Bioremediation of a soil contaminated by lindane utilizing the fungus Ganoderma australe via response surface methodology

Mixtures of a sandy soil and wheat straw were doped with the organochlorine insecticide lindane in glass tubes and were inoculated with the polypore fungus, Ganoderma australe. An evaluation of bioremediation process effectiveness was searched and five parameters identified for the solid-state system. Fungi growth is a function of temperature and requires moisture for a proper colonization. These microorganisms need inorganic nutrients such nitrogen and phosphorus to support cell growth and it is also appropriate to know the range of concentration and toxicity of the used insecticide. Thus, an orthogonal central composite design (CCD) of experiments was used to construct second order response surfaces. Five design factors, namely temperature, moisture, straw, lindane content and nitrogen content and seven optimization parameters (responses), namely lag time, propagation velocity, biomass growth rate, biodegradation rate, biodegradation/biomass, biomass/propagation and biomass content were analyzed. The optima of the responses of the adequate models were found to be the following: propagation velocity 4.25 mm/day, biomass growth rate 408 mg/day, biodegradation/biomass 56.9 μg/g, biomass/propagation 250 mg/mm and fungal biomass content in solid mixture 260 mg/cm3. The most important response for bioremediation purposes is biodegradation/biomass which is maximized at the factors levels: temperature 17.3 °C, moisture 58%, straw content 45%, lindane content 13 ppm and nitrogen content 8.2 ppm.