd)). These advantages include "easy plant operation and minimum maintenance, low construction and operation costs, high degree of pathogen removal, no requirement for external energy other than solar, and ponds are also useful for storing water for agriculture."
"Land Treatment of Wastewater" (Goldstein, N. 1981) describes operation of a few towns in the United States performing land application of wastewater to forests and crops. Land application serves three purposes:
Tertiary treatment of wastewater
Fertilisation of vegetation or crops
Capital costs for spray irrigation can be large, but operation and maintenance costs are usually much lower than for mechanical tertiary treatment processes. One drawback is that irrigated crops can assimilate toxic metals, or pathogens.
"Natural Treatment Systems" (Kruzic, A. 1994) includes a literature review of ponds. It cites a few papers dealing with sedimentation of suspended solids and scour mechanisms of soil surface in overland flow.
"Biomass Nutrient Recycling" (Braangart, M. 1997) describes a wastewater treatment project in Rio de Janeiro, Brazil. The wastewater is very successfully treated by settlement and oxidation ponds, fish ponds, and aquaculture ponds. The idea behind the treatment facilitys design is to recycle nutrients back into the soil. The effluent is used for irrigating fruit and vegetable crops. The fish grown in the ponds were fit for human consumption, however the fruits and vegetables were only fit for livestock production because of the presence of pathogens in the effluent.
"The Advantages of a Compact Filter for Individual or Semi-Collective Waste Water Treatment" (Fazio, A. 1993) discusses a compact sand filter used for treatment and disposal of septic tank effluent. The filter relies on supply regulation and improvement of the wastes surface distribution over the filter media. The purification achieved in the study using a dosing rate of 150 litres/square meter/day was over 90 percent for BOD, COD, NH4, and total nitrogen. The author attempted to optimise the efficiency by compartmentalising the filtration media, adjusting the distribution nozzle, and using a biotextile over the filtration media so as to distribute the influent evenly. Unfortunately, one of the drawbacks of biotextiles is their tendency to clog with biological growth.
"Alternative Approaches for Upgrading Effluent Quality for Lagoon Based Systems" (Evans, B. 1993), evaluates two processes for polishing lagoon effluent: intermittent sand filtration and polishing lagoons. Benefits cited by the author for intermittent sand filters following lagoons are that they nitrify very well and are effective in removing algae, which is a chronic problem in lagoons. A cost analysis was performed for the Toronto area, which found that lagoon/sand filtration processes are cheaper than conventional extended aeration plants until the flow reaches about 1 mgd.
"Lateral Flow Sand-Filter for Septic-Tank Effluent" (Check, G.G. 1994) is a laboratory study of lateral-flow sand filtration units, each filled with different permeability sand. The dosing rate used was 3.3 cm/day. After the filter matured, removal rates for BOD, total organic carbon (TOC), suspended solids, and coliform bacteria were excellent. The maturation time was about six weeks for BOD removal, but up to three months for bacteria removal and nitrification. The distribution system of the sand filter was laid with gravel and separated from the sand with a biotextile to improve flow distribution. Sand with three different values for permeability was tested. The least permeable developed a thick biomat most quickly, and the coarsest fill developed a thinner biomat. The model with the coarsest fill had the best removal rates for coliforms and the worst for viruses (viruses are much smaller than coliforms). The authors recommend the coarser sand fill due to good treatment, system longevity and free-flowing hydraulics.
"Low-Tech Systems for High Levels of BOD and Ammonia Removal" (Rich, L. G. 1996) gives case studies of lagoons and intermittent sand filters in combination that perform with high efficiency in South Carolina. Sand filters are effective in removing BOD, TSS, and pathogens as well as nitrifying. The author notes that intermittent sand filters used for septic tank effluent lost popularity in the United States after World War II due to large land requirements and odour problems. When used as a polishing step after lagoons however, twice the dosing rate can be applied or half the land is required. The dosing rate for a filter in South Carolina was observed to be 23 cm/day. However, the author cites recent studies indicating that loading rates as high as 60 cm/day can be used if the proper sand is selected.
