When diners at the National University of Singapore’s Raffles Hall toss out their food scraps, they join the vanguard of environmental sustainability. By composting unwanted food, the students take the first step to generate power that will eventually charge their cell phones.
Confused? Here’s how the energy is created: The Raffles Hall discarded food scraps are fed through an onsite, anaerobic bio-digester. Once the leftovers are placed in a bin, the automated system works like a biochemical stomach, breaking down organic matter into bio-gas.
The bio-gas is then converted into heat and electrical energy that keeps the bio-digester running. That power operates the lights, fans, the control computer, and pumps. Remaining electricity is directed toward an on-campus charging station, which allows students to plug in and power up their phones for free.
The bio-digester also produces a nutrient-dense substance, which can be converted into fertilizer. NUS’s waste-to-energy system is the brilliant design of associate professor Yen Wah Tong from the department of chemical and biomolecular engineering and research fellow Jingxin Zhang from the Environmental Research Institute.
This promising use for food waste is far more efficient than the alternative: sending scraps to a landfill for incineration.
Waste management is an urgent issue in Singapore. Forecasters expect the island nation’s only landfill will reach capacity in 20 years. Food waste has also increased 40 percent over the last decade. Currently, only 16 percent of all food waste is recycled.
NUS’s bio-digester also serves an additional purpose: raising awareness around food waste and renewable energy.
By charging phones, we’re advertising this type of utilization of food waste and encouraging people to think differently about waste.
— Yen Wah Tong
“We wanted to highlight a more public use of this electricity,” says Tong. “By charging phones, we’re advertising this type of utilization of food waste and encouraging people to think differently about waste.”
Singapore is one of many places exploring waste-to-energy (WTE) technologies, as refuse management is a worldwide concern. An estimated 800 industrial-scale WTE plants are currently in use across three dozen or so countries, converting municipal solid waste to energy via anaerobic digesters, which function much like the biodigester in Raffles Hall.
In the United States, there are more than 70 biodigestion plants, but many of the current WTE locations use various types of garbage.
In New York City, former Mayor Michael Bloomberg called food waste the city’s “final recycling frontier.” The Newtown Creek Wastewater Treatment Plant in the borough of Brooklyn -- one of the few large-scale efforts in the U.S. to add food waste into bio-digester plants -- has been adding edible garbage to a handful of egg-shaped bio-digester tanks since 2012.
The addition of the food waste boosts the plant’s methane gas production by approximately 17 percent. A portion of this bio-gas provides heat for the boilers at the plant. Plans are in the works to funnel the bio-gas energy to homes of area customers of National Grid, a utility company.
While few anaerobic digestion systems are designed exclusively for edible waste, food scraps have become increasingly recognized as a viable power source. According to research scientist Roy Posmanik of Israel’s Institute of Soil, Water and Environmental Science, a major appeal of converting food scraps to energy is basic efficiency, particularly in comparison to animal manure.
If you think of the cow itself as some kind of bio-digester, the animal fails to digest these fibers; so, it will be more challenging to engineer that digestion in a bio-digester.
— Roy Posmanik
“Using food waste is easier and faster than manure,” says Posmanik, currently a visiting scholar at Cornell University. The polymers that are dominant in all food scraps, including pulp and non-edible materials, are far more biodegradable than lignocellulosic material, which is biomass found in straw and other animal feed. “If you think of the cow itself as some kind of bio-digester, the animal fails to digest these fibers; so, it will be more challenging to engineer that digestion in a bio-digester.”
One reason food waste isn’t more popular as a renewable energy source, Posmanik thinks, is logistics. When a bio-digester produces bio-gas, an additional compartment is required to convert it into heat or electricity. Natural gas prices are also low in the U.S., making it harder for such regenerative technologies to compete. Posmanik observes that higher incentives from the government, such as reducing greenhouse gas emissions and recovering renewable resources, could result in a higher application.
Still, Posmanik is optimistic about the future: “There are lots of opportunities in this world of waste-to-resource.”
Tong and Zhang agree. Since installing the bio-digester at Raffles Hall their project has expanded to two more cafeterias. The green-friendly school is renovating a handful of cafeterias that will have infrastructure for future biodigesters.
In September, the team will partner with the National Environment Agency to bring biodigesters to “hawker centers,” which are small, affordably priced cafeterias located around Singapore. Tong also sees an opportunity to bring the concept to the regional market in South East Asia, rural areas that need food waste solutions, and beyond.
As Posmanik notes, “Food waste is a problem everywhere.”
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