Presentation on theme: "Opportunities for Sectoral Synergy in Public Sector Waste Management UNDP Waste Management Experts Meeting Havana, Cuba, October 27 - 31, 2003 Authors:"— Presentation transcript:
Opportunities for Sectoral Synergy in Public Sector Waste Management UNDP Waste Management Experts Meeting Havana, Cuba, October 27 - 31, 2003 Authors: Hugh Sealy, Ph.D., P.Eng. Kev L. Metcalfe, P.Eng. Norm J. Nuttall, P.Eng. Stantec Consulting International Ltd.
Introduction In many Caribbean countries, there exists the potential for cooperation between the agencies responsible for solid waste and domestic wastewater (sewage) management, which would result in improved operations, increased environmental and economic benefits and reduced risks.
Constraints to Cooperation Unfortunately, this potential synergy tends to be unrealized, perhaps for the following reasons: Responsibility for solid waste management and wastewater management usually resides within separate departments/ministries. The concept of an integrated approach to both waste management (solid, liquid and gas), including residuals management is not yet pervasive within the region. Funding tends to be project specific and linear in programming and does not allow for inter-agency cooperation.
Constraints to Cooperation Traditionally, low tech approaches have been used for SWM in the Caribbean, whereas it may be argued that WASA’s have been exposed to more complex technologies in the treatment and delivery of potable water and the treatment and disposal of wastewater. For example, the Barbados Water Authority (BWA) recently specified a mechanical treatment plant for septage and sludge treatment rather than “low tech” lagoons.
Objective The objective of the following paper is to present examples from the Caribbean (in particular using case studies from the Bahamas and from Barbados) where it can be shown that cooperation between solid waste and wastewater utilities in residuals management may result in benefits to both utilities.
Residuals (Liquids, Gases & Bio-solids) Leachate from landfills that have a collection system Landfill gas generated from the decomposition of wastes Septage from septic treatment systems Screenings from primary sewage and septage facilities Sludge (primary & secondary) from sewage treatment plants
Other Residuals Grease from food preparation Used motor oil Sludges from car washes Blood and by-products from abattoirs Manure Petroleum contaminated soils
Disposal Options for Residuals Leachate 1.Anaerobic / Aerobic lagoons with mechanical aeration Effective treatment 2.Recycle leachate by re-circulating it through the landfill Increased waste decomposition of solid waste in landfill Reduced strength of leachate
Disposal Options for Residuals Landfill Gas Collected and flared or used to produce energy Passive venting Re-circulation of leachate can affect rate of gas generation Approximately 40 to 80 tonne per day landfill site could generate 1 MW of energy
Disposal Options for Residuals Septage Series of lagoons: settling pond, anaerobic and aerobic Incorporated into Primary Sludge disposal
Disposal Options for Residuals Sewage Sludge Primary Treatment Sludge: Direct disposal to dedicated cells on site Primary digestors at treatment plant Secondary Treatment Sludge: Co-composting Landfarming Lagoons
Synergistic Residuals Management Options The following two technologies may provide opportunities for co-disposal of residuals in the Caribbean: Bioreactor Landfill Co-composting
Bioreactor Landfill Designed to rapidly change and biodegrade organic component of solid waste stream Adding sufficient liquids and air Aerobic, Hybrid and Anaerobic Waste Age, Phil O’Leary & Patrick Walsh, June 2002, p.64
Bioreactor Landfill Most Easily Adapted to Caribbean: Anaerobic. Moisture content most important aspect. Upwards of 65% required. Recirculating leachate alone (at least in the initial stages of the landfill life) may not achieve the desired moisture content. Leachate, storm-water, screenings, sewage sludge, septage and other waste treatment effluents can be added to achieve the desired moisture content. Benefits: Accelerated decomposition, reduced leachate treatment and disposal costs, reduced need for leachate treatment facilities, reduced post closure costs and increased landfill gas generation.
