DEVELOPMENT AND FUNDAMENTAL INVESTIGATIONS OF INNOVATIVE TECHNOLOGIES FOR BIOLOGICAL NUTRIENT REMOVAL FROM ABATTOIR WASTEWATER.

The meat processing industry requires large quantities of water, much of which is discharged as wastewater containing high levels of COD and nutrients such as nitrogen (N) and phosphorus (P). These nutrients must be removed to very low levels before any discharge into local waterways to avoid causing eutrophication in receiving aquatic systems. Reliable biological COD and nitrogen removal systems have been developed and applied for abattoir wastewater treatment using continuous activated sludge systems. However, P removal is achieved primarily through chemical precipitation with the addition of large amounts of iron or alum salts. Biological P removal is often consider as being a cheaper and more sustainable option as no chemical dosing is required and the quality of the excess sludge is usually suitable for land fertilisation purposes. Compare to well established continuous wastewater treatment systems, sequencing batch reactor (SBR) technology offers a great deal of operational flexibility and appears to be a promising vehicle for achieving high levels of N and P removal from abattoir wastewater. The overall objective of this thesis is to develop a biological process that achieves high level of COD, N and P removal from abattoir wastewater, producing effluent suitable for being discharged into river systems (i.e. over 95% of the N and P contents removed). Achieving stable and reliable biological P removal from a wastewater containing high level of nitrogen is the main obstacle to overcome to achieve this objective. This study also investigate the feasibility of using two innovative technologies, namely the simultaneous nitrification, denitrification and phosphorus removal (SNDPR) process and the aerobic granular sludge technology, to further enhance the performance of the SBR system designed. In this thesis, three different lab-scale SBRs were operated to demonstrate the feasibility to achieve high-levels of biological COD, N and P removal from abattoir wastewater. The first SBR was employed to experiment novel strategies, which can easily be implemented to current water treatment facilities used by the meat industry, to produce an effluent suitable for river discharge. The second SBR was operated to provide a platform for an in-depth investigation of the previously proposed SNDPR process, which has the potential for application to the treatment of abattoir wastewater. The third SBR was operated for the treatment of abattoir wastewater by combining together the aerobic granular sludge technology and the SNDPR process. A wide range of techniques was employed in this thesis which includes reactor process studies, microbial investigations (fluorescent in-situ hybridisation combined with confocal laser scanning microscopy) and several micro-scale techniques (e.g. microsensors, electron microscopy and light microscopy). The combination of these multi-disciplinary techniques has helped deliver significant insightful information. The main contributions of this thesis are as follow. An SBR system was demonstrated to effectively remove 95%, 97% and 98% of the total COD, total N and total P present in abattoir wastewater. It could provide a real alternative to chemical P removal, which is the common practice in the meat industry. A multi-step feeding strategy was employed to prevent the accumulation of nitrate or nitrite in the SBR providing the right condition for the development of a stable biological P removal. The incorporation of a high-rate pre-fermentor as an integrated component of the nutrient removal system was found to be important. This stream, which contains a high-level of volatile fatty acids, provides supplementary carbon sources critical for both P and N removal. Further, an aeration control strategy consisting of stopping the aeration in the SBR immediately after ammonia is fully oxidised was effective in achieving stable N removal via the nitrite pathway. It benefited the nutrient removal performance of the SBR by saving some valuable amount of COD. The investigation of the SNDPR process revealed that the production of N2O, often observed in lab-scale SNDPR bioreactors and source of concern due to the high global warming potential of N2O, was found to be linked to the loss of diversity amongst the denitrifying microbial community due to the use of synthetic wastewater containing only a single carbon source. N2O accumulation is unlikely to be an issue in a SNDPR bioreactor treating real wastewater which contains a large variety of different carbon sources. The SNDPR process and the aerobic granular sludge technology were successfully combined in a single SBR process. The size and the dense structure of aerobic granules positively contributed to the oxygen mass transfer limitation required to achieve reliable SNDPR. It was also demonstrated that the minimum hydraulic retention time (HRT) for a granular sludge system is not governed by the sludge settleability, as is the case in a system with floccular sludge. Mass transfer limitations in granules are an important factor to be considered in the design of the HRT and the COD and nutrient loading rate in a granular sludge system. The in-depth study of the structure and function of these aerobic granules fed with abattoir wastewater revealed interesting structural features that have not been reported in synthetic-fed granules. These observations initiated new hypotheses regarding the microbial structure and the fate of mature granules, the effect of pH on the granule structure stability and the role played by protozoa in the overall system performance. It also provided some new directions and recommendations for further experimental studies on aerobic granules in relation to their structure and behaviour in real systems