Treatment Of Nitrobenzene-containing Wastewater By Sequential Upflow Anaerobic Filter And Air Lift Reactors

Nitrobenzene (NB), as an important material, has been widely used for the manufactureof aniline, dyes, pharmaceuticals, pesticides and explosives. Because of its high toxicityproperties, NB and its compounds have been listed as priority pollutants by many countries.The literature survey showed that sequential anaerobic/aerobic biological treatment was oneof the most effective methods, but the traditional anaerobic treatment like acidogenic reactor,anaerobic baffled reactor (ABR) and upflow anaerobic sludge blanket reactor (UASB), facewith many problems, such as the slow start and restart process, high operational cost and pooradaption to variations of pollutant compositions and shock loadings. Otherwise, the low massand oxygen transfer rates was also the main drawbacks of the traditional aerobic reactors. This,to some extent, weakened the ability of removing NB from wastewater. So it is urgent to finda new combined method for treating NB-containing wastewater.Considering the above problems, a sequential upflow anerobic filter (UAF)/air liftreactor (ALR) was established and completed its startup process quickly after the acclimationof seed sludge from a secondary sedimentation tank of a local sewage treatment plant. First,the effect of hydraulic retention time (HRT) and NB concentration on the performance ofUAF/ALR in treating NB wastewater were investigated. The results showed that the NB waseffectively reduced to AN in UAF reactor, and AN was then efficiently degraded in ALRreactor. As HRTs in the UAF reactor varied between72and8h and influent NBconcentrations varied between100and400mg/L, COD and NB removal efficiencies could beas high as95%and100%, respectively.In the process of NB degradation, the anaerobic reduction of NB was the key step andwas easily influenced by subsrate type, common ions and their usages. So the effect ofelectron donors and acceptors on NB anaerobic reduction in UAF was also studied. Theresults showed that both of glucose and sodium acetate, except sodium formate, could act asgood substrate in present UAF, and sodium acetate was the best one to promote NBdegradation. When the influent COD: NB ratio was above5, NB removal of97%could beachieved. The results of COD/SO42-and COD/NO3--N experiments showed that, the existenceof SO42-and NO3-had adverse effect on NB removal and the opposite effect accelerated withtheir increased concentrations. For decreasing the inhibition of SO42-and NO3-on NBreduction, the influent COD/SO42-and COD/NO3--N ratios should be maintained more than2.5and3.3, respectively, at which more than97%of NB removal in UAF coule be achieved.The study showed that the UAF/ALR could be quickly started by seeding slugde from a secondary sedimentation tank and achieved the completed mineralization of NB effectively.Compared to the traditional methods, the UAF/ALR system showed excellent abilities inresisting discharge and salt shocking and can provide an effective yet low cost method fortreatment of NB-containing industrial wastewater.