Isolation And Characterization Of Polyacrylamide Degrading Bacteria For Application To Biodrying Of Dewatered Sludge

High moisture content of dewatered sludge is a common issue existing in current sludge treamtment, which directly affect subsequent process of sludge treatment. This problem is caused by many different factors, one of which is widely using of polyacrylamide ?PAM? represented organic polymer as flocculant in sewage and sludge treatment. In the dewatering process, sludge granules gathered by PAM flocculating form colloidal polymeric substance. It makes dewatered sludge difficult to dispense and evaporate, which results in time-consuming sludge dewatering under natural conditions. In this study, we aimed to screen for a PAM-degrading microorganism from dewatered sludge and evaluated its degradation characteristics. The strain was applied to bioaugment dewatered sludge drying process in the form of microbial inoculum, which degrades PAM to speed up the drying process of sludge. The main conclusions were as follows:Eleven strains could grow on the polymer medium were isolated from four sources of dewatered sludge. After the heavy metal and salt tolerance tests, strain HI3 was selected by enrichment on PAM as a sole source, which degraded 35.9% of PAM in 7 days of cultivation. It was subsequently identified as Pseudomonas putida by combining morphology, automated microbial identification and 16S rRNA gene sequence analysis results. Factors that affected microbial growth and PAM degradation were also studied.GFC results showed the average molecular weight of PAM decreased after biodegradation. The weight-average molecular weight of PAM dropped from 6.44×10⁶ Da to 1.85×10⁴ Da after 21 days of cultivation. The high molecular weight components of PAM transformed to low molecular weight components after biodegradation, which were further utilized as carbon source for microbial growth. FT-IR results showed the side-chain amide groups of PAM were converted to carboxyl groups. Hydrolyzed amino group were utilized as nitrogen source for microbial growth. LC-MS results showed a number of products contain CH₃-C=C-CHO or structurally similar derivatives were both found in PAM samples before and after biodegradation.After SDS-PAGE analysis, PAM induced extracellular amidase was found and then purified through ammonium sulfate precipitation, DEAE-Sepharose FF ion exchange chromatography and Sephadex G-200 gel filtration. The optimum temperature of enzyme was 44? and optimum pH was 7.8. Metal ion such like Mg²⁺?Ca²⁺?Mn²⁺ in low concentration could activate enzyme activity, on the contrary, Fe²⁺?Zn²⁺?Cu²⁺?Ni²⁺ inhibited enzyme activity in various concentration. Enzyme activity was completely inactivated by iodoacetic acid. The amidase also had activity toward short-chain fatty amides except nitrile compounds. The gene fragment corresponding to conserved amino acid sequence of amidase was cloned by degenerate primers desigened by CODEHOP strategy. The sequencing result indicated the enzyme is aliphatic amidase belongs to nitrilase superfamily.The optimum condition of solid state fermentation was determined by single factor analysis and orthogonal experiment. The results of sludge biodrying in lab and small-scale experiment showed that the microbial agent effectively reduced the concentration of PAM in sludge, which promoted the decrease of water content in sludge and shortened the required drying time. The pilot-scale experiment of dewatered sludge biodrying combining aerobic fermentation was held on the sewage plant site. With aerobic fermentation equipment assisted, sludge was converted into organic fertilizer in 15 days, which took less time than traditional sludge compost. This demonstration was a valuable reference for dewatered sludge stabilization and recycling.