Treatment Of Petroleum Refinery Wastewater With Aerobic Granular Sludge

Large quantities of petroleum refinery wastewater?PRW?are generated in the crude oil refining processes.PRW is complex in composition varied for the oil characteristics,refining installation as well as refining processes,which contained large amounts of hydrocarbons,benzenes,naphthenic acid,heterocyclic and other dissolved organics,poor biodegradable and toxic to microorganisms.At present,biotechnology is the core process for the treatment of dissolved organic matter and nitrogen.Although the activated sludge process is mature and used widely,problems such as large area occupation and poor settleability are occoured.In recent years,with the upgrading of environmental regulations,higher requirements have been put forward for PRW treatment.Aerobic granular sludge technology derived from activated sludge method exhibited enhanced settleability,high biomass retention and strong resistance to changes in loading impacts and influent quality,which had a great application prospect in the treatment of PRW.The feasibility of aerobic granular sludge for the treatment of PRW was studied.Sequencing batch reactor was used to cultivate aerobic granular sludge.Runing conditions and granulation process was investigated from the sludge characteristics,organic removal efficiencies,nitrogen removal performance and the microbial community.In consideration of difficulty on aerobic granule formation,the biochars based on waste oily sludge,rice husk,rice bran and walnut shell were added to the reactors.The effects on aerobic granulation,reactor performance and microbial community were evaluated and the mechanisms of biochars mediated in aerobic granulation were also studied.The results indicated that,aerobic granular sludge technology was successfully used for the treatment of PRW.The granules formed successfully within 35 days,which were compact with superior settleability and stability.The reactor was efficient at reducing COD and petroleum compounds with removal efficiencies of 95%and 90%respectively.NH₄⁺-N and total nitrogen?TN?removal efficiencies were lower than 40%due to the toxicity of petroleum wastewater for nitrificans and denitrificans and they were enhanced to almost 100%by glucose addition.The petroleum-degrading microorganisms were dominant in the granules included the genera of Propioniciclava,Micropruina,Alphaproteobacteria,Flavobacterium and Sulfuritalea.The biochars based on waste oily sludge,rice husk,rice bran and walnut shell with developed porous structure and rough irregular surface acted as nuclei in the aerobic granulation.The four biochars addition significantly facilitated aerobic granulation.Compared to the control reactor,the reactors added with biochars achieved aerobic granulation with 15 days in advance.The granules formed with compact structure and great setteability.The pollutants removal efficiencies and the resistance ability to shock loading were enhanced significantly.Moreover,the biochar addition and adjustment of aeration mode improved the TN removal performance,and the removal efficiencies of four reactors were all enhanced by 10%,compared to the control.Meanwhile,microbial richness and diversity were enhanced and more microorganisms capable of degrading petroleum were enriched in granules included Uncultured gamma proteobacterium?Mycobacterium?Acinetobacter and Gordonia.The quantities of NOB,nir S and nir K,related to nitrogen removal,also exhibited higher than those of the control.