If you live with in-house plumbing and year-round access to electricity, it can be easy to take these conveniences for granted as a standard aspect of life. However, nearly 1 billion people worldwide lack access to electricity. Over 4 billion people—60 percent of the world's population—do not have access to toilets and related sanitation infrastructure.
In modernized First World countries, infrastructure such as sewage lines and waste treatment facilities are the primary sanitization efforts. However, highly populated areas in Third World countries without this infrastructure experience over 800,000 child deaths every year.
Fortunately, innovations are underway that can provide solutions to improper sanitation methods. For example, in 2011, the Bill and Melinda Gates Foundation established a global competition to ‘Reinvent the Toilet’. This initiative gathered the world's inspired minds to solve the difficult problem of bringing safe sanitation methods to communities that lack plumbing infrastructure. Amid the variety of creative solutions, two top contenders utilized solar energy and high-efficiency electronics to help solve the problem.
Solar waste management: Seva sustainable sanitation project
This sanitization technology out of the California Institute of Technology utilizes solar panels to charge a battery system that powers an electrochemical reactor. The reactor sanitizes contaminated water and sewage. The Seva system relies on two sections that separate and sanitize human waste—a first-stage septic system and a second-stage electrochemical reactor that treats the water.
The sewage collection tank is the first step of the treatment process, where sedimentation of the solid matter occurs and anaerobic digestion by bacteria acts as a pretreatment. The byproduct of the solid matter digestion process can be safely used as fertilizer.
Then, the supernatant of the septic tank flows into a solar-powered electrochemical reactor that oxidizes human waste on an anode, while water is reduced to hydrogen at the cathode. Chloride from table salt is oxidized in this reaction to form chlorine, which is used to sanitize and treat the water. The prototype of this system is able to treat five gallons of water in less than four hours, creating sanitized water that can be reused in the toilet system or for other water needs.
The critical component that makes this sanitizing solution unique is the electrochemical reactor that relies on solar-generated electricity to initiate the sanitization process. Without the electricity harvested using the photovoltaic solar panels, the electrochemical reactor would be rendered useless. However, the electrochemical reactor is not the only component in the system that utilizes solar energy. To uphold maintenance and system continuity, the Seva project also employs a variety of low-power sensors to monitor its sanitization process and notify technicians of any notable failures via SMS. As with the electrochemical reactor, all of the maintenance notification electronic subsystems utilize solar energy.
Solar toilet design
The University of Colorado Boulder’s contribution to the “Reinvent the Toilet” challenge has received nearly $2 million in funding. This solar energy-harvesting toilet also relies on the sun’s energy to sanitize waste. Its elegant solution concentrates a large amount of solar energy onto a postage-stamp-sized surface area, rather than using traditional PV solar generators.
Using eight parabolic mirrors, solar energy is focused onto quartz rods to capture nearly 2000 times the amount of high-energy solar flux of a standard object of the same size. The quartz rods then transmit this concentrated solar energy through fiber optic cables to a pyrolysis reactor that can reach temperatures of over 300°C using only direct illumination—think burning leaves with a magnifying glass.
Each of the eight parabolic mirror and fiber optic cable assemblies is able to produce between 80 and 90 Watts, enabling the delivery of over 700 Watts to the reaction chamber. This amount of energy is enough to process the waste of up to six people in only four hours. To process the urine, which is separated in the toilet from the fecal matter, a simpler solar water heater is used to heat the urine to over 70°C, which is a high enough temperature to sterilize the urine for future use.
High temperatures in the pyrolysis reactor allow for direct elimination of bacteria and pathogens found in fecal matter. Arguably the most unique advantage of this solar energy-powered system, however, is the byproduct produced in the pyrolysis reactor: biochar.
Biochar toilet: innovative future of sanitation
Karl Linden, a professor of environmental engineering and the Sol-Char project’s principal investigator, states that a soil mixture containing only 10% biochar can hold up to 50 percent more water and increase the availability of plant nutrients. Biochar can also be burned as charcoal and provides energy similar to commercially available charcoal. With the use of various motors and actuators, Sol-Char is able to cycle through which reactor is being used and being processed. This continuous production of biochar and collection of to-be sanitized waste proves Sol-Char to be highly innovative on two largely complex global issues.
Solar energy is regarded as one of the cleanest, most impactful forms of energy on the planet. Projects such as Seva and Sol-Char continually push the bounds of technology and revolutionary problem solving. Initiatives like "Reinvent the Toilet" help to drive technologies such as new forms of solar energy harvesting, put to work in ways the world has never seen before.