Research developments

Mixed-waste processing could increase recycling and waste diversion rates

A new report that looks at processing mixed waste to extract recyclables finds potential to significantly increase recycling rates for certain materials as well as diversion rates for municipal solid waste (MSW), primarily because of improvements in processing technologies, such as optical sensors for plastics.

The report, “The Evolution of Mixed Waste Processing Facilities,” 1970-Today, by Gershman, Brickner & Bratton Inc. (GBB) of Fairfax, Virginia, notes that mixed-waste processing (MWP) facilities use a variety of technologies to separate recyclables from MSW.

In a review of evolving technologies, the study’s authors recount how MWP facilities initially were designed to capture high-energy elements from the waste stream for combustion-based energy recovery (also referred to as waste-to-energy). However, today MWP is attracting renewed interest as a means to boost recycling rates. This is important because even after many residents have separated their recyclables, the average MSW stream may contain up to half of the total volume of recyclables and, in some cases, more.

Technological advances make today’s mixed-waste processing facilities “different and in many respects better” than older versions, the report’s authors say, which could enable communities to recycle at much higher rates than under existing collection systems, the study says.

The authors conclude, “Based on its roots in single-stream sortation, today’s MWP technology appears promising. The results in terms of outputs, net revenue and reduced collection costs could be attractive for some communities.

The combination of recycling with energy recovery for nonrecycled materials is an excellent approach to managing post-use materials more sustainably.”

The report also identifies outstanding issues that need to be addressed to achieve these improvements. The authors also suggest that coupling MWP facilities with existing large material recovery facilities (MRFs) could help communities increase diversion rates.

“The potential exists to divert 180 percent more high value metals and plastics from landfill than are diverted today,” the report states.

The report was commissioned by the Plastics Division of the American Chemistry Council (ACC), Washington.

Belgian researchers turn sawdust into gasoline components

Researchers at Belgium-based KU Leuven’s Centre for Surface Chemistry and Catalysis report they have successfully converted sawdust into building blocks for gasoline. Using a new chemical process, researchers say they have been able to convert the cellulose in sawdust into hydrocarbon chains, which are used as an additive in gasoline, or as a component in plastics. The researchers reported their findings in the journal Energy & Environmental Science.

Cellulose is the main substance in plant matter and is present in all nonedible plant parts of wood, straw, grass, cotton and paper.

“At the molecular level, cellulose contains strong carbon chains,” explains Professor Bert Sels. “We sought to conserve these chains, but drop the oxygen bonded to them, which is undesirable in high-grade gasoline. Our researcher Beau Op de Beeck developed a new method to derive these hydrocarbon chains from cellulose.”

“This is a new type of biorefining, and we currently have a patent pending for it,” says Dr. Bert Lagrain. “We have also built a chemical reactor in our lab: We feed sawdust collected from a sawmill into the reactor and add a catalyst—a substance that sets off and speeds the chemical reaction. With the right temperature and pressure, it takes about half a day to convert the cellulose in the wood shavings into saturated hydrocarbon chains, or alkanes.”

Lagrain says, “Essentially, the method allows us to make a ‘petrochemical’ product using biomass—thus bridging the worlds of bioeconomics and petrochemistry.”

The result is an intermediary product that requires one last simple step to become fully distilled gasoline, explains Sels. “Our product offers an intermediate solution for as long as our automobiles run on liquid gasoline. It can be used as a green additive—a replacement for a portion of traditionally refined gasoline,” he says.

But the possible applications go beyond gasoline: “The green hydrocarbon can also be used in the production of ethylene, propylene and benzene—the building blocks for plastic, rubber, insulation foam, nylon, coatings and so forth.”

“From an economic standpoint, cellulose has much potential,” says Sels. “Cellulose is available everywhere; it is essentially plant waste, meaning it does not compete with food crops in the way that first generation energy crops do. It also produces chains of five to six hydrocarbon atoms.”