Reimagining liquid waste streams as resources can lead to recovery of valuable products and more efficient, less costly approaches to reducing harmful discharges to the environment. Pollutants in effluent streams can be captured and used as valuable inputs to other processes. For example, municipal wastewater contains resources like energy, water, nutrients, and metals. The Tarpeh Lab develops and evaluates novel approaches to resource recovery from “waste” waters at several synergistic scales: molecular mechanisms of chemical transport and transformation; novel unit processes that increase resource efficiency; and systems-level assessments that identify optimization opportunities. We employ understanding of electrochemistry, separations, thermodynamics, kinetics, and reactor design to preferentially recover resources from waste. We leverage these molecular-scale insights to increase the sustainability of engineered processes in terms of energy, environmental impact, and cost.

Academic Appointments

Professional Education

  • PhD, University of California, Berkeley, Environmental Engineering (2017)
  • MS, University of California, Berkeley, Environmental Engineering (2013)
  • BS, Stanford University, Chemical Engineering (2012)

2020-21 Courses

Stanford Advisees

  • Doctoral Dissertation Reader (AC)
    Micha Ben-Naim, Sarah Blair, Daniel Corral, Stephen Galdi, McKenzie Hubert, Jack King, Solomon Oyakhire, James Raiford, Joel Schneider, Adam Simpson, Michael Statt, Jose Zamora Zeledon, Camila de Paula Teixeira
  • Postdoctoral Faculty Sponsor
    Xi Chen, Elizabeth Corson, Hang Dong
  • Doctoral Dissertation Advisor (AC)
    Sam Bunke, Brandon Clark, Jinyu Guo, Matthew Liu, Dean Miller, Valerie Niemann, Anita Shao
  • Doctoral Dissertation Co-Advisor (AC)
    Emily Penn
  • Postdoctoral Research Mentor
    Xi Chen, Elizabeth Corson, Hang Dong
  • Doctoral (Program)
    Anna Kogler, Lorelay Mendoza Grijalva

All Publications

  • Electro-assisted regeneration of pH-sensitive ion exchangers for sustainable phosphate removal and recovery. Water research Dong, H., Wei, L., Tarpeh, W. A. 2020; 184: 116167


    Removal and recovery of phosphate from wastewater can minimize deleterious environmental impacts and supplement fertilizer supply. Hybrid anion exchangers (HAIX, with doped ferric oxide nanoparticles (FeOnp)) can remove phosphate from complex wastewaters and recover concentrated phosphate solutions. In this study, we integrate HAIX with a weak acid cation exchanger (WAC) to enrich phosphate and calcium in mild regenerants and precipitate both elements for recovery. We demonstrated an electro-assisted regeneration approach to avoid strong acid and base input. Based on demonstrated pH sensitivities of both materials, electrochemically produced mild electrolytes (pH 3 and pH 11), which are 100-1000 times less concentrated than typical regenerants, preserved 80% WAC and 50% HAIX capacities over five batch adsorption-regeneration cycles. FeOnp in HAIX facilitated regeneration due to pH sensitivity and their likely distribution on the resin particle surface, which reduced intraparticle diffusion path length. In column tests, repeatable phosphate removal (> 95%) from synthetic wastewater (3mg P/L) was achieved with 20kWh/kg P specific energy consumption. After removal, a similar 50% HAIX regeneration efficiency as batch experiments was achieved. In spent regenerant, more than 95% phosphorus was recovered as hydroxyapatite. This novel approach enhances ion exchange by minimizing chemical inputs.

    View details for DOI 10.1016/j.watres.2020.116167

    View details for PubMedID 32682079

  • Selective recovery of ammonia nitrogen from wastewaters with transition metal-loaded polymeric cation exchange adsorbents. Chemistry (Weinheim an der Bergstrasse, Germany) Clark, B., Tarpeh, W. 2020


    Extracting valuable products from wastewaters with nitrogen-selective adsorbents can offset energy-intensive ammonia production, rebalance the nitrogen cycle, and incentivize environmental remediation. Separating nitrogen (N) as ammonium from other wastewater cations (e.g., K + , Ca 2+ ) presents a major challenge to N removal from wastewater and N recovery as high-purity products. We achieved high selectivity and capacity via ligand exchange of ammonia with ammine-complexing transition metals loaded onto polymeric cation exchange resins. Compared to commercial resins, metal-ligand exchange adsorbents exhibited higher ammonia removal capacity (8 meq/g) and selectivity (N/K + equilibrium selectivity of 10.1) in binary equimolar solutions. Considering optimal ammonia concentrations (200-300 meq/L) and pH (9-10) for metal-ligand exchange, we identified hydrolyzed urine as a promising candidate for selective TAN recovery. However, divalent cation exchange increased transition metal elution and reduced ammonia adsorption. Ultimately, metal-ligand exchange adsorbents can advance nitrogen-selective separations from wastewaters.

