Feasibility and safety of papermaking wastewater in using as ecological water supplement after advanced treatment by fluidized-bed Fenton coupled with large-scale constructed wetland.

Reuse of pulp-and-paper industry wastewater as reclaimed water is an effective way to mitigate water resource shortage. In this study, the feasibility and safety of papermaking wastewater for the use as ecological water supplement after the treatment by fluidized-bed Fenton (FBF) coupled with constructed wetland (CW), were investigated from laboratory-scale to large-scale field. The optimum pH, HO, HO/Fe ratio and hydraulic retention time (HRT) of FBF were 3.5, 0.93 mL/L, 4 and 60 min, respectively, based on reduction of both total organic carbon (TOC) and genotoxicity. Furthermore, the safety of effluent was evaluated using SOS/umu assay and 8-hydroxy-2-deoxyguanosine (8-OHdG) in zebrafish. Results showed FBF followed by CW improved the conventional water quality indicators and reduced the toxicity. Average removal rates of chemical oxygen demand (COD), ammonia nitrogen (NH-N), total nitrogen (TN), total phosphorus (TP) and colority were 87.3%, 93.59%, 51.73%, 84.75% and 95.86%, respectively. The equivalent concentration of 4-nitroquinoline 1-oxide (4-NQO-EQ) decreased from 30.6 ± 1.6 μg/L in influent to 12.4 ± 1.0 μg/L after treated by FBF, then decreased to 5.9 ± 0.4 μg/L after treated by CW and to 3.2 ± 0.3 μg/L after 12-km downstream self-purification. The chronic survival rates of 21-d zebrafish significantly increased from 0.0% in influent to 58.8 ± 4.0% in effluent of CW and gradually increased to 68.8 ± 2.6% after 12-km downstream self-purification. Similarly, 8-OHdG level in zebrafish decreased from 120.0 ± 19.3 ng/L in effluent of ecological oxidation pond to 94.0 ± 7.5 ng/L in effluent of CW and gradually decreased to 42.0 ± 3.0 ng/L after 12-km downstream self-purification. The study concluded that FBF-CW is an efficient detoxication and water quality improvement technology for papermaking wastewater to be used as an ecological water supplement.