| With the gradual strengthening efforts of national environment protection,sewage sludge production from wastewater treatment plants has been increasing year by year.Sewage sludge seriously threatened the urban environment and sanitation.The selection of sludge treatment and disposal method should aim at reduction and harmlessness,and select reliable and economical technologies according to local conditions.Sludge composting process has received widely attention due to its advantages of less investment,simple operation and low operating cost.But the serious problem of nitrogen loss has not been completely solved.The nitrogen loss ratio during the composting can reach 16%~67%,mainly volatilized in the form of ammonia.As a result,air was polluted and the fertilizer efficiency of compost products were reduced.Previous studies have found that traditional conditioners are difficult to be effectively degraded by microorganisms and the addition of easily degradable carbon sources can reduce ammonia emission by changing the composition of organic matter.However,the effect of easily degradable carbon sources on the degradation of organic matter and nitrogen convertion during sludge composting is not clear.Based on the above reasons,this research systematically studied the types of carbon sources that can effectively control nitrogen loss and their using conditions.Then the best alternative bulking agent of carbon sources was selected.The effects of carbon source on the composting process,the microbial utilization abilities of carbon source and the products quality were analyzed.The results showed that under the condition of inorganic conditioners,sucrose had the best performance on controlling nitrogen loss of composting.The results of response surface methodology showed the optimum usage of sucrose were: dosage 0.02:1(w sucrose :w sludge),adding time 58.28 h,sucrose concentration 100%(solid).Under this condition,the nitrogen loss ratio was only 25.2%,which was 38.22% lower than the blank.On this basis,the beet bulp was implied as an alternative bulking agent of sucrose.According to the variation of BOD 5 content and microbial respiration rate,the effect of sucrose on microbal utilization capacity of carbon source was clarified combined with the analysis of Biolog.Through the analysis of three dimensional fluorescence spectroscopy,seed germination rate and conductivity,the quality of sewage sludge composting product was evaluated.The humification process and composting maturity could be significantly promoted by adding sucrose.From the perspective of nitrogen form conversation and the number of related microorganisms,the effect of carbon sources on nitrogen loss during sewage sludge composting process was discussed.The composting prameters related to nitrogen loss control were optimized.The mathematical relationship between carbon source and nitrogen loss was established.The results showed that the total of organic nitrogen,ammonia nitrogen and volatiled ammonia accounted for 92%~97% of total nitrogen during the sludge composting.The addition of sucrose mainly affected the mutual transformation between ammonia nitrogen and organic nitrogen.The ammonia assimilation was strengthened.The organic nitrogen content increased by 9.66%.After adding sucrose,the ammonifying bacteria were affected by acidification.Te number of ammonia assimilating bacteria increased by 2.3 times.Among the process parameters,the ventilation rate had a greater impact on ammonia emission.Under the ventilation rate of 0.1L/min,ammonia emission can be significantly reduced.Finally,the relationship between ammonia emission and water-soluble total organic carbon and nitrogen content was discussed.Using nonlinear regression analysis,the relationship between CO 2 and NH 3 was clarified.The response model was consistent with the Gaussian formula.When CO 2 production was 26.95 g/kg dry sludge(DS)~65.05g/kg DS,the amount of ammonia emission was large.The effects of carbon sources on microbial diversity and bacterial community structure were investigated.Nitrogen isotopes and enzyme activity techniques were used to analyze the effects of carbon sources on ammonia assimilation efficiency and related enzyme activities.The mechanism of carbon source strengtening ammonia assimilation was clarified.The results showed that high-throughput sequencing analysis revealed that the addition of sucrose reduced the diversity of microorganisms,but promoted the growth of dominant bacteria.From the analysis of the bacterial,archaeal,and fungal structure,the addition of sucrose could promote the growth of microorganisms contributed to the decomposition of cellulose and lignin,such as Bacillus,Streptomyces,Pseudoxanthomonas,Candida,etc..The degradation of carbon sources were increased.The average N15 assimilation rate could be increased by 27.87% after adding sucrose,mainly in the thermophilic phase and mesophilic phase.The optimal carbon-nitrogen ratio of ammonia-assimilating bacteria was 30.The concentration of ammonia-assimilating substrate ?-ketoglutarate was significantly increased after adding sucrose,up to 34.98 mg/kg dry sludge.The change of the key enzyme activity of ammonia assimilation was analysed by enzymological analysis technology.Due to the increase in the availability of carbon sources,the energy supply from the degradation of carbon sources was strengthened,and the GS-GOGAT pathway became the more dominant and universal approach of ammonia assimilation. |
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