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The aims of the research project were to observe the operation of stabilization ponds with a view to investigating the value of various existing approaches used in the design of both facultative and maturation wastewater stabilization ponds and, if possible, to produce a realistic and reliable method for pond design. This latter aim was to be carried out either through the modification of existing equations or by the development of a new approach. In addition it was also intended to investigate the phenomena of dissolved oxygen and thermal stratification within stabilization ponds. The required data for this work was obtained as a result of detailed observation of the four-pond wastewater treatment installation in the Cayman Islands, British West Indies. Details of flows, flow strengths, removal of BOD and faecal coliform organisms were collected and numerous profiles of the pond contents were carried out to investigate dissolved oxygen and thermal stratification. Information concerning temperatures, solar radiation, hours of sunshine, relative humidity, rainfall, evaporation and wind speed and direction were also recorded over the three year investigational period. The most common design methods, the first-order complete-mix approach of Marais and Shaw and the modified empirical approach of McGarry and Pescod as modified by Mara and Arthur, were studied in detail using the results collected. These two design approaches were those used for the initial design of the Cayman ponds. Suggestions were then made for modifications to the first-order, complete-mix equation with regard to the values of the reaction coefficients employed for the removal of organic matter and of faecal coliform bacteria. Modifications of the equations to obtain K (the first-order reaction coefficient for either BOD or faecal coliform removal) were suggested. Following that a new empirical design approach was developed using the data collected from the operational ponds together with the climatological information. The models were developed in three steps. Firstly, matrices of correlation coefficients were produced to discover the existance of any strong correlations between any of the dependent and independent variables considered. Secondly, the Stepwise Backward Selection procedure for multiple regression (SBS) was applied to select the most relevant preliminary variables for multiple regression models. Then finially, the relevant variables were grouped in ordinary least-squares multiple regression models using a Hierarquical Multiple Regression procedure (HMR) to construct the models. As a result of this work groups of semi-empirical and empirical models were produced_ Two semi-empirical design models were developed to express K as a function of loading and climatic factors. These two equations were for the removal of BOO and faecal coliforms in facultative ponds. Two other groups of empirical design equations with a total of fourteen possible design models relating pond efficiency to factors such as loading, retention time and climatic conditions were also produced for the design of facultative and maturation ponds in the Caribbean region treating weak and saline wastewater. Also carried out were extensive field investigations into the temporal and spatial distributions of dissolved oxygen and water temperature in the ponds and as to how these varied with climatic conditions.

The need for pathogen-free water supplies has spurred investigations into the use of ionizing radiation for the treatment of wastewater effluent and municipal biosolids. The objective of this research was to develop an electron-beam irradiation scenario to effectively eliminate microbial pathogens from municipal biosolids and wastewater effluent. The Monte Carlo N-Particle (MCNP5) radiation transport code was used to simulate the irradiation scenario. Using MCNP5, dual electron-beam sources were modeled as planar surface sources above and below a stainless steel delivery trough containing either effluent water or one of two biosolids material compositions. A dose deposition analysis was performed to assess both the planar dose distribution and 25 depth-dose curves. In addition, a density perturbation study was performed to assess the variance in the dose deposition for different mass solids concentrations. To validate the MCNP5 code for this type of application, a benchmark study was performed. Two municipal biosolids materials and water were irradiated in plastic bags on a conveyor belt using a 10-MeV electron accelerator with the exit window below the material. The experimental configuration was modeled with the MCNP5 radiation transport code. Simplified and detailed models were created and analyzed. Lastly, an economic analysis was performed to assess whether this treatment method is a financially viable alternative to current wastewater treatment methods. Processing capacity was calculated for two accelerator specifications. These capacity rates in conjunction with the operating and capital costs per dry ton to irradiate the material were compared with existing data for electron beam processing of municipal biosolids. The cost breakdown was also compared with quoted costs for existing conventional methods. The models developed showed that the use of 10MeV electron-beam technology for the treatment of wastewater effluent and municipal biosolids is effective and economically feasible. The benchmarking study illustrated the accuracy of Monte Carlo simulation for this type of application. The method development process was shown to be adaptable for various material compositions and irradiation configurations.

