AbstractOne of the primary concerns for the treatment of high strength carbonaceous wastewaters in anaerobic systems is to achieve an optimum growth environment for acidogenesis and methanogenesis. Such wastewaters with high nutrient levels could cause additional problems as anaerobic units are usually designed for the removal of organic matter. In addition, nitrate inhibition to methanogenesis in anaerobic environment could cause further problems during treatment. Therefore, a type of high rate anaerobic system is required which could accommodate nitrogen removal in addition to organic carbon removal, and comply with the increasingly stringent discharge standards adopted by environmental protection agencies worldwide. This research was carried out by developing a new reactor by using a bed of anaerobic granular sludge in an anaerobic baffled reactor, the granular bed baffled reactor (GRABBR). The aims of this study were to investigate the performance of GRABBR in terms of treatment efficiency for carbon and nitrogen removal, long term and shock load stability, occurrence and effectiveness of phase separation, characteristics of granular biomass in different phases, and to examine the physical, microbiological and kinetic parameters of biomass. A 10 litre GRABBR divided into five equal sized compartments was operated under mesophilic (35°C) conditions. The GRABBR system achieved high chemical oxygen demand removal, biomass retention and methane yield
under various operational strategies, particularly at high organic loading rates (OLRs), with synthetic glucose and brewery wastewaters. Phase separation between acidogenesis and methanogenesis mainly occurred at high OLRs. The reactor configuration and microbial environment encouraged the acidogenic dominant zone to produce intermediate products suitable for the methanogenic dominant zone. Acidogenesis in the upstream compartments of GRABBR caused breaking and flotation of granular sludge, along with the formation of microbial mass identified as mainly Gram-negative Klebsiella pneumoniae, while downstream methanogenic compartments retained the original granular structure. The reactor was efficiently operated at high OLR with short hydraulic retention time (HRT) on a long-term basis. The system was capable of treating highly varying flow rates. Simultaneous denitrification and methane production was observed in GRABBR during nitrate addition in the acidogenic and methanogenic dominant zones. It is shown that the microbial arrangement in a layered granular structure, containing vast diversity of species with strong association of facultative and methanogenic populations, and phase separation characteristics of the GRABBR, brought about simultaneous denitrification and methane production. No noticeable ammonification was observed with glucose and brewery wastewaters during nitrate reduction. The simpler forms of carbon sources, like acetate and VFA, were found to be a more efficient substrate in terms of carbon and nitrate removal than glucose. The presence of simpler forms of substrate and higher concentrations of methanogenic granules exhibited higher nitrate and carbon removal rates in the methanogenic dominant zone than the acidogenic dominant zone of GRABBR. This study demonstrated that the combination of granular bed, compartmentalisation and plug flow in a single system could achieve ideal anaerobic configuration for wastewater treatment to accomplish carbon and nitrogen removal. The findings of this research suggest that the
application of a GRABBR is suitable for the treatment of multiple pollutants of complex or high strength wastewaters, where each phase or compartment acts as a separate specialised treatment unit.
|Date of Award||Feb 2004|
|Supervisor||Joseph Akunna (Supervisor) & Phillip J. Collier (Supervisor)|