Appropriate Technology for Sewage Pollution Control in the Wider Caribbean Region	Report Contents Report in Word Format
	Caribbean Environment Programme Technical Report #40 1998	All CEP Technical Reports

Chapter 7.
Effluent Standards Workshop

 

Chapter 6 presented methodologies for selecting appropriate sewage pollution control technologies for the WCR. This chapter presents a discussion of recommendations for wastewater treatment effluent standards developed at a meeting of regional experts on pollution control. The meeting was held from 19 to 21 January 1998 in Castries, St. Lucia.

The meeting was attended by professionals in the WCR who are active in planning, design, and managing wastewater treatment systems and have an understanding of the technical, economic, and social issues associated with pollution control systems for the region. Their input was sought to assist UNEP-CAR/RCU, as Secretariat to the Cartegena Convention and its Protocols, in developing a draft Annex on appropriate wastewater treatment technologies under the draft Protocol Concerning Pollution From Land-Based Sources and Activities.

The experts discussed a draft version of the current report prepared prior to the meeting and provided input and comments on the draft report. They also identified issues that need to be addressed by negotiators of the land-based sources protocol. Sewage treatment standards were recommended for 11 parameters. A list of the participants is presented in Appendix E.

Report Comments

The following general comments on the draft report were offered. Specific report comments were given to KCM.

• Decision trees were modified to take into account effluent reuse, operation and maintenance requirements, cost factors, and human health considerations.

• Siting, operation, and maintenance of facilities should be discussed.

• Septic tanks and other on-site systems need to be covered in more detail.

• Fact sheets need to be as technically correct as possible.

• "Most Appropriate Technology" needs to take into account the environmental quality of the water into which effluent is being discharged.

• Evapotranspiration needs to be addressed as an alternate disposal method for septic tank effluent.

• The inefficiency of package plants should be emphasised since they seldom work properly.

• Each sewage treatment plant should develop a preventative maintenance programme for proper facility operation and maintenance.

• Monitoring costs must be taken into consideration for all facilities.

 

Additional Issues

The experts panel discussed the following issues that need to be discussed by negotiators for each country involved in development of the Final Protocol :

• Proper reuse needs to be an option for effluent disposal.

• Suggested treatment standards and alternatives need to be practical.

• Proper siting, installation, operation, and maintenance of sewage treatment systems are critical.

• The technologies in the report are suggested ways to meet the standards and for each standard there are appropriate technologies that can be used to meet them.

• Faecal streptococcus is a reasonable alternative measure of disinfection failure.

• There should be no direct discharge to sensitive areas from industrial facilities.

• The technologies in the report should be referenced in the Protocol Annex.

 

Effluent Discharge Control Parameters

After much discussion, the experts panel established a set of discharge parameters and a set of effluent standards for each parameter that domestic sewage treatment plants should be designed to meet. The experts panel decided that it would be best to distinguish between sensitive and non-sensitive receiving waters.

It was decided that sensitive receiving waters should be defined as those that are especially susceptible to degradation or destruction by human activities, due to inherent and/or unique environmental characteristics and/or a fragile biological or ecological situation. This definition was based on the definition used in the wastewater standards of Trinidad and Tobago. Sensitive areas in the WCR include the following:

• Mangrove swamps

• Coral reefs

• Sea grass beds

• Nursery areas (feeding and breeding areas for fish and shellfish, including migratory species)

• Recreational waters such as beaches.

 

All other receiving waters would be considered non-sensitive under the system recommended by the experts panel.

The experts panel felt that standards should be applied not only to facilities discharging to sensitive areas, but also to facilities discharging to waters impacting a sensitive area, such as an upstream area whose drainage discharges to a coral reef through an estuary.

 

Figure 7-1 presents a decision tree for effluent disposal developed at the experts meeting. The experts felt that discharge to non-sensitive waters should be the first alternative for wastewater disposal. If it is not possible to discharge to non-sensitive waters, effluent evaporation or reuse should be considered. If it is necessary to discharge to sensitive waters (the last resort), the standards for sensitive waters should be met.

Figure 7-1. Decision Tree for Effluent Standards.
(Click on image for full figure.)

Table 7-1 lists the parameters and standards recommended at the experts meeting. It was the intention of the experts panel to propose standards that could be met using appropriate technology as developed in the current report. Technologies that could be expected to meet the standards for non-sensitive discharges, for example, are either primary sedimentation or anaerobic or facultative lagoon systems. For sensitive discharges, standards could be achieved using a combination of either an integrated lagoon system or secondary treatment with disinfection by chlorination/dechlorination, ultraviolet light, or lagoon polishing ponds.

The most critical parameters for the technologies developed in this report are the suspended solids and ammonia removal requirement for lagoon systems. Experience has shown that well-operated lagoon systems yield suspended solids concentrations greater than 30 mg/L due to the presence of algae. Data available at the workshop from the Rodney Bay advanced integrated pond system on St. Lucia, for example, revealed effluent concentrations for suspended solids consistently in the range of 30 to 60 mg/L. Lagoon systems in cooler climates are often ineffective in removing ammonia. Data from the Rodney Bay system, however, indicated that the pond system was consistently producing an effluent with an ammonia-N concentration less than the proposed 5 mg/L standard.

It was not the intention of the experts to exclude well-designed and operated lagoon systems in settling the standard. It was suggested, therefore, that the standard contain a footnote, or potential for waiver, permitting the suspended solids standard to be exceeded as long as the solids are primarily algae. For receiving waters that would be damaged by suspended solids concentrations in the range of 30 to 75 mg/L—typical of well-designed and operated lagoon systems—polishing processes should be used with lagoons, such as wetland or sand filtration systems, or conventional secondary treatment should be used. It was felt that for most systems in the WCR the year-round temperature is warm enough to permit conservatively sized lagoon systems to nitrify and that the 5 mg/L ammonia-N limit would not be unnecessarily stringent.

TABLE 7-1. PARAMETERS AND STANDARDS FOR DOMESTIC AND INDUSTRIAL WASTEWATER DISCHARGES IN THE WCR
Parameter	Standard for Non-Sensitive Waters	Standard for Sensitive Waters
Total Suspended Solids	100 mg/L	30 mg/La
Biochemical Oxygen Demand (5 day)	150 mg/L	30 mg/L
COD	300 mg/L	150 mg/L
Faecal Coliformb	No standard established	43 MPN/100 mL in shellfish harvesting areas 200 MPN/100 mL in all other areas
Total Inorganic Nitrogen	No standard established	10 mg/L in nutrient sensitive waters
Soluble Phosphorus	No standard established	1 mg/L in nutrient sensitive waters
pH	6 to 10	6 to 10
Fats, Oils, And Greases	50 mg/L	2 mg/L
Ammonia as N	No standard established	5 mg/L
Total Chlorine Residual	No standard established	0.1 mg/L
Floatables	No visible floatables	No visible floatables
a. Does not include algae from treatment ponds b. Faecal strep should be considered as an alternate

 

Industrial Wastewater Disposal

The experts discussed industrial wastewater in the context of industrial facilities that discharge to municipal wastewater treatment plants. The group agreed that there should be no direct industrial discharges to sensitive waters. The standards developed for municipal discharges would still apply if a plant is accepting wastewater from an industrial discharge. It would be up to the operators of the treatment facility accepting the waste to set the influent standards so that the effluent standards can be met. Industrial facilities that handle hazardous substances and wastes should have spill containment and contingency plans.

Timing

The experts agreed that the annex should establish a target date by which the standards will be in effect for both sensitive and non-sensitive receiving waters.

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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.