In Mexico, wastewater recycling is an important alternative source of water, particularly in arid regions like the state of Sonora, Mexico. In El Valle del Yaqui, Sonora, Mexico, where 500 million m3 per year of wastewater is available for recycling in agriculture activities . The main objective of the three studies presented in this dissertation was to assess the microbial water quality of surface water, untreated wastewater, and treated wastewater for produce irrigation, as well as the impact of microbial water quality on vegetable contamination. The results suggest that the three sources of water meet Mexican and international guidelines for use in production of food crops.Despite wide differences in the concentration of bacterial indicators (Escherichia coli, Clostridium perfringens) and enteric pathogens (Cryptosporidium, Giardia, and enteroviruses) in the various types of water studied there was little impact on contamination of the produce studied (carrots, lettuce, tomatoes, and peppers) at harvest. Apparently, the time between the last irrigation event and harvesting was sufficient to allow for die-off of enteric organisms that may have contaminated the produce.

Many rural communities in Manitoba use wastewater lagoons to treat sewage, but the nutrient removal process is not fully understood. This thesis’ purpose is to improve understanding of chemical and biological nutrient removal mechanisms of wastewater lagoon treatment and compare two different stabilization ponds – one aerated and one facultative. Samples were collected from stabilization ponds and analysed for a pond average. The facultative lagoon achieved overall ammonia-N removals similar to those of the aerated lagoon, and lower orthophosphate removals. Nitrogen appears to be removed by ammonia volatilization; and assimilation into biomass. Phosphorus appears to be removed by assimilation into biomass; and precipitation at alkaline pH. There appears to be nitrogen limiting conditions in the secondary cells of both stabilization systems based on nitrogen-phosphorus ratios. There does not appear to be any significant advantage between aerated or facultative lagoons; they will meet their ammonia limits, but will require additional phosphorus treatment. / October 2016

Filamentous bulking is a problem that has long plagued activated sludge (AS) wastewater treatment plants (WWTPs). Much research has looked at its prevention and control but there is still no solution. The sludge microbiological community is very complex and there are many factors that can affect bulking. Clay addition in scaled-down activated sludge systems was investigated at concentrations of 0.4, 2.0 and 5.0 g/L along with sequencing batch reactor (SBR) parameters when run with a synthetic wastewater (SWW). The 5.0g/L concentration exhibited positive results on settling in the form of modified SVI but appeared to cause no reduction in filament length. These preliminary investigations indicate that clay may help improve sludge settling but make no difference in the abundance of filamentous microorganisms. The SBRs exhibited trends in regards to running systems with a synthetic wastewater. A loss of volatile suspended solids (VSS), coupled with increase in sludge volume index (SVI), suggested a link between lack of non-VSS and settling ability. This has implications in the importance of non-VSS such as grit or clay in research performed using SWWs.

Bromide and nitrogen are wastewater effluent constituents that have raised concern for their potential to affect disinfection byproduct (DBP) formation at drinking water treatment plants (DWTPs) downstream of wastewater discharges. Despite the toxicity of brominated and nitrogenous DBPs, wastewater treatment does not usually remove bromide and nitrogen prior to discharge. Bromide is a conservative chemical and thus is not removed from surface waters via natural transformations after being released, although it may be diluted. Nitrogen is biologically reactive; it can be transformed and removed by bacteria in the environment and in wastewater treatment plants (WWTPs). While this nitrogen cycling may reduce impacts on downstream DWTPs, it also produces nitrous oxide (N2O), a greenhouse gas, as a byproduct. Thus, interaction with the environment alters the potential impact of bromide and nitrogen on drinking water systems. The objective of this work was to examine the impacts of nitrogen and bromide present in wastewater effluent on DBP formation at downstream DWTPs, within the context of current and possible future DBP regulations. Three major conclusions were reached. First, within Southwestern Pennsylvania, an area where surface water bromide concentrations have increased due to fossil fuel extraction-based wastewater discharge, no statistically significant improvement in species-specific risk was observed over the past 20 years, despite decreasing TTHM levels. Second, nitrogen treatment decisions at WWTPs influence the formation of N-nitrosodimethylamine (NDMA), an unregulated but toxic DBP, at downstream DWTPs in areas of high de facto reuse (DFR). More plants using nitrifying wastewater treatment resulted in significantly lower NDMA detection rates and concentrations observed at chloraminating DWTPs located downstream. Third, the current approach to estimating national emissions of N2O related to wastewater treatment may underestimate emissions by an order of magnitude. Further, nitrogen removal at wastewater treatment plants reduces total N2O emissions attributable to wastewater treatment by reducing the N2O that would be generated in receiving surface waters. Thus, in both cases, impacts of WWTPs on downstream DWTP DBPs were observable. While natural cycling may remove nitrogen from surface water, in-plant removal of nitrogen prevents large amounts of N2O emissions.

