Effects of Biostimulation and Bioaugmentation on The Degradation of Pyrene in Soil

Abstract

Petroleum based products have been widely used as a source of energy for centuries. One of the main petroleum hydrocarbons of concern is Polycyclic Aromatic Hydrocarbon (PAHs) which include pyrene. Pyrene is a four ring PAHs commonly found in soils contaminated with petroleum based products. The effectiveness of the addition of nutrient (biostimulation) and Mycobacterium sp. (bioaugmentation) on biodegradation of pyrene in soil was evaluated. The addition of nutrients (biosimulation) and microorganisms (bioaugmentation) increased the number of viable cells over the control during the bioremediation process. The cell number increased by 40, 70, 59 and 132 fold for the control, biosimulation, bioaugmentation and combined bioaugmentation, respectively. A lag period of 0.5 d and a specific growth rate of 0.896 d-1 were observed with the combined biosimulation-bioaumentation treatment. The temperature results showed that the temperature of the combined biostimulation-bioaugmentation reached 41°C after two days of treatment while the maximum temperature of the control, biostimulation and bioaugmentation were within the range of 28-32°C. The moisture content decreased for all treatments reaching 45-57% but remained within the optimum range of 40-60% for bioremediation process. This was due to the fact that the moisture lost in the exhaust gas was not compensated by the water produced as a by-product of the organic matter degradation. The level of pyrene degradation was indicated by the decline in O2 concentration and the increase in CO2 concentration in the exhaust gas. The control, biostimulation and bioaugmentation treatments showed similar patterns of decreasing O2 and increasing CO2. However, the combined biostimulation-bioaugmentation treatment recorded a declining trend in O2 concentration and increasing trend in CO2 concentration in the exhaust gas at the beginning of experiment (first 7 days) followed by increasing trend in O2 concentration and decreasing trend in CO2concentration in the next 8 days of the experiment. The highest pyrene reduction in percentage (84.29%) was obtained through the combined bioaugmentation-biostimulation process followed by bioaugmentation (57.86%), biostimulation (50%) and control (37%) processes. Different pyrene degradation rates were observed during the various phases of microbial growth (lag, exponential and stationary) of combined bioaugmentation-biostimulation treatment.