Microbiological Aspects of the Treatment of Joint Oil Refinery and Municipal Wastewaters

Abstract

The bacteriological parameters of both the primary and secondary microbiological treatment of mixed oil refinery and municipal wastewaters have here been analyzed. Primary treatment was performed using activated sludge in a two grade bioreactor and for the secondary treatment, four columns with granular activated carbon were used. The first and the last column were aerated, whereas the two in the middle were without aeration. The ratios of the oil refinery (R) to municipal (M) wastewaters in the mixtures were 85:15, 70:30, 50:50 and 30:70. The microbiological analyses included the total bacterial count (direct method), the number of heterotrophs and oligotrophs with their ratios, number of coliforms, nitrifying and denitrifying bacteria (growing method). Activated sludge as well as microbial community on the activated carbon were investigated by using scanning electron microscopy. Chemical parameters, such as pH, COD, BOD, NH4+, NO2− and NO3− were determined by the standard methods. The performed microbiological analysis approved the validity of the joint oil refinery and municipal wastewater treatment. The decrease of the organic load in purified water ranged from 88 to 96 % (COD estimate) and from 91 to 99 % (BOD estimate) while the removal of individual groups of microorganisms varied from 55 to 99 %. The highest decrease was observed in the coliform bacteria (97 - 99 %). It is worth noting that a decrease in the total nitrogen in the system ranged from 59 to 74 % and that of nitrate from 56 to 61 % after secondary microbiological treatment.