Extractive Nutrient Recovery Represents A Transition from Linear to Circular Economy

Authors:

  • Samuel Jeyanayagam - CH2M
  • Wendell Khunjar - Hazen and Sawyer
  • Amit Premanik - WERF

Nitrogen (N) and phosphorus (P) are life-essential macronutrients that are extensively used in agricultural applications. Production of synthetic fertilizers containing N and P is an energy intensive process that uses non-renewable resources. For example, ammonia (NH3) is produced via the Haber-Bosch process with a high energy demand (12 kWh/kg NH3 produced). With respect to P, experts believe that economically extractable reserves are declining rapidly and would likely be exhausted in 50 to 100 years.

Our current nutrient management approach entails the application of energy and other non-renewable resources to replenish nutrient supply for agricultural uses and again to remove these nutrients from wastewater before discharge to the environment. This linear approach assumes unlimited and cheap supply of energy and resources and is not aligned with a circular economy. While nutrient recovery has been practiced for hundreds of years via land application, it is not sustainable for a variety of reasons and there is a need to adopt methods for recovering a relatively clean chemical nutrient product with low organic matter content. This approach, defined here as extractive nutrient recovery, intentionally extracts nutrients from the solids stream. Benefits include: recycle load management, chemical savings, reduced solids production, potential dewaterability enhancement, and minimized struvite scaling. Despite these benefits there remain technical, social, institutional, and economic barriers towards a wider adoption of nutrient recovery.

This paper presents technical information generated as part of a global study funded by the Water Environment Research Federation (WERF) aimed at filling the knowledge gap, accelerating the advancement of extractive nutrient recovery, capturing lessons learned through case studies, and enabling the use of best practices that favor a regenerative and circular economy. In addition, the features of the Tool for Evaluating Resource Recovery (TERRY), a high-level evaluation tool developed as part of the WERF study will also be presented.

The nutrient concentrations in water resource recovery facility influent is relatively low and a three-step framework is often needed to make nutrient recovery viable: 1) Accumulation of nutrients achieving >1000 mg N/L and > 100 mg P/L; 2) Release of nutrients to a small liquid flow;; and 3) Extraction of nutrients as a marketable product. Many facilities already have the accumulation (enhanced biological phosphorus removal) and release (anaerobic digester) steps in place and are nutrient recovery-ready. These plants require the addition of the extraction step to make nutrient recovery a reality.

For more information, please contact the author at wkhunjar@hazenandsawyer.com.

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