Low-cost Options for Treating Faecal Sludges (FS) in Developing Countries

Transcription

1 International symposium on Faecal Sludge Management (FSM) Policy Dakar May 9-12th 2006 Low-cost Options for Treating Faecal Sludges (FS) in Developing Countries Martin Strauss EAWAG / SANDEC Tel /

2 Contents Sanitation infrastructure and urban growth FS characteristics Research approach Results Open research questions 2

3 Sanitation infrastructure and urban growth e.g. Bangkok, Manila, Accra Percent of population served by on-site sanitation e.g. London, Paris, Berlin Latin America Tanzania Ghana Philippines Manila Bangkok billion urban dwellers on on-site sanitation! Number and share growing! 3

4 Sanitation infrastructure and urban growth 4

5 Challenges: how to shift our mind set? Engineers thrusts and beliefs How to empty this pit? What happens next? 5

6 FS characteristics in selected cities in developing countries Location Accra (Ghana) Accra (Ghana ) Alcorta (Argentina) Ouagadougou (Burkina Faso.) Bangkok (Thailand) Type of FS Public toilet sludge Septage Septage TS (mg/l) 52,500 12,000 (6,000 35,000 SS) 19,000 15,350 (2,200 67,200) COD (mg/l) 49,000 7,800 4,200 13,500 15,700 (1,200 76,000) NH 4 -N (mg/l) 3, (120 1,200) 6

7 Developing FS treatment options in partnership 7 Burkina Faso/Ghana Argentina Thailand/Vietnam

8 Appropriate FS treatment options in developing countries 8

9 Selected FS treatment options Constructed wetlands Settling/thickening tank Drying bed Co-composting 9

10 Design criteria and removal performances of selected low-cost options for faecal sludge treatment Treatment process or option Design criteria Solids-liquid separation Treatment goal / achievable removal Organic pollutants in liquid fraction Parasites (helminth eggs) Drying/dewat ering beds kg TS/m2/year 0.05 m 2 /cap(accra) SS : % COD: % NH 4+ -N : % To be treated for further improvement in ponds or constructed wetlands 100 % retained on top of the filtering media Constructed wetlands (planted drying beds) 250 kg TS/m 2 /year SAR: 20 cm/year (Bangkok) SS > 80 % SAR: 20 cm/year To be treated for further improvement in ponds or constructed wetlands 100% retained on top of the filtering media 10

11 Design criteria and removal performances of selected low-cost options for faecal sludge treatment Treatment process or option Design criteria Solids-liquid separation Treatment goal / achievable removal Organic pollutants in liquid fraction Parasites (helminth eggs) Settling / thickening tank SAR*: 0.13 m 3 /m 3 of raw FS HRT: 4 h S: m 2 /cap Accra SS: % COD: % To be treated for further improvement in ponds or constructed wetlands Concentrated in the settled and floating solids Facultative stabilization ponds 350 kg BOD 5 /ha/d Not for this purpose > 60 % removal of BOD 5 Removed by settlement 11

12 Removal efficiency and challenges Removal efficiency (%) TS COD N-NH4 Settling/Thickening Tank (septage+public toilet, 1:1) Constructed wetlands (septage) Drying beds (septage+public toilet, 1:1)

13 Removal efficiency and challenges Effluent concentration TS (mg/l) COD (mg/l) N-NH4 (mg/l) EC (ms/cm) Settling/Thickening Tank (septage+public toilet, 1:1) 9,000-14,000 7,000-12,000 1,000-2, Constructed wetlands (septage) 1,000-6, Drying beds (septage+public toilet, 1:1)

14 Removal efficiency and challenges Variable SS Effects and expected problems - Potential difficulties in solids removal from deep ponds; - Short-circuiting due to sludge settling - Sludge drying beds to be devised as a separate treatment NH 4 / NH 3 - Ammonia toxicity due to high concentration in undigested FS Inhibition to the development of facultative and maturation pond conditions; - Eye irritation Colouration - Dark colour of FS supernatants prevents light penetration - Algal growth and hence facultative or maturation pond conditions may not evolve Even though the organic load can be adjusted for a polishing treatment in stabilisation ponds, the high concentrations of salinity and NH4/NH3 hinder the biochemical degradation (Strauss et al., 2004) 14

15 Open research questions Seeking collaboration! a) Nitrification/denitrification in vertical flow constructed wetlands treating faecal sludge: influence of bed configuration b) Organic matter and N removal mechanism in floating macrophytes-based system treating FS effluent/percolate c) Enhancing FS dewaterability with bulking organic material: design and operation criteria d) Helminth eggs stabilisation in biosolids generated by FS treatment plant e) Anaerobic digestion cum biogas: off-site decentralised low-cost reactors reactor development 15

16 Faecal sludge management - A bridge to reach the MDGs 1 liter of FS = 100 liters of wastewater!!! 1 truck load discharge in the environment = 5000 people defecating in the open!!! Eawag/Sandec Switzerland Tel