Removal Of PAHs By Biochars With The Coexisting Of Surfactants

Biochar and surfactant have respectively been widely applied in controlling and removing environment pollutants. Nevertheless, the effect and mechanism of biochar. and the coexisting surfactant on pollutant migration and degradation are still unknown. Based on the review of the effects of biochar and surfactant to the adsorption and degradation of PAHs, this thesis studied the impacts of the biochar with coexisting surfactant on the adsorption of PAHs by biochar, and their co-effects on the degradation of PAHs. The relative contributions of adsorption and degradation in PAH-removal are emphatically analyzed in the coexistence system. The main results are shown as follows:(1) Sorption isotherms of PAHs onto five biochars had a good fitting with the Freundlich model. The sorption mechanism included surface adsorption and partition. The process of carbonization was accelerated when the temperature increasing from 300 to 700℃, followed a stronger π-π electron-donor-acceptor interaction with PAHs, accompanied with less residual organic fractions which serves as partition phase for PAHs. Because of the two different mechanisms, S500 showed a better removal performance to PAHs than S300 or S700. On the other hand, more aromatic structure forms in animal derived biochar (pig manure and chicken manure), so the removal performance of PAHs by animal derived biochar was much better than plant derived (straw) biochar.(2) All of the cationic surfactant DDPB, the non-ionic surfactant TritonX-100 and the anionic surfactant rhamnolipid could promote the PAH-sorption by biochar, and the promoting extent was depending on the dose of surfactant. Less than 350 mg/L (about 1/10 CMC) of DDPB,1/2 critical micelle concentration (CMC) of rhamnolipid and 1 CMC of TritonX-100 had a favorable promoting effect on the sorption of PAHs by biochar, due to the partition of PAHs into the biochar-sorbed surfactant. However in a higher surfactant concentration, the solubilization effect of surfactant micelles in the solution would inhibit the sorption of PAHs by biochar.(3) Three different types of surfactants (rhamnolipid, TritonX-100 and DDPB) had different effects on the biodegradation of PAHs. Rhamnolipid could significantly promote the biodegradation of acenaphthene by a PAH-degrading bacteria Pseudomonas aeruginosa JXQ, and the biodegradation ratio increased with the increasing of rhamnolipid dosage. The TritonX-100 at concentrations blew the CMC showed a positive effect on acenaphthene degradation. DDPB produced a readily toxic effect to P. aeruginosa JXQ, and completely inhibited the degradation of acenaphthene.(4) Under a surfactant-free condition, the sorption of PAHs by biochar reduced the concentration of PAHs in aqueous solution, and the bioavailable amount of PAHs for P. aeruginosa JXQ was consequently limited. However, when the biochar was coexisting with surfactant, they would not only promote the sorption removal of acenaphthene in solution, but also promote the biodegradation removal due to the surfactant-improved PAH-bioavailability. The total removal ratio of PAHs by joint application of rhamnolipid and biochar was remarkably higher than that by rhamnolipid or biochar applied individually.