Milk waste

Milk waste the Sardar Patel Renewable Energy Research Institute ( spreri) in Vallabh Vidyanagar, Gujarat, has developed a low-cost upflow anaerobic filter (uaf ) that not only treats diary effluents efficiently, but also produces biogass in substantial quantities as a byproduct, which can be used as fuel.

Diary industries generate a large amount of effluents that contain vast quantities of degradable organic matter. If untreated, these could pose a serious threat to the environment. It is estimated that about 2-4 litres of water is required to process a litre of milk.

Today, most dairies follow the conventional aerobic sludge treatment that requires oxygen for treating such wastes. The process is expensive and requires large investments in infrastructure and is also highly energy-intensive.During treatment, an offensive odour is produced, which creates unhealthy conditions near the treatment plant. However, in the uaf there is no offensive odour produced during the treatment.

The uaf comprises a vertical bed made up of chemically-inert material supporting microbial growth as a biofilm on the surface. The effluent to be treated is introduced below the lower end of the reactor. As it moves upward, it comes in contact with the micro-organism embedded surface that digests 90 per cent organic matter, biological oxygen demand (bod) and chemical oxygen demand ( cod) to produce gas. The gas is stored for use in a storage unit.

Recently, spreri commissioned a uaf at the Sumul diary in Surat. The plant treats 10,000 litres of effluents from the ghee and butter section everyday. The average values recorded in raw and treated effluents for cod were 4,735 milligramme per litre (mg/l) and 114 mg/l and for bod 2,938 mg/l and 36 mg/l. The treated effluents can be safely disposed off on land for irrigation. Besides treating the effluents, the plant also produces 32 cubic metres of biogas which contains 80 per cent methane and can be used as a supplementary fuel in the boiler in the diary.

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