"Upflow FiltersAppropriate Technology for the West Indies?" (Sammy, G.K. 1978) provides some general information, design data, and a few case studies of upflow filters used as a final, polishing treatment process. At the time, no upflow filters were in operation in the West Indies.
"Actual Experiences with the Use of Reed Bed Systems for Wastewater Treatment in Single Households" (Perfler, R. 1993) is a study of reed-bed systems designed for single households (8 to 10 person equivalents) in Austria requiring improved nutrient removal. Three configurations were examined. All received pre-treatment in settling pits and a buffering tank before application to the subsurface flow reed bed. Elimination rates for nitrogen and phosphorus varied from 60 to 70 percent. The controllable water level in the bed affects nitrogen removal. In one instance, the water level was raised to the maximum level in the bed without any outflow. This caused a noticeable increase in ammonia in the effluent.
"Constructed Reed Beds: Appropriate Technology for Small Communities" (Green, M.B. 1995) considered subsurface flow reed beds as secondary treatment for small communities (up to 50 people) and tertiary treatment for larger communities (up to 2,000 people). Area requirements for reed beds as secondary treatment were stated to be 5 square meters per person to achieve a 20 mg/L BOD effluent concentration. As tertiary treatment, 1 square meter per capita is recommended to achieve 10 to 15 mg/L BOD. Constructed Reed Beds are excellent solids removal systems, but they do not nitrify well because of anaerobic conditions. Maintenance requirements include periodic cleaning of the distribution system and keeping a weedless reed bed. The authors found that some attention to weeding is necessary in the beginning stages of the reed bed. As the bed matures, less weeding is needed.
"Development of a Land Limited Wastewater Treatment Plant for Small and Rural Communities in the Tropics" (Yang, P.Y. 1994) finds that the combination of subsurface flow wetland coupled with an aerobic fixed film treatment process provides very good BOD removal while maintaining a small footprint. BOD conversion with this coupled system occurs twice as fast as in a wetland, pond, or oxidation ditch alone. The author claimed that mosquito and fly breeding are suppressed by the biological mat of vegetation that forms on the wetland surface.
"Integrated Constructed Wetland for Small Communities" (Urbanc-Bercic, O.) considers nitrification and denitrification efficiency in subsurface flow reed-bed wetlands. Aerobic and anaerobic regions can be produced by varying flow direction and volume. The authors referenced a paper which found that intermittent dosing does not always introduce enough oxygen for nitrification. The authors also found that dense reed stands increase the efficiency of decomposition of nitrogen compounds by denitrification.
"Natural Treatment Systems" (Kruzic, A. 1994) provides a summary of 1992 and 1993 papers written on constructed wetlands treatment systems. Wetlands provide a low-maintenance system that can remove BOD, nitrogen, phosphorus, and some toxic metals often found in industrial wastewater. They can serve as primary, secondary, or tertiary treatment processes.
R. Netters (1993) "Planted Soil FilterA Wastewater Treatment System for Rural Areas" explores design parameters for subsurface-flow planted-soil filters. The hydraulic loading rate used was 0.4 to 6.0 cm/day and BOD loading rates were from 0.9 to 9.7 grams/m2/day.
The author of "The Use of Wetlands for Water Pollution Control in Australia" (Mitchell, D.S. 1995) contends that there is no overall consensus in design equations or understanding of the mechanisms involved in wetland treatment processes. Problems associated with wetland design or usage include variability in phosphorus removal efficiencies from wetland to wetland, hydraulic short-circuiting in small wetlands, lower than expected performance from scale-up laboratory experiments, and the inability of some vegetation to tolerate shock loads. Wetlands are predictable and effective as a tertiary process. When too much strain or loading is applied or if the wetland is used as a secondary process, efficiency can be unreliable.
