This thesis presents a chemical, microbiological and mathematical analysis of an anaerobic baffled reactor (ABR) treating domestic wastewater. The purpose of this study was to gain an understanding of the mechanisms of treatment of domestic wastewater in an ABR at pilot-scale, and to use this understanding to develop some guidelines for the design of ABR technology for the anaerobic treatment or pre-treatment of domestic wastewater. Previous research has been undertaken on ABR technology, but no detailed studies of the performance of an ABR on domestic wastewater at pilot-scale have been reported. In this thesis, operating data from a 3 000 ℓ pilot-scale ABR are presented and analysed. Two hypotheses were proposed: that (i) the baffled design of the reactor would facilitate phase separation whereby acidogenic and methanogenic processes predominate in different physical locations in the reactor; and (ii) the critical design parameter is the applied hydraulic retention time. The principle findings of this research were: • The pilot-scale ABR functioned as a solids retention device. Particulate material was retained through settling in the first compartment, forming a gel-like matrix. Reduction of solids occurred through anaerobic conversion to CH4 and CO2. • Partial phase separation of acidogenic and methanogenic communities was observed. • The major factor that controlled biomass washout rate and therefore reactor performance was upflow velocity in each compartment. At higher upflow velocities, slow growing microorganisms failed to establish, resulting in increased solids accumulation rates, while at lower upflow velocities, stable digestion proceeded. • Relatively poor treatment rates were obtained due to the low inherent alkalinity of waters in eThekwini municipality resulting in low operating pH values. • Insufficient pathogen reduction was observed indicating that post-treatment of effluent would be required. It was concluded that the benefit of the baffled design was related to the system’s solids retention characteristics and that the critical design parameters for an ABR domestic wastewater treatment unit were compartment upflow velocity and applied hydraulic retention time. / Thesis (Ph.D.)-University of KwaZulu-Natal, Durban, 2009.

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Thesis (M.S.)--University of Hawaii at Manoa, 2006. / Includes bibliographical references (leaves 127-132). / xvi, 132 leaves, bound ill. 29 cm

Thesis (M.S.)--University of Hawaii at Manoa, 2007. / Includes bibliographical references (leaves 121-127). / xiv, 127 leaves, bound ill. 29 cm

Errata pasted onto front end-paper. Bibliography: leaves 113-120. To obtain robust and quantitative data on the influence of UV absorption and suspended solids on UV disinfection an experimental study using commercial disinfection technology was undertaken.

The desirability of effective control of anaerobic digesters as a means of avoiding imbalance in the microbial population has become clearer and this can be seen from the literature in recent years. A number of published control strategies have been encouragingly successful, however the non-linear and time varying nature of the process generally requires a bespoke, engineered system dependant on the characteristics of the system. The 'cost of knowing' in employing control systems, is generally high. The ideal scenario for operators would be the availability of a generic control system at reasonable cost, which would be applicable to a large group of high rate reactor designs, operating on a limited (but broad) variety of waste streams. The system would be able to control from commissioning through to steady state and should be able to cope with reasonable expected shock loading conditions, albeit perhaps at some degree of sub-optimality. The aim of this work is to develop a control strategy, which will lead in future to this end. Bicarbonate alkalinity (BA) is a key parameter which indicates the buffering capacity of the anaerobic digestion system and which has the potential for helping to maintain a stable system in the face of changing organic and toxic load. This is particularly the case when used in association with other informative on-line parameters such as gas production rate, %CO2 concentration in the gas, TOC, pH and volatile fatty acids. All but the last of these have been investigated using a fluidised bed reactor and the degree to which the anaerobic process is non-linear and time varying has been assessed, as the level of complexity required to represent anaerobic digestion 'well enough' was not clear. Simple linear black box models of low order were investigated, predicting over a limited horizon and relying on current and recent data values to refine the prediction. Independent black box ARX models were identified for gas production rate, % CO 2 , bicarbonate alkalinity and Total Organic Carbon using on-line data from a fluidised bed reactor at varying organic load. Model predictions looked ahead one sample step (30 minutes) and when validated using data obtained in a different time period (separated by 4-8 weeks) gave significant predictions in each case. The non-linear nature of the process was found to have little effect over the operating conditions investigated. Also the variation of the process within 4-8 weeks period was not sufficient to cause the models to predict badly. The performance of three black box models which were parameterised and validated using data collected from the same laboratory scale fluidised bed anaerobic digester, were compared. The models investigated were all ARX (auto regressive with exogenous input) models, the first being a linear single input single output (SISO) model, the second a linear multi-input multi-output (MIMO) model and the third a non-linear neural network based model. The performances of the models were compared and it was found that the SISO model was the least able to predict the changes in the reactor parameters (bicarbonate alkalinity, gas production rate and % CO2 ). The MIMO and neural models both performed reasonably well. Though the neural model was shown to be superior overall to the MIMO model, the simplicity of the latter should be a consideration in choosing between them. A simulation with a horizon approaching 48 hours was performed using this model and showed that the method was not sufficiently accurate for use in situations where pure simulation was required. This thesis includes the use of a two population deterministic model calibrated using data from a fluidised bed reactor operating on a simulated yeast waste, in the development of a Model Reference Adaptive Control (MRAC) strategy. The strategy uses a three term adaption mechanism, which is described in the thesis as a Fast Adaption Trajectory (FAT) strategy, as it was found to be necessary to respond to catastrophic events over short time scales, in order to maintain the viability of the bacterial population. Numerical optimisation in a simulation environment was used to parameterise the controller, and this was done on the basis of only basic design information being available for the reactor which was to be controlled. The controller was tested on a significantly different Expanded Granular Sludge Blanket (EGSB) reactor operated on a sucrose based feed and which did not inform the controller design process beyond basic physical information. Two actuation strategies were explored over several months of operation, using a single on-line bicarbonate alkalinity monitor, which in the event proved to have significant reliability problems. Not withstanding the problems with the alkalinity monitor, which was dominant in determining the success or failure of the control strategy, it was found that the control strategy was able to maintain control during start-up, which was the ambition of this part of the experimentation. Both actuation methodologies showed promise although the variation of loading rate was not adequately tested by the experimentation, which was conducted. The actuation by dosing with bicarbonate proved to be better at maintaining control in the face of repeated and severe perturbations caused by failure in the bicarbonate monitor system. It is believed that the FAT controller is likely to be a transferable technique provided that unmodelled dynamics are not excessively dominant and that the reactor system is comparable to a CSTR design with predominantly soluble waste in the feed.

