Evaporation of Effluent From Peracetic Acid Bleaching: Pilot Tests, 1998 Pulping Conference Proceedings

The applicability of evaporation for peracetic acid effluent from a real TCF bleaching sequence was examined by changing the feed pH of the effluent. The tests were performed using a pilot-scale super concentrator with a rated capacity of about 120 litres of condensate per hour. The results were evaluated by analysing the quality of the condensate and concentrate as a function of total solids in the concentrate (from 0.3% to about 7-10%). The re-usability of the condensates was examined in separate laboratory bleaching tests.

The results indicate a reduction of over 96% in inorganic material (comparing the feed and condensate) which was not dependent on total solids in the concentrate or the feed pH. The reduction in chemical oxygen demand (COD) was over 70% when the feed pH of the effluent was not controlled, but over 93% after neutralisation of the feed pH. The COD concentration of the condensate was not dependent on total solids. TOC in the condensates behaved correspondingly. The laboratory-scale re-use test confirms that the condensates were of sufficiently good quality that they could be re-used in the peracetic acid stage or final chlorine dioxide stage of the bleaching process.

The precipitate fraction of the concentrate was mainly amorphous and its amount was greatly dependent on the total solids of the concentrate during evaporation. However, clear evidence of calcium oxalate deposit was found by x-ray diffraction. Nevertheless no clear scaling problems on the heat surface were observed during the pilot test.