Wastewater treatment plants (WWTP) play a major role in nitrogen management today. If the nitrogen in the wastewater discharge is not treated, it can cause various environmental and human health problems such as increased N2O pollution, eutrophication, and algae blooms. Currently, many WWTPs rely on nitrification-denitrification technologies to transform nitrogen in wastewater typically in the form of ammonia into diatomic nitrogen. However, this process is highly energy-intensive and produces an unusable product. As WWTPs start to transform into water resource recovery facilities (WRRF), there will be a need to develop technologies that can transform waste nitrogen into high-value products. Doing so can help develop a nitrogen-circular economy.

One potential pathway for recovering nitrogen from wastewater is by utilizing cyanophycin-accumulating organisms (CAOs) to transform waste nitrogen into cyanophycin. Cyanophycin is a naturally occurring biopolymer used by bacteria as a nitrogen storage compound and consists of the amino acids aspartate and arginine. Because of this structure, it has the potential to directly be used as a microbial protein source. However, the potential impacts of this technology have been unexplored. By quantifying the potential impacts of this new pathway, its feasibility compared to incumbent technologies can be understood.

Using life cycle and techno and economic analysis, the impact of implementing this technology at WWTPs that treat 25, 50, and 100 million gallons per day (MGD) of wastewater is explored. For each of the different sizes, a Monte Carlo simulation with 1000 iterations was used to evaluate the impact of different process parameters. Global warming potential (GWP), water consumption (WC), and minimum selling price (MSP) of the produced microbial protein were calculated and compared against traditional protein sources, and baseline nitrogen recovery technologies. Initial results suggest an MSP of $0.32 to $0.95, GWP of 0.04 kgCO2eq to 0.2 kgCO2eq, and WC of 0.2 L/kg MP and 0.9 L/kg MP, which makes the technology competitive against different protein sources. Additionally, with a cost of nitrogen recovery between $1.29 and $3.48, it is competitive against nitrification-denitrification for treating influent nitrogen. WWTPs can use the results from this study to evaluate the potential of the technology for their specific facility.

The majority of today’s wastewater treatment infrastructure is aging. Wastewater is no longer viewed solely as a waste stream but as an opportunity for resource recovery, reflected by a change of nomenclature from wastewater treatment plant (WWTP) to water resource recovery facility (WRRF). Nearly doubling biogas production compared to a conventional WWTP, anaerobic membrane bioreactors (AnMBRs) have been extensively studied as energy self-sufficient WRRFs, but there remains a lack of viable solutions to handle their relatively high ammonium emissions, propensity for membrane fouling, and large membrane cost. Additionally, many previous assessments of AnMBRs excluded direct dinitrogen oxide (N2O) emissions because of uncertainty. By neglecting N2O, previous studies also disregarded more than half of greenhouse gas (GHG) emissions at WRRFs performing biological nitrification. Some of the greatest reductions in GHG emission can be made in addressing direct N2O emissions, but these reductions will go unnoticed if direct N2O emissions are excluded from an assessment. This work leverages concurrent techno-economic analysis (TEA) and lifecycle assessment (LCA) of two novel anaerobic WRRFs to evaluate solutions to the obstacles of ammonia emissions, membrane cost, and membrane fouling including a discussion on direct N2O emissions.

Two WRRF utilizing novel high-flux/low-cost cloth membrane AnMBRs were assessed with different nitrogen removal options. The first WRRF utilized a novel ammonium ion exchange and ammonia electrolysis process while the second WRRF utilized biological nitrogen removal. Both WRRFs were compared to a conventional AnMBR WRRF with biological nitrogen removal and an activated sludge WRRF with denitrification. Experimental data from a pilot study at the Urbana and Champaign Sanitary District was used to develop and validate an engineering process model used for TEA and LCA. The system boundary of TEA and LCA included all treatment steps and solids processing. The functional unit of this study was 1 m3 of municipal wastewater incorporating influent and effluent quality. Results were calculated for treatment cost ($∙m−3) and GHG emissions (kg CO2-eq∙m−3).

