Descontaminación de suelos con petróleo crudo mediante microorganismos autóctonos y pasto alemán [echinochloa polystachya (H.B.K.) hitchc.]

The soils polluted with crude petroleum can be cleaned with different physical, chemical or biological technologies. The objective of the present study was to evaluate the cleaning of soils polluted with petroleum using alemán grass (Echinochloa polystachya) associated with rhizospheric native populations of bacteria and rhizospheric fungus. Thus, an experiment in a greenhouse was carried out with a 3×4×2 factorial completely randomized arrangement design with four replicates per treatment. Soil used had 98 mg kg ^-1 of total petroleum hydrocarbons (TPH) of basal origin; three petroleum concentrations (98 50 000 and 100 000 mg kg ^-1), four inoculation types (without microorganisms, with bacteria, with fungi and with bacteria-fungi association), and two of plant (with rhizosphere and without rhizosphere of alemán grass), were evaluated. The Petri dishes counting method was used to determine bacteria and fungi. TPH degradation was determined by an infrared spectrophotometer with EPA 418.1 method, and the production of vegetable biomass by dry weight. Bacteria, fungi and the association bacteria-fungi had significant largest populations at 120 d (p=0.05) in the treatments with rhizosphere and alemán grass in soil with 50 000 mg kg ^-1 of TPH. The maximum populations were 16×10 ⁷ colony former units (CPU) of bacteria per gram of dry soil and of 17×10 ⁴ CFU of fungi. In the association the population of bacteria diminished by one exponential unit; however the fungi populations increased by three exponential units. Petroleum degradation was significantly higher (p=0.05) at 120 d in soils with 100 000 mg kg ^-1 with rhizosphere inoculated with bacteria-fungi association; the treatment removed 48% of TPH. The production of dry matter was significant in the control treatment (16.3 g) and the biggest decrease was 53% in the soil with 100 000 mg kg ^-1 of TPH inoculated with bacteria.