Effects Of Cellulose On Anaerobic Biodegradation Of Polycyclic Aromatic Hydrocarbons In Sewage Sludge

Polycyclic Aromatic Hydrocarbons?PAHs?are a class of highly inert hydrocarbons that are less susceptible to degradation and stable in the environment.PAHs can enter the municipal sewage system,which come from the industrial waste water,waste,the wet and dry settlement of the atmosphere and the urban ground runoff in the environment.PAHs is a kind of difficult degration organic matter in sewage sludge commonly which are the adsorbed and accumulated in the sludge.With the increase of industrialization level and the process of urbanization,a large number of sewage treatment plants were built and put into operation,and the sludge production was greatly improved.The biological removal of PAHs in sludge was paid more and more attention.the study was carried out on the small-scale anaerobic digestion of sewage sludge.Semi-continuous sludge anaerobic digestion reactors were made of 5 mm thick plexiglass and divided into two layers under mesophilic condition?35±1??.In anaerobic digestion of sludge,three typical treatments named CA,CB and CC were set by adding cellulose in sludge,according to VS_sludge:VS_cellulose = 5:1,2:1 and 1:1.Simultaneously,the anaerobic digestion of sludge without cellulose was used as control group?CK?.After the reactors were started up successfully,the activated sludge was added into the reactors and digested sludge was discharged at 5% dosage rate every day.When the reactors run steadily,the effect of the cellulose on the biogas production,variation of biogas composition,the efficiency of PAHs removal and microbial community structure in anaerobic digestion was studied..The results show:?1?the addition of cellulose could improve the nutrient balance of anaerobic digestion,which was beneficial to the anaerobic digestion.The biogas production of four groups were 250 mL,600 mL,1200 mL and 2300 mL.methane production were about 1.6 times,2 times and 2 times.Specific methanogenic activity of three experimental groups were 45 mL/g VSS·d,73 mL/g VSS·d,94 mL/g VSS·d and 120mL/gVSS·d,respectively..?2?Compared with CK group,the addition of cellulose could improve the degradation rates of PAHs.The degradation rates of ?PAHs were 14.82%,20.75%and 19.35%,respectively.The degradation rates of 4-cyclic aromatic hydrocarbons were better than the degradation rates of 2-ring and 3-ring.The degradation rates of4-cyclic aromatic hydrocarbons were 22.12%,31.04% and 28.04%,respectively.the degradation rates of BaA were 32.48%,39.32% and 44.76%.The degradation rates of CHR were 19.35%,39.74% and 27.51%,respectively.The degradation rates of BbF were 13.48%,22.29% and 14.09%,respectively.The degradation rates of BkF were24.65%,31.43% and 28.69%,respectively.?3?It was observed that all kinds of microbial species and complicated morphology were investigated by scanning electron microscopy?SEM?in the stable phase of the anaerobic digestion.The microbes of anaerobic digested sludge were mainly composed of coccus,bacilli and filamentous.The addtion of cellulose could improve the abundance of Spirochaetaceae_uncultured,Oligosphaerales_norank,Caldithrix,Ruminiclostridium₁,Miscellaneous_Crenarchaeotic_Group_norank,Methanolinea and Methanobacterium,and Ruminiclostridium₁ was a new genus.The abundance of bacteria was different,which lead to different degradation rates on polycyclic aromatic hydrocarbons.?4?At the level of portal classification,different bacteria played a different role in different groups.The microbical species,and abundance of bacteria which could degrate PAHs in CB and CC groups were more than the microbical species,and abundance of bacteria of other groups.Bacteroidetes,Caldiserica,Spirochaetae,Firmicutes,Chloroflexi,Proteobacteria,Lentisphaerae and Unnamed Bacteria could degrate PAHs in CB group.Firmicutes,Chloroflexi,Spirochaetae,Bacteroidetes,Deferribacteres,Planctomycetes,Caldiserica,Thermoprotei and Unclassified Bacteria could degrate PAHs in CC group.