Wastewater treatment in the production of industrial bakery and pastry products

• 1. Production of industrial bread and bakery products
• 2. Composition of wastewater generated in the production of industrial bread and pastries.
• 3. Wastewater treatment in the production of industrial bread and bakery products
• 4. Function of DAF systems
• 5. Application of MBR systems
• 6. Recovery of reusable water, raw materials and by-products.
• 7. Conclusion

1. Production of industrial bread and bakery products

During the production of industrial bread and pastries, a wide variety of raw materials are used, among which the following stand out:

• Cereals such as wheat and oats
• Sunflower, palm and olive oils
• Vegetable and animal fats
• Dairy products
• Eggs
• Seeds
• Sugar
• Salt
• Yeast    

The main stages in the production of industrial bread and pastries are as follows:

1. Mixing ingredients: flour, water, yeast, salt, sugar and other ingredients are combined according to the specific recipe.          
2. Kneading: The mixture is kneaded to develop gluten, which provides structure and elasticity to the final product.
3. Fermentation: the resulting dough is left to rest and ferment. During this phase the yeast produces carbon dioxide, which causes it to expand and become spongy.
4. Resting time. Normally, a resting time is required before baking these products.
5. Baking: This operation is carried out inside specific ovens, which are preheated before baking the products for a specific time and at specific temperatures, which allows for proper internal baking and external browning.
6. Finishes and fillings: in many cases, baked products are filled and/or coated with chocolate, dairy products, sugars, cereals, etc.
7. Packaging: Finished products are subjected to strict quality controls and subsequent packaging for distribution and sale. Defective products are recycled or considered as waste to produce by-products.

2. Composition of wastewater generated in the production of industrial bread and pastries.

Although it is not an industry that consumes excessive amounts of water, its wastewater often reaches high levels of contamination, especially organic contamination.

On the other hand, many of the wastes that are carried away by wastewater can be recovered for subsequent reuse in the production of by-products, as is the case of flour, oils and fats.

During the production of industrial bread and pastries, highly polluted wastewater is generated, especially due to the high concentration of suspended matter in the flour and the high content of sugar, yeast and fats.

On the other hand, the use of strong detergents for cleaning equipment and facilities is common, as is mandatory in food production for hygienic and sanitary reasons. Discharges with detergents represent a risk for the biological treatment of wastewater.

The values of contaminants present in wastewater from this industry can vary significantly depending on several factors, including:

• Plant size
• Specific production processes
• Ingredients used
• Waste management practices

However, we can consider that the average values for the basic contamination parameters are as follows:     

COD (mg/l)	BOD5 (mg/l)	TSS (mg/l)	Oils and Gr. (mg/l)	Total Nitrogen (mg/l)	Ammoniacal nitrogen (mg/l)
1000- 3000	400 - 1000	200 -800	50 - 200	30 -100	10 - 50

3. Wastewater treatment in the production of industrial bread and bakery products

A common plant for the treatment of wastewater generated during the production of industrial bread and pastries consists of three basic stages:

Primary treatment

In this first phase, the larger solids present in the wastewater are separated, some of which can be used to produce by-products or as raw materials for other products. The most commonly used primary treatment technologies are:

• Sieves and grids for the separation of larger solids.
• Regulation, homogenization and tempering basins, to homogenize loads, flows and temperatures in the discharges generated.
• pH adjustment, to adapt the effluents to subsequent clarification and biological purification treatments.
• Addition of coagulant and flocculant reagents to verify correct separation of suspended micro solids and colloidal material.
• Clarification by sedimentation or flotation, depending on the characteristics of the effluents to be treated and the flocs formed.

Secondary treatment

After the separation of the total suspended solids, the pollutants in solution will remain, basically COD, BOD, nitrogen and phosphorus.  

The most efficient systems for eliminating biodegradable organic compounds are biological treatments. The most commonly used technologies are aerobic biological treatment and anaerobic treatment. The choice between the two depends on the type and concentration of the pollutant load.

In aerobic treatment processes such as biological oxidation, with recirculation and extraction of activated sludge, or other more specific processes such as MBBR, are applied if the high nitrogen concentrations that usually accompany these discharges are taken into account.

