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The response surface methodology coupled with central composite design was applied to optimize the operational parameters of electro-Fenton (EF) as advanced treatment of biologically pretreated coal gasification wastewater. The integration of TOC, COD, and total phenols removal was selected as the response for model establishment and optimization. A quadratic model with high significance was developed to predict the treatment performance and optimize process parameters. The optimal parameters were determined as pH 3.83, 1.44 mmol L−1of Fe2+concentration, and 16.28 mA cm−2of current density, with the predicted optimal integration removal efficiency of 73.29%. TOC decay in the EF under optimal condition followed pseudo-first-order kinetic reaction with the apparent rate constant of 0.0103 min−1. The mass transfer constant was determined to be 4.29 × 10−5 m s−1at the optimal current density. The results demonstrated that EF could serve as a technically feasible and cost-effective method with potential applications for the advanced treatment of biologically stabilized coal gasification wastewater. [ABSTRACT FROM PUBLISHER]

The study aims to: (1) investigate the adsorption of powdered activated carbon (PAC) and granular activated carbon (GAC) for phenol, indole, and their mixtures, respectively, and (2) determine the bioregeneration efficiency and reusability of PAC loaded with phenol, indole, and their mixtures. The results showed that phenol was easier to be adsorbed than indole. The adsorption using PAC was obviously better than GAC. The considerably higher bioregeneration efficiency of the phenol-loaded PAC as compared to that of indole-loaded PAC was probably due to the recalcitrant nature of indole. PAC exhibited much higher adsorption capacity for indole, especially in the presence of low concentration of phenol. Besides, phenol improved the biodegradation of indole and therefore enhanced the reusability of indole-loaded PAC. Therefore, powdered activated carbon technology (PACT) was appropriate for the treatment of similar wastewater. Within the PACT system, PAC preferentially adsorbed the recalcitrant indole while the relatively easily degradable phenol was utilized by the biomass. Besides, phenol enhanced the degradation of indole and the reusability of PAC, which resulted in a stable and efficient performance. [ABSTRACT FROM PUBLISHER]

Coal gasification wastewater (CGW) is a refractory wastewater, whose anaerobic treatment has been a severe problem due to its toxicity and poor biodegradability. Using a two-stage anaerobic digestion as a control, the two-phase anaerobic digestion of real CGW was investigated. After 210 d of operation, the maximum removal efficiencies of COD and total phenols (TP) reached 50–60% and 55–60%, respectively, in the two-phase anaerobic digestion at total hydraulic retention time (HRT) of 48 h; the corresponding efficiencies were at low levels of 40–45% and 42–50%, respectively, in the two-stage anaerobic digestion. COD and TP removal efficiencies increased to 69.7 and 65.9%, when 50% of the effluent was recirculated to the hydrolytic acidogenic reactor. Phenol utilization rate and specific methanogenic activity (SMA) were decreased to 57.6 mg phenol/(gVSS d) and 394.3 mg COD-CH4/(gVSS d), respectively, as the HRT in the hydrolytic acidogenic reactor was reduced to 18 h. After the two-phase anaerobic digestion, the wastewater concentrations of the aerobic effluent COD could reach below 150 mg/l when compared to 237.2 mg/l if two-stage anaerobic digestion was done and 328.5 mg/l if sole aerobic pretreatment was done. The results suggested that the two-phase anaerobic digestion improved significantly both anaerobic and aerobic biodegradation of real CGW. [ABSTRACT FROM PUBLISHER]