Dairy industry wastewater treatment plants for farms and processors

• 1. DAF systems for the treatment of dairy wastewater
• 2. Dairy industry wastewater treatment
• 3. Treatment options
• 4. Treatment of dairy industry wastewater for disposal or discharge.
• 5. Treatment of dairy wastewater for reuse.
• 6. DAF systems for dairy industry wastewater management.
• 7. Products and applications

The dairy industry generates a large volume of wastewater, which is generated both in the production of the products and in the packaging units. Dairy wastewater consists of a combination of water, solids, fats and cleaning agents. The volume and characteristics of dairy wastewater can vary depending on factors such as the type of dairy product produced, the processing methods used and the size of the farm.

Wastewater from the dairy industry must be properly treated before discharge, as it contains high levels of organic matter, nitrogen and phosphorus, which can contribute to water pollution.

The main contaminants found in dairy industry wastewater are as follows:

• Organic matter: Dairy industry wastewater contains high levels of organic matter, including fats, proteins and lactose. This organic matter can contribute, if not properly treated, to elevated levels of biochemical oxygen demand (BOD) and chemical oxygen demand (COD) in receiving water bodies, which can reduce dissolved oxygen levels and harm aquatic life.
• Nutrients: Wastewater from the dairy industry is rich in nutrients such as nitrogen and phosphorus, which can contribute to the eutrophication of receiving water bodies. Eutrophication is the process by which excess nutrients cause rapid growth of algae and other aquatic plants, resulting in reduced water quality, oxygen depletion and fish kills.
• Pathogens: Dairy wastewater may contain bacteria, viruses and other microorganisms that can pose a risk to human health if ingested or inhaled. These pathogens can come from animal excrement, human excrement or contaminated equipment or surfaces in dairy processing facilities.
• Cleaning agents: Dairy processing facilities use a variety of cleaning agents, such as acids, alkalis and detergents, to clean and disinfect equipment and surfaces. These agents can be harmful to aquatic life and contribute to water pollution if not properly managed.
• Antibiotics and hormones: Wastewater from the dairy industry may contain residues of antibiotics and hormones used to treat or improve milk production in dairy cattle. These residues can contribute to the development of antibiotic-resistant bacteria and pose risks to human health and the environment.

The composition of dairy wastewater also varies considerably with each product category.

In the dairy industry, the products are very diverse, mainly pasteurized and sterilized milk, yogurt, cheese, cream, butter, ice cream and powdered milk.

Wastewater characterization plays an important role in the design of the treatment system. The concentration of COD (Chemical Oxygen Demand) in dairy wastewater varies considerably depending on the product being produced. For example, the pollutant load of wastewater from a company producing yogurt is very different from the pollutant load of a company producing cheese. Since yogurt production plants have low oil-fat and COD parameters, they generally only require physical + biological treatment to meet discharge standards. However, since oil-fat and KOI (Kjeldahl Oxidizable Nitrogen) parameters are high in cheese production plants, physical + chemical + biological treatment units are generally preferred in small-scale plants.

The following table lists typical average, minimum and maximum values for some key parameters and pollutants such as BOD, COD, suspended solids, ammonia and nitrogen.

Parameter	Concentration (mgL-1) Max	Concentration (mgL-1) Min	Concentration (mgL-1) Mean
Ammonium N	100	5	25
BOD	6000	500	1800
CODs/DQOt	0.9	0.6	0.7
Soluble COD	8000	600	2500
Total COD	9000	900	3500
Nitrate N	8	2	6
Oils and fats	140	400	290
pH	6	5	5.5
Suspended solids (SS)	800	100	400
Total nitrogen (TN)	200	10	110
Total phosphorus	100	10	36
Volatile suspended solids	500	150	350

Dairy industry wastewater treatment plants for farms and processors

Many dairy producers use a combination of physical, chemical and biological treatment methods to manage their wastewater. These include clarification, filtration, biological treatment and nutrient removal processes.

The choice of technology to manage dairy wastewater depends on factors such as the volume and characteristics of the wastewater, the availability of resources and local regulations. It is essential to know the composition of the wastewater before properly designing any dairy wastewater treatment plant.

