Microbially-mediated pretreatment of aerated oil and gas produced water by addition of phosphorous or activated sludge

Abstract

Produced Water (PW) from oil and gas (O&G) producing wells is a unique source of water in water-stressed regions. Microbiota within O&G formations have been well-studied on site/in-situ but few applied works have considered their role in the treatment of PW in engineered water treatment systems. Herein, we operated a simple aeration/mixing bench-scale bioreactor fed with produced water under three conditions: 1) PW alone (control; hereafter referred to as 'baseline'), 2) phosphorous dosed daily as KH2PO4, and 3) activated sludge (AS) dosed daily from a sequence batch membrane bioreactor (SB-MBR). Aerated and mixed PW alone (baseline) was able to attenuate PW chemistry with removal of soluble chemical oxygen demand (sCOD) and ammonia by 27.6% and 17.8%, respectively. Further KH2PO4 and AS additions improved water treatment efficiency markedly; in the KH2PO4 addition reactor, sCOD and ammonia were reduced by 50.0% and 61.5%, respectively, and in the AS addition reactor by 52.5% and 59.2%, respectively. Microbial consortia determined via 16S rRNA gene amplicons differ in composition between raw PW and all reactors; order Kiloniellales was most common in raw PW while orders Rhodobacterales, Pseudomonadales, and Caulobacterales were most abundant amongst AS, KH2PO4, and baseline conditions, respectively. Several different microbial consortia are capable of treating raw PW which suggests that functional redundancy amongst microbiota in engineered treatment systems may be underappreciated. With simple addition of phosphorous and/or activated sludge to PW as part of a treatment strategy, a higher quality water can then be subjected to conventional treatment and/or local reuse.