| Author: | Zhuang, Huichuan |
| Title: | Genomic analysis elucidating celluloysis of chemical enhanced primary sludge in anaerobic digestion toward crabon neutral sewage treatment in Hong Kong |
| Advisors: | Leu, Shao-yuan (CEE) Lee, Po-heng (CEE) |
| Degree: | Ph.D. |
| Year: | 2021 |
| Subject: | Anaerobic bacteria Sewage sludge digestion Sewage -- Purification -- China -- Hong Kong Hong Kong Polytechnic University -- Dissertations |
| Department: | Department of Civil and Environmental Engineering |
| Pages: | xxii, 237 pages : color illustrations |
| Language: | English |
| Abstract: | This dissertation investigated the important anaerobic digestion (AD) treating high cellulose content (30%) municipal sewage sludge produced after chemical enhanced primary treatment (CEPT). CEPT sludge samples were investigated in a continuous AD operated at changing hydraulic retention times and organic loadings with CH4 production, the cellulose contents in bio-solids, and the volatile fatty acids closely monitored. Biological tools include meta-epigenetics, 16S rRNA gene, and meta-genomics analyses were also employed to elucidate the interspecies interaction, cellulosome related genes, and cellulosic degradation pathways. Reflecting to the performances of CEPT-AD, a stable methane yield at 0.42 m3/kg VSSin was achieved. Meanwhile, the results of mass balance suggested that for biogas conversion of CEPT sewage sludge, cellulose and protein degradation played a key factor at low organic loading operation (2 gVSS/L-day, SRT=15 days), while lipid degradation was more significant at high loading operation (3 gVSS/L-day, SRT=20 days). Microbial analysis revealed high abundance of cellulolytic bacteria, cellulosome related genes, and methanogens; and low abundance of syntrophs, suggesting effective degradation and uptake of amorphous cellulose to acetate. An unexpected result showed that cellulosome genes were identified from two high abundance species of Methanosarcina. In line with the reduced total volatile fatty acids and propionate (to 1,200 and 600 mg/L, respectively), such cellulolytic and methanogenic synergy implies unique syntrophs bypass for bioenergy production. DNA methylation study based on the third-generation sequencing platform Pacbio Sequel was conducted for characterization of mixed culture microbial methylomes. Based on the kinetics information via single-molecule real-time sequencing technology, DNA methylation status of N6-methyladenine (6mA) and N4-cytosine (4mC) in 17 draft genome bins of a laboratory-scale AD with a high celluisoic-degrading efficieny treating a chemical-enhenced primary sludge was obtained. 37,726 6mA and 7,806 4mC methylation sites were identified. From those methylation sites, 105 DNA methylation motif pattens, including seven 4mC type and ninety-eight 6mA type, were defined. And methylation motif pattens were various among genome bins. The average methylation levels of reconstructed genome bins various from 0.0% (ADbin16) to 0.57% (ADbin6). In most of the genome bins, 6mA was the major methylation type. To exploit the relationship between DNA methylation, gene regulation, and high cellulosic-degrading efficiencies, two operons in ADbin12 coding proteins relative to hemicellulose, cellulose, and starch degradation, were analyzed and discussed. The different methylation status of TTAA motifs in their promoter regions may lead different expression levels. Greenhouse gases (GHGs) emissions and energy consumption profiles of different wastewater treatment strategies were estimated according to experimental and on-site data sets. With the combination of CEPT sludge and AD, the net energy of sewage treatment can be significantly reduced, as which 0.10~0.14 kWh energy can be recovered as form of electricity which is equivalent to 0.029~0.080 kg CO2-e greenhouse gas emission reduction for per·m3 sewage treated. |
| Rights: | All rights reserved |
| Access: | open access |
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