Urban Air Pollution: Wastewater Treatment Sources and Impacts on Agriculture
The risks associated with exposure to emissions from wastewater treatment plants (WWTP) are currently uncertain and require more research, stronger regulatory frameworks and safer design consideration. Known toxic compounds, bacteria, fungi, endotoxins and viruses have been observed near WWTP the past, but their concentration and classification are still dubious. The airborne exposure route is also still poorly established due to the lack of information on aerosol characterization and transport.
The first portion of this dissertation attempts to fill some of the gaps in scientific literature by establishing a relationship between WWTP aerated basin coverage, source emission flux, particle composition, size and distribution as well as the dispersion of aerosolized particulates in Southern California. On-line measurements and filter sample collection were executed at Orange County Sanitation District (OCSD) and at two other locations along the Santa Ana River Watershed; Redlands Wastewater Treatment Plant (RWWTP) and Western Municipal Wastewater Treatment Plant (WMWWTP) for comparison. A laboratory bioreactor was also created to measure Chemical Oxygen Demand (COD), Total Organic Carbon (TOC) and Total Suspended Solids (TSS) and consequently develop a theoretical model, which will later serve as a guide to estimate real world WWTP aerosol number emission fluxes from laboratory data. In addition, the role of hygroscopic growth (CCN activity) in viral wet deposition was investigated at a relative humidity representative of the respiratory system (the upper airways and lungs). The outcome of this analysis provided critical information to further understand the probability of disease via inhalation of pathogens in WWTP aerosol. Results will provide science to aid the design of potential regulatory laws to further implement a safe and non-polluting environment when treating wastewater.
The last chapter of this dissertation provides a phytotoxic assessment on four major crops (wheat, maize, sorghum and soybean) in Mpumalanga province, the fourth-biggest contributor to South Africa's GDP and a region with a horticultural industry that the country heavily relies on. This work highlights the importance of sulfur dioxide emissions and ozone formation in the Highveld Priority Area (HPA) in terms of stressors on agriculture and food security (measured as crop yield losses). The study also compares the phytotoxic results with the potential risk to human health through the inhalation of these pollutants and it presents a monetary value for the total revenue loss within the region.