"Long-Term Impacts of Sewage Effluent Disposal on a Tropical Wetland" (Osborne, P.L. 1994) warns readers that a wetlands life span as an efficient "sieve" is finite. The author gives a case history of a wetland in New Guinea that received stabilisation pond effluent. Pictures are presented to demonstrate decline in vegetation over 25 years and a corresponding decrease in treatment efficiency. The author is not sure whether the vegetation decline was due to the wastewater pollutants or to fluctuation in flow volume. The author feels more research is needed on wetland capacity for wastewater treatment.
The author of "Experimental Plants for Very Small Communities: Choice and Design Criteria for Five Different Processes" (Boutin, C. 1993) found that efficiency improved when infiltration beds were allowed to rest between doses to facilitate oxygen transfer into the soil matrix. This can be done by alternating between two or more beds. The author feels that the greatest problem for proper operation is even distribution of effluent on the surface. This is difficult to achieve with gravity flow (the usual kind of flow in rural or medium density areas), but not if a small pump supplies the flow.
"Natural Treatment Systems" (Kruzic, A. 1994) provides a review of studies performed on rapid infiltration and soil treatment techniques. One paper in the review found an optimal infiltration rate of 2.13 m/day and an optimal wet-to-dry ratio of 1:1. Coliform removal was in the range of two to three orders of magnitude. Other attempts were made to use treated effluent as reclaimed water for non-potable and potable uses. One study found that significant nitrification occurred during the drying cycle in a system with an intermittent dosing regime. Nitrate concentrations in the groundwater increased sharply at this time.
"Wastewater Treatment of Greater Agadir (Morocco): an Original Solution for Protecting the Bay of Agadir by Using the Dune Sands" (Bennani, A.C. 1992) describes the infiltration/percolation treatment processes following anaerobic stabilisation ponds for a town of 350,000 people. At a loading rate of about 1 meter/day, nearly 100 percent of the suspended solids and 95 percent of the COD is removed while 85 percent of the nitrogen is oxidised. Also, a four to five log removal of coliforms is achieved.
"Development of a Biofilter Using an Organic Medium for On-Site Wastewater Treatment" (Talbot 1996) describes the development and commercialisation of a peat-based biofilter suitable for on-site use in areas where percolation and infiltration techniques are not viable due to poor soil permeability or a high water table. This process is meant to be used for septic tank effluent treatment and consists of a thick peat layer over a thin gravel bottom. Initial removal efficiencies of 97 percent BOD , 99 percent faecal coliform, 60 percent ammonia, 22 percent total nitrogen, and 12 percent total phosphorus were obtained treating septic tank effluent. An upper limit for the daily hydraulic loading rate (where treatment efficiency begins to drop off considerably) is 300 litres/square meter. During this period, a yellow colour is generally imparted on the effluent, and the pH may reach 4.0 or less.
"Experimental Plants for Very Small Communities: Choice and Design Criteria for Five Different Processes" (Boutin, C. 1993) evaluates five different treatment options for communities from 50 to 400 person equivalents. A trickling filter was used as one of the treatment options and was the most expensive per capita.
"The Cyclic Activated Sludge System for Resort Area Wastewater Treatment" (Goronszy, M. 1995) describes a proprietary sequencing batch reactor (SBR) treatment process. What is special about this process is the use of a contact or selector zone in the batch reactor. The influent first comes into an anoxic region that is separated from the rest of the aeration basin. The idea is to maintain a high food-to-mass ratio for the organisms in the contact or selector zone, which "selects" micro-organisms that settle well. Well-settling organisms thrive in high food and high dissolved-oxygen environments while filamentous (poor settling) organisms thrive in low dissolved-oxygen and low food conditions. The contact or selector zone will give the well-settling micro-organisms a head start in becoming the dominant seed to the mixed liquor. Timing in the basins can be adjusted to accommodate low, average, and peak flow conditions, while ensuring adequate treatment. Another advantage with sequencing batch reactor technology is the small footprint compared to continuous activated sludge systems with separate sedimentation tanks. SBRs are primary clarifiers, aeration basins, and secondary clarifiers all in one reactor. Also, there is no need for sludge recirculation pumping unless a selector tank is used. The primary drawback to the SBR process is that effluent disinfection facilities must be oversized to accommodate the intermittent flow.