    View details for DOI 10.1002/chem.202002170

    View details for PubMedID 32500617

  • Novel two-chamber tubular microbial desalination cell for bioelectricity production, wastewater treatment and desalination with a focus on self-generated pH control Desalination Jafary, T., Al-Mamun, A., Alhimali, H., Baawain, M., Rahman, S., Tarpeh, W. A., Dhar, B., Kim, B. 2020; 481
  • The role of intraparticle diffusion path length during electro-assisted regeneration of ion exchange resins: implications for selective adsorbent design and reverse osmosis pretreatment Chemical Engineering Journal Dong, H., Wu, Z., Liu, M. J., Tarpeh, W. A. 2020
  • Validation and mechanism of a low-cost graphite carbon electrode for electrochemical brine valorization ACS Sustainable Chemistry & Engineering Mu, L., Wang, Y., Tarpeh, W. A. 2020; 8 (23): 8648-8654
  • Process design tools and techno-economic analysis for capacitive deionization. Water research Hasseler, T. D., Ramachandran, A. n., Tarpeh, W. A., Stadermann, M. n., Santiago, J. G. 2020; 183: 116034


    Capacitive deionization (CDI) devices use cyclical electrosorption on porous electrode surfaces to achieve water desalination. Process modeling and design of CDI systems requires accurate treatment of the coupling among input electrical forcing, input flow rates, and system responses including salt removal dynamics, water recovery, energy storage, and dissipation. Techno-economic analyses of CDI further require a method to calculate and compare between a produced commodity (e.g. desalted water) versus capital and operational costs of the system. We here demonstrate a new modeling and analysis tool for CDI developed as an installable Matlab program that allows direct numerical simulation of CDI dynamics and calculation of key performance and cost parameters. The program is provided for free and is used to run open-source Simulink models. The Simulink environment sends information to the program and allows for a drag and drop design space where users can connect CDI cells to relevant periphery blocks such as grid energy, battery, solar panel, waste disposal, and maintenance/labor cost streams. The program allows for simulation of arbitrary current forcing and arbitrary flow rate forcing of one or more CDI cells. We employ validated well-mixed reactor formulations together with a non-linear circuit model formulation that can accommodate a variety of electric double layer sub-models (e.g. for charge efficiency). The program includes a graphical user interface (GUI) to specify CDI plant parameters, specify operating conditions, run individual tests or parameter batch-mode simulations, and plot relevant results. The techno-economic models convert among dimensional streams of species (e.g. feed, desalted water, and brine), energy, and cost and enable a variety of economic estimates including levelized water costs.

    View details for DOI 10.1016/j.watres.2020.116034

    View details for PubMedID 32736269

  • Building an operational framework for selective nitrogen recovery via electrochemical stripping. Water research Liu, M. J., Neo, B. S., Tarpeh, W. A. 2019; 169: 115226


    Recovering nitrogen from wastewater can simultaneously fulfill the roles of traditional removal technologies such as nitrification-denitrification and fertilizer production processes such as Haber-Bosch. We have recently demonstrated a proof-of-concept for selective recovery of the fertilizer ammonium sulfate via electrochemical stripping, a combination of electrodialysis and membrane stripping. In this study, we furthered electrochemical stripping from concept to informed practice by investigating the effects of influent concentration (30, 300, and 3000 mg N/L), catholyte temperature (15, 23, and 35 °C), and gas permeable membrane choice on electrochemical nitrogen removal and recovery. We also proposed and validated a nitrogen mass transport model for the experimental results, providing mechanistic rationale behind observed effects of varying operating parameters. While changing operating parameters did affect performance, electrochemical stripping exhibited robust performance over a range of realistic ambient temperatures, three gas permeable membranes, and three orders of magnitude of influent concentrations. Practically, these results demonstrate that electrochemical stripping is viable across a range of waste streams and resilient to fluctuations in temperature and nitrogen concentration; they also establish operational trade-offs between residence time and energy consumption. As a result of this work, electrochemical stripping continues to mature from concept to practice and provides lessons for developing other resource recovery technologies.