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To live a healthy life, people all around the world need access to safe water. A lot of industries,together with the fast growing population in Blantyre, a city in southern Malawi, pose a threat to theaccess of safe water for the citizens. Several of the industries in Blantyre release contaminated waterto the nearby streams. One serious pollutant emitted from a match factory is chromium (Cr),especially in the occurrence of Cr(VI) which is carcinogenic for humans. Earlier studies have shownthat the concentration of chromium in the match factory’s wastewater was higher than WHO:sguidelines. It has also been published that natural clay minerals can be used for adsorption of Cr(III).This study investigates the removal of Cr(VI) through the adsorption of Cr(VI) to clay minerals or byreduction of Cr(VI) to Cr(III) which is precipitated from solution.The laboratory work performed in this study includes both experiments for adsorption of Cr(VI) andreduction of Cr(VI) to Cr(III). The reducing agents investigated were two clays and Fe(II) sulfate. Foradsorption of negatively charged Cr(VI) compounds, the two clays where used at lower pH and themineral bauxite was also tried as adsorbent agent. Wastewater from the match factory was dilutedand mixed with the removal agents and the concentration of total chromium was measured beforeand after the mixing process. For the agent with highest potential for Cr(VI) removal, the optimalconditions due to pH, dosage of agents and contact time were inspected.None of the investigated reducing agents served its purpose which means that no Cr(VI) was reducedto Cr(III) in this study. The adsorption of Cr(VI) with clay 1 at lower pH was also not successful, butthe adsorption worked for clay 2 at lower pH and for bauxite. In the experiments bauxite adsorbed ahigher amount of Cr(VI) than clay 2. The adsorption with bauxite turned out to be independent interms of pH. The optimal conditions for bauxite in the experiments were with a dosage of 3.5 gbauxite in 50 mL wastewater and a contact time of 40 minutes. The results showed an adsorption of93 percent of total chromium with bauxite at optimal conditions.

The Walnut Creek Wastewater Treatment Plant in Austin, Texas, has recently experienced increasing influent ammonia concentrations. Nitrification, the biological process used to treat ammonia, consumes alkalinity, which makes it difficult to properly treat ammonia while still maintaining the pH above the required discharge level of pH 6. Operators have looked to the addition of chemicals to supplement alkalinity; one creative alkalinity source was CaCO₃ solids, which are generated by the lime-softening process at Davis Water Treatment Plant. In 2011, the utility began transferring solids to Walnut Creek and immediately noticed improvements in both the nitrification efficiency and the effluent pH. However, undissolved solids accumulated at Walnut Creek and had a detrimental effect on the biosolids treatment efficiency at Hornsby Bend Biosolids Management Plant. Ultimately the costs of the poor biosolids treatment forced the utility to examine an alternative alkalinity source. The objective of this thesis is to help Walnut Creek optimize the use of various alkalinity sources to find a long-term solution that will improve the alkalinity and ammonia balance for adequate nitrification. Analysis of the plant’s influent characteristics suggested that industrial users, especially the semiconductor industry, are major contributors of ammonia and sulfate to the wastewater. A theoretical modeling based on chemical equilibrium predicted that using the CaCO₃ solids would provide a maximum alkalinity benefit of 47 mg/L as CaCO₃. Experimental dissolution jar tests were conducted to verify the model predictions and estimate the kinetics of dissolution. Results from these tests showed no significant dissolution of CaCO₃, and that the solids remained unchanged throughout the test. These results indicate that CaCO₃ solids are not recommended to provide alkalinity at Walnut Creek. Finally, the use of Mg(OH)₂ for alkalinity was employed at Walnut Creek and allowed operators to reduce the blowers that provide aeration. To quantify this observation, bubbling column tests were conducted to measure differences in the oxygen transfer rate at various Mg(OH)₂ concentrations. However experimental results did not match the expectations, so future work is required. / text

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