SOME BIOCHEMICAL ASPECTS OF THE ANAEROBIC DEGRADATION OF DAIRY WASTE-WATER

Low rate of anaerobic degradation together with inhibition problems ca used by components such as milk fat and proteins were found to be reas ons for restricted activity of high-rate anaerobic reactors operated w ith dairy effluent. The present research was aimed to investigate the influence of some relevant compounds, such as casein and milk fat and their degradation compounds, on process efficiency. Methanogenic activ ity and ATP content of the sludge were used as major follow up criteri a for evaluating the influence of the tested compounds on process effi ciency. It was found that casein was not degraded by anaerobic culture s which were not pre-acclimated for this compound. On the other hand, cultures acclimated to casein, utilized it very efficiently. Amino aci ds typical for casein degradation were also used efficiently with no i nhibitory effects under the test conditions and with no need for cultu re pre-acclimatization. Milk fat was found to be a major cause for inh ibition of methanogenic activity. It was found to have an immediate in fluence on reducing gas production rate in reactors to which it was ad ded. Milk fat was also found to have long term effects: sludge pre-exp osed to milk fat exhibited reduced methanogenic activity when tested i n medium free of milk fat. Milk fat also reduced the ATP concentration in the sludge, indicating reduction of its total physiological activi ty. Oleic acid, which is a major derivative of milk fat hydrolysis was found to have inhibitory effects on methane production and on ATP con centration. According to the results of the present research, it would be advisable to treat dairy effluents by anaerobic digestion only aft er reduction of the milk fat concentration below 100 mg/L, and after c areful acclimatization of the digester culture to casein.