Mechanism, kinetics and microbiology of selection pressure driven biomass retention in solids containing agricultural waste treatment

The aims of this dissertation were to explore the mechanism of biomass retention in solids containing waste under selection pressure, and to develop a high-rate anaerobic digester treating agricultural waste containing solids. Active biomass retention is a cost-effective strategy for uncompromised anaerobic digestion rate at lower temperature without requiring heating energy. This is especially crucial for the anaerobic digestion of flushing diary manure in large-scale dairies where flushing manure management system is employed.;A methodology for determining rate-limiting step in anaerobic digestion of complex substrates was developed by supplementation of metabolic intermediates from each step of the digestion process. The concept of microbial community ratio (r) in the anaerobic degradation system was introduced and investigated in this study. The results revealed that the rate-limiting step changed according to the variation of r..;The dissertation study was also designed to test both Gravity settling (GS) and selection pressure (SP) theories applied for biomass retention, and to investigate their effects on active biomass retention in Anaerobic Sequencing Batch Reactor (ASBR) treating flushing dairy manure. The mechanism behind the opposing roles of GS and SP in settling time was also studied. Results revealed that both short and long settling time were able to retain high concentration of active microbes, though in disparate living forms.;A new strategy, improving biomass retention with fiber material presented within dairy manure as biofilm carriers, was then developed and evaluated for treating flushing dairy manure in a psychrophilic ASBR. A kinetic model for the process was also derived. It was proved that ASBR using manure fiber as support media not only improved methane production but also reduced the required HRT and temperature to achieve a similar treating efficiency compared with current technologies.;The methanogenic community from ASBR was evaluated by Terminal Restriction Fragment Length Polymorphism (T-RFLP) and clone libraries for both 16S rRNA gene and mcrA gene. Results revealed that a Methanosarcina dominated methanogenic community was successfully established in the ASBR digesters at short HRT. Diversity of methanogenic community changed with variation of HRT. The performance of the digester was also related to the diversity of microbial community.