BioCycle October 2003, Vol. 44, No. 10, p. 42
Anaerobic technology systems can offer two valuable by-products to companies that generate large volumes of high concentrated carbohydrate waste.
Steven Van Ginkel
IN the United States, the food processing industry is a $600 billion dollar industry with a total of about 20,000 companies. Major food processing states range from Iowa through the Midwest to Pennsylvania, Idaho and California. Besides animal wastes, carbohydrates are the major components of these wastes. Processing of corn, apples, potatoes, sugar beets, etc. produce high concentrations of waste starch and sugar that must be treated.
For example, a potato chip manufacturer in Pennsylvania recovers 98 percent of the waste starch that is produced from cutting a potato into a chip. The large waste potato pieces are sold as animal feed and may soon become hash browns, while the small, particulate starch is given to a paper company that needs starch for its paper making process. The two percent of the remaining waste goes to an aerated treatment system. Aeration enables bacteria that breathe oxygen to degrade the waste. Ideally, this waste should go to an anaerobic H2/CH4 bioreactor system to recover this chemical energy as high value gases which subsequently would be sold or turned into electricity via fuel cells.
Other companies in Pennsylvania that produce large volumes of highly concentrated carbohydrate waste include apple processors and candy manufacturers. The apple processor treats its waste using aerobic lagoons – a pond with floating devices that force air into the pond to keep the bacteria that degrade the apple waste breathing. The candy manufacturer sends its waste into the sewer system and when they go over their discharge limit, they get fined thousands of dollars each month.
The common denominator among food processing wastewater treatment systems is aeration, although anaerobic treatment systems are increasing in number. Aerobic bacteria are very good at degrading waste, yet aeration is expensive. In fact, aerobic bacteria are so good at degrading the waste that up to 50 percent of the waste becomes more bacteria that in itself presents a disposal problem as ‘sludge’ or biosolids.
This is where anaerobic bacteria offers a breath of fresh air – they don’t need any air. Anaerobic technology, also called fermentation, uses bacteria that don’t breathe oxygen but turns waste into high-energy products such as hydrogen and methane gases. Because these bacteria release high-energy products, only about 10 to 15 percent of the waste becomes new bacteria. This is about one-fifth of the sludge that is produced from an aerated system.
The latest wave of anaerobic technology to treat high strength food processing wastes has been the upflow anaerobic sludge blanket reactors (UASB) and the expanded granular sludge bed reactors (EGSB). These systems have a reactor configuration that highly concentrate the bacteria (biomass) enabling the system to treat a high volume of waste, to be small in size, and therefore have a small capital cost.
Traditional anaerobic treatment systems produce only methane as their high-energy/high value by-product. Our system at BioH2Energy, Inc. produces exclusively hydrogen and carbon dioxide gases in the ratio of 60 percent H2 to 40 percent CO2. The soluble products are exclusively acetic acid and butyric acid which are the precursors to methane production.
Basically, here is how the system works. We go to an agricultural field and take a soil sample. We then bake the soil at 100°C for two hours to kill all nonspore forming hydrogen-consuming bacteria that selects for spore forming hydrogen producing bacteria. Bacterial spores are one of the most resistant forms on earth so this ‘heat shock’ process does not kill them. We then take the ‘sterile’ spore/sand mixture and use this to inoculate our batch or chemostat tests. We have used six different food processing wastewaters and domestic wastewater in our batch tests. We usually take about 250 mL of the raw wastewater, add about a gram or two of the spore/sand mixture, adjust the pH to 5.5 with a buffer, add nutrients, and incubate. After about 24 hours, hydrogen gas is produced.
An important part of our process is the flocculant nature or our bacteria. They form dense clumps or granules that enable them to stay in the reactor no matter how fast we feed (and waste from) the system.
Steven Van Ginkel is in the Environmental Engineering Department of Penn State University and is a cofounder of BioH2Energy, Inc.
October 16, 2003 | General
ENERGY FROM FOOD PROCESSING WASTEWATER
BioCycle October 2003, Vol. 44, No. 10, p. 42