Soroca WWTP Project - Constructed Wetlands as a Locally Appropriate Technology Dr. Konrad Buchauer Soroca, Moldova SOROCA PROJECT LAUNCH WORKSHOP

Table of Contents 1.Reasons for choosing Constructed Wetlands 2.Constructed Wetlands – Technology and Construction 3.Project Implementation of Soroca WWTP

1. Reasons for Choosing Constructed Wetlands (CWs) LOCAL CONDITION CONCLUSION (1) Treatment targets: Carbon removal (BOD, COD, SS) Enhanced nutrient removal (N, P) Hygiene? Carbon removal of CWs is equivalent to convent. technologies. N removal – with a properly designed CW – can be brought to similar levels as with convent. technologies nowadays. P removal in CWs decreases over time, yet an acceptable mean elimination rate of 50% is considered feasible. Soroca WWTP shall be based upon 2-stage CWs. These systems feature superior pathogen removal, as compared to convent. technologies. Properly designed 2-stage CWs enable enhanced nutrient removal and even have better hygienic effluent quality than conventional technologies. Local Conditions <> Conclusions

1. Reasons for Choosing Constructed Wetlands (CWs) LOCAL CONDITION CONCLUSION (2) Cold winter temperatures and snowfall Latest design criteria take due consideration of cold temperatures. There exist about 20 years of practical experience with CWs in Central Europe under climate zones comparable to Moldova (France, Austria, Germany, Switzerland, etc.). CWs, of course, look different in winter time, but nonetheless work satisfactorily. Properly designed 2-stage CWs will continue working properly in winter time. summer winter Local Conditions <> Conclusions

1. Reasons for Choosing Constructed Wetlands (CWs) LOCAL CONDITION CONCLUSION (3) Limited financial resources, limited scope for a strong increase in water & wastewater tariffs Cost for CWs: Investment cost = US$ 3 million O&M cost = US$ 0,04 million/year CWs will reduce the financial burden on Soroca and lead to considerable lower W&WW tariffs than convent. technologies. Cost for (optimised) Activated Sludge system: Investment cost = US$ 5,1 million O&M cost = US$ 0,30 million/year (4) About 10 hectare of land are available for the WWTP The land requirement for 2-stage CWs is estimated to about 5 ha at present. Hence there is sufficient land available, offering even scope for further expansions. Local Conditions <> Conclusions

1. Reasons for Choosing Constructed Wetlands (CWs) LOCAL CONDITION CONCLUSION (5) Lack of skilled operators CWs can be satisfactorily operated by local staff after appropriate training. The Soroca WWTP project will include staff training. Even though CWs are easy to operate, this is considered indispensable and will safeguard proper operation practices according to the latest know-how. By contrast, the operation of convent. techn., such as AS, poses much higher challenges to operators. The difficulties not only relate to compliance with effluent criteria, but also to human safety. A relatively short training would not be sufficient for such a task. Typical WWTP operator training programmes in Central Europe take years, and are targeting professionals only (electrician, etc.). Local Conditions <> Conclusions

1. Reasons for Choosing Constructed Wetlands (CWs) LOCAL CONDITION CONCLUSION (6) Unreliable power supply CWs will be able to cope with unreliable power supply. The CWs as such operate without electric energy. The wastewater flows through the plant by gravity. No aeration, recirculation pumping, etc is required. By contrast, the operation of convent. techn., such as AS, is fully dependant on permanent and strong power supply. Local Conditions <> Conclusions

1. Reasons for Choosing Constructed Wetlands (CWs) 2-stage CWConvent. Technol. ENVIRONMENT  BOD / COD / SS removal ●●  Nutrient (N / P) removal ●●  Coliform / Helminth removal ● -- COST  Investment ● --  O & M ● --  Wastewater tariff ● -- TECHNOLOGY  Ease of operation, requirement for skilled operators ● --  Land requirement ● ●  Dependence on permanent power supply ● -- ● favourable -- unfavorable Summary: Technol. Appropriateness under Local Cond.

2. Constructed Wetlands – Technology and Construction Technologies for Constructed Wetlands (1) Horizontal subsurface flow (HF)(2) Vertical subsurface flow (VF) (3) Free water surface (FWS)(4) 2-stage (hybrid) CWs Suggested for Soroca: Combination of (1) + (2) Source: SWAMP 2005

2. Constructed Wetlands – Technology and Construction 2-stage CWs: French system with 2 VF Sources: Molle et al. 2004, Lienard 2003 Flow scheme Nr. of 2-stage CWs in France

2. Constructed Wetlands – Technology and Construction 2-stage CWs as compared to 1-stage CWs: Advantages Approximately 50% of land requirement, as compared to 1–stage CWs. Better treatment efficiency, particularly better nutrient and pathogen removal. 20 years of practical experience. No pre-treatment required, apart from screening (French system). No need for separate sludge treatment ( French system).

2. Constructed Wetlands – Technology and Construction Construction steps Source: Austria, BOKU 2005

3. Project Implementation of Soroca WWTP Consultant’s Key Tasks Other 2-stage CW options French CW system with 2-stage VF Analysis and definition of prevailing wastewater flow rates and load Optimization of treatment technology Detailed design & Bidding Docs Supervision of construction works Staff training Assistance during start-up & initial 6-month operation period

3. Project Implementation of Soroca WWTP Time Schedule Design and Bidding Docs Construction period Staff training2010 WWTP start-up st know-how dissemination workshop in Soroca2011