| Carbon source is a necessary nutrient element of the wastewater biochemical treatment process.But in China,the influent water of a considerable part of sewage treatment plants is relatively insufficient.When the influent carbon/nitrogen ratio(C/N)is lower than 3.4,additional carbon source must be added to ensure the biochemical treatment effect.The addition of external carbon source will directly lead to the increase of operating cost and sludge output of sewage treatment plant,which is unfavorable to the long-term operation of sewage treatment plant.In recent years,the development of internal carbon sources using sludge to enhance biological denitrification of low C/N wastewater has attracted more attention.In view of the problems of slow process and low efficiency in the process of hydrolysis,acidification or anaerobic fermentation of sludge,this project adopts the thermophilic micro-aerobic digestion(TMAD)to digest and treat sludge,so as to better meet the needs of sludge stabilization and reduction while releasing the carbon source in the sludge.In this study,the effects of different aeration intensities on the process of releasing carbon source in the sludge were investigated.The volatile fatty acids(VFA)reached the maximum values of 10308,9782 and 8536 mg/L chemical oxygen demand(COD)at 72 hours,when the inlet sludge TS was around 5% to 6%,and the aeration intensity was 0.6～0.8 0.9～1.1 1.2～1.4 L/(h·L sludge).Respectively,reducing aeration is beneficial to the accumulation of total VFA content,and improving aeration intensity will accelerate the release rate of carbon sources in sludge.However,it also accelerates the degradation of VFA.The optimal aeration intensity is 0.9～ 1.1 L/(h·L sludge).The organic compounds in the sludge digestion supernatant mainly have the diffraction peaks of microbial by-products,protein-like fluorescent substances and humic acid substances.The increase of aeration can accelerate the metabolism and transformation of microbial by-products,and the reduction of aeration is conducive to the accumulation of humic acid substances.The process of carbon source release from sludge is most obviously affected by digestion temperature.The temperature of 40,50 and 60 ℃,the three reactors at 96 hours soluble cod(SCOD)cumulant is respectively 2642,9975 and 11808 mg/L.Digestion temperature reactor under the condition of 40 ～ 60 ℃ is running,the temperature,the higher the VFA accumulation.Considering the high temperature needed extra energy consumption and temperature higher than 65 ℃ when the sludge digestion system instead of the deteriorating status,release the sludge in carbon source the best digestion temperature,digestion time for 60 ℃ and 120 h.When the digestion temperature of 40 ℃,the digestive system,fluorescence class protein substances.When temperature raises to 50 or 60 ℃,we could not detect the presence of a protein-like fluorescent substance.Compared with 40 ℃ and 60 ℃,it is more conducive to the formation of humic acids at the temperature of 50 ℃.The higher the temperature of the digestive system,the more favorable it is for the decomposition of microbial by-products into other substances.The test results of the molecular weight distribution of the supernatant in the sludge digestion system showed that the increase of temperature was conducive to the transformation of macromolecules into small molecules,and the total proportion of small molecules increased accordingly.On the basis of releasing internal carbon sources from the sludge of TMAD,this study adopted the method of co-treatment of TMAD and micro-current to release internal carbon sources from the remaining sludge.At the same time,the micro electric current on the sludge digestion and the influence of carbon source release,optimum technological parameters for digestion reaction temperature 45 ℃,the intensity of electric current 175 mA,digestion time 96 hours,SCOD largest cumulative concentration of 12189 mg/L.The combined treatment of TMAD and micro current can not only accelerate the decomposition of sludge flocs into smaller particles and release a large amount of organic matter into the digestive supernatant,leading to a rapid increase in SCOD,but also increase the ratio of C/N and C/P.During digestion time of 96 h,SCOD in R1-45 ℃ reactors and the ratio of total phosphorus(TP)and the ratio of total nitrogen(TN),compared with the control group were raised to 116.1 and 13.5,the resulting digest the supernatant could be better used to act as carbon source of low carbon source wastewater.Hydroxyl radicals generated in the co-treatment system can promote the decomposition of microbial by-products,and the oxidative degradation of hydroxyl radicals by free radical polymerization is conducive to the formation of humus substances from digested sludge.On the other hand,hydroxyl radicals can promote the transformation of metabolic intermediates into small molecules and the polymerization of macromolecular substances.Based on the basic theory and practice of TMAD digestion,this study proposed the metabolic transformation pathway of sludge organic matter in the TMAD co-microcurrent treatment technology.The microcurrent can promote the decomposition of sludge flocs and the cell wall breaking,so that the released intracellular organic matter can be converted to the terminal small molecule material faster. |
PDF Full Text Request