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Korbinian Kätzl, Manfred Lübken, Tito Gehring, Marc Wichern

• Access to improved sanitation is often lacking in many low-income countries, and approximately 90% of the sewage is discharged without treatment into receiving water bodies. The aim of this study was the development and evaluation of an efficient low-cost wastewater treatment system for developing countries. Biochar and woodchips, potential locally available and inexpensive materials, were used for anaerobic wastewater filtration and their suitability evaluated in comparison to gravel as a common reference material. Filters were fed with raw sewage from a municipal full-scale wastewater treatment plant in Germany at 22 °C room temperature with a hydraulic loading rate (HLR) of 0.05 m∙h\(^{−1}\). This resulted in a mean organic loading rate (OLR) of 252 gCOD∙m\(^{−3}\)∙d\(^{−1}\) and a mean organic surface load of 456 gCOD∙m\(^{−1}\)∙d\(^{−1}\). To determine the influence of different filter materials, the removal efficiency of chemical oxygen demand (COD), total organic carbon (TOC), turbidity, and faecal indicator bacteria (FIB) \(\textit {E. coli}\) and enterococci were tested. It was found that COD (up to 90%), TOC (up to 80%), FIB (up to 1.7 log\(_{10}\)-units), and turbidity (effluent turbidity below 35 NTU) could be significantly reduced. The findings of this study demonstrate the potential of anaerobic filters (AFs) for wastewater treatment in low-income countries to reduce water pollution and comprehensively improve water quality. The performance of biochar filters was significantly better over the entire experiment compared to woodchip and gravel filters with respect to COD, TOC, turbidity, and FIB removal, indicating the superior properties of biochar for wastewater treatment.