The Application Of Two-Temperature Anaerobic Process Treating Domestic Sewage And Enhancement Technology

As increased wastewater discharge,high wastewater hydraulic loading of waste water plant and serious water resources crisis,novel energy-saving and efficient wastewater treatment needs to be developed eagerly.Anaerobic wastewater treatment has advantages of low energy consumption,low cost,low excess sludge production and envery production in forms of methane.Novel wastewater treatment process using anaerobic technology as core unit provides wide space for the improvement and development of wastewater treatment plant.Anaerobic wastewater treatment has already been applied to tropical areas.However,low temperature leads to anaerobic hydrolysis rate slow,anaerobic biodegradable rate and growth of anaerobic biomass slow.Therefore,low temperature anaerobic wastewater treatment is worthy to study.Performance of two temperture anaerobic process treating wastewater was studied in this thesis.The main research contents are following: effects of temperature on methanogenic activity and substrate affinity of anaerobic sludge,sludge rate on the performance of the process,characteristics of soluble microbial products(SMP)of low temperature on anaerobic process,sludge retention time on SMP production and compostion,and effects of co-substrate addition on the process.The UASB reactor in the two temperature anaerobic process operated at the same temperature to wastewater influent,while the digester in the process operated at 30-35 ?C.Temperature-change is associated with sludge recirculation.Anaerobic sludge from the digester was chosen as analysis sample,the lab-scale experiment was performed to study effects of temperature-change on methanogenic activity of the sludge.The results showed that the ratio of methanogenic activity of the sludge at 15 ?C to 35 ?C was 0.11 without temperature change,and the ratio was 0.12 and 0.10 when temperature changed from 35 ?C to 15 ?C and 15 ?C to 35 ?C respectively.Effects of substrate concentration on methanogenic activity of the sludge was studied using monod equation fitting at 35 ?C and 15 ?C respectively.The fitting results of Ks was used to represent substrate affinity of the sludge.The results showed that the Ks was 2.5 and 6 mg COD/L at 35 ?C and 15 ?C respectively.The acetate affinity was still high at 15 ?C.The anaerobic treatment of low strength domestic sewage at low temperature is an attractive and important topic at present.The two temperature anaerobic process is one of anaerobic systems to challenge low temperature and concentrations.The effect of sludge rate on the process treating domestic sewage was studied in this research.The results showed that the total COD removal efficiency rose with increasing sludge rate.A sludge rate of 0.9 % of the influent flow rate led to organic solids accumulation in the UASB reactor.After the sludge rate increased from 0.9 % to 2.6 %,the stability of the UASB sludge was substantially improved from 0.37 to 0.15 g CH4 COD/g COD,and the biogas production in the digester went up from 2.9 to 7.4 L/d.The stability of the UASB sludge and biogas production in the digester were not significantly further improved by increasing sludge recirculation rate to 12.5 % of the influent flow rate,but the biogas production in the UASB increased from 0.37 to 1.2 L/d.In order to improve the performance of anaerobic wastewater treatment at low temperature,it is essential to investigate the characteristics of the effluent organic matters.In this study,lab-scale UASB reactors were performed to treat synthetic glucose and sodium acetate wastewater respectively at 15 ?C.The soluble microbial products(SMP)were found in the glucose-fed UASB effluent.However,SMP did not appear in the sodium acetate-fed UASB effluent.The average aerobic and anaerobic biodegradability of the effluent soluble chemical oxygen demand(ESCOD)was 90 % and 60 % respectively.The low molecular weight(MW)fraction of the ESCOD(lower than 10 kDa)mainly consisted of 31.7 % long chain alkanes and 13.6 % esters.As SRT prolonged,the effluent SMP content and the content of protein and polysaccharide in the effluent SMP increased.In addition,the polysaccharide /protein ratio increased from 0.6 to 1.3 as SRT increased from 40 days to 80 days.A two temperature anerobic process can achieve efficient COD removal at 15 ?C,when treating domestic sewage with a low soluble/suspended COD ratio.However,it turns less efficient for domestic sewage with a high soluble/suspended COD ratio.Therefore,adding co-substrate was applied in this study to improve the performance of the process treating domestic sewage with a high soluble fraction.After adding co-substrate,the process changed from an acetate producer to an acetate consumer,and kept the effluent acetate at a stable and low level of 31 mg COD/L.Both the specific methanogenic activity(SMA)of the UASB and the digester sludge tripled.Methane production in the UASB reactor increased by 91 % mainlyc because of the improved specific methanogenic activity.Soluble COD removal efficiency increased to a value close to the anaerobic biodegradability.In the digester,methane production also increased(corrected for the input of co-substrate COD).Adding co-substrate proved to be an appropriate tool to extend the applicability of the two temperature anaerobic process for treatment of low temperature wastewater.