Advanced Treatment Of Glyphosate Wastewater In An Oscillatory Flow Reactor Packed With Biofilms

Glyphosate is a kind of broad-spectrum,high-efficiency,low-toxic non-selective herbicide.The most glyphosate pesticides are produced in China,which results in a large amount of glyphosate production wastewater(GP W).The components of GPW are com-plex,and chemical oxidation,biochemical method,chemical precipitation and other"physicochemical+biological" combination process are usually used to treat the refrac-tory organic matter in GPW,in which the biological treatment is a key method due to environmental protection and low operating cost.However,the effluent treated by the traditional activated sludge biological method is unstable,which is greatly affected by the fluctuation of water quality.Therefore it is of great practical significance to study the efficient and stable biological treatment process.In this paper,Polyurethane fillers loaded with high-efficiency microbial strains function as biocatalysts,a two-stage packed bio-film reactor in series with anaerobic reaction and aerobic reaction is used to treat GPW,and the mass transfer process is strengthened for the first time in combination with oscil-lating flow technology.Meanwhile the environmental parameters and operation condi-tions were optimized,and the degradation kinetics of substrate was established.The main works are as follows:1.An anaerobic-aerobic two-stage immobilized biofilm oscillatory flow reactor was designed and established.Aiming at the problem that COD,ammonia nitrogen(NH4-N),nitrate nitrogen(NO3-N)and total nitrogen(TN)in wastewater are too high and diffi-cult to degrade,carbon oxidation and denitrification process is realized in anaerobic tower to remove 70%COD and over 90%NO3-N,and simultaneous nitrification and denitrifi-cation process is realized in aerobic tower to remove over 90%NH4-N and more than 75%TN.After optimization,the continuous experiment showed that the effluent COD was below 50 mg/L,NH4-N was below 5 mg/L,and TN was below 15 mg/L,the biological oscillatory flow system was stable and the effluent met the discharge standard.2.To optimize the operation conditions of anaerobic process,the effects of hydraulic retention time(HRT),oscillation conditions and water temperature were investigated.The results showed that HRT had a significant effect on the removal of COD and NO3-N.The removal rate of COD increased with the increase of HRT,and then tended to be stable.NO3-N decreased rapidly with the increase of HRT,and more than 95%of NO3-N was removed after 9 h;Appropriate oscillation intensity can strengthen the reaction.The ex-perimental amplitude range is 0～5 mm and the frequency is 0～2.4 Hz.The oscillation Reynolds number Reo is used to express the oscillation intensity.When Reo is lower than 3500,the removal rate of COD gradually increases with the increase of Reo.Compared with without oscillation,the increase can be up to 27%.Considering the coupling with aerobic reaction,the optimal operating parameters of anaerobic process are as follows:HRT is 9 h,amplitude is 3 mm,frequency is 2 Hz,water temperature is 30～35℃,COD removal rate is 70%,NO3-N removal rate is more than 95%.3.To optimize the operation conditions of aerobic process,the effects of HRT,oscil-lation conditions,dissolved oxygen concentration(DO)and pH were investigated.The results show that COD and NH4-N decrease rapidly with the increase of HRT and then tend to be stable;With the increase of Reo,COD and NH4-N decrease first and then in-crease,and the minimum values are obtained when Reo is around 2800;DO is the key to realize aerobic target.Adjusting DO can change the proportion of aerobic and anoxic ar-eas in the biofilm;pH affects the activity of aerobic bacteria,and the microbial activity is high in weak alkalinity.The optimal operating conditions are as follows:HRT is 6 h,pH is 7.5,DO is 3.5 mg/L,COD removal rate is more than 90%,NH4-N removal rate is over 95%,and total nitrogen removal rate is more than 80%.4.For the purpose of engineering design and scale-up,the kinetic model was estab-lished.Under the condition of near plug flow,the anaerobic kinetic parameters were k=217.5 mg/L/h,Ks＝698.2 mg/L,aerobic kinetic parameters were k’= 587 mg/L/h,Ks=1203 mg/L.The average relative error between COD value calculated by kinetic equation and experimental result is 6.75%in anaerobic process and 9.92%in aerobic process,which can meet the needs of engineering design and development.