The Food Processing Industry uses a lot of water and produces a lot of wastewater that contains various harmful substances. The food processing industries are the largest producers of wastewater and effluent, and need a lot of water to process food products.
With the volume of wastewater produced by food processing facilities, pretreatment is required before it may be discharged into the environment or used again. Setting up an effluent treatment plant or ETP, is required for all food processing enterprises in order to manage wastewater effectively.
In this article, we will explore the various categories of the food processing industries, composition of the food industry effluent, and the various physical, chemical and biological effluent treatment methods in food processing industries.
Various categories of the food processing industry (FPI)
· Fruit and vegetable producers,
· Dairy producers,
· Meat producers,
· Producers of speciality foods, and
· Producers of beer and wine.
Effluent characteristics of food processing industry: Composition of wastewater in the food processing industries
The following are some significant characteristics of wastewater:
· Temperature
· pH
· Physical characteristics like colour, odour, and turbidity
· BOD-5 (biological oxygen demand in 5 days)
· COD (chemical oxygen demand)
· TSS (total suspended solids)
· VSS (volatile suspended solids)
· Fats
· Total Kjeldahl Nitrogen (TKN) in mg/l
· TP (total phosphorous)
· Oils & Grease
All wastewater from the food processing industry has a comparatively high biological oxygen demand, when compared to other industries, and this value is used to determine the degree of the treatment required. The COD readings are roughly twice as high as the BOD values. Grease and oil concentrations range from 0 to 2000 parts per million (ppm).
Wide changes in the effluents' composition may be caused by:
· The amount of moisture in ingredients, products, and raw materials.
· Quality of raw materials and intermediaries processed elsewhere.
· Variation and richness of product ingredients.
· Production capacity.
· Types of equipment and technology utilised.
· Sophistication of equipment used to process the goods.
· Management's commitment to ensuring quality.
Hence, the sophistication of the processing facilities and the size of the effluent treatment plants, affect the quantity and quality of wastewater produced. In general, there will be less effluent per tonne of production, if the plant capacity is high.
Discharge of effluent from ETPs of food processing industries
It is convenient to classify the effluent waters as follows: -toxic, non-toxic and hazardous, and therefore, the effluent is discharged as:
· direct discharge to a municipal treatment facility,
· pretreatment before discharge,
· on-site treatment,
· stream discharge, or
· land application.
Effluent treatment plants for Food processing industries
How to treat effluent from food processing industries?
There are several methods of effluent treatment from the food processing industries. The processes include physical, chemical and biological processes. Let us discuss these in detail.
A) Preliminary treatment in food processing industries
1: It generally involves screening procedures which removes large particles from effluent.
2: It also consists of the grit chamber for the removal of grit.
3: Flow measurement is also necessary for the effective operation, and flow equalisation reduces flow variability for improved treatment.
B) Primary Treatment in food processing industries
Since, food processing is a traditional industry with relatively low returns on investment, fewer complex processing techniques are generally used. As a result, the majority of wastewater treatment technologies used in the food processing industry, are traditional physical separation techniques such as sedimentation, filtration, aeration, and some secondary or biological treatments.
Here, primary sedimentation is used to remove settleable materials, and lower the organic load (BOD) on the secondary wastewater treatment units.
Primary clarifiers for wastewater treatment
· Sedimentation
Sedimentation is the process of separating suspended solids from liquid using the force of gravity. Hence, the effectiveness of separation depends on the following factors:
- Gravity,
- Particle size, and
- Liquid characteristics.
Since, the other two parameters (particle size and liquid characteristics) cannot be modified independently; the efficiency of sedimentation can be enhanced by increasing the particle size. Three layers will form during the clarification or settling of solids in the sedimentation process:
- the topmost clarification layer,
- the zone-settling layer, and
- the bottom compression layer.
· Thickeners
Circular basin thickeners are the most popular form. Before the wastewater is fed into the thickener's centre well, it is treated with flocculating chemicals, if necessary. Clarification, zone-settling, and compression are the three operating layers, which make up a standard thickener.
· Filtration
Based on the assumption that the solids will have larger particle sizes, filtration is used. It is a mechanical operation for separating suspended solids from the liquid. This process involves passing the suspension through a filter cloth or other medium, which collects the larger solid particles on the filter cloth, while allowing the liquid to pass through.
Hence, the process of separation is physical. Also, certain slurries sediment well and thus, separate over a long period of time. If the solid particles are very fine, a chemical flocculant is used to flocculate them.
Traditional classifications for filtration operations include:
1: Constant pressure filtration, and
2: Constant volume filtration.
Due to the operational benefits, constant pressure filtration is typically used in industrial settings.
· Centrifugation
Centrifugal separation is a mechanical method of dividing a mixture of liquids, or of liquids and solid particles into its constituent parts. It resembles sedimentation, except the material is propelled in a centrifugal force, which behaves towards the mixture similarly to a gravitational field.
The following processes are performed using centrifugation in the wastewater treatment industry in food processing units:
- Separation of solids from highly concentrated suspensions;
- Separation of oil/fat suspensions (globules); and
- Separation of concentrated sludge.
Types of centrifuges
There are three primary types of centrifuges that are regularly used:
• Tubular bowl centrifuge: It is utilised for small-scale solid concentration;
• Disk bowl centrifuge: It is utilised for small to medium amounts of solids;
• Basket centrifuge: It is utilised as a thickener, where the main output is the liquid that has been cleared.
