We should be converting toilet paper into electricity

We’re willing to bet that once you’ve used a roll of toilet paper for its intended purpose, you don’t really think about what else it could be used for. Now that could all be about to change, with Dutch scientists having published the first techno-economic analysis of converting waste toilet paper into electricity.

Waste toilet paper (WTP) is a rich source of carbon, containing 70–80 wt% of cellulose on a dry basis. On average, people in Western Europe produce 10–14 kg waste toilet paper per person per year. Accumulating in municipal sewage filters, it is a modest yet significant part of municipal waste. In fact, Dutch wastewater treatment facilities pay around €70/ton to get rid of WTP.

WTP thus offers a great opportunity for closing loops, increasing resource efficiency and creating a circular economy. What’s more, since the cellulose in WTP comes from trees, the electricity produced is renewable. And unlike more unpredictable sources of renewable energy, such as solar or wind power, WTP is a continually available resource.

For chemists at the University of Amsterdam (UvA), the idea of using WTP as a resource for generating electricity was the ultimate waste recycling concept. UvA professors Gadi Rothenberg and Bob van der Zwaan thus proposed a simple two-step process for the conversion of WTP, partnering with colleagues from Utrech University to create a direct route from unwanted waste to a useful product.

Utrech master’s student Els van der Roest examined the possibility of combining devices for the gasification of WTP (step 1) with high-temperature solid oxide fuel cells (SOFCs) able to directly convert the WTP gas into electricity (step 2). The goal was to assess the feasibility of such a WTP-to-electricity system at a scale of 10,000 tons of WTP per year — the average amount generated by the Amsterdam region — based on real-life parameter values.

Writing in the journal Energy Technology, the researchers presented the basic system design, as well as its electricity yield and overall efficiency, based on detailed mass and energy balance calculations. Data for their calculations was obtained in collaboration with Amsterdam waste-to-energy company Afval Energie Bedrijf (AEB).

The researchers found that the overall electric efficiency was 57%, similar to that of a natural gas combined cycle plant. The levelised cost of electricity (LCOE, a measure used for consistent comparison of electricity generation methods) was 20.3 c/kWh — comparable at present to residential photovoltaic installations.

The system’s capital costs were found to be relatively high, mainly due to the fuel cell investment costs, but were expected to decrease as the market for fuel cells develops. The operating costs were also relatively low, partly thanks to the high thermodynamic efficiency (ca. 70%).

The researchers expect learning effects could make their system more competitive in future, with an LCOE of about 11c/kWh. The project team thus concluded that there is a future in turning waste toilet paper into electricity.

“When we discuss these results with companies, people get very excited,” said Professor Rothenberg. But with no Dutch company or municipal authority currently willing to invest in further development, the team is now considering taking their concept abroad.

“We might see the first WTP-to-electricity plant being built in China,” said Professor Rothenberg.