Denitrogennation Study Of Rural Domestic Sewage By A Rotating Biological Contactor Bioaugmened With Aerobic Denitrifying Bacteria

Rotating Biological Contactor(RBC)has been considered as one of the suitable technologies for rural sewage treatment as it has many good characteristic,such as simple management,low investment and energy consumption.However,the problems including biofilm falling off and low TN removal efficiency limit the application of the RBC technology.Therefore,activated carbon fiber(ACF)which has large specific surface area and strong adsorption capacity was selected as the rotating disc materials.Taking the aerobic denitrifying bacteria Pseudomonas poae NL-4 as the bioaugmentation strain,this research optimized the immobilization preparation conditions of Pseudomonas poae NL-4 and investigated the removal performance of ACF-RBC after bioaugmented with the immobilized aerobic denitrifying bacteria.The main results were as follows:(1)When CH3COONa was used as carbon source and C/N ratio was 5:1,the denitrification capacity of Pseudomonas poae NL-4 was the best.The carbon source(CH3OH?CH3COONa?C6H12O6)had a significant effect on the nitrogen removal performance of Pseudomonas poae NL-4.When the C/N ratio was 5:1,the NH4+-N and NO3--N removal efficiency of Pseudomonas poae NL-4 with CH3COONa as carbon source were 52.12%and 80.39%,respectively,significantly higher than those of CH3OH(39.81%and 25.66%)and C6H12O6(19.11%and 10.01%).On this basis,the effect of different C/N ratio(1:1,2:1,3:1,5:1 and 7:1)on the denitrification ability of Pseudomonas poae NL-4 was studied with CH3COONa as the carbon source.The results showed that Pseudomonas poae NL-4 exhibited the best nitrogen removal performance when the C/N ratio was 5:1.And the NH4+-N and NO3--N removal efficiency was 50.90%and 80.39%,respectively.Thus,the best carbon source of Pseudomonas poae NL-4 was CH3COONa,and the optimum C/N was 5:1.(2)To determine the best adsorbents,this study compared the NO3--N,NH4+-N,COD and microorganisms adsorption capacities of different adsorption materials.The adsorption materials include activated carbon,zeolite,coconut shell biochar,nutshell biochar,charcoal and ACF.The results indicated activated carbon had the best adsorption ability.The NO3--N,NH4+-N,COD and microorganisms adsorption capacities of AC reached up to 1.45g·kg-1,0.54g·kg-1,7.07g·kg-1 and 1.36g·kg-1,respectively.Therefore,activated carbon was selected as the immobilization carrier to carry out the immobilization tests of Pseudomonas poae NL-4.(3)The optimal amount of NO3--N?NH4'-N?COD and activated carbon in water was obtained.The optimization of adsorption immobilization test on Pseudomonas poae NL-4 test was studied by a single factor test using activated carbon as the test material.The results showed the optimal immobilization temperature was 30 ?,pH was 7.0,the bacteria to solid ratio was 1:10,and the immobilization time was 7h.The TN and NH4+-N removal abilities of the immobilized Pseudomonas poae NL-4 reached up to 5.45g·kg-1 and 3.92g·kg-1 respectively after 72 h' cultivation.On this basis,the crosslinking condition optimization test has been carried out with the activated carbon immobilized Pseudomonas poae NL-4.The results indicated the optimal crosslinking agent was glutaraldehyde.The optimal crosslinking time was 4 h,the crosslinking agent concentration was 0.1%,and the crosslinking temperature was 30?.The removal ability of NH4+-N and TN of the adsorption-cross-linking immobilized Pseudomonas poae NL-4 can reach up to 5.01 g·kg-1 and 7.92g·kg-1,respectively.(4)Under the conditions of 30?,pH 7.0,the ratio of bacteria to solid 1:10,the immobilization time was 7 h,and 0.1%glutaraldehyde was used as crosslinking agent,and crosslinked at 30? for 4 h.The removal performance of the ACF-RBC which used activated carbon fiber as the disc material was investigated when the influent TN,NH4+-N and COD concentrations were 40 mg·L-1,35 mg·L-1 and 400 mg·L-1,respectively.The average TN,NH4+-N and COD removal efficiency of ACF-RBC treating simulated domestic sewage was 60%,98%and 90%,respectively,when the operation condition was as follows:HRT was 6 h,the reflux ratio was 200%,and the rotary speed was 15 r·min-1.After inoculated with the immobilized Pseudomonas poae NL-4,the TN removal efficiency of ACF-RBC reached up to 80%,increased by 20%.The parameters optimization results showed that the optimal HRT was 6 h,the reflux ratio was 200%,and the rotary speed was 15 r·min-1.While operating at the above conditions,the average TN,NH4+-N and COD removal efficiency of the ACF-RBC can reach up to 91.74%,97.10%and 96.86%,respectively,which can meet the level A discharge standard of GB19818-2002.(5)The 16S rRNA high-throughput sequencing results showed that the dominant phylum of ACF-RBC were Proteobacteria,Chloroflexi and Bacteroidetes,respectively.However,the microbial structure diversity in the first,second and third disks was significantly different.The relative abundances of Chloroflexi and Nitrospirae on the first disk were 35.08%and 43.35%,higher than the other disks,whereas the relative abundance of Nitrospirae on the third disk was about 5.58%,higher than the other parts of the ACF-RBC?In conclusion,Pseudomonas poae NL-4 was used to bioaugmentation of ACF RBC in this study,and the operation parameters of ACF RBC after strengthening were determined.This research can provide important theoretical basis and technical support for the application of ACF RBC to rural domestic sewage treatment.