Researches On Process Optimization And Molecular Diversity Of Microbial Communities In Anaerobic Digestion Of Cotton Stalk

Biogas fermentation of cotton stalk is one of effective measurements to utilize cotton stalk. However, biogas fermentation of cotton stalk is different from other stalks due to the special structure of cotton stalk. It is necessary to make researches on the potential and process of biogas fermentation of cotton stalk. Therefore, a series of researches were carried out. The result could provide a theoretical basis for raising fermentation efficiency and provides a scientific guidance to practical popularization and application of biogas fermentation of cotton stalk.(1) Acclimation and screening of inocula of biogas fermentation of cotton stalk were carried out. The method of inocula acclimation and screening was established. It was thought that the best inocula adapted to biogas fermentation of cotton stalk came from the domestication of river bottom sludge with cotton stalk powder and sand.(2) The biogas fermentation potential of cotton stalk as raw material at intermediate temperature of(35±2)℃as well as degradation characteristics of cellulose, hemicellulose and lignin in the process of fermentation were investigated. The results showed that biogas yield potential of cotton stalk was 202 ml/g·TS in 250-ml bottle in 53 days. The cellulose content of cotton stalk decreased by 12.4%, and hemicellulose by 21.0%, however, the lignin content was almost not decreased. Moreover, comparative research on the biogas yield and biogas-producing efficiency of cotton stalk, wheat stalk, rice stalk and corn stalk at ambient temperature of(28±2)℃was conducted. The results showed that the biogas fermentation potential of cotton stalk was less than other stalk materials. Nevertheless, cotton stalk was a potential resource for obtaining bioenergy by means of biogasification.(3) In 250-ml bottle at intermediate temperature, orthogonal test was carried out in order to obtain optimal technological conditions of biogas fermentation of cotton stalk. The best technological conditions were: 30% of inoculation amount, 7 % of TS , 30:1 of C/ N, 7.0 of started pH. At the same time, biogas fermentation process of cotton stalk in 1L-bottle was studied. The result was that activity peak of protease, glucoamylase, amylase and cellulose as well as content peak of volatile organic acid were in the peak period of yield, which suggested that above enzymes and volatile organic acid were all closely related to effiency of biogas fermentation.(4) An effective approach for extraction of PCR-compatible DNA from biogas slurry of biogas fermentation of cotton stalk was established. The approach was combined treatment successively using humic acids removing buffer, lysozyme, SDS,hydroxybenz- ene /chloroform, isopropanol and ethanol.(5) A research method of microbial community structure diversity during the process of biogas fermentation of cotton stalk using PCR-DGGE technology was established. Genomic DNA was extracted directly from the activated sludge which were sampled in different period of fermentation .The 16S rDNA genes V3 region were amplified by using the bacterial universal primers, and separated by DGGE. The result showed that the bacterial structure diversity was abundant and changed along with biogas fermentation. The bacterial community structure was related to the biogas yield and material degradation.