The efficiency of anaerobic biofilters (AnBF) as low-cost wastewater treatment systems was investigated. Miscanthus-biochar was used as filtration media and compared with sand as a common reference material. Raw sewage from a municipal wastewater treatment plant was stored in a sedimentation tank for two days to allow pre-settlement of wastewater particles. Subsequently, wastewater was treated by AnBFs at 22 °C room temperature at a hydraulic loading rate of 0.05 m•h −1 with an empty bed contact time of 14.4 h and a mean organic loading rate of 509 ± 173 g coD •m −3 •d −1 . Mean removal of chemical oxygen demand (COD) of biochar filters was with 74 ± 18% significantly higher than of sand filters (61 ± 12%). In contrast to sand filters with a mean reduction of 1.18 ± 0.31 log-units, E. coli removal through biochar was with 1.35 ± 0.27 log-units significantly higher and increased with experimental time. Main removal took place within the schmutzdecke, a biologically active dirt layer that develops simultaneously on the surface of filter beds. Since the E. coli contamination of both filter materials was equal, the higher removal efficiency of biochar filters is probably a result of an improved biodegradation within deeper zones of the filter bed. Overall, performance of biochar filters was better or equal compared to sand and have thus demonstrated the suitability of Miscanthus-biochar as filter media for wastewater treatment.www.nature.com/scientificreports www.nature.com/scientificreports/ degradation during storage time. To avoid sedimentation, the storage reservoir was continuously stirred (IKA RW 10 R, IKA-Werke, Staufen, Germany) and renewed every two days.The filters were fed by peristaltic pumps (Watson Marlow 205 S and Watson Marlow 323 S; Falmouth, United Kingdom) with a constant HLR of 0.05 m•h −1 . The mean organic surface load was 366 ± 125 g COD •m −2 •d −1 and 111 ± 37 g TOC •m −2 •d −1 , respectively. This resulted in a mean OLR of 509 ± 173 g COD •m −3 •d −1 and 154 ± 52 g TOC •m −3 •d −1 (Table 1). The experiment was performed at constant room temperature (22 ± 1 °C) with an empty bed contact time of 14.4 h.Sampling. Before the first sampling filters were operated with wastewater for six days. Samples of influent and effluent were taken in sterile 50 mL tubes and tested immediately for FIB E. coli and enterococci, temperature, pH, EC and turbidity as well as stored for further physico-chemical analysis, namely NH 4 -N, P tot , COD and TOC at −20 °C. To develop a removal profile over filter depth, water samples were taken at the sampling ports (b), (c), (e) and the effluent (f, Fig. 6) 50 days after filter activation and analyzed for FIB concentrations.After 70 days, one sand and one biochar filter have been dismantled to sample filter material at the filter depths 0-5 cm (direct below the schmutzdecke), 10-15 cm, 20-25 cm and 40-45 cm. Filter material was tested for FIB and prepared for scanning electron microscope (SEM) and confocal laser scanning microscope (cLSM) analysis. Scientific RepoRtS |(2...

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