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)

Stanford Advisees

  • Doctoral Dissertation Reader (AC)
    Hassan Aljama, McKenzie Hubert, Joel Sanchez, Joel Schneider
  • Postdoctoral Faculty Sponsor
    Hang Dong, Linchao Mu
  • Doctoral Dissertation Advisor (AC)
    Brandon Clark, Matthew Liu
  • Postdoctoral Research Mentor
    Hang Dong, Linchao Mu

All Publications

  • 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