· Air Flotation
Air flotation is a common industrial process for lowering BOD levels in wastewater by aerating the system. To separate the suspended materials in the wastewater, air is pumped into the mixture under pressure, and then released at atmospheric pressure in a flotation tank or basin.
When the air is released, it creates tiny bubbles that join with the suspended material to form froth, which floats on the water's surface. It can then be eliminated using a skimming device. The organic matter's need for oxygen is met in part by air sparging, which leads to the formation of sludge (popularly known as biomass).
· Chemical treatment of wastewater
Precipitation and the application of sanitising chemicals like chlorine-based sanitizers, quaternary ammonium compounds, and amphoteric bactericides are two examples of chemical techniques of treatment.
It is crucial to keep in mind the sanitizers' intended usage when using them, namely whether to remove:
• Organic components, such as lipids, proteins, plants, or animal products
• Bacteria, fungus, or any other pathogenic organisms;
• Microorganisms connected to the organic substance.
C: Secondary treatment/Biological techniques in food processing industries
Biological techniques are mostly employed to lower wastewater's Biological Oxygen Demand. BOD is a crucial indicator of the amount of organic pollutants in wastewater. It gauges how much putrescible organic stuff there is in water, which would require oxygen. Hence, a low BOD suggests clean water, while a high BOD indicates contaminated water.
Thus, the goal of biological treatments is to lower BOD by satisfying the microorganisms' need for oxygen, by bringing oxygen into close contact with them. Two techniques, mechanical agitation (activated sludge method) and non-mechanical modes of mixing are used to accomplish it.
· Activated sludge process (ASP)
It is a well-liked technique for treating wastewater. This technique uses two tanks (basins). Air is introduced into the first tank's feed water from the bottom using a competent sparging mechanism. Air bubbles rise to the top, causing good agitation and providing the necessary amount of oxygen for the microorganisms (bacteria). In the presence of oxygen, they consume the organic material in the wastewater and form cellular biomass.
The next tank will receive this biomass, also known as sludge, but there won't be any agitation to allow the biomass to settle. The biomass is released from the bottom, and the clean water is decanted from the top. To serve as an inoculum for the growth of further biomass, some of the biomass is recycled into the first tank.
Some modifications of the activated sludge process
- Complete mix ASP
- Contact stabilization tank
- Extended aeration system
- Tapered aeration system
- Oxidation ditch ponds
- Membrane bioreactors (MBRs)
- Sequencing batch reactors (SBRs)
· Trickling filters
These filters use a form of packed bed arrangement where the packing is pebbles or rocky stones, and the wastewater is sprayed on top of the materials. From below, air is blasted.
The packing materials on which the slime (fungi, algae) forms come into touch with the feed water, which is sprayed from the top. In the presence of slime, water comes into touch with air and increases biomass.
The packaging materials facilitate closer contact between the slime and the water. When a significant amount of biomass is produced, it either naturally sinks to the bottom of the bed or the process is stopped, and the biomass is scraped.
Oxidation Ditch
· Lagoon systems
- Aerobic lagoons
- Facultative lagoons
- Partial-mixed aerated lagoons
- Tertiary lagoons
- Anaerobic lagoons
C: Advanced treatment processes in food processing industries
To treat the complex nature of wastewater from food processing industries, some specific and advanced treatments are used, such as activated sludge combined with fluidized media, and up flow anaerobic sludge bed reactor system.
· Dissolved air floatation (DAF) systems
These are excellent for usage in the food processing industry and can be utilised to treat a variety of industrial effluent streams. Because, of the unit's counter-current surface scraping design, solids are captured and overall performance is guaranteed. The range of standard unit capacities is 1 kl/h to 1000 kl/h.
The cleaner water runs beneath the bottom baffle and overflows into a holding tank, which serves as the treated water storage tank, as the DAF causes the suspended material in the wastewater to separate, with the impurities floating to the top.
Dissolved air flotation systems
· Membrane filtration
Reverse osmosis [RO] Plants and, specifically, the low pressure membranes known as nano-filters, are examples of membrane separation methods.
Each membrane system is uniquely created to satisfy the requirements of the particular user. The systems have a normal recovery rate of 80-98 % and operate at a relatively low pressure, giving the user a larger return on investment. To prevent scale build-up in the elements, a polymeric material is added before the pre-filter unit.
Membrane Processes include:
- Microfiltration
- Ultrafiltration
- Nanofiltration
- Reverse Osmosis
Significance of ETP's for the Food Processing Industries
1. Practical and effective
2. Easy to use
3. Increased effectiveness in upholding the law
4. Enhances the industry’s image
Conclusion
As a by-product of their manufacturing process, the majority of the food processing sectors produce large amounts of wastewater, also known as effluent. Many pollutants and toxins are present in the effluent/wastewater produced.
High concentrations of suspended solids, total solids, BOD (Biological Oxygen Demand), COD (Chemical Oxygen Demand), dissolved oxygen, oil and grease, fats, sugar, colour, preservatives, and typically nutrients like nitrogen, ammonia, and phosphate, are found in the effluent or wastewater from the food processing industries. Therefore, an effluent treatment plant can assist in the removal of these contaminants/pollutants.
Affordable effluent treatment solutions for the food processing industries
Designing an effluent treatment plant for the food processing industries requires careful consideration of various factors.
If you are curious to know more about the effluent treatment processes in the food processing sector, feel free to contact Netsol Water Solutions at +91-9650608473 or enquiry@netsolwater.com. We also provide wastewater treatment solutions to businesses, including automotive, pulp & paper, refineries, pharmaceutical, textile, hotels, schools, hospitals, office buildings, etc.
