Dairy industry generates between six to 10 litres of effluent per litre of milk processed, depending upon the technology used and product manufactured.

A team led by SS Marwha, from the department of biotechnology, Punjabi University in Patiala, isolated from dairy effluents 15 yeast strains and tested each of them for their pollution-reducing ability.

They identified three strains ``candida parapsilosis,'' ``candida haemulonit'' and ``candida versatitis'' that could reduce by more than 80 per cent both the biological oxygen demand (Bod) and chemical oxygen demand (Cod) -- two main parameters to assess pollution, the team reported in ``Pollution Research.''

Dairy effluent contains very large amount of milk constituents- casein, lactose, fat, inorganic salts -- besides detergents and sanitizers which are used for washing.

Thesebiodegradable organic matter increase Bod and Cod to limits which are in excess of the permitted levels.

The researchers collected effluent samples from composite milk plant in Ludhiana, with Bod values varying between 175 milligrams per litre (mg/l) and 580 mg/l.

The Cod values ranged between 330 mg/l and 2270 mg/l.

Treating effluent samples by all the three strains individually for 24 hours showed ``C Parapsilosis'' to be most efficient in removing pollutants, with Bod reducing by 85 per cent and Cod reducing by 87 per cent, the report said.

While ``C Haemulonii'' could reduce Bod by 85 per cent and Cod by 84 per cent, the report said, ``C Versatilis'' could bring down Bod by 81 per cent and Cod by 84 per cent.

The three strains ``possessing good potential for treating effluents'' can help alleviate the problem caused by discharge of untreated waste water, the researchers said.