Evaluation of Different Approaches for Respiratory Quotient Calculation and Effects of Nitrogen Sources on Respiratory Quotient Values of Hydrocarbon Bioremediation

Abstract

Respiratory quotient (RQ) is a parameter proposed as a tool for practical and online monitoring of petroleum hydrocarbon biodegradation. Various environmental factors and remediation conditions affect RQ values. Occasionally, actual RQ values deviate from theoretical RQ values of petroleum hydrocarbon biodegradation. In addition, different RQ calculation and interpretation approaches investigated in literature make it difficult to compare the results. In this study, different RQ calculation and interpretation methods given in the literature were compared and the effects of nitrogen biostimulation with ammonium and nitrate salts on RQ values of petroleum hydrocarbon biodegradation were investigated. Respirometric reactors were used in bioremediation of diesel fuel–contaminated soils. Ammonium sulfate and potassium nitrate were amended to enhance hydrocarbon biodegradation. Total n-alkane levels in the soils were analyzed after the incubation period. RQ values were calculated based on continuous CO2 and O2 measurements. Biostimulation with ammonium and nitrate led to significant contaminant biodegradation. The nitrogen source type affected RQ values significantly. It was concluded that in evaluating hydrocarbon biodegradability properties and interpreting biostimulation properties, the use of graphical RQ evaluation methods that include plotted statistical approaches allows access to more useful information than using individual theoretical RQ values.