Evaluation of a membrane bioreactor for treating a dairy processing industry effluent that discharges into Santa Lucía River Basin

In Uruguay, the watercourses are deteriorating mainly because industrial and agricultural discharges without the appropriate treatment. One of the major environmental problems in the country is the pollution of the Santa Lucía River Basin, which is the main source of drinking water for almost 60% of the population of the nation. Food processing industries have been identified as one of the most important sources of pollution of this river basin. Among the food industries, the dairy industry is considered to be one of the most important polluters, because of its large water consumption and wastewater generation. The effluent of this industry commonly has high concentrations of organic matter and nutrients. The dairy industry is one of the main productive activities in Uruguay and this sector has been continuously growing. Pond systems are currently used for treating effluents from this industry, but several problems have been reported with this type of treatment process, mainly because of its inefficiency in the removal of nutrients. This research aims at evaluating a modern wastewater treatment technology for alleviating the impact of the dairy effluent discharges in the Santa Lucía River Basin. An aerobic submerged membrane bioreactor (MBR) was tested for the treatment of wastewater from the largest dairy industry cooperative in Uruguay (CONAPROLE). It was a pilot-scale reactor designed for a capacity of treating 1 m3/day of effluent and by a combination of biological treatment using activated sludge with ultrafiltration membrane separation. The research was carried out in Uruguay and the practical work consisted of: i) characterizing of the MBR influent ii) locating the MBR at the site of the WWTP of the dairy industry; iii) starting up of the plant; iv) optimizing and controlling the operational conditions; v) defining the membrane cleaning regime; iv) collecting and analyzing of samples. The reactor was operated under the conditions of total sludge retention, a HRT of 24 h and a mean mixed liquor suspended solids concentration of 3.5 g/L. After initial starting up problems, optimization of the operation, and identification of the optimal location of the MBR at the WWTP of the diary industry, a pseudo steady state was reached. The mean removal efficiency of COD, BOD and NH4-N after reaching the pseudo steady state were 94.1, 98.1, and 99.6 %, respectively. It was found that with a COD/N ratio above 10, TN and TP were optimally removed with mean efficiencies of 93.1 and 91.0% respectively. The effluent quality obtained in dairy processing wastewater was within the Uruguayan standards for discharged into a watercourse. The results obtained indicate that the MBR is an efficient solution for the dairy industry and for the protection of the Santa Lucia River Basin. The bacterial concentration in the effluent of the MBR was also determined; the MBR provided a high quality effluent when considering reuse standards. However, there is still presence of bacterial contamination and pathogens in the effluent. A post disinfection treatment will be required to destroy all pathogens, considering reuse in the industry is considered. An economical evaluation was performed showing that a full scale MBR is a viable alternative for the existing WWTP. This depends to a large extend on the level of the penalties imposed by the governmental agencies for the non-compliance of the Uruguayan discharged standards. However, the critical situation of the Santa Lucia River Basin and the environmental requirements might force the dairy industry to achieve the discharge standards, irrespective of economical considerations