In general, a combination of the following technologies can be used to achieve the desired level of effluent treatment and reuse or discharge:

• Physicochemical treatment: Physicochemical treatment methods such as coagulation, flocculation and dissolved air flotation can be used for the separation of solids, nutrients and metals from wastewater. These methods consist of adding chemicals to the wastewater to form flocs, which can be easily removed by clarification.
• Anaerobic digestion: Anaerobic digestion is a biological process that converts organic matter in wastewater into biogas, which can be used for energy production. This process can help reduce the organic content of wastewater, eliminate pathogens and generate renewable energy.
• Aerobic treatment: Aerobic treatment consists of using bacteria and oxygen to break down organic matter in wastewater, thereby reducing BOD and COD levels in wastewater and eliminating pathogens.
• Membrane filtration: Membrane filtration technologies, such as ultrafiltration and reverse osmosis, can be used for the removal of solids, organic matter, nutrients and pathogens from wastewater. These technologies can be effective in producing high quality effluent for reuse or discharge.
• Advanced oxidation: Advanced oxidation technologies, such as ozone and hydrogen peroxide, can be used to break down organic matter and pathogens in wastewater. These technologies can be effective in producing high quality effluent for reuse or discharge.

Treatment process	Characterization	Efficiency (%)	Main references
Chemical precipitation	Ferrous sulfate and ferric chloride as coagulant.	BOD: 64% (ferrous sulfate) and 85% (ferric chloride)	[25]
Chemical precipitation	Pretreatment Ca(OH)2 and FeSO4 used	High COD removal	[26]
Coagulation	Alum and ferrous sulfate as coagulant.	Alum was more effective than ferrous sulfate and removed 5% more COD than ferrous sulfate.	[27]
Coagulation	Iron chloride, aluminum sulfate and calcium chloride as coagulants.	Calcium hydroxide: organic matter: 40%, suspended solids: 94%, phosphorus: 89%.	[28]
Coagulation	FeCl3 as coagulant Pretreatment	The addition of 0.10 to 0.15 mg FeCl3 -6H2 O/mg COD, or approximately 0.20 mg Al2 (SO4 )3 , 18H2 O/mg COD, was sufficient to obtain good organic matter removal. Maximum removal efficiencies of 67 % to 90 % of total COD.	[29]
Coagulation/flocculation	FeCl3, Fe2(SO4)3 and alum Pretreatment	FeCl3 and Fe2(SO4)3: COD: >70% Alum: COD: >65%	[30]
Coagulation/flocculation	FeCl3 as coagulant	FeCl3 Weak wastewater: Dosage: 550,180, 180 mg/l COD: 76, 88 and 82%, respectively Strong wastewater: Dosage: 500, 500, 500 mg/l COD: 45, 28 and 29%, respectively	[11]
Adsorption	Low-cost adsorbents such as powdered activated carbon, bagasse, straw dust, sawdust, fly ash and coconut fiber as adsorbents.	TSS: activated carbon had a better removal efficiency	[31]
Adsorption	Bentonite modified with lanthaum as adsorbent	Phosphate: 100% in the first 15 min.	[32]
membrane process	Reverse osmosis	95% water recovery with an average flow rate of about 10-11 L/h.m2 TOC: 99.8%, TKN: 96%, conductivity: 97% and lactose: 99.5%.	[33]
membrane process	Reverse osmosis	Conductivity: 98.2%, COD: 97.8%.	[34]
membrane process	Ultrafiltration + reverse osmosis (wastewater pretreated with coagulant and PAC before)	Dairy industry wastewater can be recycled and reused	[35]
membrane process	Membrane bioreactor + nanofiltration	MBR: COD: 98%, nutrients: 86% (86% nitrogen and 89% phosphorus) NF: COD: 99.9%, TSS: 93.1%.	[36]
Electrocoagulation		COD: 98% (under optimal conditions in an electrolysis time of 7 min)	[16]
Electrocoagulation	Soluble aluminum anode as used.	Phosphorus: 89%, nitrogen: 81%, COD: 61%.	[37]
Electrocoagulation	iron electrodes	organic matter: 97.4% (at final pH of 7.4)	[38]
Combined electrode system	Iron and aluminum electrodes.	20 min of electrolysis was sufficient for COD treatment.	[39]
Electrochemical oxidation	Coated anodes of IrO2-Pt/Ti	After 360 minutes, removal of 3700 mg/L COD was completed at a current density of 100 mA/cm2 using an IrO2 /Ti electrode and complete decolorization was achieved in less than 60 minutes.	[40]
electrochemical process	Sn/Sb/Ni-Ti coated anodes	COD: 98% at a current density of 50 mA/cm2 at 10 min.	[41]
Electrocoagulation	Aluminum electrodes were used in the presence of potassium chloride as electrolytes.	98.84% COD removal, 97.95% BOD5 removal, 97.75% TSS removal and >99.9% bacterial indicators at 60 V for 60 min.	[42]
Electrocoagulation	DC aluminum plates were used as sacrificial electrodes.	COD: 87% (the optimum current intensity, pH and electrolysis time for 1070 mg/dm3 were 3A, 9, 75 min, respectively. The average energy consumption was 112.9 kWh/kg).	[43]

