| Waste activated sludge(WAS) as the inevitable by-products is produced in wastewater treatment process. WAS has been considered as the cheap resource due to abundant organics matters. Anaerobic digestion for methane production is one of the most popular research foci. Howerver, in sludge anaerobic digestion, the slow hydrolysis, sensitive methangens, and low ratio of carbon and nitrogen(C/N) always lead to the failures of methanogenesis. To solve these problems, pretreatment technologies were used to accelerate sludge hydrolysis. Simultaneously, anaerobic sequencing batch reactor(ASBR) and expanded granular sludge bed(EGSB), two-phase anaerobic digestion process, was proposed. That is, the transformation from carbon sourece in sludge to short chain fatty acids(SCFAs) was completed in ASBR reactor, and the kitchen waste hydrolysate was added into ASBR to control C/N for enhancing protein degradation and SCFAs production. Then, the acidification liquid was pumped into EGSB for subsequent methanogenesis. The characteristics of granule sluge and microbial community dur ing cultivation and domestication process were investigated.Ultrasonic and alkaline, ultraosonic and β-cyclodextrin, and low-temprature thermal hydrolysis were used to disintegrate sludge structures, and the methanism for cell dissolution was analyzed. At the same time, the batch tests were designed for determining the optimal pretreated parameters for SCFAs production. The results showed that ultrasonic and alkaline pretreatment, and low-temprature thermal hydrolysis effectively destroyed the extracellular polymeric substances(EPS), which resulted in the partical size decreased from 212 to 10 μm, while in ultraosonic and β-cyclodextrin pretreatment, the particle size increased to 160 μm again because of the refloculation of disintegrated sludge at β-cyclodextrin of 0.3 g/g DS. Soluble proteins were main component in any pretreatments, while the humic likes substances increased with increase of β-cyclodextrin dosage. The static acidification experiments suggested that the SCFAs productions had a positive correlation with soluble organic matters, and the SCFAs concentrations followed the order: ultrasonic and alkaline(2543.7 mg/L) > ultrasonic and β-cyclodextrin(2281.1 mg/L) > thermal hydrolysis(1811.4 mg/L).ASBR reactor was employed for hydrolysis and acidification of disintegrated sludge, and the effects of HRT on SCFAs production were investigated. The results showed that HRT of 3 days was benefit for SCFAs production of pretreated sludge, and the SCFAs concentrations maintianed at 2200 mg/L. Corresponding acetic and proponic acids are the main SCFAs, accounting for more than 65%. According to the issues of low C/N and protein degradation, the kitchen waste hydrolysate after thermal hydrolysis(150℃; 30 min) was added into ASBR to condition WAS anaerobic digestion. The results showed that the voloum ratio of sludge and kitchen waste of 10:1 effectively enhanced the SCFAs concentration from 2099 to 7167 mg/L. The fermentation type was changed significantly by kitchen waste, acetic and butyric aci ds were the main SCFAs. Compared with cntrol, the percentage of SCFAs in acidifation liquid increased 1.92-fold, and the percentage of proteins decreased one third at volume ratio of 10:1, indicating that kitchen waste did promote the proteins degradation and SCFAs production. Microbial analysis indicated that kitchen waste obviously changed the microbial communities. In terms of phlum level, the Chloroflexi and Proteobacteria decreased to 3.17% and 8.48%, while Bacteroidetes and Firmicutes increased to 43.3% and 30.1%。In terms of class level, Bacteroidia, Bacilli and Clostridia which were responsible for the degradation of carbohydrates increased to 17.61%, 13.67% and 29.49%. In addition, the change of shannon index suggested that microbial diversities were enhanced by kithen waste, creating the conditions for stable operation of ASBR.EGSB reactor was used in methanogenic phase of sludge acidification liquid. Firstly, the studies on cultivation and domestication of granule sludge suggested that smooth, dense and spherical particles were formed on the 90 th day, and the granule sludge was mainly composed of particle sizes of 0.63-0.8 mm and 0.8-1.0 mm, corresoponding methane yiled reached 0.32 m3/kg COD. Macro genome sequencing results showed that Firmicutes, Proteobacteria, Bacteroidetes and Chloroflexi were four major phylum. Hydrogen-producing acetogenesis Pelotomaculum and homoacetogenic bacteria Acetobacterium, belonging to Firmicutes, and hydrogen-producing acetogenesis levilinea, belonging to Chloflexi, all increased with increase of acidification liquid. Also, no obvious changes of Syntrophobacter, belonging to Proteobacteria, were observed with SCFAs increasing. On the 90 th day, Methanosarcina and Methanosaeta were the major archaea in EGSB reactor, accounting for 54.11% and 31.8%, respectively. It was obvious that these two microb es adapted to high SCFAs concentration, and should be responsible for high methane production. Secondly, the effects of HRT on methane production at stable stages of EGSB were investigated. The results showed the the optimal HRT for methane production should be controlled at 12 h when the temp rature was 35±2℃ and the reflux ratio was 4:1. |
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