Trends in Biotechnology
Volume 38, Issue 9, September 2020, Pages 990-1006
Journal home page for Trends in Biotechnology

Review
Waste or Gold? Bioelectrochemical Resource Recovery in Source-Separated Urine

https://doi.org/10.1016/j.tibtech.2020.03.007Get rights and content

Highlights

  • Resource recovery is a key strategy to keep up with a consumption-driven society.

  • Providing an abundant source of energy and nutrients, source-separated urine has proven its potential for sustainable recovery.

  • The performance of urine-fed BES-based resource recovery is showing increasing promise.

In recent years, source-separated human urine has been highlighted as an effective resource for energy and nutrient recovery. However, even though several technologies exist for resource recovery, they have not been widely implemented. Among these technologies, bioelectrochemical systems (BESs) hold promise as technically and economically interesting alternatives for sustainable resource recovery from source-separated urine. Here, we review the resource recovery performance of BESs, including microbial fuel cells (MFCs) and microbial electrolysis cells (MECs), fed with source-separated urine over the past decade, and suggest an effective path forward toward their widespread implementation.

Section snippets

The Potential of Urine for Resource Recovery

An accelerating human population and consumption growth rate mean that the global demand for food will not decrease anytime soon. To make matters worse, this booming competition for water, nutrients, and energy will affect the global capacity to produce enough food. Moreover, the need to control the negative impacts of human activity, including food production, on the environment will also increase [1].

There is no simple solution to meeting the ever-increasing food expectations of ~8 billion

Bioelectrochemical Systems: MFCs and MECs

BESs (see Glossary) are emerging technologies that have been developed as different reactor setups (Box 2) following the discovery that some microorganisms (Box 3) can catalyze various anodic or cathodic reactions (Box 4). Source-separated urine could be a suitable influent for BESs to recover nutrients, energy, fuel, and valuable compounds. Figure 1 provides an overview of the basic working principles in BESs and centers around the most common BESs: MFCs and MECs.

The growing number of recent

Bioelectrochemical Systems Fed with Source-Separated Urine

Key BESs, including MFCs and MECs, with applications envisaged for the treatment of wastewater streams, have been in the spotlight for the past two decades. Unfortunately, there are two main obstacles to their use: low ionic conductivity and low buffering capacity of most wastewater streams [21]. However, source-separated urine overcomes these obstacles with an average ionic conductivity of 20 ms.cm–1 and a buffering capacity of 660 mM because of its urea concentration of 20 g.l–1 [23].

Concluding Remarks and Future Perspectives

Given its high energy and macronutrient content. including N, P, and K, source-separated human urine is an ideal candidate for sustainable nutrient and energy recovery. Numerous technical approaches have been introduced throughout the recent decades, yet they all have drawbacks that limit their widespread implementation. The production of electrical power and value-added products, COD removal of >90% [40,47,49,62], and P and N recoveries of >90% [33] and >50% [35], respectively, over the past

Acknowledgments

The authors would like to acknowledge the Iran National Science Foundation (INSF) and Razi University for the full financial support provided for this research work.

Glossary

Bioelectrochemical systems (BESs)
systems capable of converting the chemical energy of organic waste into electricity, hydrogen, or other useful chemicals.
Chemical oxygen demand (COD)
indicative measure of the oxygen required to oxidize organic matter in a water sample.
Coulombic efficiency (%)
fraction of charge output to charge input by which the electrons are transferred and an electrochemical reaction is facilitated.
Current density (A.m2)
amount of charge generated or applied to a

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