Treatment options

There are different actions that can be carried out with the wastewater generated by the dairy industry.

• Store the wastewater and send it to a waste manager. For producers with large volumes of wastewater, as is often the case, this option is extremely costly.
• Discharge of wastewater into the sewage system. In this case the wastewater will require treatment to bring it into compliance with the discharge regulations in force in the territory where the production plant is located.
• Discharge of wastewater into the natural environment. As in the previous case, the water discharged into the environment must be treated to comply with the discharge limits established by law.
• Reuse wastewater. The most environmentally efficient option, but also involves the installation of a more advanced and complete wastewater treatment plant. Reclaimed water can be reused for activities such as irrigation and washing.

Dairy industry wastewater treatment for disposal or discharge

The steps involved in a typical process to manage the various pollutants present in dairy wastewater (nutrients, oils and fats, chemical oxygen demand (COD), biological oxygen demand (BOD), total suspended solids (TSS), and organic and inorganic substances) for discharge are outlined below:

• The pH level is adjusted using pH regulators such as caustic soda or acid. The emulsions are then broken and the solids are precipitated with the aid of a demulsifier.
• The key steps in this process are coagulation-flocculation and dissolved air flotation. The wastewater is coagulated and then pumped to a slow mixing zone, where the particles are agglutinated into larger flocs through flocculation before being treated in the DAF system.
• Bubbles from the air flotation system are driven from a recycled air dilution system that blows the treated effluent into the air flotation system.
• The sludge is then passed through the filter press and disposed of in accordance with environmental requirements.

If the wastewater is to be discharged into the environment, it is necessary to include a biological treatment process in the wastewater treatment plant prior to discharge of the water.

Dairy wastewater treatment for reuse

If high quality water is to be obtained for reuse in the production process, the dairy wastewater treatment plant must include some additional steps. A common process to obtain high quality reusable water is as follows:

• Screening: The first step in the process is to screen the wastewater to remove large particles and debris that could clog auxiliary equipment. This is usually done using a mechanical sieve or a bar screen.
• Dissolved air flotation (DAF): The wastewater is then sent to a DAF system, where micro bubbles are used to separate suspended solids and fats from the water. The solids and fats rise to the surface of the water and are skimmed off, resulting in a clarified water effluent.
• Biological treatment: the effluent obtained after treatment in the DAF equipment is sent to a biological treatment system, such as an activated sludge process, in which bacteria and other microorganisms are used to break down the organic matter in the water. This process can remove nutrients such as nitrogen and phosphorus from the water.
• Membrane filtration: water is sent to a membrane filtration system, usually consisting of an ultrafiltration unit followed by reverse osmosis, to remove any remaining solids, nutrients and pathogens from the water. This step produces a high quality effluent that can be reused for non-potable purposes such as irrigation or cleaning.
• Disinfection: Water can be disinfected prior to reuse by applying methods such as ultraviolet (UV) light or chlorine to eliminate any remaining pathogens and ensure that the water is safe for reuse.
• Storage and reuse: clean water is then stored in a tank or reservoir and reused for non-potable purposes such as irrigation, cooling or cleaning.

