Introduction to Food Industry Wastewater Treatment Methods
The nature of wastewater refers to the combined characteristics exhibited by a complex system composed of water and various impurities, and these characteristics are expressed through water quality indicators. Water quality indicators can be divided into physical indicators, chemical indicators and biological indicators. The various indicators can express the type and quantity of impurities in the water and can be used to judge whether the water quality is good or poor and whether discharge standards are met. In wastewater treatment, determining the degree of treatment and selecting the process flow, as well as designing the treatment process and managing its operation, all require a full understanding of the nature of the wastewater; otherwise good results cannot be achieved. The main water quality indicators of wastewater are as follows.
The physical indicators of wastewater mainly include temperature, colour, odour and solids content, of which chromaticity and solids content are the two most commonly measured.
1. Chromaticity. Food industry wastewater often contains organic matter or inorganic dyes, biological pigments, inorganic salts and organic additives that colour the wastewater, sometimes very deeply. In water quality analysis, the indicator used to measure the degree of colour is chromaticity. Generally, the true colour after the removal of suspended solids is taken as the standard, and colorimetric analysis is used to compare the colour of a standard coloured solution of known concentration with that of a water sample of unknown chromaticity in order to obtain the result.
2. Solids content. Most of the impurities contained in wastewater are solid matter, which exists in the water in dissolved or suspended form; together these are known as total solids and include organic compounds, inorganic compounds and various organisms. In water quality analysis, besides measuring total solids, several other indicators must also be measured, such as suspended solids, volatile suspended solids and dissolved solids.
(1) Total solids (TS) refers to the residue remaining after a given quantity of water sample is dried at 105-110 degrees Celsius in water quality analysis, expressed by weight.
(2) Suspended solids (SS), or suspended matter, is the portion of total solids in a suspended state; it contains both organic and inorganic components.
(3) Volatile suspended solids (VSS) is the weight loss of suspended solids after ignition at 600 degrees Celsius and represents the organic fraction of suspended solids. Part of it is biodegradable suspended solids (BVSS) and part is non-biodegradable (NBVSS).
(4) Non-volatile suspended solids (NVSS) is the residual portion of suspended solids after ignition, also known as ash, and represents the inorganic fraction of suspended solids.
(5) Dissolved solids (DS), or dissolved matter, refers to the portion of total solids present in a dissolved state; it is obtained by drying and weighing the filtrate of a given quantity of water sample.
The food industry uses a wide range of raw materials and produces many kinds of products, so the volume and quality of the wastewater discharged vary greatly.
(1) Solid matter floating in the wastewater, such as vegetable leaves, fruit peel, meat scraps and poultry feathers;
(2) Substances suspended in the wastewater, such as fats and oils, proteins, starch and colloidal matter;
(3) Acids, alkalis, salts and sugars dissolved in the wastewater;
(4) Silt and sand carried in with raw materials, along with other organic matter.
The general characteristics of food industry wastewater are a relatively high content of organic matter and suspended solids, a tendency to putrefy and, in general, low toxicity. Its main harm is that it causes eutrophication of water bodies, which can lead to the death of aquatic animals and fish, promote the generation of odours from organic matter deposited on the bottom, degrade water quality and pollute the environment.
Apart from appropriate treatment based on the characteristics of the water quality, biological treatment is generally suitable for food industry wastewater. Wastewater from the food processing and manufacturing industry is highly biodegradable, rich in organic matter (a carbon source) and non-toxic, which makes it suitable as a supplementary carbon source for municipal wastewater treatment plants and enables resource utilisation of the wastewater. For wastewater with large concentration fluctuations, pretreatment measures such as hydraulic screens and equalisation tanks can be installed for regulation [5]. If the requirements on effluent quality are very high, or if the organic content of the wastewater is very high, two-stage aeration tanks, two-stage biological filters or multi-stage rotating biological contactors can be used, or two biological treatment units can be used in combination; an anaerobic-aerobic series biological treatment system is also an option.
In the field of wastewater treatment, food industry wastewater, being highly biodegradable, rich in organic matter (a carbon source) and non-toxic, can serve as a supplementary carbon source for municipal wastewater treatment plants. For example, Mengniu Dairy (Wuhan) Co., Ltd. collects 455,700 tonnes of wastewater each year and, after pretreatment, sends it as a carbon source supplement to the nearby Jinyinhu wastewater treatment plant. Similar applications are also found in the beer, baijiu and sugar industries. The Discharge Standard of Water Pollutants for the Food Processing and Manufacturing Industry (GB 46817-2025), implemented on 1 January 2026, provides policy support for such practices, allowing food processing and manufacturing enterprises to negotiate indirect discharge with wastewater treatment plants. This collaborative treatment model reduces treatment costs for enterprises while also cutting carbon emissions by nearly 400 tonnes per year [5].
In terms of selecting polyacrylamide as a sludge dewatering agent for food wastewater, a medium-cationic polyacrylamide is generally chosen. This is fairly similar to the treatment of biochemical sludge at domestic sewage treatment plants: we know that the sewage at domestic treatment plants also has a relatively high organic content, and most of it comes from the catering wastewater, faecal wastewater and bathing wastewater of daily life. In terms of the complexity of the wastewater source structure, it is very similar to food wastewater. [1]
Food industry wastewater is rich in carbon sources and is suitable as a supplementary carbon source for wastewater treatment plants, thereby reducing carbon emissions. According to calculations from a 2026 case study, Mengniu Dairy (Wuhan) Co., Ltd. can cut carbon emissions by nearly 400 tonnes per year by converting its wastewater into a carbon source. [5]
