Research On Low C/N Ratio Sewage Treatment And Optimization Of Highway Service Area Based On Artificial Zeolite

As an important supporting service facility of the highway system,the normal operation of the highway service area is crucial,and the sewage treatment of the service area is an important part of it.Most of the service areas are far away from urban areas,and the sewage generated from daily operation cannot be discharged into urban sewage treatment plants for centralised treatment,so sewage treatment facilities need to be built in the service areas for treatment.The quality and quantity of sewage from highway service areas is closely related to the traffic flow,climate and pedestrian flow,and has outstanding problems such as high nitrogen and phosphorus content,low C/N ratio and large fluctuations in water quality and quantity.Based on the above problems,this study uses artificial zeolite to pre-treat the wastewater to achieve a significant reduction in ammonia nitrogen concentration and increase the C/N ratio of the wastewater,further screening coagulants to achieve efficient phosphorus removal from the wastewater,and finally through combined treatment with the A/O process to build a "zeolite-coagulation-A/O" combination process.The combined process is used to treat the wastewater from the highway service area and achieve stable and standard discharge.The main research results are as follows:(1)Based on the effect of natural zeolite and artificial zeolite 1#and 2#on the treatment of service area wastewater,it shows that artificial zeolite has a better effect on reducing the concentration of ammonia nitrogen and CODcr in wastewater than natural zeolite.For artificial zeolite 1#,the larger the dosage,the better the effect of wastewater treatment,and the 24-h removal rate of ammonia nitrogen,CODcr,TN and TP by 80 g/L artificial zeolite 1#can reach 93.09±0.14%,34.77± 1.09%,91.59±30.50%and 20.80±32.88%for ammonia,CODcr,TN and TP respectively,while significantly increasing the C/N ratio from 1.05±30.01 to 8.17±30.24,which is more conducive to the subsequent biochemical process.(2)The results of the orthogonal experiments with artificial zeolite 1#showed that the optimum conditions for zeolite treatment were:aeration intensity of 1.0 L/min,dosage of 80 g/L,and an ammonia nitrogen concentration of 50 mg/L,and according to the range analysis,it can be seen that the dosage has the greatest effect on the removal of ammonia nitrogen.The adsorption kinetics and temperature thermodynamic analysis of the artificial zeolite 1#on ammonia nitrogen showed that the adsorption process of the artificial zeolite 1#on ammonia nitrogen was more in line with the quasi-secondary adsorption kinetic model,and the whole adsorption reaction was a heat absorption process.(3)The experimental results of coagulation and precipitation treatment of service area wastewater show that PFS is more effective than PAC,PAM and Ca(OH)2 in reducing the CODcr and TP concentrations of service area wastewater,and the removal rate is positively correlated with the dosing concentration.When 600 ppm PFS is dosed,the removal rate of CODcr can reach 64.55±0.13%,and the TP concentration can be reduced to 0.79±0.01%.After coagulation,PFS,PAC and PAM had no effect on the pH of the effluent,while Ca(OH)2 increased the pH value and the effluent was alkaline;coagulation and sedimentation time and agitation rate had no significant effect on the coagulation treatment effect,but increasing the agitation rate slightly increased the removal rate of ammonia,TN and TP.(4)The operating results of the combined process of "zeolite+coagulation+A/O" showed that the average removal rates of ammonia nitrogen,CODcr,TN and TP reached 92.87%,65.84%,79.89%and 90.97%,respectively,and the average concentrations were 1.87 mg/L,35.89 mg/L,7.46 mg/L and 0.36 mg/L,respectively.For service area B,the average removal rates of ammonia nitrogen,CODcr,TN and TP reached 97.38%,80.03%,89.82%and 94.48%,corresponding to the average concentrations of 2.71 mg/L,37.74 mg/L,11.60 mg/L and 0.42 mg/L,respectively.It can be seen that after the combined process of "zeolite+coagulation+A/O",the concentration of each water quality index of the corresponding effluent in the two service areas is stable and reaches the Class I A standard of Discharge standard of pollutants for municipal wastewater treatment plant(GB 18918-2002).(5)In order to better analyse the changes in the microbial diversity of the sludge,the sludge from different stages of the aerobic tank of the A/O process was selected and analysed by Illumina high-throughput sequencing for the diversity of the microbial flora.The relative abundance of Proteobacteria ranged from 23.58%to 33.64%,followed by Actinobacteriota,Chloroflexi and Bacteroidota,with relative abundance ranging from 14.40%to 20.31%,10.98%to 16.66%and 9.93%to 15.50%respectively.At the genus level norank_f_norank_o_Saccharimonadales was the dominant genus before and after sludge domestication with a relative abundance of 4.87%,5.23%and the dominant genus of microflora after treatment of effluent was Nitrospira with a relative abundance of 4.05%.