Evaluation of the absorbing pervaporation technique for ammonia recovery after the Haber process

Sustainable ammonia recovery from low strength wastewater by the integrated ion exchange and bipolar membrane electrodialysis with membrane contactor system

Water contamination is ubiquitous and persists across our water resources and supply. Much attention is given to newly identified and emerging contaminants, but we also struggle to successfully mitigate “old”, or well-known, contaminants, which have included ammonia, nitrate, and, more recently, phosphate in municipal wastewaters. However, these compounds are also critical nutrients used to support the global industrialized agriculture sector. Phosphate is of particular importance and concern because phosphate-based fertilizers are currently produced through the mining of phosphate rock, a limited resource mineral. The world’s known available supply of phosphate rock is predicted to become limited within the range of 30 – 200 years, and the flow of phosphorus through the agricultural food cycle is unidirectional, with large portions of mined phosphorus ending up in the environment and landfill. Ammonia is produced for fertilizer and other chemical uses via the Haber-Bosch process, which, annually, uses 2% of global fossil fuel energy demand and contributes 450 M metric tons of CO2 to global emissions. Meanwhile, the technical treatment train for municipal wastewater treatment facilities targets removal of ammonia and phosphate as contaminants, enabling this one-way flow of nutrients from mineral sources and energy-intensive processes through food to waste. This scenario is no longer tenable as we face limited phosphorus world-wide, as well as energy and food security challenges.In our research, we focus on a magnesium anode-based electrochemical system for the precipitation and recovery of ammonium and phosphate nutrients from municipal wastewater sources. In this study, we have evaluated four different natural wastewater sources, three municipal and one industrial meat processing source to understand how differences in wastewater source water composition affect phosphate and ammonium recovery, and inversely, how the electrochemical treatment process affects resulting wastewater chemistry post-treatment. In this talk, I will discuss our recent results that have shown that phosphate removal kinetics are affected by key water chemistry parameters of chloride concentration, ammonium concentration, calcium concentration, and total organic carbon. Phosphate removal through precipitation showed a two-stage kinetic behavior, with a fast kinetic regime prior to 1 min, and a zeroth order rate from 1 min to 30 min. Corrosion rates of the magnesium anode varied over an order of magnitude and are correlated with the differences in water chemistry. Experimental Mg consumption during the electrochemical process is greater than theoretical Mg consumption resulting in an underestimate of costs, highlighting the importance of experimentally-measured Mg consumption as the more appropriate measure of treatment cost.

Recovery of ammonium from aqueous solutions using ZSM-5

Membrane stripping enables effective electrochemical ammonia recovery from urine while retaining microorganisms and micropollutants

