Fundamental Research Of Low Consumption Domestic Sewage Treatment Technology Based On Enhanced Primary Treatment

In order to develop a domestic sewage treatment process with less investment,low operation cost and less sludge production,this paper first pretreated the urban and rural domestic sewage through the chemically enhanced primary treatment?CEPT?,and on this basis,the anaerobic digestion and methanogenesis of the sludge produced were studied.The effect of different dosage of iron salt and aluminum salt on the removal of pollutants in domestic sewage was explored,and the best flocculant type and dosage were optimized.Then,the constructed wetland?CW?reactor was used to carry out low-consumption treatment of rural domestic sewage pretreated by CEPT,and the characteristics of the start-up and enhanced operation mode of the CW reactor were studies.Finally,the paper also studied the nitrogen removal performance and the nitrogen loading rate?NLR?shock resistance in the rapid-biofiltering anammox reactor,in order to provide technical options for the low consumption treatment of domestic sewage pretreated by CEPT.The main results and conclusions are as follows:?1?When the CEPT process was used to pretreat domestic sewage,the removal effect of Al³⁺addtion was better than Fe³⁺addtion at the same dose.Considering the economic benefits and treatment effects,the best flocculant for the removal of pollutants was aluminum salt and the optimal dosage was 20 mg/L.When the dosage was 20 mg Al³⁺/L,the SS concentration in rural domestic sewage could be reduced from125.00 mg/L to 9.00 mg/L,and the TP concentration could be reduced from 5.38 mg/L to 0.44 mg/L.The SS concentration in urban domestic sewage could be reduced from206.00 mg/L to 26.00 mg/L,and the TP concentration could be reduced from 10.75mg/L to 2.45 mg/L.It showed that the concentration of SS and TP could be greatly reduced by CEPT process.?2?The anaerobic digestion test of flocculated sludge showed that the addition of different dosages of Fe³⁺and Al³⁺inhibited the anaerobic methane production of sludge,and the inhibition increased with the increase of dosages.At the same time,the inhibition of Al³⁺was stronger than Fe³⁺at the same dosage,leading the cumulative gas production of methane to lower.The inhibition of anaerobic methane production was more obvious when the dosage of Fe³⁺and Al³⁺was equal or greater than 10 mg/L and 5mg/L,respectively.Compared with the naturally settled sludge,the cumulative gas production of methane was reduced by 41%when the dosage of flocculant was 20mg Al³⁺/L.Therefore,the type and dosage of flocculant need to be further explored if the further energy recovered from the flocculated sludge is considered.?3?When the CW reactor was used to treat the pretreated rural domestic sewage,the average removal rates of NH₄⁺-N and TN were only 25.30%and 20.53%in the stage without artificial aeration,respectively.After the aeration enhanced operation mode was adopted,the removal rate of NH₄⁺-N increased with the increase of the aeration amount.Under the same total aeration amount,the change of aeration mode had little effect on the removal of NH₄⁺-N,but affected the removal of TN,where the intermittent aeration was better than that of continuous aeration.The effluent concentrations of NH₄⁺-N and TN remained below 5 mg/L and 15 mg/L for a long period,respectively under the intermittent aeration mode with the gas water ratio of6.75:1.?4?Analytical results of nitrogen and phosphorus removal pathways in the CW indicated that the contribution rates of plants,fillers and microorganisms to nitrogen removal were 2.27%,5.93%and 91.80%respectively,while to phosphorus removal were 15.72%,77.58%and 6.70%respectively.It showed that the removal of phosphorus in the CW mainly depended on the adsorption of ceramsite and volcanic rock,while the removal of nitrogen basically depended on the action of microorganisms.?5?The NLR of the biofilter reactor was increased from 0.96 kgN/?m3·d?to 4.86kgN/?m3·d?gradually when the low nitrogen wastewater partially nitrified?NH₄⁺-N?50.0±3.0 mg/L,NO₂^--N?52.0±3.0 mg/L?was used as influent.The longest adaptation period of the biofilter reactor was 24 days,and the average removal rate of TN remained stable at 86.24%,leading the average effluent concentration of TN to remaine stably at 14.20 mg/L?below 15 mg/L?under 32 min of HRT when the NLR was 4.86 kgN/?m3·d?.?6?The change in water quality along the biofilter reactor indicated that the main functional zone was in the region of 0–20 cm in the reactor,where the biomass concentration remained at 21.61 gSS/L,and the SAA reached 0.82 mgN/gVSS·d.Microbial identification results showed that the relative abundance of anammox bacteria in the whole reactor was more than 50%,and the relative abundance of Candidatus Brocadia in the biofilm of 20–47 cm zone reached 71.10%.It showed that the continuous upflow and the gradually shortened HRT operation mode promoted the accumulation of high abundance anammox bacteria in the reactor,which was the basis of the high nitrogen removal efficiency of this reactor.