Dairy processors turn raw milk into an ever increasing number of products—pasteurized milk, yogurt, kefir, soft and hard cheese, butter, ice cream, whey powders, desserts and more. Dairy processing is also regarded as the world’s largest source of food manufacturing wastewater. One scientific article states that the industry produces between 0.2 to 10 litres of effluent per litre of milk processed and asserts that sweet whey is 60 to 80 times more polluting than domestic sewage. If you’re in dairy processing, this article will help you understand your wastewater so you can better manage your systems and save money.
What are the types of dairy effluent?
Dairy processor effluent falls into three major types, based on where the effluent comes from and what it contains.
Processing water. This type of effluent is produced when milk is cooled or condensed, and when water condenses during the evaporation of milk or whey. Processing water is generally free of pollutants, but it may contain milk or whey. It requires little pre-treatment before being reused (provided the reuse doesn’t involve contact with your product) or discharged.
Cleaning effluent. This effluent contains the water that’s been used to clean equipment, as well as any product that’s in the cleaning water and any detergents or sanitizers that have been used for cleaning. Cleaning effluent characteristics vary depending on what’s being cleaned (pipes, tanks, manufacturing equipment, trucks etc.), the cleaning methods used (e.g. clean-in-place), periodic changes in processes (e.g. product changeovers, start-up and shutdown of equipment), equipment breakdown, equipment maintenance, and operator error. Cleaning effluent is produced in large volumes and requires significant treatment.
Sanitary wastewater. This effluent isn’t much different from what’s produced in residential homes, since it is water from toilets, sinks and showers. It’s usually discharged into the sewer system and treated by a municipal wastewater treatment plant.
What’s in your dairy plant’s wastewater?
It’s difficult to characterize dairy effluent in a standardized way, given the wide range of products that are manufactured across the industry, seasonal variation and differences in the quantity of milk being processed. That being said, universal components of concern include:
- High fat loads
- pH that can range from 2 to 13
- Suspended and dissolved solids
- Trace organics
- Minerals, including phosphorus and sodium
What problems can dairy effluent cause?
The fats, proteins and carbohydrates in dairy wastewater result in it having high chemical oxygen demand (COD) and biological oxygen demand (BOD). This means the effluent will deplete oxygen from a body of water quickly, through both chemical reactions and bacterial action. This is a concern because fish and other aquatic organisms depend on oxygen and will die if it’s not available.
Odour is another concern. As milk products spoil, they release smells that people describe as similar to rotting fish and sewage, which causes issues with neighbours. These smells can come from poorly aerated onsite lagoons and inadequate onsite wastewater pre-treatment systems.
Many dairy processors simply send their effluent into the sewage system, paying a surcharge to have municipal wastewater treatment plants deal with the problem. This can be an expensive option for companies, as there is a high volume of wastewater produced and charges are usually levied per m3. It can also be a problem for municipalities, since pipes can get clogged from organic matter (coagulated milk, milk film, flavouring agents, cheese and curd, for example) and from protein and fat that gets deposited on pipe surfaces.
12 ideas for managing your dairy wastewater better
Now you know what’s in your dairy plant effluent and why it’s a concern, you can take action to reduce its impact on the environment and your company’s bottom line. Here are 12 ideas.
- Conduct a wastewater audit. The audit will determine where your effluent is coming from, identify any equipment or processes that are wasting water and adding unnecessary components of concern to the water, and help you determine solutions. Wessuc has a free wastewater audit tool that takes the guesswork out of the exercise.
- Train your employees. Improperly used and maintained dairy processing equipment is a major source of product loss.
- Use the right equipment. If improper equipment is used, milk waste can result. Check equipment that’s used for receiving, cooling, storing and processing of milk and other products used in your manufacturing processes.
- Keep your cool. Maintain accurate temperatures on plate, tubular and surface coolers to prevent freeze-on, as this will result in wasted product.
- Remove solids from water before sending it to the sewer. Technology such as Wessuc’s rotary vac drum dewatering system can achieve total suspended solids of less than 16mg/L after treatment, with little energy, water or polymer use. Dewatering your effluent will often eliminate your sewer surcharges. The solids that result from the process can often be applied as fertilizer or used in other beneficial ways.
- Reuse water in non-food processes. Water used in one process can often be captured and reused in a secondary process, provided that it won’t come in contact with food products. Cooling water and discharged steam can both be used to wash cases, for example.
- Give waste a second life. Don’t send raw materials down the drain—invent a use for them instead. For example, HANS Dairy saved almost $60K a year when it reimagined the pasteurized milk and water used to flush pipes as an ingredient in its smoothies.
- Perform regular checks and maintenance on equipment. Keep your vats, tanks and pipes in good working order. Check for leaks in gaskets, seals and joints.
- Recover ingredients and final product. Install technology, such as pigging systems, to recover the maximum amount of an ingredient or product from your pipes before cleaning them. This will save you money twice: first on ingredient costs, and second on wastewater treatment.
- Avoid overflows. Control liquid levels using automatic pump stops, alarms and other technology on tanks, vats, filler bowls and other liquid storage and processing equipment.
- Reduce the water that’s used in cleaning. Meter the water used by your sanitation crews. Install automatic shut-offs on hoses.
- Focus on culture. Start at the top to create a company culture that values waste reduction. Reward employees for ideas that will minimize the amount of wastewater your plant produces, recover ingredients and product, and reuse water safely.
In conclusion, effluent from dairy processing plants can be harmful to the environment, noxious to neighbours and expensive to manage. Examining your systems, thinking creatively about your processes and supporting a waste reduction culture at your facility are keys to more effective management.