Effect of sludge management systems on overall pulp and paper industry wastewater treatment plant cost

Kağıt endüstrisi, en fazla atıksu üreten endüstriler arasındadır ve oluşan atıksuyun özellikleri üretilen kağıdın tipine ve kalitesine bağlı olarak değişmektedir. Genel olarak kağıt sanayi atıksuları yüksek organik kirliliğe ve yüksek askıda katı madde konsantrasyonlarına sahip atıksular oldukları için çoğunlukla biyolojik arıtma işlemleri kullanılarak arıtılmaları tercih edilmektedir. Ancak, içerdikleri zor parçalanabilir maddeler nedeniyle biyolojik arıtmada arıtılmaları her zaman iyi sonuç vermemektedir. Bu durumda kimyasal arıtma, kimyasal oksidasyon, anaerobik arıtma vb. alternatifler de değerlendirilmektedir. Uygun arıtma alternatifi belirlenirken en önemli hususlardan birisi de yatırım ve işletim maliyetidir. Bu çalışmada, kağıt endüstrisi atıksu arıtma tesislerinde, çamur işleme ve bertaraf ünitelerinin yatırım, inşaat ve işletme maliyetlerinin toplam arıtma maliyeti içerisindeki yerinin belirlenmesi hedeflenmiştir. Orta kirlilik yüküne sahip kağıt endüstrisi atıksularını temsil edebilecek atıksu özellikleri belirlenerek 3000 – 10000 m3/gün arasında değişen debiler için bu endüstrinin atıksularının arıtıldığı tesislerde maliyet hesabı yapılmıştır. Bu amaçla, orta kirlilik yüküne sahip kağıt endüstrisi atıksularının arıtılabileceği kimyasal arıtma, aerobik ve anaerobik biyolojik arıtma işlemlerini kapsayan üç alternatif akım şeması oluşturulmuş ve her bir alternatif için yatırım ve işletme maliyetleri hesaplanmıştır. Çamur işleme üniteleri olarak yoğunlaştırma havuzu ve bant filtrenin kullanıldığı su alma ünitesi dikkate alınmıştır. Yapılan hesaplamalar neticesinde, atıksu arıtımında olduğu gibi çamur işleme ve bertaraf işlemleri açısından da, kimyasal arıtma kullanılmayan yukarı akışlı anaerobik çamur yataklı reaktör ve klasik aktif çamur sisteminin birlikte kullanıldığı alternatifin en az maliyete sahip olduğu belirlenmiştir. Anahtar Kelimeler: Çamur, maliyet, kağıt endüstrisi, arıtma.Pulp and paper industry is one of the most in high amount wastewater discharge, and the properties of the wastewater change depending on the type and quality of the paper produced. In general, this industry effluent has high organic material and suspended solids. Since biological treatment does not adequate to treat by itself due to the non-biodegradable organic material content of the wastewater, additional treatment processes such chemical treatment, anaerobic treatment is required. During the decision stage of appropriate treatment plant from among the alternatives, investment and operational costs are two of the most important subjects. In an effort to counteract wrong choices of evaluating the treatment alternatives and construction stages, detailed cost analysis have to be done and the economical solution needed to select by comparing the alternatives. This evaluation must also be done for sludge handling and disposal systems during the determination of the most suitable treatment process. In this study, it was aimed to evaluate the effect of the investment, construction, and operational cost of sludge handling and disposal systems on overall pulp and paper effluent treatment costs. Cost analyses were carried out depending on medium strength pulp and paper industry effluent. For this purpose, various flow rates changing between 3000 to 10000 m3/day were chosen and three alternative treatment plant flow schemes were generated. Chemical treatment or biological treatment processes are not adequate itself to reduce the effluent to the expected discharge concentrations for the medium strength effluents of paper and pulp industry wastewaters. Therefore the combinations of chemical treatment and activated sludge (CT+AS), chemical treatment and extended aeration activated sludge (CT + EAS), and up-flow anaerobic sludge blanket reactor and activated sludge (UASB + AS) were used in generated treatment plant flow scheme. Gravity thickener and belt filter were taken into consideration as sludge handling units. The projecting and cost analysis calculations have done by computer program which was developed in MS Excel. During the projecting of treatment plants, average assumptions have done to realize the cost of the plant. Authors preferred the assumption values between the literately boundary values and biased more negative conditions. Investment cost was composed of civil works cost, footprint cost of the plant, and mechanical instrument costs. Besides transportation, electrical works, piping, consultancy costs were taken into consideration as percentage of investment cost. The investment cost of blowers and belt-press which was chosen as dewatering equipment was selected from the catalogs of manufacturers. One of the most notable aspects on cost analysis is that the construction and maintenance costs are not only the major components of total cost of the plants in its economic life. Operation, maintenance and rehabilitation costs also acts important role in total cost. Since the investment cost like construction and mechanical installation and monthly costs like operation, maintenance and rehabilitation are not occur at the same time, these costs have to be written in same form to make sufficient comparison. Hence, in this study the investment cost uniformly distributed with 8% of discount rate to months for its determined 20-year of economical life. Sludge handling and disposal cost analysis includes both investment and operational cost. Besides traditional operational cost components like electricity and chemical consumption, final disposal payments for landfilling, transportation of sludge cake was also taken into consideration. The percentages of investment costs to the total costs of CT + AS, CT + EAS, and UASB + AS combinations were found as 53%, 47%, and 29% respectively. The percentages of operational costs were more than investment costs: 65%, 69%, and 52% of the total operational costs were results of sludge production mechanism of CT+AS, CT + EAS, and UASB + AS combinations, respectively. Finally, alternative flow schemes which include chemical treatment process were found as the most expensive option for sludge handling and disposal. This result was not a surprise; this was because of huge amount of sludge produced during the chemical treatment. In general, anaerobic biological treatment process produces less sludge. The results also confirm this rule. The combination of UASB + AS was found the most economic solution. Keywords: Sludge, cost, pulp and paper industry, treatment