The U.S. spends $2.2 billion annually on remediation of harmful algal blooms (eutrophication), primarily caused by anthropogenic nitrogen pollution in wastewater discharge.1 Eutrophication perturbs coastal ecosystems by disrupting food chains, decreasing biodiversity, and causing nutrient deficiencies.2 Selective nitrate reduction (NO3RR) of wastewater is an attractive remediation strategy that prevents eutrophication and recovers a value-added commodity chemical in the form of ammonia. Recovering ammonia from nitrate in fertilizer runoff and municipal wastewater could offset up to 13% of ammonia produced worldwide through the Haber-Bosch process.3–6 With renewable-sourced energy, this strategy would also offset 320,000 metric tons of CO2-eq in greenhouse gas emissions.7 In this study, we present a Co-centered macrocycle, called Co-DIM, as a homogeneous molecular catalyst for the selective reduction of nitrate to ammonia. The advantages of Co-DIM include high water solubility, tunable product selectivity by ligand modification, and a wide range of pH operability.8 Despite comprehensive studies of promising molecular catalysts performed in the CO2 reduction (CO2RR) literature,9 NO3RR has not received a similar level of attention, and comparative frameworks do not yet exist to critically evaluate catalyst activity, selectivity, and stability. In this study we combine electroanalytical techniques in model systems to bench-scale, membrane-separated electrolysis in real wastewater. By doing so, we quantify the performance of a model NO3RR electrocatalyst, and demonstrate a generalizable approach for comparative benchmarking against heterogeneous and homogeneous reduction catalysts for other reactions (e.g., CO2RR).Determining the reaction mechanism of homogeneous molecular electrocatalysis requires careful understanding of the reaction environment. Using electroanalysis techniques, such as cyclic voltammetry (CV), and electrode surface identity modification (through atomic layer deposition and self-assembled monolayers), we were able to probe the electron transfer kinetics of Co-DIM activation and NO3RR catalysis. We found that Co-DIM is activated by an outer-sphere electron transfer mechanism, thereby deemphasizing electrode material identity for catalysis. We also leveraged key features of the obtained sigmoidal CVs to build the first ever TOF-eta relationship for a NO3RR molecular catalyst. Finally, we demonstrated greater than 50% removal of nitrate using Co-DIM in electrolysis of municipal wastewater. With this experiment, we present the novelty of using rational cell architecture and observable electrocatalysis in real wastewater for substantial nitrate removal and ammonia recovery. This work aims to encourage a framework for NO3RR evaluation to foster next-generation catalyst design and device implementation for large-scale nitrate removal from wastewater.(1) Dodds, W. K.; Bouska, W. W.; Eitzmann, J. L.; Pilger, T. J.; Pitts, K. L.; Riley, A. J.; Schloesser, J. T.; Thornbrugh, D. J. Eutrophication of U.S. Freshwaters: Analysis of Potential Economic Damages. Environ. Sci. Technol. 2009, 43 (1), 12–19. https://doi.org/10.1021/es801217q.(2) Kemp, W. M.; Boynton, W. R.; Adolf, J. E.; Boesch, D. F.; Boicourt, W. C.; Brush, G.; Cornwell, J. C.; Fisher, T. R.; Glibert, P. M.; Hagy, J. D.; Harding, L. W.; Houde, E. D.; Kimmel, D. G.; Miller, W. D.; Newell, R. I. E.; Roman, M. R.; Smith, E. M.; Stevenson, J. C. Eutrophication of Chesapeake Bay: Historical Trends and Ecological Interactions. Mar. Ecol. Prog. Ser. 2005, 303, 1–29. https://doi.org/10.3354/meps303001.(3) Wastewater: The Untapped Resource; Unesco, Ed.; The United Nations world water development report; UNESCO: Paris, 2017.(4) Food and Agriculture Organization of the United Nations. World Fertilizer Trends and Outlook to 2020. 2020, 38.(5) Kato, T.; Kuroda, H.; Nakasone, H. Runoff Characteristics of Nutrients from an Agricultural Watershed with Intensive Livestock Production. J. Hydrol. 2009, 368 (1), 79–87. https://doi.org/10.1016/j.jhydrol.2009.01.028.(6) Lang, M.; Li, P.; Yan, X. Runoff Concentration and Load of Nitrogen and Phosphorus from a Residential Area in an Intensive Agricultural Watershed. Sci. Total Environ. 2013, 458–460, 238–245. https://doi.org/10.1016/j.scitotenv.2013.04.044.(7) Smith, C.; Hill, A. K.; Torrente-Murciano, L. Current and Future Role of Haber–Bosch Ammonia in a Carbon-Free Energy Landscape. Energy Environ. Sci. 2020, 13 (2), 331–344. https://doi.org/10.1039/C9EE02873K.(8) Xiang, Y.; Zhou, D.-L.; Rusling, J. F. Electrochemical Conversion of Nitrate to Ammonia in Water Using Cobalt-DIM as Catalyst. J. Electroanal. Chem. 1997, 424, 1–3.(9) Costentin, C.; Robert, M.; Savéant, J.-M. Catalysis of the Electrochemical Reduction of Carbon Dioxide. Chem Soc Rev 2013, 42 (6), 2423–2436. https://doi.org/10.1039/C2CS35360A.

Simultaneous nitrogen and phosphorus recovery from municipal wastewater by electrochemical pH modulation

Solar enhanced membrane distillation for ammonia recovery

Bio-electrochemical ammonium recovery (BEAR) can close the cycle between anthropogenic emission of reactive nitrogen and energy intensive nitrogen fixation in the Haber-Bosch process. BEAR is currently limited by the bio-electrogenic degradability of the treated wastewater. Here, we investigated the degradability of blackwater, hydrolyzed human urine, cow manure and pig manure as prospective wastewaters for BEAR in a standardized experimental design.We found that bio-electrochemical conversion efficiencies ranged from 63% (blackwater) to 42% (cow manure) and 41% (urine) to 26% (pig manure) after 5 days. These values correspond well with the relative VFA content of soluble COD for blackwater and cow manure, while additional compounds must have been converted for urine and pig manure.The degradability of blackwater and cow manure was sufficiently high to theoretically be able to remove all TAN already after < 0.5 d. The actual recovery potential (consisting of conversion efficiency and COD/TAN ratio) of pig manure was just high enough to remove all TAN. Human urine would require additional electron donor to remove all TAN in BEAR. Therefore, combining the maximum recovery potential with the relative VFA content of soluble COD can give a good estimate of the actual recovery potential of a wastewater.

