During the wastewater treatment process in food factories, sludge, waste oil, waste acid, waste alkali, and animal and plant waste generated during processing must also be treated to be non-hazardous. Food processing wastewater mainly originates from three production sections.

(1) Raw Material Cleaning Section. A large amount of sand and debris, leaves, leather, scales, meat, feathers, and hair enter the wastewater, resulting in a high concentration of suspended solids.

(2) Production Sections. Many components of the raw materials are not fully utilized during the processing, with some entering the wastewater, which contains a large amount of organic matter.

(3) Forming Process. To enhance the taste, color, and aroma of the food, and to extend its shelf life, various food additives are used, some of which leak into the wastewater, making the chemical composition of the wastewater complex.

The water quality characteristics of food processing wastewater are mainly reflected in six aspects:

(1) Production varies with the seasons, as does the quality of the wastewater.

(2) The wastewater volume varies greatly across the food industry, ranging from small-scale household operations to various large factories. Product variety is extensive, and raw materials and processing scales differ significantly, with wastewater volumes ranging from several cubic meters per day (m3/d) to several thousand cubic meters per day (m3/d).

(3) Food industrial wastewater contains many degradable components. For general food industries, raw materials come from natural organic matter, and the composition of their wastewater is mainly natural organic matter, free of toxic substances, hence excellent biodegradability. BOD5/COD ratio is as high as 0.84.

(4) There's a lot of high-concentration wastewater.

(5) The wastewater contains various microorganisms, including pathogenic ones, and is prone to rot and produce odors.

(6) High nitrogen and phosphorus content in wastewater.