The Potential of Subsurface Infiltration for the Treatment of Vermibed Effluents Generated by the Biofil Toilet

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In countries such as Ghana, where a significant proportion of the population depend upon ground water sources for domestic consumption, and where onsite sanitation is the predominant means of sanitation, the occurrence of water and sanitation related diseases due to contamination of groundwater remains the commonest public health problem. To safeguard groundwater from contamination a variety of treatment barriers have been practiced in various countries. The use of sub-soil infiltration in a form of soil aquifer treatment was one of such interventions that have long been practiced in this regard. In this study, effluent from a biofil toilet has been studied under laboratory based soil columns simulating Ghana environmental conditions to see the performance of different soil types in removing potential contaminants. Four different soil columns were characterized and installed; namely-sandy soil, clay soil, loamy soil and red lateritic soil and a multi-layer sand filter (MLSF) was also used to see the possibility of developing compact treatment system. In every soil column, sampling ports were positioned at 0.3m, 0.8m and 1.5m depths and 0.45m depth for MLSF only one port at the bottom. The results obtained showed that, the biofil digester was successful in reducing various contaminants. It achieved about 93% faecal coliform, 95% total coliform, 50% BOD, 54% COD and 88% TSS removals. Its performance for nutrient reduction was 25% total nitrogen with 79% NO3-N and 67%NO2-N removal, while Total phosphorous removal was 35% and 31% PO4-P. With respect to organic matter removal, sandy soil and red lateritic soil columns were able to produce quality effluent (TSS and BOD) well below the Ghana EPA guideline values (50mg/l). Superior performance up to 99% COD removal was observed in red lateritic soil column. Pathogen removal potentials of soil columns also show an average of 2 to 5 log removal of pathogen. Red lateritic soil specifically achieved 5 log removals at 1.5 m depth. All soil columns with exception of MLSF fulfil the WHO guideline value for NO3-N in drinking water (<10mg/l) and very low concentrations of PO4.
A Thesis Submitted to the Department of Civil Engineering, Kwame Nkrumah University of Science and Technology in Partial Fulfilment of the Requirements for the Degree of Master of Science in Water Supply and Environmental Sanitation