Experiment series in environmental engineering: Experiment 7 (NUS ChBE, AY 2004/2005, Semester 1)

Dehydrogenase enzyme assay (DHA) has been widely used in the bioremediation field to assess the condition of the soil before the soil decontamination work is started. DHA is a general measure of the microbial activity of the soil of all microorganisms. Thus the value obtained can be used as a general indicator of the general soil quality. This initial assessment is important in determining the amount of nutrients that need to be added to the soil in order to allow microbiological degradation of the contaminant compounds to proceed smoothly. DHA is actually a measure of the electron transport chain (ETC) activity. It makes use of the competitive NAD⁺ inhibitor, 2,3,5-triphenyltetrazolium chloride (TTC) to measure the ETC activity. The DHA method accomplishes this by conversion of the pale yellow, slightly soluble TTC to a deep red insoluble precipitate, triphenylformazan (TPF). The concentration of TPF can then be assessed by the use of the UV-Visible Spectrophotometry. The objectives of this experiment is to determine the effect of nitrogen, phosphorus and glucose addition to the soil microbiological activity using the DHA. From the results of the experiment, 0.5% glucose is determined to have the greatest positive impact on the soil microbial activity. The other conclusions that can be drawn from this experiment are on weaker grounds as they do not agree with theoretical predictions. In this experiment, 2.5% glucose + 4% ammonium nitrate together with 2.5% glucose + 4% potassium hydrogen phosphate would produce a microbial activity that is lower than that of 0.5% glucose. This result may be due to 0.5% glucose. This result may be due to experimental errors. Further studies should be conducted to investigate the effect of nitrogen and phosphorus addition to the soil microbial activity of this soil. Done by: Luo Jinjing, Lian Juan and Ng Wenf