The novel WRRFs with cloth membranes achieve energy self-sufficiency by lowering transmembrane pressure and reduce the cost of water treatment through AnMBR from 1.21 $∙m−3 to 0.92–0.93 $∙m−3, depending on nitrogen removal technology. In this range, the novel WRRFs are competitive with traditional—activated sludge—wastewater treatment with denitrification. Both novel WRRFs achieve energy self-sufficiency, but their GHG emissions vary. Their lower energy requirements are offset by increased consumption of chemicals and materials, mainly for ion exchange and electrolysis. Excluding direct N2O emissions, the WRRF utilizing the ion exchange process has higher emissions than an activated sludge WRRF (0.35 kg CO2-eq∙m−3 compared to 0.19–0.22 kg CO2-eq∙m−3). In contrast, the WRRF utilizing biological nitrogen removal presented lower emission than an activated sludge WRRF (0.08 kg CO2-eq∙m−3). However, when direct N2O emissions are accounted for, the ion exchange WRRF stands out with the lowest emissions because it avoids biological nitrogen removal and has no direct N2O emissions. This work emphasizes that a comprehensive approach, including emission from electricity, the chemical supply chain, and direct N2O and CH4, is required to understand environmental impact.

Wastewater treatment plants (WWTPs) are significant industrial emitters, contributing 44 million metric tonnes of CO2 annually, primarily due to their elevated energy consumption. This has sparked interest in exploring innovative technologies capable of treating contaminated waters while reducing greenhouse gas (GHG) emissions. Algal Turf Scrubber (ATS) systems emerge as a promising wastewater treatment technology that can simultaneously remove nutrients from contaminated waters and provide a biomass co-product for chemicals, nutraceuticals, and biofuels. However, ATS systems have been traditionally used to treat surface waters, limiting the scalability of the technology. The effluent discharged from primary treatment, in existing WWTPs, is a potential source of high nutrient loads, where algal wastewater treatment effectively removes nitrogen and phosphorus while addressing concerns around GHG emissions. This study aims to compare the economic and environmental implications of ATS WWTPs with conventional WWTPs in terms of nitrogen and phosphorus removal.

By integrating engineering process modeling with Techno-Economic Analysis (TEA) and Life Cycle Assessment (LCA), this study evaluates the economic feasibility and environmental impacts of ATS WWTPs. The process model leverages geographically resolved weather and point-source nutrient datasets to model the wastewater treatment process and biomass harvesting for multiple sites across the continental United States. The mass and energy flows of each ATS facility were modeled based on nutrient availability and used to inform the TEA and LCA. In the TEA, costs are subjected to a discounted cash-flow rate of return analysis that includes capital expenses, operational costs, and potential revenues from the biomass co-product. The LCA considers the life cycle environmental impacts of the ATS system within the system boundary and across different environmental metrics such as acidification, eutrophication, air quality, and human health impacts. Results from the TEA and LCA, including the minimum wastewater treatment selling prices (MWWTSPs) and global warming potential (GWP), are then compared to those of conventional WWTPs to assess the competitiveness of algal wastewater treatment.

Preliminary modeling indicates significant potential for ATS systems to replace secondary and tertiary WWTP infrastructure. Results include MWWTSP ($/m^3) and GWP (g CO2-eq/m^3) for three point-sources in Alabama, Minnesota, and Montana. ATS treatment costs were determined to be 0.45, 1.07, and 2.93 $/m^3 in Alabama, Minnesota, and Montana, respectively. ATS systems demonstrated cost competitiveness when compared to the MWWTSP of conventional WWTPs (0.94 $/m^3). Sites in northern latitudes exhibited higher MWWTSPs due to lower operational days and suboptimal conditions for algal growth. The primary factor contributing to increased MWWTSPs is the combination of high nutrient loads with low biomass productivity. The GWP of electricity use was notably lower for ATS WWTPs at 14.21 g CO2-eq/m^3 compared to conventional WWTPs (125.35 g CO2-eq/m^3). Initial conclusions support the potential economic and environmental advantages of ATS over conventional WWTPs, offering competitive costs that can be reduced by increased productivity and the integration of high-value co-products. Additionally, the lower electricity use of ATS WWTPs implies a potential reduction in GWP.