Secondary treatment may be sufficient to produce treated effluents with reduced pollutant loads that do not exceed the discharge limits established by law.

Tertiary treatment

Tertiary treatment is applied when it is intended to reuse wastewater and incorporate it as process water in elements such as boilers, cooling circuits, machinery and piping washings, etc. Tertiary treatments include membrane filtration technologies (ultrafiltration, nanofiltration and reverse osmosis) and ion exchange technologies (IX).

Sludge treatment

Both the sludge and suspended solids separated in primary treatment (meals, oils and organic matter) and the sludge from secondary treatment (biological sludge) can be recovered for reuse.

For this purpose, different technologies are available, the choice of which depends on the type of sludge to be treated, among which the following stand out:

• Thickeners
• Mechanical drying
• Vacuum concentration
• Anaerobic digesters for energy production

4. Function of DAF systems

Dissolved air flotation (DAF) is used in the primary treatment of wastewater produced by the bakery and pastry industries. is used during the primary treatment of wastewater produced by the bakery and pastry industries.

It is a very efficient process for the removal of suspended solids, grease, oil and other pollutants present in this type of effluent.

These are the stages that take place during primary treatment by dissolved air flotation:

1. Effluent conditioning: Before being subjected to flotation, the effluent is screened to remove larger solids, and others that may cause mechanical problems in the DAF equipment installation. For this purpose, systems such as screens, grids, grease traps, etc. are used.
2. Air microbubble generation: The DAF process involves the dissolution of pressurized air in the treated effluent flow out of the equipment, which is recirculated to the inlet. The air is supplied in a contact balloon or saturator.
3. Mixing and contact: The mixing of the air microbubbles with the effluent occurs homogeneously in the contact chamber of the DAF.
4. Flotation and separation of suspended solids: The mixture of air and contaminants present in the water is conveyed to a flotation chamber, where the previously coagulated and flocculated particles are separated and rise, as they are less dense, to the surface of the tank, where they form a layer of foam that is collected by a skimmer system.

A DAF system offers a number of important advantages compared to other primary treatment technologies for wastewater from industrial bread and bakery production:

• High efficiency in the separation of suspended solids, oils and grease.
• It can operate with variable effluent loads and compositions.
• They require less space than alternative treatments.
• They allow continuous and automated operation, thus reducing human intervention in their operation.
• They facilitate the recovery of reusable materials for the production of by-products.

DAF systems are also often used after the biodegradation treatment of dissolved contaminants in the secondary treatment of effluents. The flotation process is often used instead of secondary settling tanks, due to the advantages mentioned above.

5. Application of MBR systems

Effluents from primary treatment contain some suspended solids and soluble solids, which are mostly organic compounds.

Due to their size and nature, they can be susceptible to partial separation by membranes, but given the high contaminant load, prior oxidation of the contaminants is required.

For biodegradable effluents, as is the case here, biological treatment is the best option due to its economy, high performance and simplicity.

The only case in which an advanced oxidation chemical treatment should be applied is when there is a refractory COD that cannot be decomposed by the bacteria in the biological treatment. This circumstance is rare in the production of industrial bread and pastries, since, although disinfectants and cleaning agents are used, they are applied in specific controlled areas, and with reagents that affect biological treatment as little as possible.

On the other hand, the growing demand for methods that allow reuse of wastewater in processes of the same factory or for auxiliary services, makes it necessary to use tertiary treatments that reduce pollution to a minimum. In this sense, an MBR system is an optimal solution, since it combines a biological process with a separation of pollutants by means of ultrafiltration (UF) membranes, while maintaining a correct concentration of active sludge for biodegradation and facilitating the removal of excess sludge.

