Waste Not
TP, Organic Waste Could Become Sources of Clean Energy, Low-Carbon Building Materials

From used bathroom tissue to banana peels, researchers and innovators are fueling a sustainable future by giving new life to previously overlooked waste streams. While scientists in the Netherlands are tapping sludge from water treatment facilities to generate clean energy, Arup is using organic waste to generate low-cost, low-carbon building materials.

As if the idea of pee power wasn’t already odd enough, scientists at the University of Utrecht and the University of Amsterdam in the Netherlands have uncovered a way to convert used toilet paper into energy in a completely unexpected twist on the concept of remanufacturing.

To do this, researchers developed a two-step process in which used toilet paper — a product traditionally designed for single use — is reclaimed from the sludge at water treatment facilities, dried and heated to 900 degrees Celsius, at which time it is transformed into a gas. After moisture and materials such as tar and ash are removed from the gas, methane, carbon dioxide and carbon monoxide remain. Scientists then feed the resulting gases into solid-oxide fuel cells.

While the end product itself signals a significant step forward for low-carbon energy, the process of producing the fuel cell is also worth noting. The entire process is optimized for sustainability: Residual heat derived from the fuel cells is harnessed to dry out the next batch of toilet paper, essentially creating a closed-loop system. The system emits a sixth of the CO2 generated by a coal plant and is on par with other renewable energy sources in regards to emission levels.

According to the researchers’ findings, which are published in Energy Technology, the process allows for the capture of two to three times more electricity than simply burning the recovered toilet paper and, if employed at the regional level, could help water treatment facilities in the Amsterdam region reduce their energy expenditure for separating toilet paper from water by 40 percent.

The energy captured in the fuel cells could also be used to provide electricity to around 6,400 homes, however, price remains a hurdle. As a waste product, toilet paper is considered a negative cost and operating costs are also low thanks to the high thermodynamic efficiency of the process, but the current status of fuel cell technology prevents the system from being cost-effective. As the market for fuel cells develops, it is expected that these costs will decrease.

Meanwhile, bananas, potatoes and maize are poised to become the building materials of the future — at least if Arup has anything to say about it.

The construction industry is one of the largest consumers of raw materials globally. In the UK alone, the sector accounts for 60 percent of all raw materials consumed. In a new report, Arup envisages the use of organic waste streams to create low-cost, low-carbon building materials to establish a completely circular system in which building waste is fed back into the biological cycle at the end of its serviceable life.

In 2014, European agriculture and forestry produced over 40 million tons of dried organic waste, a number that continues to grow. While these organic materials could be incinerated to produce energy, Arup suggests that the same material could generate more value if used to make building materials such as bricks, insulation and partition boards — approximately €6 per kilogram as opposed to .85 Euros.

And the idea isn’t so far out there — Arup has already been making progress in this area, creating the SolarLeaf, the world’s first-ever façade system to cultivate micro-algae to generate heat and biomass, and BioBuild, the first self-supporting facade panel made from bio-composite materials.

Innovative manufacturing processes, such as 3D printing of biopolymers, have been critical in enabling the development of the concept and are increasingly becoming widespread. The report, ***The Urban Bio-Loop: Growing, Making and Regenerating***, sheds light on the potential of four main organic matter products already available: peanuts, rice, bananas and potatoes. While peanuts and rice husks are being used to produce low-cost materials such as partition boards and fillers, the fruit and leaves of bananas are being transformed into rugged textiles. The peel from potatoes can be cleaned, pressed and dried to create a low-weight, fire-resistant, water-repellent, insulating material and acoustic absorber.

“As one of the world’s largest users of resources we need to move away from our ‘take, use, dispose’ mentality,” said Guglielmo Carra, Materials Consulting Lead Europe at Arup. “There are already pockets of activity, with some producers making lower-CO2 building products from organic materials. What we need now is for the industry to come together to scale up this activity so that it enters the mainstream. An important step is to work with government to rethink construction codes and regulations to consider waste as a resource, opening up the opportunity to repurpose it on an industrial scale.”


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