Constructed wetland system is a natural purifying procedure of management and disposal of water and wastewater by means of Ecological Engineering Technology. Neither additional chemical agent nor mechanical equipments and electrical power are needed in the procedure of water quality purifying. It is also a potential Ecological Engineering Technology with advantages of low-cost, easy operation and management, and easy construction. However, the limitation of this technology is the requirement of larger land space for wetland construction. Taiwan features in a subtropical climate, moderate water temperature, abundant sunlight, so its environmental condition is a good fit for constructed wetland technology, which has been verified by numerous pilot and field scales studies in recent years. Due to the necessity of large land space, it is impossible to apply it in the urban environment that is densely populated. In the rural area of Taiwan, however, with the industry development or industry moving outside, there appears a lot of fallow lands, idle lying factories. Moreover, the undeveloped construction of sewage work in Taiwan (especially in rural areas) results from inadequate construction expenditure supported by government, while discharge raw sewage in urban causes water pollution and water shortage. Hence, if we could establish constructed wetlands in the programmed proper places (such as presumptive address in parks or low-rent fallow lands), less construction expenditure could be used to construct sewage work and to protect water resource. After the proper programming and management, constructed wetland has multiple functions such as sightseeing, recreation, and ecology education. In order to explore the possibility of domestic wastewater disposal by constructed wetlands, the research adopted three ecological engineering treatment systems: Erhang constructed wetland system, Gangwei constructed wetland system, and Dajia soil filtration system. In this study, the treatment efficiencies and effectiveness of water quality improvement via these three systems were investigated. Results from the monitoring results of the influents and effluents of these systems were evaluated. In the Erhang constructed wetland, results were collected from July 2004 to October 2005. During this investigation period, the average flow rate was 52 CMD, and the observed biochemical oxygen demand (BOD) removal efficiency and removal rate were 72¡Ó22¢H and 1.68¡Ó1.12 kg/day, respectively. In the Gangwei constructed wetland, results were collected from July 2004 to May 2006. During this investigation period, the average flow rate was 61.6 CMD, and the observed BOD removal efficiency and removal rate were 33¡Ó40¢H and 0.14¡Ó0.19 kg/day, respectively. In the Dajia constructed wetland, results were collected from July 2004 to May 2006. During this investigation period, the average flow rate was 21.92 CMD, and the observed BOD removal efficiency and removal rate were 79¡Ó16¢H and 0.9¡Ó0.5 kg/day, respectively. Results from this study indicate that the three systems could effectively remove the main pollutants in inflow water and the treated water is able to meet the discharged standards. Thus, the constructed wetland scheme has the potential to be developed into an environmentally and economically acceptable domestic wastewater treatment technology. Results from this study will be useful to assist environmental professionals in designing a scale-up system for future application.

A microwave enhanced advanced oxidation process using hydrogen peroxide (MW/H₂O₂-AOP) was used for the release of nutrients and the destruction of solids from secondary municipal sewage sludge. The significant factors affecting the MW/H₂O₂-AOP that would yield maximum soluble substrates were studied. Using a computer statistical software package for experimental design and data analysis, four factors including microwave heating temperature, heating time, hydrogen peroxide dosage, and sludge solids content, were selected and examined. The initial sludge TS content and hydrogen peroxide dosage were the most significant factors for the solubilization of COD and nutrients release under the experimental conditions selected in this study. Overall, the maximum solubilization of nutrients was obtained at 2.5 % of total solids content, 2% of hydrogen peroxide by weight, 5 min. of microwave heating and 120 ºC. The effects of combination of microwave treatment and oxidative reagents on solids destruction and nutrients release were also investigated. Microwave enhanced advanced oxidation processes (MW-AOP), such as MW/O₃, MW/H₂O₂ and MW/H₂O₂/O₃, were conducted at 100 °C. In terms of nutrients release and solids reduction, the MW/H₂O₂/O₃-AOP yielded the best result. Subsequently, three factors including microwave heating temperature, hydrogen peroxide dosage, and ozone dosage, were investigated. The best result, in terms of the release of phosphate and ammonia, and solids reduction, was obtained with additions of 2 % hydrogen peroxide by weight and ozone dosage of 5.09 mg/ml, and operating at 120ºC. About 95%, 32% and 78% of TP, TKN and COD were released into the solution, respectively. The microwave enhanced advanced oxidation processes, with and without an addition of ferrous sulfate (MW/H₂O₂-AOP and MW/H₂O₂/Fe+²-AOP), were also studied for reducing solids, and solubilizing nutrients from the secondary sewage sludge. For the MW/H₂O₂/Fe+²-AOP, the best results of solubilization, in terms of orthophosphate, ammonia and soluble chemical oxygen demand, were obtained at treatment temperatures of 40 ºC, the yields decreased as the temperature was increased. The highest yields of solubilization were obtained at 60 ºC for orthophosphate, and at 80 ºC for both ammonia and soluble chemical oxygen demand.