Use of bacteria and yeast strains for dairy wastewater treatment

The present investigation was carried out to study the biodegradation of dairy effluent collected from a regional dairy industry, in Tunisia, by using selected aerobic microbial and yeast isolates. The predominant microorganisms : Candida albicans, Candida krusei, Lactobacillus plantarum and Lactobacillus casei isolated from activated sludge pond of the dairy plant were used. Biodegradation tests were performed in batch into Erlenmeyer flasks containing collected dairy wastewater samples. Two sets of experiments were carried out in duplicate. For the first set of experiments, each bacteria and yeast strain was used for the preparation of four inoculums composed of single culture. These inoculums are added separately in the test samples with a concentration of 1% (v/v). For the second set of experiments, three inoculums rate (1, 5 and 10% (v/v)) were tested. A bacteria and yeast mixed culture were added separately in the test samples. A variable amount of COD, proteins and total sugars reduction was observed with individual and mixture isolates after 25 days treatment period. The chemical oxygen demand (COD) has received reduction varying between 51.6 and 71.6% with individual isolates at 1% (v/v) inoculum rate, while bacterial mixed culture and yeast mixed culture showed reduction up to 75.8 and 70.7% respectively, at 1% (v/v) inoculum rate. Isolates with inoculum rate of 5% (v/v) proved to be most efficient in the treatment of effluent. The highest reduction of total sugar content was obtained by yeast consortium while the highest reduction of protein content was obtained by bacteria consortium.