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Implementation of combined anaerobic/aerobic processes for wastewater treatment has been shown feasible, especially for industrial wastewaters with high concentration of organics. However, the utilization of this type of technology for treating wastewaters with low content of organic matter, such as domestic sewage is quite recent, and very limited information is available regarding the topic. Recent investigations have demonstrated that it is feasible to utilize a combined technology composed of anaerobic pretreatment followed by an aerobic post-treatment to efficiently treat municipal wastewater. This research is a continuation of previous investigations about the feasibility of using an anaerobic fluidized bed reactor-aerated solids contact process to treat domestic wastewater. In the proposed system the excess sludge produced in the aerobic stage is recycled to the anaerobic unit. The proposed configuration is very attractive because the anaerobic fluidized bed reactor serves as pretreatment unit and a sludge digester at the same time. The main objective of this research is to quantify the SS removal and accumulation rates in the AFBR, and determine the degree of stabilization of solids in the unit. All this to demonstrate the feasibility of avoiding separate sludge stabilization units.

Swedish people today are generally interested in environmental issues. One can assume that this would affect the way people act in their daily lives. However, research has shown that when it comes to attitudes and behavior, there is what has been described as “a gap”. Concern for the environment does not automatically mean that people act in an environmentally friendly way. The fact is that there are many barriers that prevent a so-called pro environmental behavior. This study deals with some of the factors that can influence a specific behavior, namely the sorting of food waste in the City of Lidingö – a municipality in Sweden that works to increase the number of subscribers of food waste collection. The waste is a valuable substrate when producing biogas, which is considered a renewable fuel. By replacing fossil fuels with biogas, the amounts of greenhouse gases that reach the atmosphere can be reduced. A questionnaire was sent out to more than 800 local citizens (of which half of them are subscribers of food waste collection) with questions about values, beliefs, motivation factors and opinions about efforts linked to the sorting of food waste. The results show that sustainability reasons are strong when it comes to why people decide to sort out food waste, and that a number of the subscribers of food waste collection consider it a moral obligation to take action in this matter. Several barriers, especially in the form of economic issues, preclude others from sorting. A need for more information, when it comes to the significance of this behavior, is also evident. As the thesis has its focus on pro-environmental behavior, factors in Stern’s Value-belief-norm theory, are used as the basis for the analysis. Blake’s model of barriers between environmental concern and action is used when studying what it is that prevents people from sorting out their food waste.

Historically, air and water have been considered common property resources and, therefore, over utilized as waste receptors. Dairy waste is a leading environmental concern in the North Bosque River watershed in Texas. Changing societal attitudes are forcing dairies and policymakers to balance environmental concerns with farm profitability. Dairies are entering a realm filled with technologies to combat waste concerns. Anaerobic digester technology may play a role in helping dairies balance profit and the environment. Digesters capture methane from livestock waste and transform it into electricity which can be sold to utilities or used on-farm. Because a digester facility is confined, air and water pollution can be reduced. Technological advancement and institutional factor changes allowing the sale of on-farm produced electricity and green power requirements have increased the economic feasibility of digesters. The study of the economic implications of anaerobic digesters for Texas dairies provides producers and policymakers with information to make good decisions concerning adoption and subsidization of this technology. At the beginning of this study, no digesters were operating in Texas. Dairies operating digesters in four states, therefore, were interviewed on-site to provide necessary data. The expected net present value, E(NPV), of a plug-flow digester is negative with and without selling electricity, indicating it should not be constructed based strictly on its financial contribution. At the current electricity-selling price, digesters are less economically feasible than current waste management strategies, lagoons, even after considering potential environmental penalties. However, selling electricity and capturing by-product heat for cost savings makes the digester's E(NPV) less negative than lagoons. The E(NPV) of a covered lagoon digester is positive. This indicates digesters are a potentially feasible waste management strategy. For plug-flow digesters to show a positive E(NPV), the selling price needs to be approximately 82.38% higher than the current price. The breakeven selling price is 12% higher than the current price. Below the breakeven price, lagoons have a larger E(NPV) than plug-flow digesters, therefore making lagoons the preferred waste management strategy. Results suggest changes in rules and technology efficiency make digesters economically competitive with current waste management systems.

Use of nitrifying and denitrifying bacteria to remove ammonia from waste water had been studied for a long time due to their high efficiency and low cost. Nitrifying bacteria not only grow slowly but also require high concentration of oxygen to facilitate the nitrifying process. Moreover, the followed denitrifying process needs the supply of adequate carbon sources for denitrifying bacteria to avoid greenhouse gas emission from the system. It shows the operational control to remove ammonia from waste water would be very difficult. Therefore, it is important to study the physiological and biochemical characteristics of those nitrifying and denitrifying bacteria closely. In 1995, Mulder discovered the disappearance of ammonium at the expense of nitrate and nitrogen production from their denitrifying pilot plant in the Netherlands, then van de Graaf verified an ANAMMOX reaction in the laboratory. Further studies that have revealed the combination of aerobic nitrification and anaerobic ammonium oxidation is more efficient to remove ammonia than most conventional methods. The ANAMMOX process is performed by a group of Planctomycete which involves the oxidation of ammonia anaerobically with nitrite as the final electron acceptor to yield gaseous nitrogen. Since this process is no need of supply external carbon source and oxygen, the ANAMMOX system can offer the advantages of less cost, less microbial contamination and less N2O and NO emission to the environment. This study is to summarize the bacterial species diversity, distribution in nature, their physiological characteristics, and potential biochemical pathways of those nitrogen converting microorganisms. In addition, several novel nitrogen removal technologies are also discussed for further understanding of the process optimization under both aerobic and anaerobic conditions.