Eco-Innovation in Wastewater Management Name: Magnus Williams Country: Commonwealth of Dominica Organisation: Dominica Water And Sewerage Company Limited (DOWASCO)
“Dominica: Nature Island of the Caribbean” • Climate is Tropical • Temperature range from 15 to 34 Degrees • 80 rivers pour out along the east and west coastlines as a result of rugged forest and generous rainfall • 9 of which are major rivers basins • Humidity Greater than 70% • Hurricane Season June – November • Peak of Dry Season April – May • Average Annual Rainfall 30” – 50” • 80% of population lives in coastal communities on about 24% of the available land area
COMPANY PROFILE • The Dominica Water and Sewerage Company Limited (DOWASCO) is a registered company owned wholly by the Government of the Commonwealth of Dominica. • DOWASCO was established as a water and sewerage company by an act of Parliament, Water and Sewerage act N0. 17, in December of 1989. • Services include Domestic, Commercial, and Industrial Water Supply • Water Supply to Standpipes and Fire Hydrants • Bulk Water Sales to Ships • Sewerage Collection and Treatment
Existing Sewerage Services • Sewerage treatment is by nature a green activity due to its positive environmental impact. • Sewerage Collection and Treatment for entire capital city of Roseau and environs. • Simple system comprising collection network, screening and de-gritting, preliminary treatment, and discharge via outfall. • Previously, raw sewerage discharged along shoreline of city. This practice was incompatible with the image Dominica sought to portray. • Routine monitoring of water quality levels along the cost shows a marked improvement since the commissioning of the plant. • This has contributed toward development of the tourism product and the ‘Bay Front’ area of the city in particular.
Portsmouth Sewerage System • Portsmouth is the second town with much potential for eco-tourism. • No centralized sewerage system. • Combination of bathymetry and sea currents, soil types, and high water table make the present use of septic tank an soak-away systems less than desirable. • Adverse effects on recreational water quality. • Present boom in housing in the area is making the situation worse. • Similar benefits of the Roseau experience may be realized in Portsmouth as well with introduction of a proper wastewater management system. New Sewerage Collection and Treatment System • Proposed System to consist of waste stabilization ponds (WSPs), constructed wetlands, and UV disinfection. • Tertiary treatment and effluent reuse for irrigation. • Use of renewable energy and designed for energy efficiency. System maximizes use of gravity. • Will result in vast improvement of water quality of rivers and the Prince Rupert Bay. • Positive impacts on general human health. • Mitigate against potentially catastrophic environmental effects of present tourism and housing development.
System Overview and Features • Sewage treatment by WSPs has been considered an ideal way of using natural processes to improve wastewater effluents. • Collection network • Screening and De-Gritting, Grease trap • Anaerobic, Facultative, Maturation Ponds • Constructed Wetlands • UV treatment • Design Parameters: • Influent BOD5 = 400 mg/l • Target Effluent BOD5 = 10 mg/l • Estimated Peak Electric Power Demand = 32 kW • Treatment Plant Capacity = 2,200 m3/d
The preliminary treatment process consists of physical unit operations, i.e. screening for removal of debris and rags, grit removal for the elimination of coarse suspended matter and flotation for the removal of oil and grease. Downstream of the preliminary treatment unit, a pond system is proposed for primary, secondary and partially tertiary treatment. This system is a typical stabilisation pond configuration consisting of anaerobic ponds A, facultative ponds F and maturation ponds M. The pond system is followed by constructed wetlands W. The use of constructed wetlands is a cost-effective treatment alternative for further tertiary treatment. Wetlands are land areas with shallow water depths that support the growth of emergent plants such as cattail, bulrush, reeds and sedges. The vegetation provides surfaces for the attachment of bacteria filters, aids in the filtration and absorption of wastewater constituents, transfers oxygen into the water column and controls the growth of algae by restricting the penetration of sunlight. The constructed wetland should provide better performance than a natural wetland of equal area, especially. Before discharging the effluents into the recipient, UV disinfection is proposed to improve the bacteriological quality of the treated wastewater. The effluent quality to be achieved will allow the reuse of the effluent for unlimited irrigation of crops. In any case, the quality of the treated effluent will not have any negative environmental impacts.
Funding Limitations • Originally part of the EU-funded West Coast Water & Sewerage Project, which comprised of a water component and sewer component (SFA 2008). • Feasibility Study, Final Designs, and Tender Documents Completed for both phases • Final cost estimate for sewerage component 5.6 million Euros. • Sewer component not tendered since final estimates exceeded approved budget . • Implementation of the Water component is presently in progress. • Funding for sewerage component yet to be identified. • It is critical that the project is implemented so that all the potential benefit is not lost.
Mini-Hydro Power Project • DOWASCO presently owns a bulk water pipeline used for supply of large quantities of water to ships. • A Feasibility Study was completed (funded by CREDP/GTZ, consultant Bernard Ingenieure) and designs prepared for the construction of a 220 kW Mini-Hydro Power Station at the tail end of the bulk water facility. The plant will use water from the bulk water line to generate electricity during periods when no bulk water is being sold. • Project determined to be technically and financially viable. • Estimated construction cost is 1.1 Million Euros. • Can be used to provide necessary power for nearby sewerage network pump station. • Transfer of surplus power to the national power grid, via net metering arrangement with power company. • Indirectly provide all necessary power for existing Roseau Plant and proposed Portsmouth Sewerage Plant. • Net effect is very little reliance on fossil fuels by the company and specifically for sewerage treatment. • Funding options being explored, but no commitments.
Summary • As is clearly indicated in the mission statement of the company, DOWASCO is committed toward fulfilling its mandate via the use of appropriate technology and sustainable environmental practices. • Our plans with regard to wastewater management bolster Dominica’s image as the Nature Island. • The Portsmouth Sewerage System will: • Make use of natural processes for elimination of waste. • Be Energy efficient. • Utilize a renewable energy source through the construction of DOWASCO’s Mini Hydro Power Plant. • Be environmentally friendly. • Promote agriculture via effluent reuse for irrigation. • Support sustainable tourism and economic development in Dominica’s rapidly growing second town.