Dairy and milk industry wastewater treatment

The milk and dairy processing industry are one of the main industries in the world, so the wastewater treatment facilities of dairy factories have received more attention than before. Dairy and milk industry wastewater treatment is one of the most voluminous and polluted types of industrial wastewater. Dairy industry wastewater treatment has a complex process that requires a case-by-case investigation of the production unit, experience and expertise. Water plays a key role in milk processing. Water is used at every stage of the production line, including cleaning and washing, disinfection, heating and cooling. The water needs of this industry are very high, and the majority of the wastewater of the milk and dairy industries is obtained from the production processes. It has been estimated that the amount of wastewater produced is approximately 2.5 times greater than that of processed milk per unit volume, especially in cheese manufacturing industries. The amount and characteristics of wastewater largely depend on the size of the plant, the applied technology, the effectiveness and complexity of CIP procedures Good Manufacturing Practices (GMP), etc.

The main sources of dairy factory wastewater pollutants:

The main sources of sewage from dairy factories and milk industries are as follows:

• CIP production lines
• Washing milk production tanks and milk transport tanks
• Washing the floor of the production hall
• Washing production equipment
• Underwater boilers (it should not be mixed with the sewage of the factory.)

In all these washes, large amounts of water are used, and in some parts, detergents and disinfectant solutions are also used.

The volume of wastewater in milk and dairy industries:

Changes in the volume of wastewater in milk and dairy industries are very large, and the reason for that is the daily and hourly changes resulting from washing the equipment and floors of halls. The actual concentration of pollutant effluents from the dairy industry varies widely depending on the characteristics and capacity of the company, production technology, type of equipment used, amount of wastewater reuse, loss of raw materials, waste management, etc. One of the main factors in the volumetric loading of sewage treatment plants is the immediate discharge of the produced milk and the cleaning of milk trucks and pipelines or equipment at the end of each production cycle. In such cases, the volume of wastewater is greater than the production volume, so in some cases, the volume of wastewater discharge accounts for 70% of the amount of water consumed in the factory.

Qualitative characteristics of dairy and milk industry wastewater:

Based on the reference and experiences of the Water Industry Research Company, the volume and quality (contamination) of dairy and milk industry wastewater depends a lot on the following factors:

• Type of manufactured product
• Quality and age of the equipment used in production
• Production hall management

According to the table below, the quantity and quality of wastewater from the dairy and milk industries are as follows:

کمیت و کیفیت فاضلاب لبنیات و صنایع شیر

During several projects that the water industry research company designed and implemented, it is possible to estimate the range of quantity and quality of wastewater of production units and based on that, the initial design of the treatment plant system can be done.

Wastewater treatment of dairy and milk industries:

Dairy and milk industry wastewater mainly includes the following:

• Milk or milk products lost in technological cycles (spilt milk, spoiled milk, skimmed milk and pieces of curd)
• By-products of processing operations including milk and whey discharged into the sewage
• Pollutants from washing milk trucks, washing tanks and cans and washing equipment, bottles and floor
• Materials used in CIP methods, cooling and milk products
• Sanitary wastewater, operational problems and various additives used in production

Dairy wastewater treatment has a great impact on the environment, this requires the use of effective and cheap wastewater treatment methods that guarantee the preservation of the environment and water resources of the country. There are different strategies for treating dairy wastewater.

Wastewater treatment strategy of dairy and milk industries:

Dairy industries include turning raw milk into pasteurized milk, yoghurt, cheese, cream and butter, ice cream, milk powder and whey, lactose, condensed milk, and desserts. The general differences between these dairy products are due to the reuse of skimmed milk and whey (a by-product in cheese production) and the evaporation of free water from the coagulation of milk and whey powders. In order to eliminate or reduce the environmental damage resulting from the discharge of raw wastewater from milk and dairy industries into the environment, a variety of wastewater treatment systems for milk and dairy industries including the use of mechanical, physicochemical and biological methods are used. Mechanical operation is necessary to equalize volume and mass flow changes. It also reduces portions of suspended solids. Physicochemical processes are effective in removing emulsified compounds, but the addition of coagulants increases treatment costs. Therefore, biological wastewater treatment systems are preferred due to the removal of highly biodegradable pollutants and low costs in management and operation. Therefore, the wastewater treatment strategy of the dairy and milk industries in the design of the wastewater treatment system should include the following:

• Reducing operational costs
• Reducing the area occupied by the treatment plant
• Low maintenance cost and ease of management
• Obtaining environmental standards based on irrigation of green spaces and agriculture

Dairy factory wastewater treatment process:

The wastewater treatment process of the dairy factory is relatively complicated due to the high organic load of this type of wastewater and includes the following steps:

Mechanical purification

The mechanical treatment removes suspended solids from wastewater. Conventional mechanical methods do not reduce the organic load sufficiently due to the low concentration of settle able solids in dairy wastewater. However, the faster the wastewater is screened, the better because of less TSS biodegradation and lower soluble COD increases. High changes in dairy effluents can cause instability in subsequent treatment facilities. Adequate equalization smoothest flow fluctuations, organic loading, pH and temperature changes, neutralizes residual detergents, and completely eliminates excess oxidizers. In practice, a 24-hour flow pattern at the highest load can be effectively controlled by equalizing or in other words balancing the effluent for at least 6 to 12 hours of effluent.

