Co-treatment of shale-gas produced water and municipal wastewater: Removal of nitrogen in a moving-bed biofilm reactor

Co-treatment of hydraulic fracturing produced water (PW) with municipal wastewater is a cost-effective shale gas PW management option. However, little attention has been paid to the impact of PW on the reliability of bioprocess in municipal wastewater treatment plants. In this study, a mature chemical pretreatment method was used to remove a large proportion of organic matters in real PW. Then a laboratory-scale moving bed biofilm reactor (MBBR) was established for the co-treatment of pretreated PW and synthetic domestic wastewater. Results showed that CODCr removal rate reached above 90% and acute toxicity was lowered by 20% in the pretreatment of PW using consecutive Fenton-NaClO oxidation. After 68 days of slowly increasing the mixing ratio, complete nitrification-denitrification was established with a maximum mixing ratio of 50%. The mean total nitrogen (TN) removal rate reached above 60% when the MBBR operated under maximum mixing ratio for the following 38 days. Shotgun metagenomic analysis revealed high taxonomic structure similarity between suspended and attached growth biomass in the MBBR when the mixing ratio was maintained at 50%. The functional diversity of nitrite-oxidizing bacteria may be present in the saline biological nitrogen removal system and may strengthen nitrogen and other typical element cycles. (C) 2019 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.