# Biochar for Wastewater Treatment--Conversion Technologies and Applications
## 5 Environmental Application of Biochar for Wastewater Treatment
### As a Filtration Support Media  
Biochar can be used in various water treatment designs. For instance, it can be incorporated in a biochar layer/column to a slow sand filter or bio-sand filter systems for the treatment of wastewater. The use of biochar filtration systems has received greater attention for its potential to remove particulate matter, heavy metals and reduce pathogen loads (Table 4). In a study performed by [PERSON] et al. [17], a higher removal efficiency of a _Miscanthus_ biochar filter was observed, which was better or equal compared to a sand filter. Mean removal of chemical oxygen demand of biochar filter (\(74\pm 18\%\)) was significantly higher than that of sand filter (\(61\pm 12\%\)). The biochar filter also showed higher removal of _E. coli_ with a mean reduction of \(1.35\pm 0.27\) log-units compared to that of sand filters with a mean reduction of \(1.18\pm 0.31\) log-units. [PERSON] et al. [14] evaluated the potential use of biochar as a filter media for the removal of total suspended solids, nutrients, heavy metals, and _E. coli_ from synthetic storm water. The filtration on biochar was able to remove about 86% of suspended solids, 86% of nitrate and 47% of phosphate from the storm water effluent. After filtration, the concentration of Cd,Cr, Cu, Pb, Ni, and Zn (heavy metals) were also reduced by 18, 19, 65, 75, 17, and 24%, respectively, while only 27% removal efficiency of _E. coli_ was observed. This percentage was much lower than those reported for zeolite [183] and activated carbon [184], showing removal efficiencies of _E. coli_ from storm water of about 53% and 98%, respectively. According to the authors, this difference could be due to the inflow concentration and the antecedent microbial levels as also reported by [PERSON] et al. [185]. The removal of suspended solids and organic matter in an anaerobic biochar filter, could be performed by a successive of steps, as described by [PERSON] et al. [186] (Figure 3), starting with a coagulation of suspended solids in the supernatant water layer followed by the sedimentation and the filtration of larger particles on the filter surface, smaller particles are removed by straining and adsorption in deeper filter zones, while organic matter is hydrolyzed under anaerobic conditions. The efficiency of the biochar filter increases with the increase in the surface area and the attachment sites on the biochar surface, which also support the biofilm establishment and the bacterial deposition within the filter column [186,187]. The reduction of pathogens could be governed by different key mechanisms including the filtration of larger pathogens (e.g., protozoa, amoeba) and the adsorption of negatively charged viral and bacterial cells. Other mechanisms such as the electrostatic attraction of bacteria to the biological film developed on the surface of the biochar filter [188] and the attachment of _E. coli_ to the biochar filter coupled with the increase in the water-holding capacity could interfere. The biochar after filtration becomes enriched with nutrients and therefore can be reused as a fertilizer for soil amendment. In the study performed by [PERSON] et al. [189], the biochar filter showed the same removal of pathogens as a common sand filter (1.4 log units on average). The concentration of P, Mg, and K were reduced during filtration, while N content remained unchanged. The agronomic effects of the biochar filter on spring wheat biomass production on an acidic sandy soil was evaluated. The results showed higher wheat biomass production for biochar filter (37%) treatment (20 t/ha), compared to the unamended control [189]. Figure 3: Estimated removal mechanism in an anaerobic biofiliter using rice husk biochar as biofiliter material. Reproduced from reference [186], copyright (2019), with permission from Elsevier B.V.