Physicochemical treatment

The physicochemical treatment destroys and reduces colloidal particles of milk fat as well as protein in dairy factory wastewater. Their removal is a major problem in skimmed milk factories, milk and whey separation, cheese and butter production, as well as milk bottling. Production of skim milk rarely causes such problems. Animal fat is solid at room temperature due to the high content of saturated fatty acids in its composition. Milk fat is no exception to this rule. This physical state, together with the low density of fat, allows it to be easily removed from the wastewater surface. If the balancing unit is before the degreaser, the resulting temperature drop increases the risk of fat accumulation on top of the liquid. Otherwise, the balancing unit must have enough volume to collect the peak output current.

Generally, flow balance is followed after FOG removal. Increasing the temperature of wastewater can reduce the ability to separate fat. Flotation with dissolved air has a great effect on the colloidal instability of protein and fat with the addition of coagulants such as Al2(SO4)3, FeCl3 and FeSO4 and flocculants. However, this method requires expensive and synthetic chemicals, which cause environmental problems and remove soluble substances to a lesser extent. The resulting sludge is very difficult to dewater and its combination with activated sludge is not recommended. Sludge must be treated properly before disposal. If inorganic and synthetic chemicals are replaced by biopolymers, the processed sludge can be used as animal feed.

Chemical treatment

Chemical treatment mainly removes colloids and soluble contaminants from milk processing effluent. This step involves oxidation or pH modification. During the reaction of cheese wastewater with FeSO4 and H2O2, up to 80% of fat (initial concentration 1.93 g/liter) is removed. High pH values ​​of dairy wastewater below 6.5 and above 10 can increase the corrosion of pipes and are very harmful to microbiological collections in biological processes. Therefore, this system should be modified to reduce side effects. If a dissolved air flotation (DAF) flotation unit is used, pH control is an essential step to achieving optimal coagulant conditions. However, coagulants work best at acidic pH, which requires a second pH adjustment to a neutral value prior to biological treatment.

Biological treatment

Biological treatment is one of the most reliable methods for the treatment of dairy wastewater. Such methods can absorb most of the dairy wastewater pollutants. Moreover, due to their unlimited adaptability potential, they can be used jointly in different sequences to meet specific biodegradation requirements. Depending on the oxygen demand, biological treatment has two main branches: aerobic and anaerobic processes

Aerobic processes of biological purification

Today, most dairy wastewater treatment plants are aerobic, however, they are less efficient mainly due to filamentous growth and rapid acidification due to high levels of lactose and low water buffering capacity. Problems generally encountered in activated sludge processes are -swelling and -flooding, which cause sludge settling, excess biomass production, as well as reduced system activity and efficiency at low temperatures. If such problems occur, it will take several months for the sludge to acclimate before full operating capacity is reached.

Aerobic process of adherent growth

By using these aerobic reactors, which have a fixed or Moving bed or media, attached growth will be used instead of the suspended growth of microorganisms. In this way, instead of being suspended in the reactor space, by sticking to the voids of this substrate, the microorganisms use more food and use more microbial retention time to remove the nitrogen load of the output pollution. The advantage of this method compared to the conventional activated sludge method is that, in addition to not producing excess sludge, it will reduce the organic nitrogen and (BNR) of the wastewater biologically. Combining this method with the conventional activated sludge method will increase the BOD removal efficiency by up to 95%. The operation of this reactor is zero and there will be no need to return activated sludge.

Wastewater treatment methods of dairies and milk industries:

Dairy industry wastewater treatment using wastewater stabilization ponds

Wastewater stabilization pond systems use natural processes such as light, heat, algae growth, and microorganisms that include self-supporting microbial communities to improve wastewater treatment. Development is a priority. Among the main disadvantages of their use, we can mention the need for a large area, the possible risks of surface and underground water pollution, the presence of dangerous volatile substances, and the presence of insects and pests. In general, dairy wastewater is treated in ponds under aerobic conditions. Five days are sufficient for % 85 reductions of BOD5 in aerobic ponds with milk waste at 20°C. This is despite the fact that dairy wastewater with a high pollution load is mostly treated in optional ponds, that is, it has two aerobic conditions in the upper layer of the pond and anaerobic conditions in the lower layer of the pond.

Construction of a wastewater treatment plant for dairy industries

A wastewater treatment plant in a dairy factory is the most common technique for dairy wastewater treatment, which usually includes mechanical, physicochemical, chemical, and biological methods. The proposed method of this company in dairy industry wastewater treatment includes the following steps:

• Pre-treatment includes garbage collection
• Removing Oil and Fat with an advanced PECR purification reactor or API and CPI systems
• Biological wastewater treatment includes:
• Anaerobic treatment by UABR & UAFB method
• Aerobic purification by EAAS , IFAS and MBBR method

In general, the wastewater treatment plant for the milk and dairy industries is designed in such a way that it fully covers the wastewater treatment strategy of the dairy and milk industries. The Pasenco company with more than twenty years of successful experience in providing engineering services related to the design, consulting and implementation of industrial wastewater treatment systems along with the full guarantee of obtaining environmental standards, will accompany you in this important matter and tries to Take a small but effective step in protecting this only habitable planet. If you need free expert advice, you can contact our experts through the communication methods mentioned on this page.