Biotreatment of industrial effluents containing naphthalene sulphonate

Naphthalene-2-sulphonate (NSA) is a frequently reported pollutant of industrial wastewaters. NS A was detected in the biologically treated effluent from a tannery (TE) (61.78 mg L"1 ± 0.67) and the untreated effluent from a chemical manufacturing plant (CE) (25.29 mg L"1 ± 0.06). Both effluents also contained significant concentrations of naphthalene sulphonate-formaldehyde condensates (SNFC). NSA and SNFC contributed a large fraction of the COD of TE (33.03% of total COD) and CE (48.31% of total COD). BOD5 determinations indicated that this COD fraction would be refractory to conventional biological treatment and would subsequently be discharged into the environment. Two NSA-degrading isolates, Sphingomonas sp. (RBN) and Comamonas testosteroni (BAS), were isolated from acclimated activated sludges, by enrichment with NSA as sole source of carbon and energy. Both isolates degraded NSA via a plasmid�encoded catabolic pathway analogous to the naphthalene degradation pathway. Inoculation of a suspended floe reactor treating a mixed feed containing NSA with RBN, resulted in a

112.5% increase in the NSA removal rate (¿/e) and a 29.9% increase in the total organic removal rate (k). The survival of RBN after inoculation was determined by chromosomal marking with green fluorescent protein (gfp). Sphingomonas sp. strain RBNg/p persisted in a suspended floe reactor (4.3% of total CFU) for 14 d after inoculation and increased (10.8% of total CFU) in response to shock loading of the reactor with NSA (250 mg L'1). The recovery time from shock loading of the reactor, was reduced compared to a matched reactor inoculated with plasmid-cured RBNg/£>. The results suggest that the bioaugmentation of biological treatment plants with NSA-degrading isolates would be a promising route for the remediation of NSA-contaminated effluents. It is believed that this is the first report of the use of bioaugmentation of biological treatment processes for the remediation of effluents containing NSA. Neither RBN nor BAS utilised the SNFC compound #22 as sole source of carbon and energy. Compound #22 was also not degraded cometabolically in the presence of NSA. Photochemical oxidation with Fenton reagent of compound #22 did not increase its biodegradability by RBN or its BOD5 value. It is proposed that the continued recalcitrance of compound #22, and hence SNFC in effluents, was due to maintenance of the integrity of the polymeric structure, even after extensive photo-Fenton treatment. Depolymerisation of SNFC will therefore be a prerequisite to their biodegradation.