COMBINED BIOLOGICAL-CHEMICAL (OZONE) TREATMENT OF WASTEWATERS CONTAINING CHLOROGUAIACOLS

Biological degradation of chloroguaiacols contained in sulphite pulp c hlorine bleaching wastewater was studied in four parallel biological f luidised bed reactor systems-one single aerobic, one single anaerobic and two combined anaerobic-aerobic reactors. At low loading rates, tri chloroguaiacols were removed nearly quantitatively. 4,5-Dichloroguaiac ol was only partly removed. At high loading rates the anaerobic-aerobi c recycle reactor removed individual guaiacols more than the other rea ctors. Only 4,5,6-trichloroguaiacol was removed best by the anaerobic- aerobic reactors in series. Even mixed culture biofilms adapted during several years of continuous operation did not satisfactorily remove t hese compounds. Synthetic wastewater, containing chlorinated guaiacols , treated with ozone produced formate and oxalate and quantitatively i norganic chloride. Combined ozonation-biotreatment in two reactors in series as well as in a recycle system allowed complete removal of all individual chlorinated guaiacols (<1 mu mol m(-3) remained). The effic iency of non-purgable organic carbon removal could be increased from l ess than or equal to 0.55 to about 4 mol carbon mol(-1) ozone by combi nation of ozonation with biotreatment. Simultaneously, the efficiency of removal of chlorinated guaiacols was increased by a factor of 10, w hich is essential for industrial application.