Dairy Waste Water Treatment Plant

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.

Waste water Parameters S. No

Constituents

Cheese plant Milk receiving Casein plant Butter, and Butter oil pasteurization and ghee section section

Pooled Dairy Effluent

1 Total solids

2250

3620

650

3400

1650

2 Color 3 Chlorides

White 100

White 95

Clear 70

Brown 100

White 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 8 Calcium carbonate

6.7 480

8.2 500

7.7 460

7.1 420

6.1 530

9 Absorbed oxygen

480

400

10

85

--

10 BOD 11 COD 12 Oil and Grease

2150 3130 520

1620 2600 690

200 370 --

1250 3200 1320

810 1340 290

13 COD:BOD

1.46

1.43

1.85

2.56

1.65

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 Flotation Dissolved 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 exceed 0.28–0.30 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 aerobic because of high-energy requirements associated with aeration.

 Anaerobic digestion also yields methane, which can be utilized as a heat or power source.  Less sludge is generated, thereby reducing problems associated with sludge disposal.  As ammonia nitrogen is not removed in an anaerobic system, 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)