| Constructing of large surface processing industrial parks for centralizedproduction and management is the trend for the development of electroplating industryin our country. This development mode has many advantages, such as it is convenientfor management and supervision and consequently saving resources. But this modealso brings some problems, such as incompletely distributary of wastewater will putpressure on the the central wastewater treatment plant (WWTP) in the parks. As aresult the influent of the WWTP will contain low concentration of heavy metals whichwill cause an imact on the biological system. In addition, due to a large number ofenterprises centralized in the industrial park, production can not be stopped even whenoperation fault happened, resulted in high concentration of heavy metal wastewaterentered the biological treatment in a short period of time. All of these put a threat onthe safe operation of the system.Focusing on the problem above, copper and zinc were selected in this research toinvestigate the impact of different concentration of copper and zinc on the performanceof the biological treatment system. The pollutants removal efficiency, bacterial activity,extracellular polymeric substance (EPS) and characteristic of activated sludge wereanalyzed. The effects of high concentration of copper and zinc in shock loading on thebiological system and effects of low concentration of copper and zinc in long termexposure were investigated. Powder activated carbon (PAC) was added to recover thesystem from the shock of high concentration of copper and zinc. The aim is to revealthe concentration limits of copper and zinc that will obviously repress the performanceof the system and to evaluate the capacity of the system that resists the shock load.Continuous flow experiment was conducted with zinc concentration ranged from0to30mg/L and copper concentration from0to10mg/L, respectively. It was observedthat the COD removal was obviously inhibited by30mg/L zinc or5mg/L copper.10mg/L copper severely inhibited the COD removal and the inhibition rate reached to20%. The NH3-N removal was obviously inhibited by15mg/L zinc or3mg/L copper.The denitrification capacity was severely inhibited when the concentrations of zincwas30mg/L or copper was5mg/L. Inhibition of copper and zinc on the denitrificationwas stronger than that on the COD removal. The activities of nitrifying bacteria and heterotrophic bacteria showed that sOURand AUR inhibition rate increased from0to42.67%and42.67%, respectively, whenthe concentration of zinc increased from0to30mg/L. sOUR and AUR inhibition rateincreased from0to89.12%and100%, respectively, when the concentration of copperincreased from0to10mg/L. Nitrifying bacteria are more sensitive to heavy metalsthan heterotrophic bacteria. The toxicity of zinc to nitrifier was irreversible.The change of the EPS showed that zinc and copper would not change thecomposition of the EPS. The changes of the EPS and the SVI had no correlation underthe impact of zinc. Low concentration of zinc would inhibit the synthesis of the EPS,while high concentration stimulate. The impact of zinc on the EPS and the SVI werethrough interferencing the synthesis of extracellular proteins. The result showed alinear positive correlation between EPS and SVI under the impact of copper. Lowconcentration of copper stimulated the synthesis of the EPS and high concentrationinhibited. Polysaccharide and protein in the EPS together play important roles to affectthe SVI. Sludge deflocculated when the concentration of copper exceeded5mg/L.Shock loading test showed that the A/O-MBR had a strong ability to resist highconcentration of copper and zinc shocks. With a short-time shock of30mg/L zinc and5mg/L copper, no obvious change in the performance of the system was observed. Anincreased shock load resulted in the deterioration of the performance and the recoveryof the system slowed down. With the short-time shock of90mg/L zinc and30mg/Lcopper, the COD of the effluent exceeded the discharging standard. The impact ofshort-time shock on ammonia removal was stronger than that on the organic matterremoval. The inhibitions on the activity of heterotrophic and nitrificationmicroorganisms were serious. The microorganisms became smaller and the sludgeflocs became loose at the end of the shock loading experiment.Recovery experiment showed that PAC significantly improved the performance ofthe system, the removal efficiency of COD and NH3-N increased by6.34%to10.16%.Dosing PAC is an effective way to improve the system performance. |
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