摘要：

Summary Domestic wastewater is a source of nitrogen in environmental systems. Nitrogen is known to be a major pollutant to the aquatic system. It causes eutrophication which leads to excessive algal growth or growth of other undesired water weeds such as water hyacinth. This results in disruption of the oxygen balance, release of toxins, loss of biodiversity and increased costs of water treatment; if the water resource is used as a source for drinking water production. Wastewater stabilization ponds are treatment technologies that have been adopted by many developing countries. This is due to being cheap to construct, operate and maintain than activated sludge systems. However, they suffer from high effluent total suspended solids concentration (TSS), short-circuiting, long hydraulic retention time and ineffectiveness in removing nutrients like nitrogen. The problem of nitrogen removal is attributed to low nitrifier biomass present in the water column. Several studies have shown that the introduction of attachment surface for nitrifiers in the ponds improves nitrogen removal. However, information on the introduction of baffles as attachment surface for nitrifiers under tropical conditions is scarce. This study focused on the effects of incorporation of baffles in pilot scale wastewater stabilization ponds. The pilot scale ponds were constructed at Bugolobi Sewage Treatment Works (BSTW) in Kampala, Uganda, and operated under tropical conditions. Settled wastewater was pumped from the sedimentation tank of BSTW into a 10 m3 plastic anaerobic tank (AT) having a retention time of 3 days. The wastewater was then fed continuously by gravity at a flow rate of 2.1m3 per day into a facultative pond (FP). The effluent of the FP was fed into four pilot scale maturation ponds (MP) of length, width and water depth of 4m by 1m by 0.8m at flow rates of 0.5m3 per day. The details of the design and operation of the pilot scale are presented in figure 2 chapter 2 of this thesis. Pond 1 was operated as control while in ponds 2, 3 and 4, fifteen baffles of the same surface area were installed. The baffles had different configurations (pond 2: parallel to the flow, pond 3 and 4: perpendicular to the flow) inducing different horizontal and vertical flow patterns. The ponds were operated for two periods i.e. under an influent BOD of 72±45 mgl-1 and ammonia of 34±7 mgl-1 (period 1) and an influent BOD of 29±9 and ammonia of 51±4 mgl-1 (period 2). Introduction of baffles in wastewater stabilization ponds can affect their ecology, hydraulic characteristics and performance. This was studied and presented in different chapters. Laboratory studies on bulk water and biofilm nitrification rates were conducted, to complement the pilot scale studies. The results of this study showed that nitrogen removal from wastewater can be improved by addition of extra attachment surface for nitrifiers. Experiments discriminating biofilm and bulk nitrification rates showed that biofilm nitrification rates were more important than bulk water nitrification rates (Chapter 4). Further laboratory experiments also showed that biofilm nitrification rates are significantly reduced at bulk water oxygen concentration of less than 3.2 mg l-1 (Chapter 5). The results for the pilot scale wastewater stabilization ponds showed that during period 1, the control pond performed better than the ones that had extra attachment surface (Chapter 6). Under such conditions, it was found that the bulk water TSS was high and this prevented light penetration into the deeper parts of the ponds resulting in reduction of aerobic biofilm area that is required for nitrification (Chapter 2). The higher BOD during period 1 also favored the growth of heterotrophic bacteria compared to the nitrifiers. Nitrifiers are slow growers and under high BOD loading, they are outcompeted by heterotrophic bacteria. When the 123 light conditions and corresponding algal activity of the FP were changed to increase the ammonia concentration in the influent to the maturation ponds (by covering it with a black pla

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