Treatment of domestic wastewater can recover valuable resources, including clean water, energy, and ammonia. Important metrics for these systems are greenhouse gas (GHG) emissions and embodied energy, both of which are location- and technology-dependent. Here, we determine the embodied energy and GHG emissions resulting from a conventional process train, and we compare them to a nonconventional process train. The conventional train assumes freshwater conveyance from a pristine source that requires energy for pumping (US average of 0.29 kWh/m3), aerobic secondary treatment with N removal as N2, and Haber-Bosch synthesis of ammonia. Overall, we find that this process train has an embodied energy of 1.02 kWh/m3 and a GHG emission of 0.77 kg-CO2eq/m3. We compare these metrics to those of a nonconventional process train that features anaerobic secondary treatment technology followed by further purification of the effluent by reverse osmosis and air stripping for ammonia recovery. This "short-cut" process train reduces embodied energy to 0.88 kWh/m3 and GHG emissions to 0.42 kg-CO2eq/m3, while offsetting demand for ammonia from the Haber-Bosch process and decreasing reliance upon water transported over long distances. Finally, to assess the potential impacts of nonconventional nitrogen removal technology, we compared the embodied energy and GHG emissions resulting from partial nitritation/anammox coupled to anaerobic secondary treatment. The resulting process train enabled a lower embodied energy but increased GHG emissions, largely due to emissions of N2O, a potent greenhouse gas.

NH4-N-loaded biochars are suitable candidates for soil amendment and fertilization. Sewage sludge-based biochar and biochar from the invasive species black wattle were used as sorbents for the adsorption of ammonia from a concentrated solution to mimic the wastewater treatment plant reject water stream. To increase ammonium recovery efficiency, two post-pyrolysis activation techniques were compared: steam activation and hydrogen peroxide treatment. It was found that the success of the treatment options was material dependent; therefore, post-pyrolysis treatments will require optimization for different applications based on feedstock. A simplified version of an adsorption process simulated in Aspen Tech predicts that NH4-N may be recovered at an energy cost lower than that of the Haber-Bosch process for black wattle biochar yields of below 19.5%. The biooil and syngas produced during pyrolysis can be used to lessen the energy requirements of the process, so that the solid portion may be utilized as an adsorbent and soil fertilizer. The energy-based sustainability of this technology warrants a more in-depth investigation for evaluation of the techno-economic feasibility for this class of loaded sorbents, and whether this method of nitrogen capture from wastewater is a suitable replacement of the costly Haber-Bosch process.

Life Cycle Assessment (LCA) is a multi-faced analytical approach targeted to assess environmental and economic sustainability approaches. LCA is used to evaluate challenges faced by industrial processes objectively while identifying environmental, energy, and economic hot spots. Performing LCA, researchers face several challenges: data collection and missing data, spatial and temporal variability, selection of assessment metrics, and uncertainty. This thesis evaluates three different approaches to LCA applicable for bioenergy and marginal supply of nutrients for agriculture. Economic assessment is performed along with LCA to consider the feasibility of bioenergy and nutrient recovery pathways. Three primary objectives define the thesis consisting of: (a) combining LCA and economic assessment of air-stripping technology to evaluate the cost-effectiveness of producing ammonium sulfate (AS) fertilizer from anaerobic digestor effluent at wastewater treatment plants, (b) developing an optimization framework to assess barley-to-ethanol biofuel pathway for its relevance as an advanced fuel under the federal Renewable Fuel Standard (RFS2), and (c) evaluating forest residue and willow short-rotation crop feedstocks for residential heating as alternatives to the use of heating oil and natural gas. The study estimates a reduction of 83% in greenhouse gas emissions from AS if produced by air-stripping technology at Philadelphia's WWTP compared to the conventional Haber Bosch process. Significant energy savings are observed for the ammonia recovery process compared to nitrogen and hydrogen's catalytic reaction to form ammonia in the Haber Bosch process. Economic evaluation considering capital and operational costs for Philadelphia's WWTP flow capacities estimates a break-even selling price of $0.11 per gallon AS (100% w/w concentration). This study demonstrates a point estimation of LCA methodology to identify a prospective future technology's economic and environmental feasibility based on local parameters. In the second objective, an optimization framework is developed to minimize upstream feedstock costs of producing ethanol, which selects winter fallow cropland for growing barley for ethanol production. The framework uses simulations of soil greenhouse gas emissions and crop yield estimated from the DAYCENT biogeochemical model, where parameters related to weather cycle, soil properties, and fertilizer management options affect emissions and crop yield. A generalized additive mixed modeling approach is used to accommodate temporal and spatial autocorrelation and variation. A mixed-integer optimization approach is used to minimize upstream production cost while maximizing the cropland acreage per choice selection. As a case study, for a biorefinery producing 2.08 x 108 liters of barley-ethanol per year, the average carbon intensity is estimated at 0.74 gCO₂e MJ-1 when all co-products are used. This shows that winter barley-to-ethanol can be classified as an advanced biofuel under RFS2. Credit incentives such as California state's Low Carbon Fuel Standard are found to have a negligible effect on cropland selection. The study also found that the favored management approaches for reducing greenhouse gas emissions largely match the farmers' choices to choose the most economical fertilizer management option. The third study implements Bern cycle modeling of atmospheric greenhouse gas retention and decomposition for estimating radiative forcing of alternative residential heating infrastructures over 30 production years and a total of 100 observation years. Natural gas and biomass feedstock-based heating scenarios are significantly more environmentally efficient than conventional heating oil. District heating (DH) infrastructure is similarly efficient as decentralized (CH) infrastructure for natural gas use. The study suggests using forest residues when available because if kept unused, it undergoes natural decay, emitting greenhouse gas emissions, which adversely affects radiative forcing for the 100 observed years. When forest residues are not available as feedstock, alternative bio-feedstock such as willow short rotation crop grown on marginal land can be planned for use in residential heating infrastructures. In addition, carbon capture and storage technology implementation can facilitate further reduction of radiative forcing when forest residues or willow short rotation crops are used as feedstocks. The study demonstrates the radiative forcing-based analytical framework that implements time-heterogenous greenhouse gas accounting of biomass-based residential heating. Keywords: Biomass for bioenergy, Life cycle assessment, Nutrient recovery, Portfolio optimization, Temporal GHG emissions

