EFFECT OF NONIONIC SURFACTANT ADDITION ON BACTERIAL METABOLISM OF NAPHTHALENE - ASSESSMENT OF TOXICITY AND OVERFLOW METABOLISM POTENTIAL

Two factors potentially accounting for the variability of bioremediati on outcomes when surfactant micelles are used to increase polycyclic a romatic hydrocarbon (PAH) bioavailability were investigated: (1) surfa ctant toxicity and (2) the link between microbial metabolism and the i ntended effect of surfactant addition, enhanced solubilization and mas s transfer from a solid phase. The nonionic surfactant, octaethylenegl ycol mono n-dodecyl ether, did not alter the metabolism of succinate a nd glucose by an isolate from a creosote-contaminated soil indicating that the surfactant is nontoxic. When the culture was supplied with so lid naphthalene, growth was limited by the dissolution of solid naphth alene after the aqueous-phase naphthalene was depleted. Moreover, incr easing dissolution rate by increasing interfacial surface area increas ed the microbial growth rate. However, increasing bioavailability furt her by increasing interfacial surface area, introducing convective mas s transfer, and adding surfactant were all found to reduce growth rate and prompt incomplete metabolism of naphthalene to a compound whose U V absorption corresponds to 1,2-naphthaquinone. Lowering the surfactan t concentration diminished the metabolic overflow and permitted sustai ned growth. The results suggest that different mismatches between solu bilization/mass transfer and metabolic capacity may be among the facto rs responsible for variable bioremediation outcomes.