Removal and destruction of organic contaminants in water using adsorption,steam regeneration, and photocatalytic oxidation: A pilot-scale study

The overall objective of this pilot-scale study is to investigate the techn ical feasibility of the removal and destruction of organic contaminants in water using adsorption and photocatalytic oxidation. The process consists o f two consecutive operational steps: (1) removal of organic contaminants us ing fixed-bed adsorption; and (2) regeneration of spent adsorbent using pho tocatalysis or steam, followed by decontamination of steam condensate using photocatalysis. The pilot-scale study was conducted to evaluate these opti ons at a water treatment plant in Wausau (Wisconsin) for treatment of groun dwater contaminated with tetrachloroethene (PCE), trichloroethene (TCE), ci s-dichloroethene (cis-DCE), toluene, ethylbenzene (EB), and xylenes. The ad sorbents used were F-400 GAC and Ambersorb 563. In the first treatment strategy, the adsorbents were impregnated with photo catalyst and used for the removal of aqueous organics. The spent adsorbents were then exposed to ultraviolet light to achieve photocatalytic regenerat ion. Regeneration of adsorbents using photocatalysis was observed to be not effective, probably because the impregnated photocatalyst was fouled by ba ckground organic matter present in the groundwater matrix. In the second treatment strategy, the spent adsorbents were regenerated usi ng steam, followed by cleanup of steam condensate using photocatalysis. Fou r cycles of adsorption and three cycles of steam regeneration were performe d. Ambersorb 563 adsorbent was successfully regenerated using saturated ste am at 160 degrees C within 20 hours. The steam condensate was treated using fixed-bed photocatalysis using 1% Pt-TiO2 photocatalyst supported on silic a gel. After 35 minutes of empty bed contact time, more than 95% removal of TCE, cis-DCE, toluene EB, and xylenes was achieved, and more than 75% remo val of PCE was observed. In the case of activated carbon adsorbent, steam regeneration was not effec tive, and a significant lass in adsorbent capacity was observed.