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Mainstream deammonification at low DO values and employing granular biomass
Language: English This thesis is written in English
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Marco Salmistraro, KTH, Royal Institute of Technology, 2014-15
Marco Salmistraro
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Water treatment techniques constitute a primarily relevant technical subject when sustainability is advocated; due to the stringent emergency of the topic, dedicated operational choices are required in order to ensure maximum efficiency. This thesis focuses on the possibility of reducing the incoming nitrogen load of mainstream municipal wastewater through naturally occurring biological processes, namely partial nitrification and ANAMMOX. Available scientific articles on the topic almost exclusively focus on the treatment of wastewater at high temperatures and nitrogen loads, as in the case of sidestream effluents; on the contrary, the intent of this research was to investigate treatment options for mainstream fluxes, notably characterized by lower temperatures, alkalinity reserves, and N strength. The whole work started with a thorough literature review: the studied process was inserted in a more general framework regarding state-of-the-art nitrogen removal techniques. Later on, the attention shifted to the experiment, identifying key functional parameters, defining them and assigning them optimal value ranges. More specifically, the study encompasses the performance of a lab-scale batch reactor, fed with an artificially prepared solution; this was modeled on the typical composition of municipal mainstream water fluxes, as reported in dedicated literature publications (Mosquera-Corral et al, 2005). Modifications on its content were brought sporadically, and with the sole purpose of accommodating the evolution in the reactor conditions. The operational choices that were taken included the maintenance of low DO values, ensuring appropriate out-selection of nitrite oxidizers (NOB), and the employment of AOB-enriched granular bacterial culture, both for the partial nitrification and for the anaerobic oxidation step. Results showed satisfactory N removal rates, while little quantities of nitrates were observed in the system; though turning out successful, the employment of granular biomass caused some issues for the biomass retention. Constant monitoring of relevant physical and chemical values was carried out, and provided a solid basis for further analysis. In fact, obtained results were studied and compared to presently available data on analogue processes for the treatment of different kinds of wastewater. Similarities and divergences were highlighted, and employed as a basis for the formulation of suggestions and possible improvements, both on the analytic and the operational side of the project. Particular attention was put to the possibility of saving organic carbon during the removal of nitrogen for further reuse in energy-developing processes, such as anaerobic digestion. Similar solutions are particularly tempting, as they could represent a first step in the direction of energetically auto-sufficient water treatment processes (Gao et al, 2014; Jetten et al, 1997).