The demand of municipalities and industry for clean fresh water is increasing together with the need for efficient and economically viable treatment methods previous to effluents release in nature. Depending on the regulation, various levels of chemical oxygen demand (COD), biological oxygen demand (BOD), phenols, and other chemical concentrations need to be reached after treatment. In spite of the variety of methods used for wastewater treatment, remaining wastes are maintaining high COD and phenol levels and are considered as "hard COD" compounds. Lignin is a major contributor to this "hard COD" population, its derivatives and phenol compounds are hazardous to aquatic animals and plants (Borisutpetch, 2002 and Sreekrishnan, 2001). Therefore, the development of affordable lignin removal methods is a key objective for water cleaning industry.
Pulp and paper mills are large producers of wastewater containing high concentration of lignin from wood origin, inducing high COD levels, and elevated levels of various types of phenols (Environmental Technology Office, 2000). It has been demonstrated that laccases, oxidoreductases belonging to the multinuclear copper-containing oxidases, are able to reduce lignin and COD levels from pulp and paper mill effluents (Wu et. al., 2005). These oxidase enzymes catalyze substrates at the expense of molecular oxygen and produce water as the only by-product. Because of their broad substrate range, interest in these essentially 'ecofriendly' enzymes has grown significantly in recent years. Historically, fungal laccases were largely studied because of their high redox potential and enzymatic activity (Cho et al., 2004). However, industrial usages of fungal laccases are limited since the yield of fungal protein production and the fermentation time of fungi are not economically viable. In the other hand, bacterial laccases are easy to produce in large quantity but are less active than fungal ones (Kunamneni A et al., 2008).
Current developments in biotechnology and microbiology allow yield improvements of bacterially produced enzymes together with considerable production price reduction allowing economically viable applications in industry (Gavrilescu and Chisti, 2005). Other challenges faced when enzymes are wished to be implemented within an industrial process are the conditions at which the process is conducted. Differently to chemicals, enzymes perform optimally in conditions rather different than the industrial ones.
The pH, reaction temperature, solvents and reaction time rarely match with natural conditions at which microorganisms are growing. At MetGen Oy, we use a technology platform to modify enzymes properties by mutations of their amino acid sequence in order to increase their activity and fit the conditions required by industry (pH, temperature, solvents tolerance...). An intelligent design of mutations to be introduced within the sequence and a subsequent screen of the various mutants in industrial conditions permit the selection of the best clone to be produced in large scale and implemented in the industrial process.
References:
Wu J, Ya-Zhong Xiao YZ and Yua HQ (2005). Degradation of lignin in pulp mill wastewaters by white-rot fungi on biofilm. Bioresource Technology. 96, 12,1357-1363.
Borisutpetch, P. (2002). Level of Tannin that Effect to Fish Dead and Fish Organisms. Master Thesis in Biological Science, Khon Kaen University.
Sreekrishnan, TR. (2001). Aquatic Toxicity from Pulp and Paper Mill Effluent. Advances in Environmental Research Vol. 5. New Delhi.
Cho NS, Shin W, Jeong SW, Leonowicz A. Degradation of Lignosulfonate by Fungal Laccase with Low Molecular Mediators. Bull. Korean Chem. Soc. (2004) 25, 10, 1551-1554
Kunamneni A , Camarero S, García-Burgos C, Plou FJ, Ballesteros A, Alcalde M. Engineering and Applications of fungal laccases for organic synthesis. Microbial Cell Factories 2008, 7:32
Gavrilescu M, Chisti Y. Biotechnology-a sustainable alternative for chemical industry. Biotechnol Adv. (2005) Nov;23(7-8):471-99
