Study On Response Rule Of Anammox To Temperature Change

As one of effective biological nitrogen removal methods,anaerobic ammonia oxidation(anammox)technology has been widely researched and used in some practical wastewater treatment.However,most of operating temperature of these systems are controlled within the scope of medium temperature(35?),which caused some troubles for actual wastewater in a state of ambient temperature and low temperature,and an effective and stable system of anammox at low temperature would solve this problem.Therefore,in this article,the rule of effects of temperature change on anammox activity was studied,and nitrogen removal performance,physicochemical properties of sludge as well as microbial structure change were investigated by using a lab-scale upflow anaerobic sludge bed(UASB)anammox system with the gradient decrease of operating temperature.The main conclusions were as follows:(1)The results of long-term experimental study indicated that the ability of nitrogen removal in the system was gradually decreased and the average total nitrogen removal rate(NRR)decreased from 7.587 kgN m-3 d-3 in 33 ? to 4.47 and 3.192 kg N m-3 d-3 in 13? and 8?,respectively.The effluent quality fluctuated obviously during the initial time of temperature decrease,and the lower temperature was,the higher effluent concentrations of ammonia and nitrite were and then the longer the restore time of the system was.During the whole experimental process,the concentration of influent free nitrous acis(FNA)was the key factor of the stable system and the inhibition threshold of FNA was about 60 ?g/L.When the concentration of FNA was higher in the reactor,the total nitrogen removal efficiency of the system also dropped.(2)The in situ and ex situ special anammox activity(SAA)for different temperature were analysed.The results showed that the maximum in situ activity of sludge decreased as the reactor temperature dropped,and SAAmax of sludge during 33 and 13?were 0.102 and 0.023 gN g-1VSS d-1,respectively.The ex situ activity of sludge during different phases also decreased with the decrease of temperature,which seemed that the optimum growth temperature of anammox sludge did not change,and was still around 33 ?.For the sludge under low temperature environment for a long time(18,13?),its activity in low temperature range was obviously higher compared with the sludge under 33 ?,which owed to the long-term acclimation in low temperature.According to the Arrhenius equation,the activation energy(Ea)under 23-13 and 33-23?in this experiment were 89.6 and 16.4 kJ/mol,respectively.The lower the temperature was,the more obvious the influence of temperature on the reaction was.(3)As temperature decreased,not only the color and shape of sludge changed,but also the concent of extracellular polymers substance(EPS)significantly varied.The lowest EPS concent was found under 23?,but when the reactor temperature dropped from 23 to 13?,this value increased again.Compared to polysaccharide(PS),the greater fluctuation of protein(PN)content was found.In addition,the average particle size of sludge increased from 2.693(33 ?)to 3.389 mm(28 ?)firstly and then gradually decreased along with the drop of temperature,the value of 13? was 2.275 mm.The range of most granules was from 2.5-3 mm in 33? to 1.5-2 mm in 13?.The change of sludge settling velocity was negatively correlated with changes of VSS/SS.(4)When temperature dropped,the diversity of microbial community also declined,especially for 13?.The relative abundance of Planctomycetes rose from 16.02 % to 9.04 % when temperature increased from 33 to 23?,but an obvious decrease was found when temperature dropped to 13?.Interestingly,after long term acclimation,the abundance of Planctomycetes abruptly increased to 56.34 % in 199 d.The results of microbial genus level showed that Candidatus Kuenenia was the only anammox bacteria in seed sludge in this study,and at the end of the experiment(199 d),its abundance was up to 98 % in Planctomycetes and 55.18 % in the total bacteria.No more other anammox bacteria was found,which meaned that dominant bacteria in anammox system did not change with the change of temperature.In addition,results of qPCR showed that,as temperature dropped,copy numbers of gene of anammox bacteria firstly decreased at 33-23?,and then increased gradually at 23-13?,however,the variation trend of values of cell-specific anammox activity was opposite.