Domestic Sewage Treatment Options for conventional mechanised treatment
The following are well-written textbooks or manuals on conventional, mechanised treatment technologies:
Recommended Standards for Sewage Works (Ten State Standards), 1978.
Design of Municipal Wastewater Treatment Plants Vol. I & II (ASCE 1992, WEF Manual of Practice No. 8);
Appropriate Wastewater Treatment Technologies for the Caribbean (Millette, E. 1992);
Innovative and Alternative Technology Assessment Manual (U.S. EPA 1980)
Municipal Wastewater Treatment Technology Fact Sheets (U.S. Department of Commerce 1991).
"15 Years of Practical Sewage Treatment in Venezuela" (Lansdell, M. 1996) describes a few municipal treatment plants in Venezuela that use activated sludge processes to treat flows from a population of up to 5 million. It emphasises simplicity of operation and avoiding technological dependence on other countries for imported spare parts ("unskilled manpower is plentiful and foreign currency is in short supply"). Technologies included are simple activated sludge systems, modified sequencing batch reactors (MSBRs), oxidation ditches, and lagoons.
"An Evaluation of the Efficiency and Impact of Raw Wastewater Disinfection with Peracetic Acid Prior to Ocean Discharge" (Ruiz, C.S. 1995) explores an alternative disinfection strategy for wastewater. Peracetic acid (PAA) disinfection was observed in 5 to 10 minutes using doses of 2 to 80 mg/L. One advantage of PAA is that it quickly degrades into benign compounds, acetic acid and active oxygen. PAA is most suitable for disinfecting wastewater to be discharged to the sea. The author suggests that the optimal dose is 20 mg/L with a contact time of 10 minutes. Higher concentrations of PAA did not significantly improve disinfection efficiency. Neutral or slightly acidic wastewater improved PAA disinfection efficiency, while in alkaline wastewater (pH>8.l; pKa PAA=8.2) disinfection efficiency was lower. One wastewater sample with a pH of 7.9 was given a 20 mg/L PAA dose with 15 minutes of contact time and achieved a coliform inactivation rate of 6.45 logarithmic units. The main drawbacks of peracetic acid disinfection is that it is almost as hazardous to handle as chlorine and it may lower the pH of the receiving water.
"Feasibility of Anaerobic Sewage Treatment in Sanitation Strategies in Developing Countries" (Alaerts, G.J. 1993) discusses the feasibility of anaerobic treatment of sewage for on-site systems, mid-size communities or townships, and centralised off-site systems in developing countries. The author feels that anaerobic treatment is most economical in off-site centralised treatment schemes. Although BOD removals are not as good as most aerobic treatment units, there are many advantages to anaerobic treatment. Methane production can be significant at large-flow plants, biomass (sludge) production is about half of that produced in aerobic processes, the sludge produced can be well stabilised and thickened (5 to 8 times thicker), helminth ova removal is excellent, and effluent is high in nutrients, which makes it suitable for irrigation. Some disadvantages are that BOD removal is in the 25 to 80 percent range, and virtually no nutrients are removed. Consequently, some sort of aerobic treatment unit is usually needed to meet effluent requirements. If nitrification is a requirement, anaerobic systems are much less attractive as an alternative, according to the author.
"Mexican Project Combines Industrial and Municipal Wastewater Treatment" (Unknown 1994) provides a discussion of a wastewater treatment plant that treats both domestic and industrial sewage. The treatment plant, at Salamanca, Mexico, receives domestic wastewater from a population of 500,000 and wastewater from an oil refinery. The combined flow first goes through dissolved air flotation (DAF), where much of the oil is skimmed and sent to a centrifuge for further separation. The effluent from DAF then goes to aerobic digesters. After aerobic treatment, calcium carbonate is added for clarification, and then the effluent is chlorinated. Part of the effluent is routed back to the oil refinery for reuse, and the rest goes into a river.
