When Pacific Biodiesel Technologies’ Big Island Biodiesel refinery came online last year, it was marketed as a state-of-the-art, zero-waste plant. The facility, scaled at 16,000 gallons a day, was Hawaii’s first since 2000 and boosted the state’s capacity by 500 percent. The phrase “zero waste” has gained popularity over the past year, perhaps as a result of Pacific Biodiesel’s marketing efforts, or maybe simply because it’s part of industry maturation to evolve beyond the inefficiencies of its legacy refineries. The term, however, means different things to different people.

To Will Smith, engineering manager at Pacific Biodiesel responsible for process technology design and implementation at Big Island Biodiesel, being a zero-waste plant is not necessarily about being green or sustainable—although those attributes come as a nice added benefit. To him and others, it’s purely economical.

“Zero waste means we’ve made the necessary capital investments to eliminate all of the traditional waste products that can come out of a biodiesel process,” Smith says. And depending on the feedstock utilized at a particular plant, there can be a multitude of varying waste streams generated from virtually every stage of the process. Smith documented all possible waste streams from biodiesel processing and has developed a matrix he shared with Biodiesel Magazine identifying uses of those side stream waste products, from most to least favorable.

Feedstock refining or pretreatment produces several waste streams. If the plant is processing used cooking oil (UCO), there are wastewater and solids to contend with. The most favorable use of wastewater and solids from pretreatment of UCO, according to Smith, is anaerobic digestion, followed by composting and landfilling. Gums and foots are a side stream of oil degumming practices, and lecithin upgrading is preferred over selling direct to the feed market or, lastly, landfilling. Also, soapstock from caustic refining, spent bleaching clay and deodorizer distillate are more potential wastes generated from feedstock refining or pretreatment. The best route for soapstock would be to split to acid oil and esterify to biodiesel; second is direct sale of acid oil to feed markets. The clay can be composted or landfilled. Lastly, the best option for deodorizer distillate is selling for vitamin E recovery, or sold directly to feed markets.

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