Study On Enzymatic Activities In A Facultative-Aerobic System For Dye Wastewater Treatment

Dye wastewater is one of the main pollution sources of water bodies and the treatment of such wastewater is focusing on biological techniques.During wastewater biotreatment,complex communities of microorganisms utilize both intracellular and extracellular enzymes to hydrolyze and ultimately mineralize organic pollutants,while the enzymatic activity reflects the activity of microorganisms.Therefore,it is significant that study on enzymatic activities in wastewater biotreatment system contributes to going deep into reaction mechanism and improving removal efficiency.In this study,intracellular enzyme of dehydrogenase and extracellular enzymes of lipase and esterase were selected to analyse enzymatic activities and distribution of the enzymes, to know the properties of the enzymes,to investigate the environmental factors effect on enzymes, and to establish the relation between enzymatic activities and effluent quality in a facultative-aerobic dye wastewater process.The study on the enzymatic activities and distribution of the enzymes showed that,the dehydrogenase activity in the facultative and aerobic reactors reached 1.245μmol/(g·h) and 0.118μmol/(g·h),respectively.The lipase displayed predominant activity(0.136μmol/(g·h)) in the facultative reactor,while the activity in the aerobic reactor only accounted for half of that in the facultative reactor.The esterase activity in the facultative and aerobic reactors reached 0.482μmol/(g·h) and 0.408μmol/(g·h),respectively.The intracellular enzyme 0.8%～1.7%of dehydrogenase activity was detected in the supernatant.71.5%～73.1%of lipase activity and 74.5%～77.1%of esterase activity were associated with microbial cells in the biofilm and activated sludge,which demonstrated that most of lipase and esterase were associated with cells or immobilized in extracellular polymeric substrates.The properties of the enzymes study showed the dye concentration increased enzymatic activities first and then decreased the enzymatic activities within 0～2000mg/L,the dye concentration in facultative reactor was less than aerobic reactor when the enzymatic activities reached the maximum.Inhibitor PMSF decreased enzymatic activities obviously and inhibitory of 28.6%～59.4%was observed after the addition of 0.10mmol/L PMSF in facultative reactor,while 0.10mmol/L PMSF had little effect on the enzymatic activities and the inhibitory was 6.3%～13.8%in aerobic reactor.Low concentration of inhibitor EDTA and zinc chloride increased dehydrogenase activity under facultative condition but decreased the lipase and esterase activities. An decrease of dehydrogenase activity occurred with 0～600W ultrasonic irradiation in the mixture, while the activities of lipase and esterase increased first and then went down;20min ultrasonic process accelerated dehydrogenase activity in the system but had an inhibitory effect on lipase and esterase.The environmental factors effect on enzymes study showed the highest enzymatic activity appeared at 60℃.Enzymatic activities were accelerated under alkaline condition(pH=8～9) and increased with increase of substrate concentration.The optimum enzymatic activity conditions of the three enzymes were shown as followings:temperature of 60℃,substrate concentration of 50μmol/L and pH value of 8.Under these conditions enzymatic activities reached 1.58～6.44 times higher than the normal conditions.The key factors affecting the enzymatic activities were the temperature and the concentration,while the pH was the lowest.Thus,high enzymatic activities were expected to obtain through controlling the related conditions.The study on the relation between enzymatic activities and effluent quality showed that,in facultative and aerobic reactor,the COD removal rates were 78.4%and 79.2%,the color removal rates were 81.9%and 70.3%,and the overall COD and color removal rates reached 95.5%and 96.1%,respectively.The COD and color removal in facultative reactor reached 7.8 and 4.6 times higher than in aerobic reactor.The tested enzymatic activities were closely correlated with COD and color removal rates(0.7672～0.9292).It could be considered enzymatic activity used as a assessor of wastewater treatment efficiency.