This process is capable of producing high quality water that can be reused on site, reducing the demand for freshwater resources and protecting the environment.

Dissolved air flotation (DAF) equipment for dairy industry wastewater management

Dissolved air flotation (DAF) systems can be used to treat wastewater generated by the dairy industry and are a common choice for many dairy producers. DAF technology is a physical separation process that uses micro air bubbles to separate suspended solids and fats from wastewater. The micro bubbles attach to the suspended solids and fats, causing them to float to the surface of the wastewater, where they can be skimmed off.

DAF systems are very effective in removing solids and fats from dairy wastewater, which can reduce BOD and COD levels in the effluent. This makes the wastewater suitable for reuse or discharge to the environment. In addition, DAF systems are relatively easy to operate and maintain.

These systems can perform different functions depending on the specific needs of the dairy producer and the configuration of its wastewater treatment system. DAF systems can be used as a stand-alone treatment system for dairy wastewater or as part of a larger treatment chain that includes other treatment technologies.

In some cases, DAF systems are used as a primary treatment step to remove solids and fats from dairy wastewater prior to treatment with additional technologies such as aerobic or anaerobic digestion, membrane filtration or chemical treatment. In this configuration, the DAF system serves as a pretreatment step that reduces the organic content of the wastewater, making treatment with downstream processes easier and more efficient.

In other cases, DAF systems are used as a stand-alone treatment system, where the effluent is either discharged directly to the environment or reused on site for non-potable purposes such as irrigation or cleaning. In this configuration, the DAF system must achieve a higher level of treatment to comply with local regulations and to protect the environment and public health.

Coagulation/flocculation processes

In most dairy wastewater treatment systems, precipitation and coagulation-flocculation occur simultaneously and take place before the wastewater enters the dissolved air flotation system.

Coagulation/flocculation processes are basically used to separate suspended, colloidal and dissolved contents from wastewater, and are applied directly to raw wastewater. The process is divided into two categories:

• Coagulation is the chemical process used to remove solids from water by manipulating the electrostatic charges of particles suspended in the water. This process introduces small, highly charged molecules into the water to destabilize the charges of suspended particles, colloids or fatty materials.
• Flocculation, which causes destabilized particles to coalesce into larger flocs that can be easily separated in the flotation system.

Products and applications

The proposed solutions can be effectively applied to the treatment of wastewater generated during the production of all dairy products.

The dairy industry manufactures a wide range of products based on milk and dairy ingredients. Some of the most common dairy products are as follows:

• Milk: this is the most basic and fundamental product of the dairy industry. It is used as a beverage and as an ingredient in other products.
• Cheese: Cheese is made by coagulating the milk proteins and separating the curds from the whey. The curd is then pressed, molded and ripened to create different types of cheese, such as cheddar, mozzarella and parmesan.
• Butter: butter is made by churning cream to separate the fat from the liquid. It is used as a spread and as an ingredient in cooking.
• Yogurt: Yogurt is made by fermenting milk with bacteria, which convert lactose into lactic acid. This gives yogurt its characteristic sour taste and creamy texture.
• Ice cream: ice cream is made by combining milk, cream, sugar and flavorings, and freezing the mixture while churning to create a smooth, creamy texture.
• Whey protein: Whey protein is a by-product of cheese manufacturing, rich in protein and used as a dietary supplement.
• Milk powder: Milk powder is made by removing the water from the milk and drying the remaining solids. It is used as a convenient and stable alternative to fresh milk.
• Condensed milk: condensed milk is made by removing most of the water from milk and adding sugar. It is used as a sweetener and ingredient in desserts and pastries.
• Cream: cream is the fat-rich layer that rises to the top of milk. It is used as a dressing and as an ingredient in cooking.
• Evaporated milk: Evaporated milk is obtained by heating milk until approximately 60% of the water evaporates. It has a slightly caramelized flavor and a thicker consistency than regular milk, widely used in recipes for cakes, pies and other desserts.