Effect Of Salinity On Removal Performance And Activated Sludge Characteristics In Sequencing Batch Reactors

The sources and components of saline wastewater are complicated.There are not only a large amount of inorganic salts in saline wastewater,but also organic matters and nitrogen.Therefore,performance especially nitrogen removal of wastewater treatment plants are affected considerably,and it is usually more difficult to meet the discharge standards of the effluent.Recently,many investigations focused on developing different treatment methods to improve removal rates.However,there are few studies on the effect of salinity on the removal efficiency of nitrogen and phosphorus in activated sludge systems.Moreover,the influence of salinity on activated sludge characteristics is also not available.Therefore,this research focused on the effect of salinity on removal performance and activated sludge characteristics in sequencing batch reactor?SBR?.It purposed through this study could demonstrate the mechanism of the change of removal performance and activated sludge characteristics when salt existed.At the same time,it supposed to be referred for better design and operation of biological treatment processes for saline wastewater.Two parallel lab-scale SBRs with an effective volume of 2.5 L were used in the experiments,and the initial mixed liquor suspended solids?MLSS?concentration of reactors was approximately 4500 mg/L.One of them named SBR1 was the control reactor,for which sodium chloride was not added in the influent stream.The other one named SBR2 was salt-adding reactor,for which salinity in the influent was gradually increased from 0 to 20 g/L.Firstly,the removal efficiency of NH₄⁺-N,TP and COD with the increase of salinity in SBR was measured.And the variation of NH₄⁺-N,NO₃^--N,NO₂^--N and TP during an operation cycle was investigated.Results showed that salinity deteriorated the removal performance.Removal rates of ammonium?NH₄⁺-N?,total phosphorus?TP?and chemical oxygen demand?COD?were gradually dropped from 95.34%,93.58%and 94.88%?0 g/L?to 62.98%,55.55%and 55.77%?20 g/L?,respectively.Furthermore,the removals of NH₄⁺-N and TP were mainly influenced during aerobic phase.Secondly,the effects of salinity on sedimentation performance,extracellular polymeric substances?EPS?and dehydrogenase activity?DHA?of activated sludge were evaluated.Results showed that salinity increased the EPS content of activated sludge,decreased the content of protein?PN?and loosely bound extracellular polymeric substances?LB-EPS?which led to better settleability of activated sludge.Moreover,salinity inhibited the DHA of activated sludge.When the salinity was higher than 10 g/L,the DHA of activated sludge was inhibited dramatically,the abundance and diversity of microbial community were decreased,and finally deteriorated the removals of NH₄⁺-N,TP and COD in SBR.Thirdly,the effect of salinity on microbial community was analyzed.Sequence analysis illustrated that Thioclava was halotolerant bacteria.And the increase of salinity had side effect of microbial community.Moreover,the difference of microbial community under high salinity was likely caused by the variation of richness.Therefore,increasing aeration rate,extending aeration duration moderately or adding halotolerant bacteria?such as Thioclava?could improve nitrogen and phosphorus removal for the treatment of saline wastewater.