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