    View details for DOI 10.1016/j.watres.2019.115226

    View details for PubMedID 31765946

  • Selective Hydrogenation of Furfural in a Proton Exchange Membrane Reactor Using Hybrid Pd/Pd Black on Alumina CHEMELECTROCHEM Carl, S., Waldrop, K., Pintauro, P., Thompson, L. T., Tarpeh, W. A. 2019
  • Sanitation for Low-Income Regions: A Cross-Disciplinary Review. Annual review of environment and resources Hyun, C. n., Burt, Z. n., Crider, Y. n., Nelson, K. L., Sharada Prasad, C. S., Rayasam, S. D., Tarpeh, W. n., Ray, I. n. 2019; 44 (1): 287–318


    Sanitation research focuses primarily on containing human waste and preventing disease; thus, it has traditionally been dominated by the fields of environmental engineering and public health. Over the past 20 years, however, the field has grown broader in scope and deeper in complexity, spanning diverse disciplinary perspectives. In this article, we review the current literature in the range of disciplines engaged with sanitation research in low- and middle-income countries (LMICs). We find that perspectives on what sanitation is, and what sanitation policy should prioritize, vary widely. We show how these diverse perspectives augment the conventional sanitation service chain, a framework describing the flow of waste from capture to disposal. We review how these perspectives can inform progress toward equitable sanitation for all [i.e., Sustainable Development Goal (SDG) 6]. Our key message is that both material and nonmaterial flows-and both technological and social functions-make up a sanitation "system." The components of the sanitation service chain are embedded within the flows of finance, decision making, and labor that make material flows of waste possible. The functions of capture, storage, transport, treatment, reuse, and disposal are interlinked with those of ensuring equity and affordability. We find that a multilayered understanding of sanitation, with contributions from multiple disciplines, is necessary to facilitate inclusive and robust research toward the goal of sanitation for all.

    View details for DOI 10.1146/annurev-environ-101718-033327

    View details for PubMedID 32587484

    View details for PubMedCentralID PMC7316187

  • Quantitative Evaluation of an Integrated System for Valorization of Wastewater Algae as Bio-oil, Fuel Gas, and Fertilizer Products ENVIRONMENTAL SCIENCE & TECHNOLOGY Li, Y., Tarpeh, W. A., Nelson, K. L., Strathmann, T. J. 2018; 52 (21): 12717–27


    Algal systems have emerged as a promising strategy for simultaneous treatment and valorization of wastewater. However, further advancement and real-world implementation are hindered by the limited knowledge on the full energetic and nutrient product potentials of such systems and the corresponding value of these products. In this work, an aqueous-based system for the conversion of wastewater-derived algae and upgrading of crude products was designed and demonstrated. Bio-oil, fuel gas, and fertilizer products were generated from algal biomass harvested from a municipal wastewater treatment facility. Experiments showed that 68% of chemical energy contained in the algal biomass could be recovered with 44% in upgraded bio-oil and 23% in fuel gas (calculated as higher heating values), and 44% and 91% of nitrogen and phosphorus element contents in the original feedstock could be recovered as fertilizer products (ammonium sulfate and struvite), respectively. For 1,000 kg of such dry algal biomass, these products had an estimated total value of $427 (in 2014 US dollars). For the first time, experiment-based energy and nutrient recovery potentials of wastewater-derived algae were presented in an integrated manner. Findings also revealed critical research needs and suggested strategies to further improve resource recovery and waste valorization in these systems.

    View details for DOI 10.1021/acs.est.8b04035

    View details for Web of Science ID 000449722200077

    View details for PubMedID 30256626

  • Effects of operating and design parameters on ion exchange columns for nutrient recovery from urine ENVIRONMENTAL SCIENCE-WATER RESEARCH & TECHNOLOGY Tarpeh, W. A., Wald, I., Wiprachtiger, M., Nelson, K. L. 2018; 4 (6): 828–38

    View details for DOI 10.1039/c7ew00478h

    View details for Web of Science ID 000434312500008

  • Electrochemical Stripping to Recover Nitrogen from Source-Separated Urine ENVIRONMENTAL SCIENCE & TECHNOLOGY Tarpeh, W. A., Barazesh, J. M., Cath, T. Y., Nelson, K. L. 2018; 52 (3): 1453–60


    Recovering nitrogen from separately collected urine can potentially reduce costs and energy of wastewater nitrogen removal and fertilizer production. Through benchtop experiments, we demonstrate the recovery of nitrogen from urine as ammonium sulfate using electrochemical stripping, a combination of electrodialysis and membrane stripping. Nitrogen was selectively recovered with 93% efficiency in batch experiments with real urine and required 30.6 MJ kg N-1 in continuous-flow experiments (slightly less than conventional ammonia stripping). The effects of solution chemistry on nitrogen flux, electrolytic reactions, and reactions with electro-generated oxidants were evaluated using synthetic urine solutions. Fates of urine-relevant trace organic contaminants, including electrochemical oxidation and reaction with electro-generated chlorine, were investigated with a suite of common pharmaceuticals. Trace organics (<0.1 μg L-1) and elements (<30 μg L-1) were not detected at appreciable levels in the ammonium sulfate fertilizer product. This novel approach holds promise for selective recovery of nitrogen from concentrated liquid waste streams such as source-separated urine.