"Submarine OutfallsGeneral Overview, Basic Design Concepts and Data Requirements for Latin America and the Caribbean" (UNEP 1994) provides an alternative view of wastewater disposal in coastal communities. Submarine disposal of wastewater can be just as effective as wastewater treatment, provided that dilution of discharged sewage is sufficient to reduce contaminant concentrations below water quality standards. A minimum initial dilution of 100:1 is common, and is adequate for achieving most water quality standards, if not all. Three mechanisms are considered in dilution calculations for an outfall: initial dilution; horizontal transport and dispersion; and kinetic reaction. The contaminant of concern for wastewater outfalls to open oceans is pathogen content. In bays or estuaries (or anywhere with limited exchange with the open ocean), nutrients and BOD become important concerns. Total dilution is the product of initial dilution, horizontal dilution, and coliform reaction/disappearance. Initial dilution and bacterial die-off are usually much more significant than horizontal dilution. For non-degradable substances, initial dilution is the most important factor in determining total dilution. This can be an economical alternative to conventional wastewater treatment. Receiving-water quality and currents must be characterised before submarine outfalls can be considered, however.
An extension of this article is "Submarine OutfallsA Viable Alternative for Sewage Discharge of Coastal Cities in Latin America and the Caribbean" (UNEP 1993). The author gives an overview of the population distribution of this region and the cities or regions that use submarine outfalls for sewage disposal. At the time of writing, 84 outfalls were listed in Latin America and the Caribbean; almost half (39) are in Venezuela, and only one exists in Martinique in the Caribbean Sea.
"Wastewater Treatment and Reuse Aspects of Lake Valencia, Venezuela" (Lansdell, M. 1991) describes environmental problems of the Lake Valencia Basin and the treatment plan that has been funded by the Inter-American Development Bank. The author argues that reuse plans for developing countries must avoid excessive technological dependence. Availability of land and warm climate allows for the efficient operation of lagoons and wetlands. Primary objectives of the Valencia plan include: treatment of domestic and industrial wastes; effluent reuse in irrigation; recharging groundwater aquifers; desalination of groundwater aquifers; and reduction of artificial fertiliser usage by farmers.
A few comprehensive and reference books on industrial wastewater treatment are:
- Industrial and Hazardous Wastewater Treatment(Nemerow, N. 1991)
- Industrial Wastewater Treatment Technology(Patterson, J.W. 1985)
- Handbook of Industrial Waste Disposal(Conwya, R.A. 1980)
All of these reference books provide valuable information on types of pollutants from different industries, appropriate treatment technologies for specific pollutants, and management issues.
Management of Industrial Wastewater in Developing Nations (High Institute of Public Health 1981) is a collection of articles from the "Proceedings of the International Symposium" held in Alexandria, Egypt in March of 1981. There are 41 articles in this collection, many of which are relevant to this project. Specific treatment processes for certain industries are included, along with effluent quality issues, water reclamation and reuse, and policy development and other related planning issues.
"Industrial Wastewater Management in the Caribbean Region" (Sammy, G.K. 1995) reviews the types and volumes of wastewater produced from 13 industries in the Caribbean. Effluent limits are discussed, and the concept of "reduce, reuse and recycle" is emphasised. The author states that more progress needs to be made in this area, since little has been done in the past.
