IMPROVING STARCH REUSE WORLD PULP&PAPER 64 The results show that enzyme inhibitor is superior when compared to biocides in starch protection. an inhibitor. Retention and Strength Improvement by Using Different Retention Systems Retention of recycled starch. In order to find out the best retention system for capturing non-ionic starch, different retention systems were studied. By adjusting conductivity and hardness levels of dilution water, the experiments were carried out in conditions simulating low water consumption in a mill using recycled fibre raw material. Figure 2 shows that non-ionic starch did not retain by itself. With PAC alone, less than 10 % of the starch was retained. Addition of silica improved starch retention slightly, but the best result was obtained by combining PAC, silica and FennoSil 55D polymer. With conventional medium-molecular- weight cationic polyacrylamide (CPAM), starch retention remained lower than that achieved with FennoSil 55D. only a minor effect. A similar result was obtained with several other biocides (glutaraldehyde, chlorine dioxide, performic acid, DBNPA, CMIT/MIT; data not shown). The results show that enzyme inhibitor is superior when compared to biocides in starch protection. This is analogous to other situations in paper making. For example, anaerobic microbes can produce acids into their surroundings and decrease the pH of process water. Biocides can kill the anaerobic microbes, but this treatment does not neutralise the microbially produced acids. The process water pH remains low unless you add an alkaline substance, which can react directly with the acids, into the process. Similarly, with biocides you can kill bacteria, but the amylase enzymes they have added into their surroundings degrade starch and remain in circulation as impurities and unless they are deactivated with Table 3. Chemical additions in hand sheet test 1 for OCC + kraft pulp furnish. Table 4. Chemical additions in hand sheet test 2 for OCC furnish. Figure 1. Starch degradation can be prevented using amylase enzyme inhibitor Time,s Addition -45 wire water -45 surface size starch (50kg/t) -40 Novel amphoteric polymer -15 Conventional CPAM -10 bentonite 0 Drainage Time,s Addition -600 PAC, (10 kg/t comm.) -15 Silica, (3 kg/t comm.) -10 Novel amphoteric polymer -10 Conventional CPAM 0 Drainage Prevention of Starch Degradation Paper machine water containing starch was treated with different concentrations of amylase enzyme inhibitor product FennoSpec 1200 or with a biocide. 1000 mg/l starch was added into a wire water sample and it was treated with biocide (monochloramine 20 ppm as active chlorine) or with different concentrations of amylase enzyme inhibitor product (concentrations of mg/l, as per a commercial product). Starch concentrations were measured using iodine staining after 2 h incubation at + 45 °C. RESULTS AND DISCUSSION Prevention of Starch Degradation How starch can be protected from degradation with different treatments was studied. Figure 1 shows that enzyme inhibitor was efficient in starch protection and there was a clear dose response. Biocide had