The influence of sorption on polyaromatic hydrocarbon biodegradation in the presence of modified nonionic surfactant organoclays

• Monomer/micelle surfactant-modified organoclays generate a partition effect that change the PAH distribution.
• PAH biodegradation is increased obtained by the addition of nonionic surfactant-modified organoclay.
• Bacterial community and physiological profiles are not affected by the nonionic surfactant-modified organoclays.

This study examined naphthalene (NAP) biodegradation in the presence of organoclays (Ca-Mon) modified by two nonionic surfactants (TX-100 and Brij 35). The nonionic surfactants are adsorbed onto the clay and this provides extra organic matter, which then generates a partition effect that affects NAP biodegradation. NAP biodegradation was found to be affected by the presence of monomer (MN) or micelle (CMC) surfactant-modified organoclays. The pseudo first-order rate constants for NAP biodegradation were as follows: NAP-Brij35-MN > NAP-Brij35-CMC > NAP > NAP-TX-100-MN > NAP-TX-100-CMC, exactly opposite to the soil organic carbon–water partitioning coefficient (koc) values for NAP in the presence of different nonionic surfactants. The bacterial community and physiological characteristics of PAH biodegradation were different between the free-living bacteria and the particle-attached bacteria and was not associated with the surfactant used. The dominant free-living bacteria involved in NAP biodegradation were Brevundimonas diminuta, Caulobacter spp., Mycoplana bullata, Acidovorax spp. and Pseudomonas aeruginosa. Community-level physiological profiling showed significant differences between free-living bacteria and particle-attached bacteria. Significant extracellular enzyme activities, such as esterases and phosphatases, were associated with the TX-100-MN/CMC modified organoclays. Practically, the results suggest that Brij 35 MN-modified organoclay is the most suitable substrate when using a nonionic surfactant for NAP bioremediation.