A modified nitrification inhibition test for high-salinity wastewater

Ravi Kumar Chhetri,Sofoklis Karvelas,Diego Francisco Sanchez,Ariadni Droumpali,Argyro Kokkoli,Henrik Rasmus Andersen

doi:10.1016/j.cej.2021.132460

Abstract

Nitrification inhibition is a standard test for industry wastewater received by wastewater treatment plants (WWTPs). Standard tests such as ISO9509 cannot differentiate the effect of toxicity from relevant chemicals and the temporary inhibition of bioactivity that is induced by a change in osmotic pressure, which occurs if a sample has a high salt concentration. This, however, is unrealistic, as salt does not result in nitrification inhibition on real WWTPs, as their nitrifiers adapt to salt concentration in the same way that nitrification occurs in the oceans. To provide a more realistic inhibition test, we cultured nitrifiers on biofilm carriers in wastewater constantly high in salt content and fortified the salinity of the tested samples to the salt concentration used for culturing, thus eliminating the salt effect. The salt tolerance test was compared with the existing ISO9509 method on statistical uncertainty with results for the common type of salty wastewater from oil extraction and a solution of single chemicals relevant to this wastewater. The nitrification inhibitions of formaldehyde and methanol were similar between the salt-adapted method and the ISO9509 method, while lower inhibition at biocide tetrakis(hydroxymethyl)phosphonium sulphate (THPS) was observed with the salt adapted method. The new methods standard deviation of nitrification inhibition around the 50% inhibition level was below 3%. Thus the method is well suited to test nitrification inhibition in salty water samples as both repeatability and sensitivity are similar or better than the ISO9509 method.

Highlights

Wastewater contains pollutants such as pathogens, nutrients and oxygen-demanding substances, which, if they left untreated and dis charged, can compromise the water quality of receiving water bodies [1,2]
Nitrification inhibition test dilutions covered the entire range of outputs from the test, with almost complete nitrification inhibition observed at dilutions of 300 mL/L and 150 mL/L, while dilution at 10 mL/L illus trated typical regulation thresholds of 20 or 30
Produced water tested in relation to interand intra-day repetition showed almost complete nitrification inhibition for 300 mL/L and 150 mL/L dilutions, i.e. an average of 24% inhibition for a 10 mL/L dilution, and almost no inhibition for a 1 mL/L dilution

Summary

Introduction

Wastewater contains pollutants such as pathogens, nutrients and oxygen-demanding substances, which, if they left untreated and dis charged, can compromise the water quality of receiving water bodies [1,2]. Wastewater treatment plants (WWTPs) are facilities that combine various physical, chemical and biological processes able to treat and remove pollutants from such waters [3,4]. Among many pollutants present in wastewater, ammonium is an oxygen-demanding nutrient that consumes oxygen up to 4.57 g O2/g NH4-N and is toxic to aquatic microorganisms [5]. The treatment of ammonium is mandatory, and it is removed in the biological stage of WWTPs by the nitrification process [2,4]. Nitrification is a two-step biological process where in the first step, the ammonium oxidizing bacteria (AOB) oxidize the ammonium (NH4-N) to nitrite (NO2-N) (equation (1)). Nitrite oxidizing bacteria (NOB), oxidize the generated nitrite into nitrate (NO3N) (equation (2)), which is the end-product of nitrification process [2,6,7]

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Conclusion