Dairy Waste Water Treatment plant

Dairy Industry:

The dairy industry involves processing raw milk into products including milk, butter, cheese, yogurt, Evaporated milk, whey, Ice cream.

Various processes such as chilling, pasteurization, Deodorisation and homogenization takes place.

Huge amounts of water are used during the process producing effluents containing dissolved sugars and proteins, fats, and possibly residues of additives.

SOURCES OF WASTEWATER:1. Processing waters It include water used in the cooling and heating processes. These effluents are normally free of pollutants and require minimum treatment.

2. Cleaning wastewaters Which emanate mainly from the cleaning of equipment that has been in contact with milk or milk products, this water contain milk, cheese, whey, cream & has high BOD load, require proper treatment.

3. Sanitary wastewater which is normally piped directly to a sewage works.

S.No

Constituents Cheese plant Milk receiving and

pasteurization section

Casein plant Butter, Butter oil and ghee section

Pooled Dairy Effluent

1 Total solids 2250 3620 650 3400 1650

2 Color White White Clear Brown White3 Chlorides 100 95 70 100 115

4 Volatile solids 25 75 55 65 60

5 Suspended solids 600 1300 100 2200 650

6 Phosphates 12 10 5 2 10

7 pH 6.7 8.2 7.7 7.1 6.18 Calcium carbonate 480 500 460 420 530

9 Absorbed oxygen 480 400 10 85 --

10 BOD 2150 1620 200 1250 81011 COD 3130 2600 370 3200 134012 Oil and Grease 520 690 -- 1320 290

13 COD:BOD 1.46 1.43 1.85 2.56 1.65

Waste water Parameters

Components of Treatment plant :

1. Segregation: Waste streams should be segregated – for example, whey

can be reused to produce whey powder or stock feed.

Spent cleaning solutions should be separated as they can be treated to recover cleaning agents.

Highly saline water discharged separately to an evaporation pond where the salts can be recovered and recycled.

2.Physical Screening: It remove large particles or debris that may cause damage

to pumps and downstream clogging.

It prevent increase in the COD concentration due to solid solubilisation.

3.Equalisation:

It is necessary because discharged dairy wastewaters can vary greatly with respect to volume, strength, temperature, pH, and nutrient levels.

pH adjustment and flow balancing can be achieved by keeping effluent in an equalization tank for 6–12 hours.

During this time, residual oxidants can react completely with solid particles, neutralizing cleaning solutions.

Mechanical aerators or Baffle walls are used to create enough turbulence, so that solid particles can’t settle.

4. pH Control: The optimum pH range for biological treatment

plants is between 6.5 and 8.5.

Alternative pH control can be achieved by using spent acid and alkali cleaners to neutralise each other.

The most commonly used chemicals are H2SO4, HNO3, CO2, NaOH, or lime.

Balancing tank should be large enough to allow a few hours extra capacity to handle unforeseen peak loads and not discharge shock loads to public sewers

5. Fats, Oil, and Grease Removal:(i) Gravity Traps It is self-operating, and easily constructed system, in which

wastewater flows through a series of cells, and the FOG mass(Fat, Oil, Grease), which usually floats on top, is removed by retention within the cells.

It requires frequent monitoring and cleaning to prevent FOG build-up, and has low efficiency at pH values above 8.

(ii) Air Flotation OR Dissolved Air FlotationDissolved Air Flotation involves aerating a fraction of recycled wastewater at a pressure of 400–600 kPa in pressure chamber

Then water is sent into a flotation tank containing untreated dairy processing wastewater.

The dissolved air is converted to minute air bubbles under the normal atmospheric pressure in the tank.

Heavy solids form sediment while the air bubbles attach to the fat particles and the remaining suspended matter.

The resulting scum is removed and disposed of according to approved methods.

Whereas in the Air Flotation air bubbles are introduced directly into the flotation tank containing the untreated wastewater, by means of a cavitation aerator coupled to a revolving impeller.

Air Flotation is more economical than Dissolved Air Flotation

Biological Treatment(i) Activated sludge process It is a continuous treatment that uses a consortium of microbes suspended in the wastewater in an aeration tank to biodegrade the organic pollutants.

Aerobic filters The slimy microbial mass growing on the carrier medium

absorbs the organic constituents of the wastewater and decomposes them aerobically.

The organic loading for dairy wastewaters not exceed0.28–0.30 kg BOD/m3

Rotating Biological Contactors (RBC) The discs, rotating at 1–3 rpm, are placed on a horizontal

shaft so that about 40–60% of the disc surface protrudes out of the tank.

The primary advantages are the low power input required, relative ease of operation and low maintenance.

Sequencing Batch Reactor (SBR)

Lagoons/Ponds

Anaerobic Biological Systems

Anaerobic systems are more economical than aerobicbecause of high-energy requirements associated with aeration.

Anaerobic digestion also yields methane, which can beutilized as a heat or power source.

Less sludge is generated, thereby reducing problemsassociated with sludge disposal.

As ammonia nitrogen is not removed in an anaerobicsystem, Complementary treatment is necessary.

Contact Digester Because the bacteria are retained and recycled, this type of

plant can treat medium-strength wastewater (200–20,000 mg/L COD) very efficiently at high OLRs.

A major difficulty is the poor settling properties of the anaerobic biomass from the digester effluent.

Fixed-bed Digester(down or up flow)

The reactor is filled with gravel, rocks, coke, plastic media& thus no need for biomass separation and sludge recycling.

The main drawback is the potential risk of clogging by undegraded suspended solids or the bacterial biomass.

Fluidized-bed Digesters The carrier medium is constantly kept in suspension by

powerful recirculation of the liquid phase. Problems of channelling, plugging, and gas hold-up

commonly encountered in packed-beds are avoided.

Land Treatment Nutrients such as N and P are contained in

biodegradable processing wastewaters , so it is use as organic fertilizers.

Land application of these effluents may, however, be limited by the presence of toxic substances, high salt concentrations, or extreme pH values

Sludge Disposal

Sludge thickening, dewatering, drying, or incineration may be performed.

References

1.Manual of Environmental guidelines for the dairy processing industry by environment protection authority ,state government of victoria.

2. Treatment of Dairy Processing Wastewaters.pdf by Trevor J. Britz

3. Manual of cleaner production assessment in dairy processing prepared by COWI consulting engineers and planners AS, Denmark

4. http:// www.dairyforall.com(accessed on 31.10.2011)

5. http://www.ecologixsystems.com (accessed on 31.10.2011)