The MBR process process consists of the following basic steps:

1. Biological reactor: The effluent is introduced into a bioreactor tank, where biological decomposition of organic contaminants by microorganisms takes place. In this aerobic process, bacteria and other microorganisms metabolize the organic compounds present in the effluent.
2. Membrane filtration: After the biological stage, the effluent is pumped through ultrafiltration or microfiltration membranes. These membranes have very small pores that retain suspended solids, bacteria and other microorganisms, allowing only water to pass through.
3. Sludge Recirculation and Concentration: Biological sludge generated in the bioreactor is recirculated into the system to maintain a controlled, active and efficient microbial population. The sludge concentration in the MBR can be considerably higher than in conventional systems, resulting in higher treatment efficiency and a reduction in equipment size.
4. Disinfection: Depending on discharge requirements, the treated effluent may be disinfected before final discharge to the environment. This can be accomplished by chlorination, ozonation, ultraviolet radiation, or other disinfection methods.
5. Nitrification and denitrification: To reduce the nitrogen pollutant load present in this type of effluent, an anoxic chamber is installed upstream of the biological reactor. This nitrification chamber is followed by the aerobic biological purification process and the denitrification process.

MBR technology offers significant advantages over other wastewater treatment processes:

• High efficiency in the elimination of organic pollutants and suspended solids.
• Production of a high quality effluent that meets the strictest regulatory standards and, in many cases, can be reused.
• Significant reduction in space requirements compared to conventional wastewater treatment systems.
• Increased operational flexibility and resistance to load variations and operating conditions.

6. Recovery of reusable water, raw materials and by-products.

As we have seen throughout the article, there are different technologies that allow the reuse of water and the valorization of wastes present in the wastewater generated in the production of industrial bread and pastries.

Recovering valuable resources that are present in the waste effluent helps to optimize costs and minimize environmental impact.

These are some examples of waste generated in the production of industrial bread and pastries that can be recovered:

• In addition to liquid waste, the bakery and pastry industries also generate solid waste, such as flour waste, packaging and discarded products. This waste can be segregated, recycled or treated for proper disposal, thus minimizing the environmental impact of production.
• Water Recycling: Treated water can be recycled and reused in various operations within the production plant. For example, treated water can be used for washing equipment, cleaning facilities or even for some process water. This reduces the demand for fresh water and reduces the amount of wastewater that needs to be treated and discharged.
• Nutrient recovery: Nutrients such as nitrogen and phosphorus, which are present in wastewater, can be recovered and used as fertilizers in agriculture, or in the production of bioproducts. Nutrient recovery processes can include chemical precipitation or biological extraction to concentrate these compounds in the form of fertilizers.
• Recovery of raw materials: Some components present in wastewater, such as fats and oils, can be recovered and reused in industrial processes or even in the production of biofuels. Flour residues or other production by-products can also be valorized as ingredients in animal feed or in biogas production.
• Technologies such as reverse osmosis or electrocoagulation make it possible to further concentrate the pollutants present in wastewater and facilitate their recovery. This can be especially useful for the recovery of salts or other specific compounds present in discharges.
• Energy Recovery: Organic wastes present in wastewater can be a potential source of energy. Anaerobic digestion of the sludge generated in the treatment process can produce biogas, which can be used as a fuel to generate electricity and heat. This approach not only reduces dependence on fossil fuels, but also helps mitigate greenhouse gas emissions.

7. Conclusion

The production of industrial bread and pastries generates wastewater that can be a significant source of pollution if not properly managed. This wastewater contains a variety of contaminants, such as fats, oils, greases, carbohydrates and other organic compounds, which require treatment before discharge into the environment.

Dissolved air flotation is the best option for the primary treatment of these wastewaters, thanks to its efficiency in removing suspended and fatty contaminants.

By providing effective separation of contaminants prior to entering treatment processes, DAF flotation contributes to the improvement of final effluent quality and compliance with environmental and regulatory standards.

Membrane bioreactors (MBRs) are an efficient and robust solution for the removal of organic contaminants and suspended solids. By integrating biological processes with filtration membranes, an MBR system provides a complete and reliable treatment that ensures the production of a high quality effluent that can be reused for proprietary processes. The recovery of effluent and wastewater residues contributes to the protection of the environment, while generating economic benefits by recovering valuable resources and reducing treatment and disposal costs. A comprehensive approach that combines advanced treatment technologies with resource recovery strategies is essential for sustainable effluent and waste management.

Bibliography and consultations

UPV|Course: THE INDUSTRIAL BREAD AND BAKERY INDUSTRIES October-2021

Process: Baking Industry - Virtual Library VirtualPro.co

TRAINING PROGRAM. Basic bakery and pastry operations (1library.co)