Novel applications of peracetic acid as a biocide in the pulp and paper industry

Environmentally toxic chemicals have traditionally been utilized for preventing microbiological contamination in industrial water circulations. In recent years the search for novel solutions to replace the most toxic chemicals has gained momentum. Peracetic acid technology has been applied in industries ranging from food to pulp and paper. Peracetic acid has strong oxidizing and biocide properties. Therefore, it was hypothesized and experimentally verified that peracetic acid could be utilized as a disinfectant in the paper industry. Repeated doses from 10 to 20 mg/l of peracetic acid that would remain sub-lethal for numerous microorganisms were successfully applied to destroy the biofilm structure and prevent the growth of microorganisms in water circuits. The effectiveness of the applied technique was confirmed based on the literature, and in a series of laboratory and full-scale industrial studies, 12 % peracetic was shown to be the most suitable for disinfection in paper mill targets. The results further facilitated the work for developing completely closed water circuits of paper mills. The decomposition properties of peracetic acid were also studied, indicating that no active chemical remains 30 minutes after dosing. It was demonstrated for the first time that the use of chlorine in industrial untreated fresh raw water can be replaced by peracetic acid in the pulp and paper industry. Peracetic acid decreased the count of microorganisms and had no adverse effects on auxiliary chemicals such as pigments, clays or starch, which have been utilized as binding chemicals in papermaking. In deinking plants, peracetic acid and hydrogen peroxide were studied for inhibition of the activity of the enzyme catalase. Peracetic acid is also crucial in limiting pathogenic bacteria and spores in food-contact paper or packaging. The results presented in this dissertation indicate that the activity of catalase enzyme can be controlled by using peracetic acid solution as a biofilm destroying biocide, rather than by direct disinfection. Understanding the behavior of peracetic acid in the environment of catalase activity supported understanding of its effects in paper machines. Concern about toxic residues that might disturb the wastewater treatment plant led to an investigation of peracetic acid reactions in wastewater. It was observed that wastewater treatment plants suffering from sludge bulking were befitted from peracetic acid oxidation within one week of the dosing scheme. The results presented indicated that 100 mg/l of peracetic acid is an environmentally acceptable solution for sludge bulking problems. Another wastewater-based innovation was odor control with peracetic acid. The corrosive and oxidizing properties of the chemical can be controlled with appropriate maintenance and suitable materials.