The petroleum industry is the largest BOD contributor to coastal waters in the Caribbean. The following three books provide useful information about pollutants in typical petroleum industry wastes, and treatment processes that can reduce these pollutants before they are discharged:
Pollution Control in the Petroleum Industry (Jones, H.R. 1973)
Pollution Control for the Petrochemicals Industry (Borup, M.B. 1987)
Aqueous Wastes from Petroleum and Petrochemical Plants (Beychok, M.R. 1967)
"Biodegradation of Petroleum Refinery Wastewater in a Modified Rotating Biological Contactor with Polyurethane Foam Attached to the Disks" (Tyagi, R.D. 1993) explores aerobic rotating biological contactor (RBC) technology for significant BOD removals from oil refinery wastewater. The foamy material acts as a porous support for more biomass than a conventional RBC, thus increasing contact opportunity for the biomass with the soluble organic materials. Up to 87 percent removal was observed with this technique.
Management of Water Discharge: Design and Operation of Oil-Water Separators (American Petroleum Institute 1990) provides design guidance for gravity-type oil-water separators for use in petroleum refineries. The manual also provides practical advice for solving operational problems and improving the performance of oil and water separation facilities.
"Innovative Technologies for Treatment of Oily Wastewater" (Benedek, A. 1992) discusses the energy-intensive technology of membrane filtration techniques to remove emulsified oil from wastewater.
The author of "Petrochemical Wastewater Treatment with Aerated Submerged Fixed-Film Reactor (ASFFR) Under High Organic Loading" (Park, T.J. 1996) found that 92 to 97 percent COD removal is possible at a volumetric organic loading rate of 0.9 to 6.3 kg COD/cm/day. COD removal increased with the packing ratio. Clogging and channelling typical of stationary filters were avoided since this filter has a separate settling zone.
"Skimming Oily Wastewater" (Hobson, T. 1996) emphasises the benefits of oil skimming. It is useful not only as a pre-treatment step, but can stand alone as a treatment process in light of recent advances in skimming technology. The author discusses design conditions and criteria such as reservoir design, turbulence, reservoir depth, and skimmer media.
"Treatment of Wastewater From Oil Manufacturing Plant by Yeasts" (Chigusa, K. 1996) explores the process of using yeasts to degrade wastewater from soybean oil manufacturing plants. The yeast strains were isolated out of the waste stream and found to perform well enough that dissolved air flotation was unnecessary as a pre-treatment step. Nine different yeast strains were studied.
Several other useful journal articles on oil and petrochemical refinery waste treatment were obtained through the Purdue Industrial Waste Conference Proceedings. These annual proceedings are an excellent resource for current developments on industrial waste treatment and management, and should be the starting point for any literature review related to industrial wastes. The journal articles obtained from the proceedings are:
"Wastewater Reclamation and Reuse in a Petrochemical Plant" (Wong, J.M. 1995)
"Evaluation of Physical, Chemical, and Biological Treatment to Remove Fats, Oils, and Grease from Petroleum Refinery Waste Effluent Prior to Recycling to Cooling Towers" (Mitchell, D.B. 1994)
"Land Treatment of Petroleum Waste in Regina Area, Saskatchewan" (Viraraghavan, T. 1994)
"Hazardous Sludge Reprocessing and Reduction in Petroleum Refining" (Engelder, C.L. 1993)
"Environmental Solutions Based on Recycling of Water, Oil, and Sludge at an Integrated Oil Refinery" (Galil, N. 1992)
"Disposal of Hazardous Wastes from Petroleum Refineries" (Bryant, J.S. 1991)
"Pilot Testing and Design of an Activated Sludge System for Refinery Wastewater" (Copeland, E.C. 1991)
"A Comparative Study of RBC and Activated Sludge in Biotreatment of Wastewater from an Integrated Oil Refinery" (Galil, N. 1990)
"Removal of Oil and Grease in the Hydrocarbon Processing Industry" (Rhee, C.H. 1988).
"Anaerobic/Aerobic Combination Treats High-Strength Wastewater" (Ulrix, R.P. 1994) reviews a successful treatment process for wastewater from a beet sugar refinery. A single-stage upflow anaerobic reactor was used to treat the high strength waste. Following the anaerobic reactor was a polishing aerobic/anoxic phase to further lower BOD and nitrogen levels. The plant was able to treat a large seasonal fluctuation in organic loading over time, which is characteristic of many food-processing industries.
