Study On Optimization Of Carbon Source Recovery And Utilization In Typical Urban Wasterwater Treatment Plants

Traditional processing technology of urban sewage treatment removed various contaminants from waste water,mainly by“energy consumption”method.This not only caused the loss of original carbon source of waste water low efficiency of utilization ratio,but also leaded to high energy consumption of processing waste water and high yield of leftover sludge and also caused the problems of“high energy consumption”and“high carbon-emitting”with the lack of carbon source needed by nitrogen and phosphorus removal under which circumstances a large amount of external carbon source was needed and this increased the cost of sewage treatment.The future high efficiency low-carbon processing technology of urban sewage treatment to solute the above mentioned problems would improve the utilization ratio of transformed carbon source during the sewage treatment process,which would be an important way to realize the high efficiency renewable low-carbon method,by means of extraction,transformation and recycling the organic material from waste water as carbon source and energy substrate to improve the utilization ratio of transformed carbon source during the sewage treatment process.This thesis gived priority to urban sewage treatment plants as subjects for study,studying the method of extraction,transformation and recycling of insoluble organics from sewage.In this method,studying the recovery efficiency of insoluble organic materials from waste water through different enhanced pretreatments?chemical enhanced flocculation,biologic enhanced flocculation,chemical biological enhanced flocculation?,and analyzing the effect of medicament,the dosage of leftover slugde and the ways of adding flocculants on the recovery efficiency of insoluble organic material from waste water;in the way of transforming insoluble organic material,during process of anaerobic hydrolysis,we studied transformation efficiency of insoluble organic material and content or variations in ratios of products,Volatile fatty acids?VFAs?,of hard-degraded organic material,making comparison analysis of the hydrolysis conformation ratio of primary sludge,excess sludge and chemical biological enhanced flocculating sludge;The distribution of carbon source and utilization approach was analyzed during the sewage treatment process,which served as a theoretical underpinning for urban sewage treatment plants to exploit the carbon source and high efficiency utilization.The survey of recovery chemical enhanced flocculation,biologic enhanced flocculation,and chemical-biological enhanced flocculation results indicated that with preprocessing chemical enhanced flocculation,the entrapping effect of Suspended solid?VSS?,chemical oxygen demand?COD?,soluble chemical and oxygen demand?SCOD?raised obviously along with the increasing of dosages of flocculant FeCl₃,and when the dosage of FeCl₃ reached to 60 mg/L,entrapping ratio of COD,SCOD,ISCOD and SS reached to 60.5±4.5%,31.5±2.9%,74.1±3.6%and75.3±2.5%;with preprocessing biological enhanced flocculation,the entrapping effect of SS,COD,SCOD from waste water and the removal ratio of contaminates,such as phosphorus and nitrogen,raised obviously along with the increasing of dosages of biological flocculant,when the dosage of excess sludge?MLSS 8g/L?was 1.06 g/L,the investigation showed that the entrapping effect of COD,SCOD,ISCOD and SS thereached to 66.5±4.3%,38.4±4.2%,79.5±3.7%and 78.4±4.1%;the experiment of chemical-biological enhanced flocculation used FeCl₃ as inorganic flocculant and excess sludge as biological flocculant,with the dosage of FeCl₃ and excess sludge reaching to 60mg/L and 0.86 g/L,it performed well in entrapping COD,SCOD,ISCOD and SS from waste water and removing phosphorus and nitrogen,reaching to75.9±4.0%,49.8±4.4%,87.7±3.7%and 83.6±3.5%,and then the removing effect was apparently higher than single chemical and biological flocculation,at the same time,it was the superior way that adding inorganic flocculant?FeCl₃?and biological flocculant?excess sludge?in chronological order.The indicates in the transformation ratio of insoluble organic material and its products in the process of anaerobic hydrolysis showed that under the condition with which 25 degrees temperature and 10 PH,reference to primary and excess sludge,with densities of chemical and SCOD released by chemical-biological flocculating sludge reached to 748.6±24.4 mg/g VSS,which was 1.7 times and 1.2 times released of excess and primary sludge;the yield of VFAs reached 410.3±26.8 mg COD/g VSS,which was 1.2 times and 1.9 times densities of released of primary and excess sludge.The VFAs content of various hydrolysis products of sludge was in the order as:acetic acid>propionic acid>isovaleric acid>butyric acid>isobutyric acid>valeric acid.Relative to primary sludge and excess sludge,chemical-biological enhanced flocculating sludge had the highest yield of acetic acid and propionic acid in total yield of VFAs?77%?.Through the analysis of carbon source allocation and utilization in wastewater treatment process,it could be concluded that after chemical-biological enhanced flocculation treatment,the carbon source supplement required for biological denitrification in the secondary treatment unit was about 271.5 mg COD/L,which accounted for 52%of the VFAs content resulting from hydrolytic acidification of chemical-biological enhanced flocculation sludge produced by the unit influent.