For topsoil application – <1 nematode egg per kilogram wet weight and <1000 fecal coliforms/L Requires 14 days at >50°C – Generally, small digesters only reach mesophilic temperatures. – The temperature inside the digester may not be steady state. Treatment Requirements
Sterilization Treatments Temperature 110 min to reach 99% Ascaris ova inactivation above 50 ° C Digester design which reaches 50 ° C Well-maintained and turned windrow composting >3 months with palm/plantain leaf roof structure Nitrogen loss through NH3 volatilization Alkaline stabilization 24 days to reach 99% Ascaris ova inactivation at pH 12 and 30 ° Post-treatment curing for 30 days with ash Nitrogen loss through NH3 volatilization Ammonia 16 days to reach 99% Ascaris ova inactivation with 1000mg/L NH3 – The digester produces ammonia
Design Recommendations Continually test the effluent for pathogen (mainly Ascaris) incidence in the laboratory of SOIL Install thermometers in the reactors to evaluate thermodynamics of digestion Evaluate how much ammonia is produced in the digestion process If necessary, store effluent covered, away from homes, foot paths, and “play” areas
Storage Quantities V=75x10 n m 3 slurry 188x10 n kg dry slurry/day * 20 day retention time m= 3760x10 n kg dry slurry/digester 35.4% mass lost during digestion m=1331x10 n kg dry effluent/digester 1331x10 n kg dry effluent/digester * 0.001kg/t * (90day composting treatment/20day digester cycle) For compost: need storage capacity of 6x10 n t/digester 1331x10 n kg dry effluent/digester * 0.001kg/t * (30day ash treatment/20day digester cycle) For ash treatment: need storage capacity of 2x10 n t/digester
Effluent Use as Soil Conditioner The soils of Haiti demonstrate severe erosion and low fertility. Fertilizers are not accessible. Sludge effluent is a proven soil amendment and fertilizer. Effluent should be buried or worked into the soil at least 3 months before crop harvest. Effluent should not be applied to crops that will be eaten raw.
Application Recommendations Corn 24 t/ha Lowland Haitian Soils: 0.5g N/kg, 10 mg P/kg, 30mg K/kg Digester effluent will provide AT LEAST: 4.6 kg N /t, 2.42 kg P/t, 9.79 kg K/t Application for low yield by crop: Dry Bean 14 t/ha Plantain 15 t/ha
Farmer Experimentation Groups After the effluent meets application standards… SOIL can work with a small group of farmers willing to experiment with the effluent Experimentation groups can establish local ownership and application best suited to local contexts. The effort can be aligned with the compost being harvested from the community composting toilets. SOIL/EWB can hold a short training on appropriate application. If the project expands, initial project participants can train new farmers interested in using the technology. Farmers can continue experimentation with liquid effluent as a natural pesticide.
References Gillette, R Soils and inputs available - Haiti. In Tropical Cropping Systems. Cornell University. Available online at > Isaac, L.; C.W. Wood; D.A. Shannon Hedgerow species and environmental conditions effects on soil total C and N and C and N mineralization patterns of soils amended with their Prunings. Nutrient Cycling in Agroecosystems 65: 73–87. Pecson, B.M et al The effects of temperature, pH, and ammonia concentration on the inactivation of Ascaris eggs in sewage sludge. Water Research, 41: Raccurt CP, et al Human cryptosporidiosis and Cryptosporidium spp. in Haiti. Trop Med Int Health, 11(6): Schooning, C. and T.A. Stenstrom Guidelines for the Safe Use of Urine and Feces in Ecological Sanitation Systems. EcoSanRes Publications. Stockholm Environment Institute. Sophea, K. and T.R. Preston Comparison of biodigester effluent and urea as fertilizer for water spinach vegetable. Livestock Research for Rural Devleopment, 12 (6). Thy, S; T.R. Preston; and J. Ly Effect of retention time on gas production and fertilizer value of biodigester effluent. Livestock Research for Rural Development, 15 (7). Wright, P Overview of Anaerobic Digestion Systems for Dairy Farms. Natural Resource, Agriculture and Engineering Service (NRAES-143).