EFFECTS OF ALKALINE TREATMENT ON DISSOLVED CARBOHYDRATES IN SUSPENSIONS OF NORWAY SPRUCE THERMOMECHANICAL PULP

The effects of alkaline treatment on dissolved carbohydrates in suspen sions of Norway spruce thermomechanical pulp (TMP) were studied by agi tating 1% consistency TMP suspensions at different pH values (5.4 to 1 2) for 3 h at 60-degrees-C, followed by acidification and centrifugati on to obtain water samples for analysis. It was found that at pH value s above 8, dissolved galactoglucomannans were deacetylated, resulting in their substantial adsorption onto the TMP. Galacturonans began to d issolve from-the TMP at pH values greater than 8. The amount of arabin ogalactans apparently remained constant throughout the various alkalin e treatments. At pH values above 10, arabino-(4-O-methylglucurono)xyla ns began to dissolve from the TMP. The amount of dissolved and colloid al substances (DCS), measured by TOC, could be substantially decreased by alkaline treatment of filtrate from the 1% consistency suspension, followed by acidification and remixing the filtrate with its original pulp.-At 10 m3/t specific water consumption, the TOC of laboratory-pr epared circulation water dropped about 20% due to the alkaline treatme nt. The decrease in TOC was attributed mostly to the adsorption of dea cetylated galactoglucomannans. Alkaline treatment of fiber-free mechan ical pulp circulation water may be a useful technique to reduce the am ount of organic substances circulating in process waters and leaving t he pulp or paper mill in the effluent stream.