The sugar industry processes sugar cane and sugar beet to manufacture edible sugar. A high rate anaerobic system followed by an activated sludge process to 'polish' the effluent is presently the best available technology not entailing excessive costs for the treatment of wastewater from sugar processing factories. Upflow anaerobic sludge blanket (UASB) reactor systems are the most commonly implemented, with the higher loaded expanded granular sludge bed (EGSB) type systems gradually replacing at least some of the UASB applications. This higher loading carries with it a greater risk of process instability, especially given the irregular quantity and composition of sugar processing wastes. Control actions are required for process efficiency, preferably with appropriate control parameters monitored on-line. The need to balance economics (with regards to quantities of chemicals dosed) with the safety/stability of the process further exacerbates the need for close control. There are a limited number of control actions available e.g. bicarbonate alkalinity (BA) dosing, temporary diversion of load by feed rate variation, or dilution with final effluent. Monitoring of conventional anaerobic digester systems typically consists of a combination of intermittent manual sampling followed by off-line analysis coupled with qualitative observations. Hence a decline in reactor performance could go unnoticed for a significant period of time. A simple yet reliable control system could not only minimise labour, but could also react to any changes in reactor conditions as soon as they occurred, leading to more efficient process operation, higher quality treatment and ultimately greater economic gain. The industrially recognised 'bottleneck' in the quest for automatic control is the availability of reliable and cheap on-line analysers. In the work presented here a series of experiments have been carried out on a simulated sugar processing wastewater using an on-line BA monitor in conjunction with an adaptive control strategy developed in a parallel PhD project. The possibility of achieving successful automatic control of an EGSB reactor through its start up phase and also during steady state operation (including some degree of process optimisation) and a series of organic step-change experiments was investigated. Two different control actions to maintain a BA set-point in the reactor, organic loading rate (OLR) variation and BA dosing, were compared. Research was carried out on a 30 1 EGSB reactor rig operating at 37 °C, fitted with on-line sensors to measure temperature, gas production, carbon dioxide percentage and pH. All sensors were interfaced with a PC configured to scan the sensors at one minute intervals. Five attempts to automatically start-up the EGSB reactor were made (Experiments 1-5), using OLR variation as a control action at a constant hydraulic retention time (HRT) of 23.3 hours, with various improvements and adjustments made to the reactor and control system after each. It was concluded that it was not possible to automatically control start-up to steady state using OLR as a control action using the BA monitor and controller in their present forms. Main reasons for this were the susceptibility of the laboratory-scale BA monitor to blockage by biomass washed out of the reactor (a common occurrence during the start-up phase) and the severity of loading rate oscillations. For Experiment 6 BA was dosed according to the relationship of the on-line BA monitor output to the BA setpoint, and OLR was changed approximately weekly according to operator expertise based on on- and off-line data and visual observations. HRT was maintained at 22 hours. A successful, sustainable startup was achieved, with mean % COD removal during the first 10 weeks being 78 % at a mean OLR of 9 kgCOD/m3 /day. After the successful start-up period, the reactor's HRT was approximately halved to 11.2 hours, and two OLR stepchange experiments (from 10.0 kgCOD/m 3/day to 28.1 kgCOD/m3 /day, and from 11.8 kgCOD/m3/day to 32.4 kgCOD/mVday) of twelve hour duration were carried out, followed by a removal of the control system and a similar organic step-change experiment (13.0 kgCOD/m 3/day to 32.9 kgCOD/m 3/day). It was found that approximately halving the HRT had no significant effect on the biomass or biomass activity. The HRT change did however adversely affect the smoothness of control, although control was not lost, as the on-line BA was always kept between 1500 and 2000 mgCaCO3/l. All parameters measured (pH, BA TVFA, effluent COD, carbon dioxide percentage, off-line methane percentage) indicated that conditions were less severe during and after organic step-changes when control was present. The controller also minimised the time spent at pH values potentially damaging to the bacteria (time spent at pH less than 6.0 in the two OLR step-change experiments where control was present (Experiments 6.3 and 6.4) was no greater than one hour, and in the experiment with no control (Experiment 6.5) was 8 hours) and returned the reactor to conditions conducive to efficient waste water treatment faster than when no control was present. Throughout all experiments controller oscillations remained severe. In this case, BA dosing as a control action was preferable, as the destructive effect of severe oscillations in the volume of BA dosed was considerably less than the effect of severe oscillations in the OLR, which repeatedly led to washout. Although it was possible to control the reactor subjected to OLR step-changes using the BA monitor based control system, control of the start-up phase was problematic. The BA monitor was not reliable or robust enough to provide the requisite data for use in the automatic control of the start-up of a high rate anaerobic digester. A thorough professional re-engineering of the B A monitor to deal with a greater sample flow rate, deliverable by a full-scale reactor (using wider bore tubing and larger flows, a more precise pumping system, and possibly with a suitable low maintenance sample filtration unit) could provide a suitably reliable and robust instrument.

