Disinfection of Liquid Human Waste through Photoelectrochemical Treatment

Currently, one third of the world population does not have sufficient access to clean water for personal sanitation and proper wastewater disposal.¹ Global population growth, climate change, and pollution from human activities pose an even heavier burden on the available water resources.^1,2 Therefore, sustainable methods that can disinfect liquid human waste (LHW) into reusable water before discharging into the environment are urgently needed to address water and energy challenges.^1,3

Photoelectrochemical (PEC) processes are a promising method to address this challenge by utilizing inexhaustible solar energy to reclaim water from LHW and generate/store energy. In a typical PEC device, the semiconductor/liquid junction is formed spontaneously when a semiconductor is immersed in an electrolyte. Owing to the band bending of the semiconductor (n-type as an example), photoexcited (e^-)/(h⁺) pairs in the depletion region of the semiconductor are then separated and migrate to the interfaces of electrode/electrolyte to drive reduction (e.g., proton reduction for H₂ production) and oxidation (e.g., oxidizing organics or water) reaction respectively.

In this presentation, we will present the preliminary data showing PEC process as a viable process to reclaim LHW, which consists of human urine, as well as bacteria and organics from solid waste. Human urine consists of water (>95 wt.%), urea ~9g/L, chloride 2g/L, sodium 1g/L, potassium ~1g/L, and other organics such as tryptone. The possibility of generating chlorine oxidative species through PEC with LHW as the electrolyte for disinfection will be shown. We will also present the generation rate of chlorine oxidative species through PEC using TiO₂ nanowire-based electrodes (Fig. 1), as well as the effects of organics in LHW on chlorine oxidative species generation rate by using model electrolytes. Fig 1 shows that total Cl oxidative species generation rate with photocurrent of TiO₂ nanowire (NW) electrode. The electrode with 1.8mA photocurrent is about 3 times of the electrode area of 0.5mA. The effect of the supporting electrolyte, light scattering/absorption, and biofouling of the PEC electrode surface on the disinfection process will also be included in the presentation. In summary, we will show the promise of a PEC strategy for reclaiming water from LHW, along with challenges to be overcome for practical implementation of this method.

Reference:

1              Grant, S. B., et.al. Taking the "Waste" Out of "Wastewater" for Human Water Security and Ecosystem Sustainability. Science 337, 681-686, (2012).

2              Vorosmarty, C. J., et al. Global threats to human water security and river biodiversity. Nature 467, 555-561, (2010).

3              Cho, K., Kwon, D. & Hoffmann, M. R. Electrochemical treatment of human waste coupled with molecular hydrogen production. Rsc Advances 4, 4596-4608, (2014).