PULP AND PAPER MILL SLUDGE UTILIZATION POSSIBILITIES IN TERMS OF ENVIRONMENTAL PROTECTION

Environmental protection and sustainability, in terms of reducing forest harvesting and saving the water resource is forcing the paper industry to look for alternative fiber resources. The solution can be sought in the recycling process of old used paper, but recycling process, in addition to cleaned fibers, generates waste sludge which must be treated further. Generally, it can be said that pulp and paper mill sludges originate mainly from primary and secondary water treatment in pulping and paper making process and from deinking process. In the primary sludge (after primary clarifier) the fiber concentration is high and the sludge consisting of coarse particles can be easily dewatered. In the secondary bio sludge (after secondary clarifier), less fibers are present and dewatering process is difficult resulting in low solid concentrations in paste-like form. The sludge from deinking process, where the recycled fibers are separated from additives and inks, besides fibers have high concentrations of inorganic minerals (kaolin, clay, calcium carbonate, titanium dioxide) and can be dewatered easily. In mill the sludge can be mixed before dewatering and often the origin of the sludge constituents are examines after dewatering faze (Latva-Somppi, 1998; Bajpai, 2015).Primary and secondary sludge production in pulp and paper mills has increased lately because the mills are struggling to close their water circuits entirely, so the improvement in water treatment represent the main reason of higher sludge production. The production of deinking sludge also recorded an increase because of paper recycling rate which has rapidly expanded during recent years. It is recorded that 72.5 % of all paper consumed in Europe was recycled in 2016 (CEPI, 2017). The generating sludge amount in paper industry varies within different regions from 100 kg (Bajpai, 2015), to 600 kg (Nosek et al. 2017), for each 1 ton of recycled paper. The reason can be found in the region development, different recycling rate and also in the fact that some mills have internally wastes treatment which reduce the solid waste generation (Bajpai, 2015). The total paper production in Europe in 2016. was 91 million tones and the recycled paper production at the same period was 47.8 million tones. If 14.3 million tons of deinking sludge which was generating at that period were being deposit without treatment, the negative influent to the environment is inevitable (CEPI, 2017). Otherwise with adequate treatmen