Recirculation of reject water in deep-dewatering process to influent of wastewater treatment plant and dewaterability of sludge conditioned with Fe2+/H2O2, Fe2+/Ca(ClO)2, and Fe2+/Na2S2O8: From bench to pilot-scale study

Evaluation of Sludge Deep-Dewatering Filtrate Recirculation to Wastewater Treatment Plant by Toxicity Detection with Microbial Fuel Cells

“…The optimal chemical dosages and conditioning methods are described in our previous study (Table ). Each batch of 18.29 kg sludge was conditioned and dewatered by a laboratory-scale diaphragm filter press system equipped with three diaphragm plates (250 mm × 250 mm) (Text S1 and Figure S2 of the Supporting Information). After dewatering, the dewatered sludge cake was detected with water content and organic matter content.…”

“… a The doses of reagents were based on the volatile matter of sludge in the advanced oxidation pretreatments according to our previous study b The doses of reagents were based on the dry solid of sludge in the traditional conditioner of Fe 3+ /CaO. …”

“… a The doses of reagents were based on the volatile matter of sludge in the advanced oxidation pretreatments according to our previous study …”

“…In our previous study, the dewatered filtrate only accounted for less than 1% of the total influent of WWTPs. 12 However, the production of dewatered filtrate in WWTPs was intermittent and uneven with time. For instance, more than half of the dewatered filtrate would be generated at the beginning of the 20% dewatering process of diaphragm filter press dewatering.…”

“…Normally, the filtrate from the sludge dewatering process is recirculating back to the mainstream and mixed with influent of wastewater and treated by a microbial treatment process in WWTPs. − Compared with influent of mainstream wastewater, deep-dewatering filtrates have significantly different characteristics, e.g., pH value, chemical oxygen demand (COD) content, conductivity, and chemical component, due to the usage of chemical reagents in sludge conditioning, which can be regarded as a new source of “potential pollution” in WWTPs. For instance, the deep-dewatering filtrate of sludge conditioned by FeCl 3 and lime was characterized by a high pH value (>12), which could induce irreversible damage to microbial cell walls with 5 min of exposure as the pH increased, especially above pH of 10 . Acidic deep-dewatering filtrates from AOP conditioning reduced the pH of mainstream wastewater of WWTP, posing a threat to filamentous swelling of activated sludge .…”