Isolation and Identification of Bacterial Strains from a Mixed Wastewater Treatment System Used to Treat Petrochemical Effluents

Petrochemical industry generates highly toxic effluents with a large variety of chemicals, being most of them recalcitrant and toxic such as: organic chlorinated compounds (mainly 1,2 dichloroethane) and volatile and semivolatile organic compounds. The most common wastewater treatment systems used in Mexico to treat this kind of effluents are activated sludge and aerated lagoons. Treatibility studies in batch aerated reactors were made to define the best operating conditions that could treat efficiently a mixed effluent from several petrochemical industries. Operating conditions evaluated were F/M relationship in a range of 0.2 – 0.7, kg COD/kg VSS*day, volumetric organic load, HRT 2-4 days, kg COD ≥ 0.25 m day. Organic matter removal achieved was more than 80 %. Some of the persistent molecules identified after treatment were: 1,1,2 trichloroethene, 1,2 dichloroethane, ethilbenzene and 1,4 dicholorobenzene. This highly toxic compounds are removed by aeration and the residual concentration degradated by the microbial biomass produced for each condition. Mixed liquor volatile suspended solids (MLVSS) were in the range of 2000 mg/L. During the experiment, microbial activity was followed and a selection of bacterial biomass was observed in the reactors; the main bacterial strains isolated were: Pseudomonas aeruginosa, Pseudomonas fluorescens, Pantoea sp., Chryseomonas luteola, Proteus peenneri and Serratia sp. This native microorganisms were acclimated to this kind of residues and are potentially suitable to biodegradation bioremediation in the wastewater petrochemical industry.