Establishing economic treatment technology for safe disposal of photo-processing waste (PW) has most recently become an urgent environmental concern. This paper describes a new biological treatment process for PW using sulfur-oxidizing bacteria (SOB) in conjunction with activated carbon (AC). Batch-type acclimation and adsorption experiments using SOB/PAC, SOB/PNAC, and SOB reactor type systems demonstrated that AC effectively adsorbs the toxic/refractory compounds which inhibit thiosulfate oxidization of SOB in PW. Thus, to further clarify the effect of AC, we performed a long-term (≈ 160 d) continuous-treatment experiment on 4- to 8-times dilution of PW using a SOB/GAC system which simulated a typical wastewater treatment system based on an aerobic activated sludge process that primarily uses acclimated SOB. The thiosulfate load and hydraulic retention time (HRT) were fixed during treatment such that they ranged from 0.8-3.7 kg S2O32-/l/d and 7.7-1.9 d, respectively. As expected, continuous treatment led to breakthrough of the adsorption effect of GAC. Renewing the GAC and continuing treatment for about 10 d demonstrated good treatment effectiveness.
