COD removal of wastewater from hydrothermal carbonization of food waste: Using coagulation combined activated carbon adsorption

Hydrothermal carbonization (HTC) can convert food waste into carbon fuel, thus to provide renewable energy. The wastewater, derived from HTC of food waste, contains complex organic pollutants, with a high COD value and low BOD/COD, which is not feasible for direct anaerobic fermentation. This work studied coagulation combined activated carbon (AC) adsorption to reduce the COD in HTC wastewater to promote its biodegradability. The experimental results indicated that poly aluminum ferric sulphate (PAFS) and polyacrylamide (PAM) are the optimal coagulant and coagulant aid, respectively. With the dosage for PAFS, PAM, and AC was 6 g/L, 10 mg/L, 30 g/L, respectively, it can achieve 68.41% of the COD removal ratio, and promote the transmittance of the wastewater from 23% to 89%. Xarthene, carbamide, ferulic acid and inorganic compounds composed of calcium, magnesium, and aluminum plasma from the sediment were detected by X-ray diffraction analysis (XRD), which proved the synergistic effect between coagulation and AC adsorption. The typical pollutants in HTC wastewater were reduced from 19 to 8 kinds after treatment. BOD/COD ratio also increased from 0.30 in wastewater to 0.75 in liquid residual after treatment, improved for subsequent biochemical treatment. Therefore, the coagulation combined adsorption treatment is thought as a promising method in HTC wastewater pretreatment, and a possible prerequisite in the industrial utilization of food waste HTC technology.