    View details for DOI 10.1021/acs.est.7b05488

    View details for Web of Science ID 000424851700059

    View details for PubMedID 29303251

  • Evaluating ion exchange for nitrogen recovery from source-separated urine in Nairobi, Kenya Development Engineering Tarpeh, W. A., Wald, I., Omollo, M. O., Egan, T., Nelson, K. L. 2018; 3: 188-195
  • Life-Cycle Cost and Environmental Assessment of Decentralized Nitrogen Recovery Using Ion Exchange from Source-Separated Urine through Spatial Modeling ENVIRONMENTAL SCIENCE & TECHNOLOGY Kavvada, O., Tarpeh, W. A., Horvath, A., Nelson, K. L. 2017; 51 (21): 12061–71


    Nitrogen standards for discharge of wastewater effluent into aquatic bodies are becoming more stringent, requiring some treatment plants to reduce effluent nitrogen concentrations. This study aimed to assess, from a life-cycle perspective, an innovative decentralized approach to nitrogen recovery: ion exchange of source-separated urine. We modeled an approach in which nitrogen from urine at individual buildings is sorbed onto resins, then transported by truck to regeneration and fertilizer production facilities. To provide insight into impacts from transportation, we enhanced the traditional economic and environmental assessment approach by combining spatial analysis, system-scale evaluation, and detailed last-mile logistics modeling using the city of San Francisco as an illustrative case study. The major contributor to energy intensity and greenhouse gas (GHG) emissions was the production of sulfuric acid to regenerate resins, rather than transportation. Energy and GHG emissions were not significantly sensitive to the number of regeneration facilities. Cost, however, increased with decentralization as rental costs per unit area are higher for smaller areas. The metrics assessed (unit energy, GHG emissions, and cost) were not significantly influenced by facility location in this high-density urban area. We determined that this decentralized approach has lower cost, unit energy, and GHG emissions than centralized nitrogen management via nitrification-denitrification if fertilizer production offsets are taken into account.

    View details for DOI 10.1021/acs.est.7b02244

    View details for Web of Science ID 000414887200003

    View details for PubMedID 28948786

  • The sanitation and urban agriculture nexus: urine collection and application as fertilizer in Sao Paulo, Brazil JOURNAL OF WATER SANITATION AND HYGIENE FOR DEVELOPMENT Chrispim, M. C., Tarpeh, W. A., Salinas, D. P., Nolasco, M. A. 2017; 7 (3): 455–65
  • Comparing Ion Exchange Adsorbents for Nitrogen Recovery from Source-Separated Urine ENVIRONMENTAL SCIENCE & TECHNOLOGY Tarpeh, W. A., Udert, K. M., Nelson, K. L. 2017; 51 (4): 2373–81


    Separate collection of urine, which is only 1% of wastewater volume but contains the majority of nitrogen humans excrete, can potentially reduce the costs and energy input of wastewater treatment and facilitate recovery of nitrogen for beneficial use. Ion exchange was investigated for recovery of nitrogen as ammonium from urine for use as a fertilizer or disinfectant. Cation adsorption curves for four adsorbents (clinoptilolite, biochar, Dowex 50, and Dowex Mac 3) were compared in pure salt solutions, synthetic urine, and real stored urine. Competition from sodium and potassium present in synthetic and real urine did not significantly decrease ammonium adsorption for any of the adsorbents. Dowex 50 and Dowex Mac 3 showed nearly 100% regeneration efficiencies. Estimated ion exchange reactor volumes to capture the nitrogen for 1 week from a four-person household were lowest for Dowex Mac 3 (5 L) and highest for biochar (19 L). Although Dowex Mac 3 had the highest adsorption capacity, material costs ($/g N removed) were lower for clinoptilolite and biochar because of their substantially lower unit cost.

    View details for DOI 10.1021/acs.est.6b05816

    View details for Web of Science ID 000394724300054

    View details for PubMedID 28098981