"Anaerobic Codigestion of Agricultural Industries Wastewater" (Gavala, H.N. 1996) explores the idea of combining different food-processing industries wastewater in a central facility, to minimise the seasonal flux of organic loads, which can shut down anaerobic treatment processes. A mathematical model is developed describing the codigestion process. The model is capable of predicting COD and fatty acid dependence on operating conditions, and should be useful for designing codigestion processes.
"Anaerobic Digestion of High Strength Molasses Wastewater Using Hybrid Anaerobic Baffled Reactor" (Boopathy, R. 1991) examines the process efficiency of the anaerobic baffled reactor, which essentially produces plug-flow-like conditions. The HABR successfully treated
20 kg COD/cm/day. The biomass in the reactor quickly adjusted to a change in feed volume, and high loading rates were observed without any biomass washout. Also, granulation was achieved more quickly than in other upflow anaerobic systems.
"Wastewater Treatment Technologies" (Farmer, J.K. 1991) provides an overview of treatment requirements for U.S. food processing industries and pre-treatment processes used to achieve them. Most U.S. food processing industries discharge to public sewerage systems that have pre-treatment requirements. The author notes that aerobic biological treatment units are the predominant technique, and that SBR technology is worth consideration.
"Brewery Wastewater Treatment in UASB Reactor at Ambient Temperature" (Yan, Y.G. 1996) is an academic study on granule development. BOD and hydraulic loading rates were determined for optimal sludge granule growth.
"Using an Anaerobic Filter to Treat Soft-Drink Bottling Wastewater" (Carter, J.L. 1992) describes the pre-treatment processes for the wastewater generated by for Shasta Beverage Company in Kansas. The effluent from the plant is discharged to the municipal wastewater district. The untreated wastewater, which ranges in BOD from 200 to 4,000 mg/L needs to be reduced to an EPA-required level of 200 mg/L as a weekly average. Detailed design information is provided. "Treatment of Soft Drink Syrup and Bottling Wastewater Using Anaerobic Upflow Packed Bed Reactors" (Capobianco, D.J. 1990) gives experimental results of 5 bench scale upflow anaerobic reactors. Impressive COD removals of over 85 percent were obtained with less than seven hours of hydraulic detention time. The influent COD values were close to 5,000 mg/L at times. The reactors also demonstrated an ability to withstand short term shock loads in COD.
"Application of Anaerobic Digestion to the Treatment of Agroindustrial Effluents in Latin America" (Borzacconi, L. 1995) surveys the use of anaerobic treatment processes in Latin America. The four most important industries in Latin America are breweries, distilleries, dairy production, and yeast plants. More and more industries are using anaerobic treatments to reduce BOD loads on municipal treatment facilities or receiving waters. The warm climate in many parts of Latin America, the generation of biogas as an energy source, and the ability to handle high-strength wastewater is making anaerobic reactors popular.
"A New Process to Treat Strong Biological Waste" (Henry, D.P. 1993) explores the idea of trickling brewery and piggery wastewater down a vertical curtain consisting of two layers of polyurethane foam. Attached biomass would provide treatment. The idea is to provide a large surface area for biomass to adhere, and thus provide more efficient treatment. Maintenance includes harvesting excess growth. A surface area of 1 square meter with a 4-meter fall will adequately treat 15 L/day of waste containing 60,000 mg/L total oxygen demand (TOD).
"Strategies in Agroindustrial Wastewater Treatment" (Sendic, M.V. 1995) describes the waste treatment processes of the three most important industries in Uruguay: slaughterhouses, wool scouring factories, and tanneries. The waste stream from wool scouring industries carries significant amounts of grease and COD, slaughterhouses produce a high COD and TSS load, and tanneries generate high COD loadings along with some metals (chromium and sulphides). Wool scouring factories and slaughterhouses require DAF with anaerobic reactors, while tanneries need chemical treatment to remove the metals from the waste stream.
