Sustainability assessment of wastewater treatment plants with water reuse for urban agriculture: A case study in Hyderabad, India.

摘要

Wastewater reuse in urban agriculture is a widespread practice in many developing world cites that has many advantages (water savings, nutrient cycling, and livelihoods) and disadvantages (pathogen health risk). Energy use and associated greenhouse gas (GHG) emissions in centralized wastewater treatment plants (WWTPs) can mitigate some of the health risks, however these tradeoffs have not been quantified. The objective of this thesis is to conduct a sustainability assessment of WWTPs with water reuse for urban agriculture in India. Three stages of work were included.;1) The role of water and wastewater (W/WW) infrastructures in urban energy metabolism was explored first. W/WW infrastructures were found to contribute 3 to 16% of community-wide electricity use and greenhouse gas (GHG) emissions for 16 Indian cities; for another 23 the proportion was less than 3%. Energy intensity for drinking water supply and wastewater treatment averaged 1.3+/-0.7 Wh/gal (n=7) and 0.4+/-0.2 Wh/gal (n=5), respectively. Energy intensity for water pumping/treatment was more than double that for wastewater, the reverse of cities in Colorado, USA, likely due to poorer source water quality in India.;2) A life cycle assessment (LCA) was conducted of Nallacheruvu (8MGD) WWTP in Hyderabad, India that used upflow anaerobic sludge blanket reactor followed by oxidation ponds, yielding 99% and 81% removal of fecal coliforms and BOD5, respectively. The LCA showed energy use and GHG emissions of 0.7Wh/gal and 1gCO2e/gal, 48% of the later from on-site electricity use, 41% from methane process emissions, 10% from embodied energy in infrastructure, and 1% from nitrous oxide process emissions. A consequential LCA, conducted using the DAYCENT model for wastewater reuse in urban agriculture, showed only 1% of the nitrogen in treated effluent was reused in urban agriculture, due to land constraints along the flow path of the wastewater. As a result, annual system-wide GHG emissions for untreated and treated wastewaters releases to the riverine system were similar at 2,463mtCO2e and 2,819mtCO2e, respectively. Avoided impacts due to reuse of biogas for electricity and avoided fertilizer each accounts for 5% reductions from the total for treated water.;3) An urban agriculture site study was conducted to assess the impact of pathogen reduction in WWTP on spinach. This was explored in a site study using three different waters: groundwater, treated effluent from WWTP, and untreated water. While E.coli in the waters consistently differed by 2--3 orders of magnitude between the three plots, the E.coli in the crop measured at the endpoint of the study (harvest conditions) was not significantly different between the groundwater and WWTP plots (t-test P>0.1), while the untreated water was slightly higher (P0.025). For Ascaris, qualitative results showed little difference between Ascaris on crop grown with treated and untreated waters (26--36 eggs/100g spinach), while groundwater-irrigated spinach had lower Ascaris levels (9 eggs/100g spinach). Unexpectedly, when the researcher carefully took crop samples, the E.coli results compared to farmer-harvested crop were one order of magnitude lower, suggesting recontamination of the crop from farmer handling and contact with soil and contaminated water. The recontamination hypothesis was confirmed (P0.1) by sampling each of the three plots, comparing sanitized handling (n=3) versus farmer handling (n=3) in each plot.;Using data from WWTP LCA and urban agriculture site study, a sustainability assessment showed that treated effluent and untreated surface water were similar in the case of GHG emissions, pathogen risk (15% and 18% probability of disease over one year based on E.coli results), yield (20kg/m² and 23kg/m² for one year) and water saved (0 gallons groundwater used), but varied in terms of economic investment (;This work contributes to: (1) The urban metabolism literature by examining energy use and intensity in water/wastewater infrastructures in developing country cities, (2) WWTP LCA literature by conducting a first LCA using operating data from an Indian WWTP with water reuse in urban agriculture, (3) The urban agriculture literature by completing a first field study of pathogen impacts from treated and untreated wastewater use, and (4) The sustainability assessment literature as it links water/wastewater, energy, infrastructure capital investments, urban agriculture, and health.