Inhibition of Nitrification in Industrial Wastewater - Identification of Sources

Abstract: The discharge of industrial wastewaters (WWs) to wastewater treatment plants (WWTPs) can be problematic due to their sometimes elevated concentrations of toxic compounds compared to municipal wastewater. Also, industrial WWs often contain compounds that are unique to the specific production, and the receiving WWTP is not always designed to remove these compounds. Hence, there is a risk that these compounds pass through the WWTP untreated. In addition, they tend to accumulate in the sludge, decreasing its quality and suitability as fertilizer. These compounds can also disturb the biological processes utilized at the treatment plant, making the removal of nutrients as for instance nitrogen perform worse. A consequence of this can be that elevated concentrations of these nutrients are discharged from the WWTP, ultimately causing eutrophication and oxygen depletion in the receiving water body. In this study, the inhibitory effect on the nitrification process by industrial WW from the company Nolato MediTor was investigated. Nitrification is a process commonly used at WWTPs to remove nitrogen, and it is used at the WWTP receiving WW from Nolato MediTor. Previous measurements have shown that the WW is inhibitory to the nitrification process; particularly the leaching WW have given high inhibition of nitrification. In this study, the investigation was taken one step further in an attempt to distinguish what is causing the inhibition and the fluctuations of inhibition in different internal streams at the industry. Laboratory tests with activated sludge were set up in order to mimic the nitrification process as carried out at WWTPs, and the inhibition among the different streams of WW were studied. In addition, solutions of single compounds were prepared and the inhibition in those were compared to the inhibition in the streams of industrial WW to estimate the individual contribution from several chemical components used at the industry. Analyses were performed regarding composition of nitrate, nitrite, ammonium and chemical oxygen demand (COD) in the test substances. Finally, the combined and separate effects from nitrate and nitrite, which are both present in the industrial WW in comparatively high concentrations, were studied in an additivity test in order to find out if the inhibitions from these compounds can be summed in order to estimate the total inhibition, or, alternatively, if they counteract or amplify the inhibition of one another, called antagonism and synergism, respectively. The standard test was further modified so that it applies to the non-linear dependence of inhibition on concentration of nitrate and nitrite, and the compounds were found to act additive at the low concentrations studied, while they tended towards antagonism at higher concentrations.