"Anaerobic Pre-treatment of Dairy Liquid Effluents" (Filho, B.C. 1996) describes an upgrade project for a facility treating dairy liquid effluent in Brazil. The lagoons used to treat the waste streams were not capable of handling the increasing COD load accompanying the dairy factorys growth. To help treat the increasing COD load (with concentrations up to
37,000 mg/L, average value of 6,300 mg/L), an upflow anaerobic reactor was added after the screening process. With a hydraulic detention time ranging from 7 to 28 hours, the COD removal efficiency ranged from 40 to 70 percent, with an average efficiency of 53 percent. Suspended solids removal was a little less than 50 percent, and the total nitrogen removal was about 28 percent.
"Anaerobic Treatment of Swine Waste by the Anaerobic Sequencing Batch Reactor (ASBR)" (Zhang, R. 1996) evaluates the performance of an ASBR with a short hydraulic detention time (two to six days). The volatile solids reduction ranged from 39-61 percent and the BOD reduction ranged from 58 to 86 percent. Surprisingly, a better removal was achieved with a three-day detention time than with a six-day detention time.
"Application of Constructed Wetlands to Treat Some Toxic Wastewaters Under Tropical Conditions" (Polprasert, C. 1996) examines removal of phenolics and heavy metals by constructed wetlands with a free water surface. Influent chromium and nickel concentrations of 1 to 10 mg/L did not have significant effects on the wetlands performance. However, when the heavy metal concentration increased to 20 or 50 mg/L, COD removal efficiencies dropped to 70 to 35 percent.
"Closed-Loop System Recycles VOCs from Refinery Wastewater" (Pollution Engineering 1992) describes a system for removing volatile organic compounds (VOCs) at two major U.S. oil refineries with greater than 98 percent efficiency. The technology combines nitrogen stripping, relative humidity adjustments, and activated carbon technologies.
SOLIDS TREATMENT AND DISPOSAL
The design manual, Sludge Treatment and Disposal (U.S. EPA 1979) provides detailed design criteria for several treatment and disposal options.
The EPA handbook, Septage Treatment and Disposal, (U.S. EPA 1984) provides design criteria for appropriate treatment and disposal alternatives for septage.
"Treatment and Disposal of Domestic Sewage Sludge and Nightsoil Sludge for Bangkok" (Stoll, U. 1996) is a survey of solids or sludge treatment and disposal methods in Bangkok. Decision trees are provided for determining the "appropriate" treatment method to use. Some options identified are agricultural use, land reclamation, landfill disposal, mono-incineration, coincineration, and other recycling or reuse options. The authors point out that waste minimisation should be the first priority for management authorities, even though this is not always economically feasible. With that in mind, mono-incineration after dewatering is recommended as a preferred process for urban centres with large volumes of sludge, followed by direct agricultural use or composting. Landfill disposal has historically been cheapest in the past, yet this is changing in large urban centres.
"Treatment of Septage Using Single and Two Stage Activated Sludge Batch Reactor Systems" (Andreadakis, A.D. 1995) provides an option for septage treatment. Septage is characterised by high strength (2.5 times stronger than typical domestic sewage). Cyclic batch-operated systems (SBR) can treat this type of load, since flocs formed from septage generally settle well, and allow for a high mixed liquor suspended solids (MLSS) concentrations (up to 8,000 mg/L). A single-stage batch aerated system with a reactor volume of 1.6 times daily septage flow, a solids retention time (SRT) of 15 days, and COD loading of 0.15 mg/mg MLSS/day produced a well-stabilised sludge and good nitrification. Further improvements were made in the study by a second-stage system with anoxic and aerobic zones to encourage denitrification.
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Chapter 1. | Chapter 2. | Chapter 3. | Chapter 4. | Chapter 5. | Chapter 6. | Chapter 7. | References | Appendix A. | Appendix B. | Appendix C. | Appendix D. | Appendix E.