High-rate anaerobic degradation of soluble organic pollutants is becoming very popular, particularly for carbohydrate-based industrial wastewaters. Despite the successes achieved, there are significant limitations in the application of this technology to more complex wastewaters. These are defined as containing other organic compounds such as particulate and soluble proteins and fats, and originate from abattoirs (slaughterhouses), meat and food processing and similar industries. Complex wastewater is often difficult to degrade and components such as solids and fats have slow degradation kinetics and can diminish process performance. Also, the growth of granular sludge, which is critical for optimal performance in upflow reactors, is slow and granule properties such as shear strength and settling velocity are poorer. This is reflected in a lower treatment efficiency of 50%-60% in systems treating complex wastewater compared with efficiencies of 85%-95% in carbohydrate fed treatment systems. This thesis examines specific aspects in the treatment of complex (proteinaceous) wastewater in high rate upflow anaerobic treatment plants and the influences of different conversion processes and microbial characteristics on design and operation. The research problem was approached in two ways: The macroscopic conversion processes were examined by investigating and modelling a two-stage full-scale high rate hybrid reactor in Spearwood, Western Australia, designed and operated by ESI Ltd. This allowed localisation of the key conversion process; specifically hydrolysis of solids, which was found to occur mainly within the methanogenic reactor. Degradation of soluble proteins was rapid and all proteins were fully acidified in the acidogenic (first) stage even at very low retention times. Because of the rapid protein degradation rates, partial acidification, which is often a strategy to improve granulation rates, is incompatible with pH, flow and concentration equalisation. The influence of a protein feed on granulation compared with a carbohydrate feed was examined by sampling granules from the above reactor, as well as two full scale brewery fed reactors and a full scale reactor fed fruit and vegetable cannery wastewater. The cannery fed granules had the highest shear strength and settling characteristics while the protein fed granules had low strength and density , low settling velocity and a comparatively wide size distribution. Both brewery fed granules had very similar and suitable properties. Molecular studies using fluorescent in-situ hybridisation (FISH) probing and microscopy indicated that the granules from the complex (protein) wastewater fed reactor had limited structural characteristics , possibly due to limited reaction rates (as opposed to diffusion rates). Granules from the cannery reactor and both brewery reactors had structures that appeared to be the result of diffusion limitations. Therefore, the critical operational constraints when treating complex wastewater are the particulate biomass and particulate substrate. Awareness of process status could be increased by monitoring of biological and substrate solid inventory in the methanogenic reactor. The model developed in this thesis can greatly assist this. Complications due to particulate substrate and poor granule properties may be intrinsic to complex feeds. These constraints are probably best addressed by design of a methanogenic reactor specifically for complex wastewater. The design should attempt to separate substrate hydrolysis, minimise shear on the granules and retain solids.
| Identifer | oai:union.ndltd.org:ADTP/253799 |
| Creators | Batstone, Damien John |
| Source Sets | Australiasian Digital Theses Program |
| Detected Language | English |
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