Ammonium (NH4+) recirculation from the streams generated in the dehydration stage of the sludge generated in the anaerobic digestion of urban wastewater treatment plants (WWTPs), known as centrate or sidestream, produces a reduction in the efficiency of WWTPs. Given this scenario and the formulation that a WWTP should be considered a by-product generating facility (biofactory), solutions for ammonia/ammonium recovery are being promoted. These include a nitrogen source that reduces the need for ammonia production through the Haber–Bosch process. Therefore, the recovery of nutrients from urban cycles is a potential and promising line of research. In the case of nitrogen, this has been aimed at recovering NH4+ to produce high-quality fertilizers through membrane or ion exchange processes. However, these techniques usually require a pretreatment, which could include an ultrafiltration stage, to eliminate suspended solids and organic matter. In this case, the coagulation/flocculation (C/F) process is an economical alternative for this purpose. In this work, the sidestream from Vilanova i la Geltrú WWTP (Barcelona, Spain) was characterized to optimize a C/F process before being treated by other processes for ammonium recovery. The optimization was performed considering a bibliographic and experimental analysis of several operating parameters: coagulant and flocculant agents, mixing velocity, and operation time, among others. Then, the removal efficiency of control parameters such as turbidity, chemical oxygen demand (COD), and total suspended solids (TSS) was calculated. This optimization resulted in the use of 25 mg/L of ferric chloride (FeCl3) combined with 25 mg/L of a flocculant composed of silicon (SiO2 3%), aluminum (Al2SO4 64.5%), and iron salts (Fe2O3 32.5%), into a 1 min rapid mixing process at 200 rpm and a slow mixing for 30 min at 30 rpm, followed by a final 30 min settling process. The numerical and statistical results of the process optimization reached 91.5%, 59.1%, and 95.2% removal efficiency for turbidity, COD, and TSS, respectively. These efficiencies theoretically support the enhanced coagulation/flocculation process as a pretreatment for a higher NH4+ recovery rate, achieving 570.6 mgNH4+/L, and a reduction in the dimensioning or substitution of other membrane processes process due to its high TSS removal value.

