| After the biological process of sewage treatment in urban sewage plants,a large amount of residual sludge mainly composed of microorganisms is generated,and its production also shows a continuous upward trend with the increase of sewage treatment capacity.Surplus sludge contains a large amount of organic substances that can be utilized,such as proteins and polysaccharides,as well as toxic and harmful substances such as heavy metals and antibiotics,which also leads to the dual attributes of"resource"and"pollution"in surplus sludge.If the remaining sludge is not properly treated and disposed of,it will cause environmental pollution and resource waste.This article takes the surplus sludge from a sewage treatment plant in a certain town of Shijiazhuang as the research object.By screening dominant thermophilic bacteria and mutagenic modification of the strains,the mutagenic effect of thermophilic bacteria on the surplus sludge is explored.Dissolvable COD,protein,amino acids,peptides,and particle size are used as hydrolysis indicators.The main results achieved are as follows:1)The DC8 strain with the highest extracellular enzyme activity was screened from the compost samples.The strain DC8 was identified as Geobacillus thermodenitrificans.Under the optimal reaction conditions:solid content of 4%,crude enzyme dosage of 20%,t=8h,T=60℃,p H=7,the maximum protein extraction rate of the remaining sludge can reach 32.2%.Moreover,through the scanning electron microscope of the sludge,it can be seen that the sludge floc particles become finer,with a larger specific surface area and more developed pore structure.2)According to the optimal mutation conditions:after 180 seconds of UV irradiation,1.5%DES mutation treatment was carried out at 55℃for 25 minutes.The protease activity of the selected mutant strain KT16 reached 416.8 U·m L-1,which increased by about 45.1%compared to the original strain,and its genetic performance was stable and not easily changed.After comparing and analyzing the genome resequencing data of the mutant KT16 with the original strain DC8,it was found that the gene enrichment analysis of SNP and In Del mutation sites using COG,KEGG,and GO databases showed that the SNP/In Del mutation sites were mainly involved in the basic synthesis and metabolism of cells.During the amino acid synthesis process,genes related to pathways such as serine,glycine,arginine,and substance transport were affected,resulting in changes in protease production.3)In the residual sludge reaction system with DC8 added,after 8 hours of hydrolysis,the content of SCOD,protein,peptides,and amino acids increased by 3917,1410.5,533.6,and 241.3 mg·L-1 compared to the original sludge,respectively.The residual sludge treated with KT16 showed an increase of 4594,1933.8,521.3,and 510 mg·L-1 in four indicators,respectively.The average particle size of the remaining sludge treated with KT16 decreased by 9.25μm.The sludge treated with DC8 only decreased by 6.96μm compared to the original sludge.Therefore,the hydrolysis effect of mutant KT16 is better than that of DC8. |