Leachate Generation Estimated Leachate Generation Quantities – New Providence Year of Landfill Operation Annual Leachate Quantity (cu. ft.) 480,000 8 500,000 121,000,000 162,500,000 20 2,000,000
Co-composting Defined as: composting of organic waste supplemented with a range of materials (e.g. septage, sludge, abattoir wastes). Carbon to Nitrogen Ratio (C:N) is key. The ideal C:N ratio is 25-30:1. The C:N ratio of MSW has increased over the years as the paper content has increased. A typical MSW ratio is now 60:1. To lower the C:N ratio, the modern trend is to add sewage sludges. The following table describes the C:N ratio of various materials.
C/N Ratio of Various Wastes MaterialC/N ratio Night soil6-10 Urine0.8 Blood3.0 Cow manure18 Poultry manure15 Horse manure25 Raw Sewage sludge11 Activated sludge6 Grass clippings12-15 Sawdust200-500 MSW60
Typical Small Island State Operations Leachate: left in the landfill, treated, recycled or released Landfill Gas: ignored, passively vented Septage: lagoon treatment, effluent discharged Screenings: landfilled, dedicated disposal cells Sewage Sludge: stored, land spread Other Residuals: uncontrolled
Caribbean Case Study- Bahamas New Providence New Providence Sanitary Landfill Operated by DEHS 60 mil HDPE Liner Leachate Collection Gas Collection Piping Installed Septage & Sludge Facility Operated by W&SC HDPE Liner Treats waste from septic tank pumpouts
Present Situation in New Providence Landfill Leachate Liquid Disposal (Deep Well) Treatment (Lagoons - Future) Septage & Sludge Lagoons (Anaerobic/Aerob ic ) Drying Beds (Future) Liquid Disposal (Deep Well)
Caribbean Case Study - Barbados Current situation: 9,000 m3 /day secondary wastewater treatment system at Bridgetown, producing primary and secondary sludges which are land spread. 9,000 m3/day advanced preliminary treatment plant for the South Coast, producing ~ 750 kg /day of screenings, currently bagged and landfilled. In-situ incineration is planned, at an estimated capital cost of ~ US$1.0 million.
Barbados Case Study Continued New engineered sanitary landfill (1.0 m of compacted clay liner) at Greenland with leachate collection and treatment capacity (anaerobic, facultative and aerobic lagoons in series). Built in 1997. Not yet in use. Current landfill at Mangrove being extended, with new cell having a composite liner and leachate collection system. However, leachate is currently being recirculated onto a section of the landfill that is not lined. Special wastes (abattoir wastes, grease) currently being land spread at another location.
Too Many Cooks? In Barbados, the administration of waste management includes the following agencies: Design of new landfill – Sewerage & Solid Waste Project (S&SWPU) Ministry of Health Design of Extension to old Landfill – Sanitation Services Authority (SSA) Min. of Health Operation of old landfill – SSA Design and construction of the South Coast Sewerage Project (SCSP) – S&SWPU
Too Many Cooks? Operation of the SCSP and the Bridgetown WWTP – Barbados Water Authority – Ministry of Utilities. Result: not only are different agencies responsible for solid and liquid waste management but different agencies are responsible for design vs. operation. This is typical in the Caribbean with a notable exception being St. Vincent & the Grenadines with the CWSA responsible for both solid and liquid waste.
Recommended Synergistic Approach Dispose of residuals from the SCSP (screenings) by bagging and landfilling and abandon the incineration plan. Abandon the plan to build a separate mechanical treatment septage and sludge handling facility. Dispose of these residuals at the landfill and operate the new cell at the existing landfill as a bioreactor. Special wastes (blood and grease) can be co- composted with yard waste at the proposed national composting facility or added to the liquid stream recirculated to the bioreactor cell at the landfill.
Conclusion: Real World? Solutions can appear very simple on paper yet are little more complicated to implement in the real world On a daily basis, landfills, sewage treatment plants and septage and sludge facilities throughout the Caribbean continue to operate and generate residuals The responsibility for cost effective business practices rests on the shoulders of the General Managers and the Directors of these operating entities
Conclusion It can be concluded that there is merit in investigating cooperative solutions that could result in cost savings, a higher level of environmental protection and reduced risk The benefits are numerous: Residuals from one stream could benefit another system resulting in a useable end product Capital and operating costs could be reduced Risk of damage to the environment from the mismanagement of these residuals could be prevented