How to Treat Food Industry Wastewater? Common Process Methods
The nature of wastewater is the comprehensive characteristic exhibited by a complex system composed of water and various impurities, expressed through water-quality indicators. Water-quality indicators can be divided into physical, chemical, and biological indicators. Each indicator represents the type and quantity of impurities in water and can be used to judge water quality and whether discharge standards are met. In wastewater treatment, determining the treatment level, selecting the process flow, and designing and operating the treatment process all require a full understanding of wastewater nature; otherwise good results cannot be achieved. The main wastewater quality indicators are as follows.
The physical indicators of wastewater mainly include temperature, color, odor, and solid content; the two commonly tested are colority and solid content.
1. Colority: Food industry wastewater often contains organic or inorganic dyes, biological pigments, inorganic salts, and organic additives that color the water, sometimes very deeply. In water-quality analysis, the indicator for water color degree is colority. Generally, the true color after removing suspended solids is used as the standard, obtained by comparing an unknown sample with a known-concentration standard colored solution using a colorimetric method.
2. Solid content: Most impurities in wastewater are solid substances existing in dissolved or suspended form; the sum is called total solids, including organic compounds, inorganic compounds, and various organisms. In water-quality analysis, besides total solids, indicators such as suspended solids, volatile suspended solids, and dissolved solids are also measured.
(1) Total solids (TS): the residue of a certain volume of water sample dried at 105-110 C in water-quality analysis, expressed by weight.
(2) Suspended solids (SS): the portion of total solids in suspended state, containing both organic and inorganic components.
(3) Volatile suspended solids (VSS): the weight loss of suspended solids after ignition at 600 C, representing the organic portion of suspended solids, part of which is biodegradable suspended solids (BVSS) and part non-biodegradable (NBVSS).
(4) Non-volatile suspended solids (NVSS): the residue after igniting suspended solids, also called ash, representing the inorganic portion of suspended solids.
(5) Dissolved solids (DS): the portion of total solids existing in dissolved state, obtained by filtering a certain volume of water sample, drying, and weighing the filtrate.
The food industry uses a wide range of raw materials and produces many product types, so the volume and quality of discharged wastewater vary greatly.
(1) Solid substances floating in wastewater, such as vegetable leaves, fruit peels, meat scraps, and poultry feathers
(2) Substances suspended in wastewater, such as grease, protein, starch, and colloidal matter
(3) Acids, alkalis, salts, and sugars dissolved in wastewater
From the perspective of polyacrylamide selection for food-wastewater sludge dewatering, a medium cationic PAM is generally chosen, which is similar to the treatment of the biochemical sludge from domestic sewage treatment plants. We know that sewage from domestic plants also has relatively high organic content, mostly from our daily catering wastewater, fecal wastewater, and bathing wastewater. In terms of source-structure complexity, it is quite similar to food wastewater. [1]
The general characteristics of food industry wastewater are high organic matter and suspended solids, easy putrefaction, and generally low toxicity. Its harm is mainly eutrophication of water bodies, causing death of aquatic animals and fish, promoting odor from organic matter deposited at the bottom, degrading water quality, and polluting the environment.
Besides appropriate treatment according to water-quality characteristics, food industry wastewater generally should adopt biological treatment. Wastewater from food processing and manufacturing has high biodegradability, is rich in organic matter (carbon source), and is non-toxic, making it suitable as a supplementary carbon source for municipal sewage treatment plants to achieve resource utilization. For wastewater with large concentration fluctuations, pretreatment measures such as hydraulic screens and equalization tanks can be used for conditioning [5]. If very high effluent quality is required or the organic content is very high, two-stage aeration tanks or two-stage biofilters, multi-stage rotating biological contactors, a combination of two biological treatment devices, or an anaerobic-aerobic series biological treatment system can be used.
(4) Sand and other organic matter carried in with raw materials
In the field of sewage treatment, food industry wastewater, with its high biodegradability, rich organic matter (carbon source), and non-toxic nature, can serve as a supplementary carbon source for municipal sewage treatment plants. For example, Mengniu Dairy Wuhan Co., Ltd. sends 455,700 tons of annually collected wastewater, after pretreatment, as a carbon-source supply to the nearby Jinyinhu Sewage Treatment Plant. Similar applications are also seen in beer, liquor, and sugar industries. The 'Discharge Standard for Water Pollutants from Food Processing and Manufacturing' (GB 46817-2025), effective January 1, 2026, provides policy support for such practices, allowing food processing manufacturers to negotiate indirect discharge with sewage treatment plants. This collaborative treatment model, while reducing enterprise treatment costs, can also cut carbon emissions by nearly 400 tons per year [5].
Food industry wastewater is rich in carbon source and suitable as a supplementary carbon source for sewage treatment plants to reduce carbon emissions. According to a 2026 case calculation, Mengniu Dairy Wuhan Co., Ltd. reduces carbon emissions by nearly 400 tons per year by converting wastewater into a carbon source. [5]
