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    Some effects of aeration on anaerobic digestion : a thesis presented ... for the degree of Master of Technology
    (Massey University, 1972) Bhuwapathanapun, Supapong
    Anaerobic treatment is a process which has been used extensively for the stabilisation of strong biologically degradable organic waste materials. This process is commonly used for stabilisation of raw sewage sludge or the sludge produced from aerobic treatment processes. Anaerobic digestion has also been modified and applied to the treatment of some strong industrial wastes, such as meat works wastes. One such process is similar to the activated sludge process and is commonly known as the anaerobic contact process. An essential feature of the anaerobic contact system is that an appreciable amount of the sludge biomass cells in the effluent is concentrated and recycled to the head of the system where it is mixed with the incoming waste water. In this way, Kirach and Sykes (2) reported, a high level of cells is retained in the system, and the hydraulic retention time can be shortened to the economical level of approximately 6-12 hours. This system is similar to aerobic activated sludge process and has been often referred to as the anaerobic activated sludge process. The system can be shown disgrammatically as in Figure 1. [From Introduction]
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    Operation of an activated sludge plant for fellmongery wastewater treatment : a thesis submitted in partial fulfilment of the requirements of the degree of Master of Technology in Environmental Engineering at Massey University, Palmerston North, New Zealand
    (Massey University, 2000) Bourke, Christopher Denis
    Activated sludge is one of the most common wastewater-treatment processes used to reduce pollutant loads on the receiving environment. For efficient operation, there must be an effective process control and operation strategy in place to ensure that process problems are avoided. This research is a case study into the process control and operation of an activated sludge plant used for fellmongery wastewater treatment. Analysis of the pretreated fellmongery wastewater showed that it is characterised by high total and volatile suspended solids concentrations, and high organic nitrogen concentrations. The plant was experiencing frequent problems that were attributed to the high influent suspended solids load coupled with ineffective solids management. Operation of bench-scale simulations showed that solids retention time (SRT) control at 5 or 10 days will produce acceptable effluent suspended solids concentrations and soluble chemical oxygen demand (COD) removal. Soluble COD removal for both 5 and 10 days was high at 85 and 80 % respectively at a hydraulic retention time of 6.4 days. Effluent suspended solids concentrations were 100 and 157 g/m 3 respectively. A steady state control model was developed based on, mass balances of biochemical oxygen demand (BOD) and volatile suspended solids (VSS), process performance equations, and the solids retention time (SRT). The model used three control points, the clarifier underflow pump, the clarifier influent pump and the waste sludge pump. The model was incorporated into an off-line Activated Sludge Operation Program (ASOP) to provide a user-friendly interface between the plant and operator. The main output from ASOP includes values for the three control points and suggestions to help avoid problems. A process control and operation strategy was developed using ASOP, the knowledge gained in this research, and an operation manual developed from accepted operation practises.
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    Modeling and microbiology of a New Zealand dairy industry activated sludge treatment plant : a thesis presented in partial fulfillment of the requirements for the degree of Master of [Technology in] Environmental Engineering at Massey University
    (Massey University, 1997) Rule, Glenys Jane
    An extended aeration activated sludge plant treating dairy factory wastewater was studied. The effectiveness of organic and nutrient removal was investigated in conjunction with the causes of existing foaming and bulking problems. Excellent removal efficiencies of 99.7% BOD5, 98.8% COD, and 96.9% TKN were achieved thoughout the period studied. The removal of total phosphorus however, was only 33.8% and this may become an issue that requires attention in the future. The dominant filamentous organisms in the sludge were identified as Type 0914, Type 0092, Nocardia pinensis, Nocardia amarae-like organisms, and Nostocoida limicola III. It was determined that these organisms were the major cause of the bulking and foaming conditions at the Waste Treatment Plant, although the use of surfactants in the factories and nitrogen and iron deficiencies were probably also contributing. All of the dominant filaments identified have been previously found to exist in large numbers in low food to organism ratio/high sludge age conditions. It was therefore recommended that the sludge age be reduced and the F/M ratio increased by increasing the amount of sludge wasted from the treatment plant. Existing kinetic coefficients were used, together with the Activated Sludge SIMulation programme utilising Activated sludge Model No. 1, to successfully model the existing system. This model can now be used by treatment plant employees (with some training required) to predict the results of alterations to plant operation and/or configuration.
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    Activated sludge treatment of dairy processing wastewaters : the role of selectors for the control of sludge bulking : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy at Massey University
    (Massey University, 1996) Leonard, Anne M.
    The typical wastewater from a milk processing facility producing butter and milk powder was treated in a modified activated sludge system in order to establish process characteristics and investigate operational problems. A synthetic wastewater was developed with similar average physical and chemical characteristics to that from a full scale facility. The relative biodegradability of the wastewater fractions was assessed and basic microbial growth parameters also determined. A laboratory scale activated sludge reactor configuration was then established and its performance monitored. Although effective treatment was achieved in terms of suspended and soluble organic matter removal, the use of a completely mixed reactor resulted in the system becoming inoperable due to the excessive growth of filamentous microorganisms, with Type 0411 being the dominant filament. In order to inhibit filamentous bulking, various selector reactor configurations were trialed. As nitrification of feed stream proteins had been indicated, unaerated selectors were used with the intention of effecting anoxic substrate removal in the initial selector zone; but due to the limited supply of oxidised nitrogen, insufficient substrate removal occurred in the selectors to prevent filamentous bulking, with Type 021N becoming dominant. The next series of trials used aerated selectors, with some configurations demonstrating the ability to both prevent and cure filamentous bulking. The unsuccessful trials resulted in the proliferation of Haliscomenobacter hydrossis. From selector trials conducted it was established that the requirements for successful suppression of filamentous growth were the incorporation of an initial selector zone in which greater than 95% of removable soluble substrate was removed and the bulk solution was maintained in a fully aerobic state. Serial selector configurations demonstrated improved performance over a single selector. From observations of the physical conditions and substrate concentrations in the reactor configurations employed, a correlation of filament type to environmental condition can be tentatively made: Types 0411 and 021N were indicated to be low organic loading type filaments, whereas H. hydrossis was indicated to be a low dissolved oxygen filament. Rapid substrate removal rates were attributed to biosorption, accumulation and storage mechanisms, increasing as the selector configuration trials progressed. In general floc formers possessed a higher specific growth rate and substrate affinity than the filamentous microorganisms. Filament Type 021N was indicated to lack biosorptive capacity, however H. hydrossis was indicated as having a greater biosorptive capacity than the floc formers present. The highly degradable nature of the substrate and high substrate concentration gradients imposed by the selector configuration caused rapid oxygen uptake rates; resulting in aerobic, anoxic and anaerobic substrate removal mechanisms all occurring in the initial selector zone. The occurrence of simultaneous nitrification, denitrification and phosphorus accumulation resulted in significant nutrient removals from the aerated selector reactor system, with influent nitrogen and phosphorus levels each reduced by up to 96% in the effluent stream. This study found that an activated sludge process was an appropriate method for the effective treatment of milk processing wastewaters, as effluent suspended solids of less than 10 g.m-3 and soluble COD of less than 30 g.m-3 were consistently obtained, however a modified configuration would be required to prevent the growth of filamentous microorganisms and attendant operability problems. Due to the nature of dairy processing wastewaters, a selector reactor configuration could be employed not only to overcome potential filamentous bulking problems, but also to provide an opportunity for biological nutrient removal without the inclusion of dedicated anoxic / anaerobic reaction steps or the complex flow regimes conventionally employed for nutrient removal activated sludge systems.