PV-Powered Electrochemical Toilet Wastewater Treatment with Hydrogen Gas Cogeneration: Field Application

Novel technologies are needed to address 2.5 billion people in the world that don’t have access to safe sanitation facilities [1]. One of the main barriers is expensive wastewater infrastructure and the scarcity of water in many regions.

An off-the-grid electrochemical system that decontaminates wastewater and produce hydrogen is under development to provide a solution for on-site wastewater treatment in rural and peri-urban communities [2]. The system has at its core photovoltaic-powered electrochemical reactors. Each reactor is composed of a series of anodes and cathodes: the anodes are bismuth oxide/titanium dioxide semiconductors coated on a titanium plates (BiOx_x/TiO_x2/Ti) [2]; the cathodes are stainless steel plates. Cathodes and anodes are assembled together with 2 mm separation.

In a slightly saline solution of sodium chloride (concentration equals or higher than 20 mM) and when a voltage higher than 2.5 V is applied between the electrodes, the chloride can be oxidized at the anode to form reactive chlorine species (Cl•) that will undergo reduction/oxidation reactions to finally oxidize the organic matter present in the solution, if any. In parallel the main reduction reaction at the cathode is the production of hydrogen [3].

The fundamental concept has been tested on bench-scale (1 anode, 2 cathodes, 40 mL process volume) and prototype-scale (20 L process volumes) with primary and secondary effluents from wastewater treatment plants in a totally integrated, off-the-grid “proof of concept” prototype with photovoltaic panels, charge controller and lead-acid batteries. The specific design elements and the treatment approach have been proven to be viable for the treatment of raw domestic wastewater on a prototype-scale reactors and human urine, human feces and synthetic human waste analogues on lab-scale reactors [4, 5].

 Even though the system was tested with various wastewater effluents, efforts are on the way to use this technology directly with toilet effluents in developing countried. These effluents are more concentrated in organics (high COD), dissolved solids and bacteria. This field study is performed in two locations in India: Ahmedabad (Gujarat) and Kottayam (Kerala).

References:

[1] Progress on Sanitation and Drinking-water, in Joint Monitoring Programme (JMP) for Water Supply and Sanitation2013, WHO / UNICEF.

[2] Hoffmann, M.R., et al., Self-contained, PV-powered domestic toilet and wastewater treatment system, 2013.

[3] Kim, J., et al., Electrolysis of urea and urine for solar hydrogen. Catalysis Today, 2013. 199(0): p. 2-7.

[4] Cid, C.A., et al., Development of an On-site Self-contained Electrochemical Wastewater Treatment System with Hydrogen Production.224th ECS Meeting, San Francisco, CA, US, 2013.

[5] Park, H., et al., Electrochemical oxidation and microfiltration of municipal wastewater with simultaneous hydrogen production: Influence of organic and particulate matter. Chemical Engineering Journal, 2013. 215–216(0): p. 802-810.