Removal and Recovery of Nutrients from Wastewater in Urban and Rural Contexts
Efforts to remove and recover nutrients from wastewater are motivated by the United Nations Sustainable Development Goals and the National Academy of Engineering Grand Challenges of Engineering. Of the seventeen Sustainable Development Goals (SDGs), multiple SDGs relate to managing nutrients in wast...
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| Format: | Others |
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Scholar Commons
2019
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| Online Access: | https://scholarcommons.usf.edu/etd/7880 https://scholarcommons.usf.edu/cgi/viewcontent.cgi?article=9077&context=etd |
| Summary: | Efforts to remove and recover nutrients from wastewater are motivated by the United Nations Sustainable Development Goals and the National Academy of Engineering Grand Challenges of Engineering. Of the seventeen Sustainable Development Goals (SDGs), multiple SDGs relate to managing nutrients in wastewater. SDG 6, which is to “ensure availability and sustainable management of water and sanitation for all,” contains targets that aim to improve water quality by reducing pollution, halve the amount of untreated wastewater released to the environment, and increase recycling and safe reuse of wastewater (UN, 2017). SDG 2 seeks to improve food security and SDG 12 seeks to sustainably manage natural resources. Similarly, the National Academy of Engineering Grand Challenges of Engineering highlight managing the nitrogen cycle and providing access to clean water (NAE, 2019).
Centralized wastewater treatment plants (WWTPs) have historically been designed to remove nutrients (such as nitrogen and phosphorus) and other contaminants prior to discharge. Modern wastewater treatment practices integrate recovery of resources including nutrients, energy, and water. The many available technologies, coupled with competing priorities, can complicate community decision-making on the choice of technology and the scale at which to implement the technology (i.e. building, community, or city), as well as determining how new upstream treatment may affect existing downstream treatment. Technologies that recover energy or manage nutrients such as anaerobic digestion, struvite precipitation, and microbial fuel cells can be implemented at a variety of scales in urban settings and may also be viable for influent types such as agricultural waste. Therefore, the overall goal of this dissertation is to contribute to the achievement of multiple sustainable development goals through the removal and recovery of nitrogen and phosphorus from a variety of influents at a variety of scales.
One type of decision-making tool that assists in the choice of nutrient management technologies is a House of Quality. I developed a tool based on the House of Quality that integrated multiple priorities at three scales in a sewershed and produced rankings that generally align with current wastewater treatment practice. Accordingly, top-ranked city-scale technologies are those commonly employed (e.g. A2O, oxidation ditch) that use the dissolved organic carbon present in the wastewater to drive denitrification. Similarly, conventional treatment (e.g. flush toilet connected to a sewer) is ranked highest at the building scale because of its easy maintenance, small footprint, and inoffensive aesthetics. However, future trends such as technology development will likely affect the technologies, weightings, and scores and therefore improve the ranking of novel and emerging technologies. This trend may be amplified by the implementation of test beds, which can provide opportunities to improve the technical characteristics of developing technologies while minimizing risk for municipalities.
The House of Quality planning tool was utilized in an in silico case study to analyze nutrient management technologies at three scales across the Northwest Regional Water Reclamation Facility sewershed in Hillsborough County, FL. The study demonstrated that employing treatment technologies upstream from the centralized wastewater treatment (i.e. building-scale source separation and community-scale technologies) could reduce nitrogen loading to the mainstream treatment train by over 50%. Sidestream treatment (i.e. the liquid effluent of anaerobic digestion that typically recycles back to the beginning of the mainstream treatment process) has minimal impact in nitrogen reduction, but is effective in reducing phosphorus loading to the mainstream due to high quantities of phosphorus recycling back to the head of the plant. These results can inform decision-makers about which context-specific nutrient management technologies to consider at a variety of scales, and illustrate that sidestream technologies can be the most effective in reducing phosphorus loading while building- and community-scale technologies can be most effective in reducing nitrogen loading to the centralized treatment plant.
Struvite precipitation and microbial fuel cells (MFCs) can be used in combination to manage nutrients and recover energy in sidestreams of centralized WWTPs. Because the liquid effluent from engineered struvite precipitation often contains high concentrations of total nitrogen, I constructed and demonstrated a fixed-film nitrification reactor and a two-chambered MFC to further reduce total nitrogen and recover energy. The primary benefit of the MFC in the technology demonstrated here is not its ability to produce energy, but rather its ability to remove additional nitrogen through nitritation and denitritation. The sidestream nutrient removal prevents nutrients from returning to mainstream treatment, reducing operational costs. Such improvements to wastewater treatment processes can facilitate the transition to the resource recovery facility of the future by becoming a net-energy producer while also achieving the simultaneous benefits of nutrient recovery/removal and reduced costs associated with mainstream treatment.
Nutrients and energy can also be recovered in agricultural settings. In this dissertation I studied an agricultural waste treatment system comprising a small-scale tubular anaerobic digester integrated with a low-cost, locally produced struvite precipitation reactor. This study investigated two digesters that treated swine waste in rural Costa Rica. I also facilitated construction of a pilot-scale struvite precipitation reactor that was built on site using local labor and local materials for approximately $920. Local products such as bittern (magnesium source) and soda ash (base) allowed for the production of struvite, a fertilizer that can replace synthetic fertilizer for rural farmers. Liquid-phase concentrations of PO43–-P and NH4+-N in agricultural wastewater increased by averages of 131% and 116%, respectively, due to release from the swine waste during anaerobic digestion. Despite this increase in liquid-phase concentrations, an average of 25% of total phosphorus and 4% of total nitrogen was removed from the influent swine manure through sedimentation in the digesters. During struvite precipitation, an average of 79% of PO43–-P and 12% of NH4+-N was removed from the waste stream and produced a solid with percentages (mass basis) of Mg, N, P of 9.9%, 2.4%, and 12.8%, respectively, indicating that struvite (MgNH4PO4) was likely formed. The treatment system offers multiple benefits to the local community: improved sanitation, removal of nutrients to prevent eutrophication, recovery of struvite as a fertilizer, and production of a final effluent stream that is suitable quality to be used in aquaculture. These are examples of how, more generally, quantifying nutrient recovery from agricultural waste and understanding recovery mechanisms can facilitate progress toward multiple sustainable development goals by improving sanitation, promoting sustainable management of wastes and natural resources, improving food security, and supporting local ecosystems.
Managing nutrients from a variety of influent types at different scales can contribute to the achievement of multiple sustainable development goals. Worldwide trends of population growth and resource depletion highlight the need for models to easily allow decision-makers the ability to understand the fate of nutrients and implement infrastructure accordingly. |
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