Modelling the interaction between physico-chemical and bacteriological characteristics of oilfields produced water from a waste management facility

Bacteriological quality of oil and gas-related produced water is a function of the interaction of a complex set of factors, which invariably determine the ease with which this waste material may be treated effectively. Hitherto, only few studies have examined the interplay of these sets of factors on the incidence of coliform bacteria. The American Public Health Association (APHA) standard methods for the examination of wastewater were used to assess levels of 20 physicochemical and bacteriological parameters. Subsequently, negative binomial regression models were fitted to the coliform bacteria counts in the produced water data obtained from a waste treatment facility in Ghana. Zero-order relationships indicated that temperature, turbidity, BOD, COD, oil and grease, total phosphorus and nitrates were significant predictors of total coliform count unlike pH, conductivity, salinity, total dissolved solids and chloride. Except oil and grease, the relationships between incidence of coliform bacteria and BOD, COD and nitrates were not robust and disappeared in the organic, nutrients and demand model at the multivariate level. However, the significant relationships were restored when physical parameters were subsequently accounted for indicating that the latter suppressed the relationship in the organic, nutrients and demand model. pH was a significant predictor of coliform bacteria incidence only when physical and chemical parameters were taken into account in the multivariate model. Both sets of factors mediated the relationship between BOD and coliform bacteria incidence. Given the complex interactions between bacteriological and physicochemical quality of oilfields produced water, it is imperative to adopt a holistic and nuanced approach in managing waste emanating from oil and gas production.