The Gates Foundation “Reinvent the Toilet Grand Challenge”: From a Concept to Manufacturing in 5 Years



Michael R. Hoffmann 

Academician of the American National Academy of Engineering

Foreign academician of the Chinese Academy of Engineering

Professor, Department of Environmental Science, Caltech



The Gates Foundation “Reinvent the Toilet Grand Challenge”: From a Concept to Manufacturing in 5 Years.


With support from the Bill and Melinda Gates Foundation, we have developed, tested, and implemented transportable reactor systems and public toilet systems that are designed for the onsite treatment of domestic wastewater with the total recycle of treated water as flushing water.  Our research and development efforts are a major component of the Gates Foundation “Reinvent the Toilet Challenge (RTTC)“.  After pre-treatment with a sequential anaerobic/aerobic baffled bioreactor, the effluent is processed sequentially through semiconductor electrochemical arrays where the COD and microbial loads are reduced to below US EPA reuse standards.  Special mini-reactors are used to convert the treated wastewater to handwashing and drinking water standards.   The treated black water is recycled bqck into flushing water reservoirs without discharge to the surrounding environment.   Human wastewater can be clarified with the elimination of suspended particles along with >95% reduction in chemical oxygen demand (COD), and a total elimination of fecal coliforms, E. coli, viruses, and total coliforms.  Enteric organism disinfection is achieved for bacteria and viruses via anodic reactive chlorine generation from in situ chloride coupled with cathodic reduction of water to form hydrogen. Improvement of the performance and durability of the core semiconductor anodes along with materials modifications to lower their production costs ongoing. Third-generation prototypes are undergoing field-testing in locations that lack conventional urban infrastructure for wastewater discharge and treatment; the packaged treatment systems can operate without an external source of electricity or fresh water.  Two Caltech-China joint-venture companies, Eco-San and Entrustech, have been established in Yixing, Jiangsu Province to manufacture solar units for the developing world and to provide associated biochemical and electrochemical reactor systems. Additional industrial collaborations have been established in India with ERAM Scientific and with the Kohler Company (USA/India) for production of units to be used in urban and peri-urban environments in India. At the current time, larger-scale systems (> 1000 users/day) are being assembed for use in South Africa, Peru, Southern China, and Cambodia.  In late 2017, President Xi Jinping lauched the “Chinese Toilet Revolution“ to provide improve public toilets throughout China.


September 17 (Monday)

9:30-11:20 am


Room 121, Mingjing Building, Siping Campus, Tongji University, No. 1239 Siping Road, Yangpu District