Research on Food Processing Wastewater
Update 2003

Karen Mancl, Professor Food, Agricultural & Biological Engineering, OSU
Olli Tuovinen, Professor Microbiology, OSU

The Department of Food, Agricultural & Biological Engineering at The Ohio State University has an ongoing research program on the treatment of food processing wastewater. Wastewater from meat and milk processing plants, restaurants and even dairy farm milking facilities are significantly different from domestic and municipal sewage. Food processing wastewater has four to ten times higher COD and BOD5 levels because of the presence of fats, oils and grease. These wastewaters are difficult to treat using conventional wastewater treatment systems or soil absorption systems.

The OSU research program is studying the treatment of cheese and turkey processing wastewaters through gravel/sand bioreactors. Properly designed and intermittently loaded, these laboratory-scale bioreactors remove over 99% of the COD, BOD5, suspended solids and fats, producing effluent suitable for permitted stream discharge.

Some of the initial research findings include:

• Gravel/sand bioreactors are "fail-safe" which means that if overloaded or neglected they back-up rather than discharge poorly treated wastewater. In this way the negligent operator is penalized, while protecting Ohio's environment.
• The media in the bioreactors are colonized by naturally occurring microbes from the wastewater and the soil. Over the first two weeks of bioreactor operation, the microbial inoculum develops a biofilm on surfaces of gravel and sand particles to achieve subsequent peak performance.
• Media selection is an important design criterion. Layers of clean, graded fine sand, coarse sand and pea gravel have shown the best performance.
• The loading rate is another important design criterion. For wastewater containing slowly biodegradable waste products such as fat, the COD loading rate must be carefully tested to ensure high treatment levels without clogging.
• Dosing is the third necessary design criterion. Dosing of up to three times per hour is beneficial in preventing overloading and clogging. Frequent dosing can be combined with increasing loading rates.
• Gravel/sand bioreactors are tolerant of
  • fluctuations of wastewater flow and BOD5 and fat concentration;
  • transient fluxes of cleaning agents used to sanitize food processing equipment;
  • periodic shut-downs of the facility -- in fact, periodic resting for a few weeks will restore the treatment capacity of a clogged bioreactor.