sábado, 27 de julio de 2013

Supercritical Sanitation Systems

ORIGINAL: Duke / U of Missouri

At supercritical water conditions, organics in sewage are converted to harmless carbon dioxide, clean water and energy in seconds.

Engineers at Duke University and the University of Missouri, with funding from the Bill & Melinda Gates Foundation, are investigating the potential of Supercritical Water Oxidation (SCWO) and Supercritical Water Gasification (SCWG) in helping solving the world’s sanitation challenges.

The team is designing and building a demonstration unit that fits into a 20 ft. shipping container and will be ready for testing in a developing country in 2014.

Neighborhood-Scale Sewage Treatment. Image: Duke

Project Overview

A Shared Vision

According to the World Health Organization, “2.4 billion people do not have access to any type of improved sanitation facility. About 2 million people die every year due to diarrheal diseases; most of them are children less than 5 years of age.[i] The United Nation’s Millennium Development Goals Report from 2012 states that “sanitation coverage increased from 36 per cent in 1990 to 56 per cent in 2010 in the developing regions as a whole. Despite progress, almost half of the population in those regions … still lack access to improved sanitation facilities.[ii] As sanitation goals remain out of reach, the associated health hazards and poor living conditions persist.

Unfortunately, established sewage system standards in developed countries do not provide a feasible model for developing countries which do not have sewage infrastructure, lack the economic means to build and sustain such elaborate systems, and do not have the water required to operate them. Resolving the sanitation issue in developing countries will require new, innovative sanitation solutions.

The Water, Sanitation and Hygiene program of the Bill & Melinda Gates Foundation has identified the sanitation challenge as their top priority. The foundation fosters the development of new technologies and tools that can help deliver sustainable sanitation where it is needed. As part of this strategy it is funding numerous investigations into a wide variety of potential technologies by universities and commercial entities worldwide. In April, 2013, Duke University received a ‘Reinvent the Toilet Challenge’ grant from the Gates Foundation to develop a demonstration unit for community scale sewage treatment.

Our Project
The Gates Foundation diagram above depicts a sanitation solution that starts with the individual and the toilet, includes the storage, transportation and treatment of human waste, and ends, ideally, with safe, usable byproducts such as fertilizer, fuel or clean water. Engineers at Duke University and the University of Missouri are designing a unit that addresses the treatment of human waste and possible reuse of the system’s byproducts. It will sanitize the collected waste of approximately 1200 people—a neighborhood-scale solution. The goal of this project is to produce a demonstration unit that fits into a 20 ft. shipping container and will be ready for testing in a developing country by summer 2014. A successful design will have a running cost of less than 5 cents per person per day at commercial volumes.

The technology being employed to meet this challenge, supercritical water oxidation (SCWO), is promising because it works quickly and generates energy in the forms of hot water and steam from the treatment of human waste. Furthermore, it does not require prior dewatering or drying of fecal sludge, and it effectively eliminates all types of harmful organisms. SCWO technology has already been implemented in several research and commercial applications to treat waste products, including polychlorinated biphenyls (PCBs), chemical weapons and sewage sludge. Duke and the University of Missouri seek to demonstrate that both SCWO and supercritical water gasification (SCWG), a related technology, have prominent roles to play in solving the world’s sanitation challenges. In addition, we will produce a business model plan that quantifies and optimizes the economic, environmental and social benefits of the unit.

Our Team

Before and after pictures from a SCWO unit
at University of Missouri.
The project is being led by Marc Deshusses of Duke University’s Department of Civil and Environmental Engineering in collaboration with Jay Golden of Duke’s Center for Sustainability and Commerce. The Carbon Recycling Center, led by Bill Jacoby of the University of Missouri’s Biological Engineering Department, provides engineering expertise where the rubber meets the road. Some of the key challenges the team will be addressing include the corrosion associated with sewage at high temperature and pressure as well as designing a system that can be successfully operated in a low-tech environment. In parallel with the technology development, sustainability experts at Duke will be leading the environmental and socio-technological investigations of the value proposition and creating a business model for the sanitation solution. Throughout the project, existing research and first hand site visits to cities and neighborhoods in India, South Africa and possibly Ghana will be utilized to help inform the optimum design of the sewage treatment unit and lay out the best path toward commercial implementation.
Our Timeline
The experimentation and design phase, using process development units at Missouri, will take place in the spring and summer of 2013. Construction of the demonstration unit in an actual shipping container will take place at Duke in the late summer and fall of 2013. In the winter and early spring of 2014, the demonstration unit will be tested at a local sewage treatment plant near Duke University in North Carolina. By summer 2014, the unit should be ready for field testing in a chosen city in South Africa, India or Ghana.

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