The current state of centralized nitrogen (N) management has destabilized global environmental cycles via Haber-Bosch (HB) ammonia-N manufacturing which contributes 1.2% of global anthropogenic CO2-eq emissions.1 The majority of this N that is discharged to wastewaters goes untreated, leading to harmful algal blooms that threaten coastal and river ecosystems, which already costs the U.S. an estimated $210 billion per year in health and environmental damages.2 Furthermore, the production of HB ammonia, and the subsequent discharge of wastewater nitrogen, is expected to substantially increase in the next three decades as the human population climbs to 9 billion people.3 Simultaneously removing nitrogen pollutants and recovering value-added products can preserve national water quality and supplement supply chains of nitrogen consumables with renewably sourced electricity. The electrochemical nitrate reduction reaction (NO3RR) can be leveraged in reactive separation processes to convert wastewater nitrates to commodity products, such as ammonia. Engineering catalytic NO3RR processes that operate at feasible rates and faradaic efficiencies is challenging because the majority of nitrate-rich wastewaters (e.g., fertilizer runoff) are dilute in nitrate concentration (< 5 mM).4 Molecular catalysts are uniquely suited to reduce nitrate at low concentrations in real wastewaters due to their strong substrate recognition (reactant selectivity) and product selectivity. In this study, we benchmarked the performance of the molecular catalyst Co-DIM (a Co-N4 macrocycle complex and the only known molecular NO3RR catalyst selective for ammonia5) in a reactive separations process for the treatment of real, nitrate-rich wastewaters.We first demonstrated by cyclic voltammetry (CV) and controlled-potential electrolysis (CPE) that selective Co-DIM-mediated NO3RR is feasible in nitrate-rich secondary effluent (municipal wastewater after biological nitrification). We then employed Co-DIM in electrochemical stripping (ECS): a membrane-separated cell that facilitates reactive separation of produced ammonia.6,7 From real secondary effluent (28 mg NO3-N/L), we achieved greater than 60% nitrate removal with a faradaic efficiency of 25% and ammonia selectivity of 98%. However, the energy consumed for ECS per unit mass of N is 16 times the combined energy requirement for conventional wastewater N removal and HB ammonia synthesis. By introducing a mixed feed of ammonia- and nitrate-rich wastewater and performing electrodialysis (ED) to concentrate the reactant nitrate before ECS, the energy requirement for N removal and ammonia recovery was decreased by three times while the ED process became the dominant energy consumer in the overall process. Additionally, the increase in nitrate removal could not be explained by an increase in nitrate concentration alone. The ED process changes the concentrations and relative ratios of competing anions and buffering species, which can inhibit or promote the molecular electrocatalytic activity. We therefore explored a matrix of anion identities and concentrations by rotating-disk voltammetry and CPE to elucidate plausible inhibition and promotion mechanisms associated with catalyst activation and NO3RR catalysis. This study therefore (1) benchmarks current and future efforts to reactively separate ammonia from real nitrate-rich wastewater with a molecular catalyst and (2) highlights molecular and process-level improvements to realize a circular nitrogen economy.References1 C. Smith, A. K. Hill and L. Torrente-Murciano, Energy Environ. Sci., 2020, 13, 331–344.2 D. J. Sobota, J. E. Compton, M. L. McCrackin and S. Singh, Environ. Res. Lett., 2015, 10, 025006.3 J. W. Erisman, M. A. Sutton, J. Galloway, Z. Klimont and W. Winiwarter, Nature Geoscience, 2008, 1, 636–639.4 Unesco, Ed., Wastewater: the untapped resource, UNESCO, Paris, 2017.5 S. Xu, D. C. Ashley, H.-Y. Kwon, G. R. Ware, C.-H. Chen, Y. Losovyj, X. Gao, E. Jakubikova and J. M. Smith, Chem. Sci., 2018, 9, 4950–4958.6 W. A. Tarpeh, J. M. Barazesh, T. Y. Cath and K. L. Nelson, Environ. Sci. Technol., 2018, 52, 1453–1460.7 M. J. Liu, B. S. Neo and W. A. Tarpeh, Water Research, 2020, 169, 115226.

Continued growth of the world’s population as well as shifting socio-economic trends have been tied to increasing demands for food and water. Due to upcoming worldwide environmental crises, there needs to be a shift towards a circular economy, where key nutrients are not lost but repurposed. For example, high-yield food crops depend on the application of nitrogen and phosphorus-based fertilizers, which are respectively made using highly energy intensive methods, like the Haber-Bosch process, and non-renewable limited resources, such as phosphate rock. In addition, water that has been contaminated by human activity is being treated in a multitude of manners, with the overarching drawbacks being high energy consumption and, in some cases, the production of a secondary waste stream. In particular, wastewater sludge is a nutrient-rich waste stream with high levels of nitrogen and phosphorus stored in organic bonds that is most commonly sent to landfills for disposal.In this talk, we focus on the electrochemical oxidation of wastewater sludge for the recovery of ammonia and other nutrients. We used a synthetic wastewater sludge composition to better understand the contributions of each component on the formed end-products. We probed the potential dependence of these end-products by conducting fixed-potential tests in a H-cell with Ni foam electrodes. This work contributes to the ongoing efforts in the Center of Advancing Sustainable and Distributed Fertilizer Production (CASFER).

A highly-efficient hybrid technique – Membrane-assisted gas absorption for ammonia recovery after the Haber-Bosch process