Research On Enhanced Phosphorus Removal Technology Of Integrated Biofilm Reactor

In view of the characteristics of rural sewage distribution and water quality,small biofilm reactors show the advantages of economy,high efficiency and simple maintenance,but their phosphorus removal efficiencies were poor.In this paper,a laboratory-scale small Anoxic/Oxic(A/O)biofilm reactor was used to explore two technologies of electrocoagulation(EC)and sponge iron to enhance the efficiency of phosphorus removal,and the economic cost was estimated preliminarily.The results were as follows:A small A/O biofilm reactor was employed to treat simulated domestic sewage,the total phosphorus(TP)in the effluent was 3.98±0.31 mg/L during stable operation,and the average removal efficiency was less than 20%.With continuous operation,it was found that the phosphorus removal efficiency was below 10%.In order to enhance the phosphorus removal efficiency of the biofilm reactor,an electrocoagulation was introduced to the biofilm reactor.Firstly the static electrocoagulation phosphorus removal tests,and the appropriate period of polarity switching were obtained.Secondly,the treatment efficiency of enhancing phosphorus removal of electrocoagulation as a post-processing of biofilm method under the influence of multiple factors was studied.The optimum conditions were found to be inter-electrode distance of 1.8 cm,current density of 2.1 m A/cm~2and EC reaction time of 34 min by response surface method,and the TP removal efficiency reached90%,which was lower than 1 mg/L.By comparing the two modes of non-switching polarity and periodic polarity switching by scanning electron microscope(SEM)and X-ray photoelectron spectroscopy(XPS),it is found that the flocs formed under the periodic polarity switching mode were more compact than those formed under the non-switching polarity mode.The periodic polarity switching mode improved the phosphorus removal efficiency by 10%.The effect of electrocoagulation-biofilm combination method enhancing phosphorus removal process(the electrocoagulation was placed in the first aerobic zone of the biofilm reactor)was further studied.The test results showed the phosphorus removal efficiency reached more than 90%with current density of 0.36m A/cm~2,and the unit phosphorus removal energy consumption and current density were lower than that of electrocoagulation as a post-processing of biofilm method.The current density range of 0.06～0.36 m A/cm~2had little effect on the COD removal efficiency(>90%).The electrocoagulation could inhibit the removal of ammonia nitrogen,and the inhibition effect was more obvious when the current density exceeded 0.12 m A/cm~2.Low current density promoted total nitrogen removal,and when current density was higher than 0.12 m A/cm~2,the total nitrogen removal efficiency was significantly reduced.Through high-throughput analysis of community diversity of each reaction zone,the results showed that the current increased the community richness of aerobic zones,but reduced that of the anoxic zone.Current significantly reduced Proteobacteria in the first aerobic zone,while Actinobacteria in each zone were less affected by current.Meanwhile,it affected the denitrification efficiency of the biological system by changing the proportion of Firmicutes in the anoxic zone.Current reduced the number of phosphorus accumulating bacteria to a certain extent,and inhibited Bacillus growth in the second aerobic zone.By studying sponge iron to enhance phosphorus removal,the test results showed that iron release from sponge iron was the combined effects of oxygen consuming corrosion and biological corrosion when sponge iron was put into water,and the dissolved iron mainly existed in flocs and precipitation.By comparatively analyzing the sponge iron method and electrocoagulation enhancing biological treatment,the electrocoagulation combined with biofilm treatment had the total phosphorus of less than 0.5 mg/L in the effluent with current density of 0.36 m A/cm~2,and the corresponding operating cost(0.042 yuan/g P)was only 1/5(0.246 yuan/g P)of the sponge iron system.The results depicted that the electrocoagulation biofilm method enhanced phosphorus removal process had higher removal efficiency and lower energy consumption.Therefore,in the actual sewage treatment process,incorporating electrocoagulation into the biological treatment stage was suggested to improve the phosphorus removal effect of sewage.