Abstract
Decentralized, energy‐efficient waste water treatment technologies enabling water reuse are needed to sustainably address sanitation needs in water‐ and energy‐scarce environments. Here, we describe the effects of repeated recycling of disinfected blackwater (as flush liquid) on the energy required to achieve full disinfection with an electrochemical process in a prototype toilet system. The recycled liquid rapidly reached a steady state with total solids reliably ranging between 0.50 and 0.65% and conductivity between 20 and 23 mS/cm through many flush cycles over 15 weeks. The increase in accumulated solids was associated with increased energy demand and wide variation in the free chlorine contact time required to achieve complete disinfection. Further studies on the system at steady state revealed that running at higher voltage modestly improves energy efficiency, and established running parameters that reliably achieve disinfection at fixed run times. These results will guide prototype testing in the field.
Highlights
An estimated 2.5 billion people worldwide lack modern electrical and clean water infrastructures, resulting in millions of deaths annually from diseases acquired through the use of unsafe water resources (Wardlaw et al 2010; Elledge & McClatchey 2013)
We demonstrated that electrochemical disinfection with an off-the-shelf mixed metal oxide (MMO) electrochemical cell was effective at disinfecting both model waste water and blackwater, consisting of fecal-contaminated urine and recycled flush water, from our toilet prototype, but that the latter required longer running times and greater energy inputs per liter to achieve adequate disinfection (Sellgren et al 2017)
Water and Environment Journal published by John Wiley & Sons Ltd on behalf of CIWEM
Summary
An estimated 2.5 billion people worldwide lack modern electrical and clean water infrastructures, resulting in millions of deaths annually from diseases acquired through the use of unsafe water resources (Wardlaw et al 2010; Elledge & McClatchey 2013). Distribution of clean water depends upon having the energy available to treat waste water effectively. One approach to quickly address the lack of clean water in lower income countries is to reduce the dependence on energy- and infrastructure-intensive waste water treatment technology. We demonstrated that electrochemical disinfection with an off-the-shelf mixed metal oxide (MMO) electrochemical cell was effective at disinfecting both model waste water (diluted urine spiked with Escherichia coli) and blackwater, consisting of fecal-contaminated urine and recycled flush water, from our toilet prototype, but that the latter required longer running times and greater energy inputs per liter to achieve adequate disinfection (Sellgren et al 2017). We expand on those observations, and describe: (1) the accumulation of solids in our system over many flush cycles, wherein blackwater is repeatedly disinfected and recycled, (2) the impact of repeated recycling on the energy requirements for effective disinfection and (3) efforts to improve energy efficiency of the electrochemical process under steady state conditions
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