Anaerobic digestion dung filtrate recycling

This experiment investigated whether the water demand of low-tech anaerobic digestion (AD) systems in rural areas of sub-Saharan Africa could be reduced by continuous recycling of filtered digestate. We used 2 different concentrations of cow dung and filtrate, with 3 replicates and ran a semi-continuous system over 79 days with a reactor retention time of 25 days. We found that a higher chemical oxygen demand (COD) removal efficiency was achieved with dung and undiluted filtrate than with dung and diluted filtrate, indicating that AD could potentially be implemented more widely than is currently practiced, as labour could be saved for water collection activities. We regularly measured the COD, total solids (TS) and volatile solids (VS) content of the digestate and present the mean values with standard deviation here.