Biochemical Oxygen Demand (BOD) and Nutrient Removal
from Food Processing Wastewater...

Technology Required...

The food processing industry seeks cost effective biological treatment technologies to remove organic matter (BOD) and nitrogen from food processing wastewater containing high levels of suspended solids and nitrogenous compounds.

Problem and Impact of Solution...

Enforcement of wastewater discharge regulations and escalating sewage surcharges have forced the food processing industry to look for cost effective technologies to provide pretreatment or complete treatment of their wastewaters. Historically, food processors located within or adjacent to the municipalities have relied on local publicly-owned treatment works (POTWs) for wastewater treatment and disposal. Increasingly, this option is becoming less available. Especially in the last five to ten years, due to increasing enforcement pressure to comply with wastewater discharge permits and dwindling federal grants for constructing new and upgrading existing POTWs, municipal and regional sewer authorities are applying more pressure upon industries to reduce their organic (BOD and COD) and solids loading to the sewers. Food processing wastewaters are particularly targeted because of the high BOD concentrations typically contained, especially high strength wastewaters with high levels of suspended solids, ammonia and protein compounds. Food processors are looking for cost effective and application specific treatment technologies to manage their wastewaters effectively.

Biological treatment uses microorganisms to remove organic solids and nutrients (nitrogen and phosphorus) from wastewaters. It is generally considered to be more cost effective in treating high organic strength wastewaters, such as food processing wastewater, as compared with physical and chemical treatment methods. The biological treatment systems include aerobic and anaerobic systems. The aerobic systems firstly applied to food processing wastewater include activated sludge, trickling filter, and oxidation ditch, and the anaerobic systems include anaerobic lagoons and continuously stirred tank reactor. Constant effort by industry and municipalities to reduce their energy consumption costs have led to increased interests in anaerobic treatment technologies. Anaerobic treatment is a low energy input treatment process that can substantially reduce the strength of a wide range of high and low organic strength wastewaters. In many cases, anaerobic treatment will yield a net surplus of energy during the treatment process in the form of biogas which contains between 60% and 70% methane by volume. Several types of high-rate anaerobic treatment processes have been developed. Application of these technologies for food processing industry is still in an infant stage and successful demonstrations are needed. Most of these systems are well suited for treating highly soluble wastes, but not for handling the wastewater containing high levels of suspended solids. Efficient treatment systems are sought to help food processors manage their wastewater effectively.

State of the Art...

Both anaerobic and aerobic technologies have been applied in treating food processing wastewaters. High rate anaerobic technologies currently available include continuously stirred tank reactor, anaerobic contact reactor, anaerobic sequencing batch reactor, anaerobic filter, upflow anaerobic sludge blanket, and anaerobic fluidized bed. Aerobic technologies include activated sludge, oxidation ditch, trickling filter, and sequencing batch reactor. In many cases, anaerobic and aerobic processes are combined into one treatment system. Anaerobic treatment is used for removing most of organic matter from the wastewater and aerobic treatment is used as a polishing step to further remove residual organic matter and also remove nutrients from the wastewater. Due to increased concerns of food and public safety associated with the disease-causing and pathogenic microorganisms that may be present in the wastewater, incorporation of thermophilic (55 - 60 degree C) treatment has become an important feature in designing a biological treatment system. Effective handling of high levels of suspended solids (> 2 %) in the wastewater is still a challenge for most of these current technologies. New treatment technologies with improved efficiencies and reduced cost are needed.

Technology Specifications and Constraints...

The technology must be of biological nature, and possesses the following advantageous features, low energy input, high BOD and nitrogen removal efficiencies, low operational and maintenance requirement, and low land area requirement for system installations. The treatment system must be able to easily handle high levels of suspended solids (> 2 %) contained in the wastewater. In addition, the capability of destroying disease-causing and pathogenic microorganisms is desired. The treatment system may utilize anaerobic or aerobic treatment principles or a combination.

The characteristics and generation rates of food wastewater are highly variable, depending on the specific types of food processing operations. Even within one food processing plant, the wastewater discharged from different unit operations may be different with respect to flow rates and compositions. The new technology should be easily adaptable to a variety of plant operations.