Study On Biodegradation Of Cationic Polyacrylamide In Sludge By Functional Bacteria Enhanced High Temperature Aerobic Composting

The expansion of the scale of urban wastewater treatment in China has led to a dramatic increase in the production of sewage sludge（referred to as sludge）,which needs to be disposed of safely to mitigate its negative impact on the environment.Polyacrylamide（PAM）,which is highly bioresistant,is used more in the field of water treatment,where cationic polyacrylamide（CPAM）applied in the process of sludge dewatering can enter the environment and exist for a long time in the process of landfill and land use,posing a serious threat to the ecological environment and people’s health.High-temperature aerobic（HA）composting systems use aerobic microorganisms to achieve degradation of difficult organic pollutants at higher temperatures,and bioaugmentation techniques that add specific functional microorganisms to the system can effectively improve the degradation efficiency of pollutants.In this paper,we firstly constructed a HA composting system,screened CPAM-degrading functional bacteria from the HA system,and on this basis,constructed an Enhanced high-temperature aerobic（EHA）composting system with functional bacteria to study its degradation effect on CPAM in sludge.The main findings of the study are as follows:（1）The maximum temperature of the pile in the HA composting system was60.3°C,and the high temperature period of composting temperature above 50°C was maintained for 10 d.The water content,organic matter and organic carbon content at the end of composting decreased to 53.5%,77.4%and 33.94%,and the p H,Electrical Conductivity（EC）and Germination Index（GI）values were 7.6,1670μs·cm^-1 and107%,respectively.The physicochemical indexes indicated that the compost was basically harmless and met the compost maturation requirements.（2）The concentration of CPAM decreased from 1.33 mg·g^-1 to 0.69 mg·g^-1during HA composting process,and the degradation rate was 60.36%,among which,the degradation rate was the fastest when composting high temperature CPAM,and the high temperature degraded CPAM accounted for 68.03%of all composted degraded CPAM.（3）The diversity of bacterial communities in the HA composting process showed an overall trend of decreasing,then increasing and then decreasing again,and the richness showed an overall decreasing trend.The differences in bacterial community structure were significantly greater during the warming and high temperature periods of composting,and the community differences were smaller during the cooling and decaying periods.At the phylum level,Proteobacteria and Actinobacteriota were the dominant phylum in the warming period,Firmicutes and Actinobacteriota were the dominant phylum in the high temperature period,and Firmicutes and Proteobacteria were the dominant phylum in the cooling and decaying periods.At the genus level,Bacillus and Pseudomonas were the dominant genera in the warming phase,Geobacillus,Thermobispora,and Thermopolyspora were the dominant genera in the high temperature phase.Geobacillus,Thermobacillus,and Achromobacter were the dominant genera in the cooling Geobacillus,Thermobacillus,and Achromobacter were the dominant genera in the cooling and decaying periods.（4）Six strains of CPAM-degrading bacteria were screened from the HA composti ng system,and by comparing their CPAM degradation rates,the highly efficient CPAM degrading functional bacteria CPAM4 was selected,and after morphological and 16Sr RNA sequence analysis,CPAM4 was identified as Bacillus novalis.（5）The HA composting system was enhanced with coconut shell biochar as a carrier for CPAM4,and an EHA composting system was constructed.the maximum temperature of the pile in the EHA composting system reached 63.9°C and the high temperature period lasted for 20 d.Compared to the HA composting system,the EHA composting system had higher overall p H,EC,GI and TN values and lower water content,organic matter and TOC concentrations.The degradation rate of CPAM at the end of the high temperature period of the EHA composting system was 67%,accounting for 87.18%of all compost degradation,and the final degradation rate of CPAM was 76.85%,which was 16.49%higher than that of the HA composting system.（6）The addition of biochar immobilized with CPAM4 significantly enhanced the diversity of composting bacterial communities.At the phylum level,Firmicutes,Actinobacteriota and Proteobacteria were the dominant phylum in the EHA composting system,and the relative abundance of Actinobacteriota and Proteobacteria showed an increasing trend.At the genus level,the relative abundance of Bacillus in the microbial community of EHA composting system（11.36%～62.91%）was significantly higher after CPAM4 intensification compared to HA composting system.unclassified＿f＿＿Streptosporangiaceae（family Streptosporangiaceae）and Saccharomonospora also had higher relative abundance.