The quantity of organic ...

The quantity of organic substances is normally determined in the form of.

1. Biological oxygen demand (BOD).
2. Chemical oxygen demand (COD).
3. Calcining loss.
4. Total organic carbon (TOC)

Dairy Pollutants divided into three categories.

1. Cooling water
2. Sanitary waste water
3. Industrial waste water

Dairy factory wastes probably contain little soluble colour, although after various forms of treatment true colour may result.. The concept of turbidity is closely related to this phenomenon. Milk wastes contain significant quantities of material that will result in turbidity of discharges.

Milk powder and butter plants tend to have a strongly alkaline wastewater while the production of lactic acid in the wastewater from cheese, casein and whey plants makes the wastewater from these plants acidic.

Waste minimisation Waste minimization is the:

 1 Reduction in the generation of waste.

 2 Reuse of waste materials/by-products.

3 Recycling of waste materials.

WASTEWATER TREATMENT

Dairy processing wastewaters contain substantial quantities of organic matter, nitrogen and phosphorus. If excessive concentrations of these enter waterways, oxygen depletion and plant growth in the waterways may reach nuisance proportions. The manufacturing dairy industry uses two main methods of treating wastewater:

Biological treatment in extended aeration systems and by spray irrigation to pasture.

1. Pre-treatment- Pre-treatment in the dairy industry for many years meant some form of dampening flow, pH or organic load variations and a rudimentary fat/solids tank.
2. Land treatment-Land treatment systems are used extensively used. Use the soil as a biological medium to treat the components of the applied wastewater and hence they need to be designed to the appropriate criteria to ensure efficient operation. When wastewater is applied to pasture, soil microorganisms convert the organic matter present to carbon dioxide and water. During this process, biological slimes and additional bacteria are produced. On fine textured soils the production of slimes etc. can inhibit the movement of liquid through soil pores and lead to undesirable effects such as ponding. Dairy factory wastewaters can contain high concentrations of BOD5 primarily due to their lactose, fat and protein content.
3. Nutrient Loading (a) Nitrogen When wastewaters are applied to soils, microorganisms mineralize organic forms of nitrogen. Organic nitrogen is converted to the ammonium and then nitrate forms which can be directly utilized by plants. Nitrate can also be lost to the atmosphere by the process of de nitrification, or can leach to the groundwater.
4. Phosphorus- Phosphorus leaching at wastewater irrigation sites is not usually a problem in most soils because either the phosphorus loading on the soil is limited by the type of wastewater irrigated or the processes that immobilize phosphorus in soils are very active. Phosphates can be fixed by silicate clays, take part in anion exchange reactions, incorporated into organic matter and precipitated by iron, aluminium, manganese and calcium salts. Phosphorus is therefore generally retained in the soil profile.

Biological treatment

The dairy industry uses aerobic or anaerobic treatment, or a combination of both, to treat the wastewater. Aerobic systems require an energy source to provide the oxygen required to assimilate the organic matter in the wastewater and hence are more suited to low to moderate strength wastewaters, since the higher the organic content the greater the oxygen demand and the greater the costs. Anaerobic systems have been developed for their ability to treat high strength wastes and the utilization of the methane gas.

Aerobic systems

In aerobic treatment systems, bacteria, in the presence of oxygen, convert the organic components of the waste to carbon dioxide,water and bacterial biomass. All aerobic treatment systems have the potential to cause odours if operated incorrectly.

Anaerobic treatment

 Considerable experimental work has been undertaken on the anaerobic digestion of whey from casein and cheese plants. Various forms of high rate anaerobic digestion systems have been investigated with whey. However, few anaerobic systems treating whey have been installed, despite such systems being operationally viable and the value of methane produced from these systems as the industry values the components of the whey more highly.

Nutrient removal

 Dairy factory wastewaters contain substantial quantities of the plant nutrients nitrogen and phosphorus. If excessive concentrations of these enter waterways then they will promote the growth of plants in the waterways. Eventually these may grow to nuisance proportions. Wastewaters from dairy manufacturing are usually treated in either extended aeration activated sludge plants and discharged to suitable waterways, or are irrigated onto land after primary treatment. Activated sludge systems can remove some of the nitrogen and phosphorus in the waste sludge because these same nutrients are also required for bacterial growth. However, overall removals will, in some cases, be insufficient to meet environmental demands. Under these circumstances an alternative form of treatment or an add-on to the existing treatment will be required to meet discharge requirements.