Treatment Of Petrochemical Wastewater Using Intensified A/O Biofilm Reactors

In this paper, two A/O biofilm reactors were developed to enhance the removal of organicpollutants in petrochemical wastewater. The reactor was composed by an anoxic phase (phaseA) and two aerobic phases (phase O1and phase O2). A fixed bed bioreactor filled withmacroporous plastic ball with modified polyurethane foam and a moved bed bioreactor filledwith modified polyurethane foam were built up and their performance was compared. Theremoval rate of chemical oxygen demand (COD), nitrogen and total phosphorus (TP) wasevaluated under the conditions of influent with different characteristics. The effects on theinfluence of treatment causing by changes of HRT and sludge return rate were studied. Thevariation in the characteristics of influent and effluent as well as the biofilm bacteriacommunity were analyzed.Results showed that the COD removal rate of over72%and ammonium removal rate ofover90%were achieved at a hydraulic retention time (HRT) of30h and a sludge return rateof100%in the two reactors. Meanwhile, the concentration of biochemical oxygen demand(BOD5) was lower than5mg/L with a bad biodegradability and the concentration of TP waslower than1mg/L mainly composed with orthophosphate. The removal rate of COD and TNwas the highest at the ratio of mixed petrochemical and domestic wastewater of3:1. CODand ammonium were mainly degraded in O1phase and enhanced in O2phase. The movedbed had a better capacity to resist the loading shock and denitrify, fixed bed had a bettercapacity to degrade organic matter and ammonium. At a HRT of15h, the removal rate ofreactor had not changed much, and TP removal rose obviously. At a sludge return rate of200%, the effluent COD and ammonium reduced, TP and nitrate had no change.The soluble microbial products (SMP) contributed about50%to the effluent COD andfixed bed reactor produced less SMP. The ratio of the main composition of SMP (protein andpolysaccharide) was about1:1. The molecular weight (MW) of organic matter in the influentwas mainly ranged in less than1kDa (70.9%) and more than100kDa (10.4%). In theeffluent, the MW was mainly in less than1kDa (56.6%and54.1%, respectively) and1-5kDa (26.2%and38.0%respectively). The distribution ratio of organics with a MW of higher than10kDa decreased, indicating that A/O biofilm reactor had a good capacity to degrade themacromolecular organics.Results of454pyrosequencing analysis showed that the moved bed biofilm had a betterabundance and evenness of microbial flora, but a lower species diversity, meaning a goodstability while less dominant species. Proteobacteria accounted for most of sequence (60.0%and60.4respectively), then Planctomycetes (16.9%and20.2%respectively) at the phylumlevel. The moved bed had a better capacity to denitrify. The fixed bed had a higher proportionof Chloroflexi, Acidobacteria and Nitrospirae and had a better capacity to nitrify and degradepolysaccharide. At the genus levels, Nitrosomonas and nitrite oxidizing bacteria (NOB)Nitrospiraceae Nitrospira was highly enriched, and was more in fixed bed, which wasconsistent with the good nitrification. Denitrifier Azospira, Thermomonas and Thauera werehigher in moved bed, which was consistent with the good denitrification.The study showed that A/O biofilm reactor was a promising petrochemical wastewatertreatment technology.