Effective treatment of wastewater is an important process in reducing the environmental impact of industry and human activity. Although conventional water treatment systems can adequately remove the principle components of waste (i.e. substances that can be represented the majority of biological and chemical oxygen demand) several materials are poorly or slowly removed. Tertiary treatment polishing processes are therefore required to remove these contaminants to ensure complete wastewater treatment. This thesis reports investigations made using film reactors that are used to remove recalcitrant materials such as ammonia- nitrogen and endocrine disrupters that although present in low concentrations, if left untreated can have a strong impact on the environment. Film reactors potentially offer several process advantages over conventional activated sludge treatments systems as they allow very long residence time and contact with high concentrations of fixed microbes with the low concentrations of pollutants so enhancing kinetic performance and efficiency of the process. Two reactor configurations, a partial fixed bed (PFBR) and moving bed biofilm reactors (MBBR) were investigated. A thirty liter reactor with a working volume of 16 liters was constructed and contained fixed microbial films on either free suspended or fixed beds plastic packing (K2 AnoxKaldnes). The investigation of ammonia-nitrogen oxidation showed that after a suitable acclimation period (2 weeks) that ammonia was oxidise rapidly reducing the feed concentrations of 35 mg/L to < 2 mg/L in the effluent. To assess the performance for ammonia-nitrogen removal the reactors operated for long periods (up to 3 months) with continuous feed using the reactor in either PFBR or MBBR modes in addition of 17alpha-ethynylestradiol (EE2) and mestranol (MeEE2), the endocrine disrupting compounds commonly found in municipal wastewater. These substances is derived from a synthetic hormones if found in the natural environment can reduced the productivity of the fish as this can cause feminization in aquatic organisms with disastrous consequences on fish populations. The MBBR and PFBR systems were used to investigate the co-metabolism of ammonia-nitrogen, 17alpha-ethynylestradiol (EE2) and mestranol from model waste water feed containing 35 mg/L of ammonia-nitrogen and 100 mug/L of 17alpha-ethynylestradiol (EE2) and mestranol (MeEE2). A kinetic analysis of the systems were made and for the PFBR reactor, the specific growth rate, mumax of 7.092 d-1 with saturation constants, Ks of 1.574 mg/L. The kinetic analysis for the MBBR system was 6.329 d-1 for the mumax with the K.S of 0.652 mg/L. When the PFBR was used removal of EE2 represents 70% MeEE2 was removed. MBBR were shown to be more effective and efficient in removing ammonia-nitrogen reducing the levels under good conditions to > 2 mg/L while the PFBR could also achieve 2 mg/L. The MBBR system was also more competent in the removal of 17alpha-ethynylestradiol (EE2) and mestranol compared to PFBR. This work demonstrates that there are considerable advantages to using thin film reactors as polishing step for the tertiary treatment of waste waters when to compared to other processes in reducing the inorganic pollutants as endocrine disrupting compounds. The significance of these results is discussed in this context.