Soroca WWTP Project - Constructed Wetlandsas a Locally Appropriate Technology
Dr. Konrad Buchauer
10.12.2007Soroca, 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 CW Convent. 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
1 2 3
4 5 6Source: Austria, BOKU 2005
3. Project Implementation of Soroca WWTP
Consultant’s Key Tasks
Other 2-stage CW optionsFrench 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 2007 - 2008
• Construction period 2008 - 2010
• Staff training 2010
• WWTP start-up 2010
• 1st know-how dissemination workshop in Soroca 2011