Waste paper recycling has increased dramatically in recent times, and will continue to do so in the foreseeable future. Ink removal constitutes one barrier to converting this raw material into quality products. Enzymatic deinking represents one approach to lowering this barrier. Enzymatic processing, offers potential opportunities for changing the pulp & paper industry towards more environmentally friendly and efficient operations compared to conventional methods. The study addresses two (2) commercial enzymes (lipase and esterase) for their efficiency and suitability used in deinking of laser-printed paper and how their sequences can facilitate the best result of the deinking process. Results revealed that both are with great potential with lipase is superior to the esterase in the deinking of laser printed paper.
Lipase from Geobacillus thermodenitrificans nr68 (Lip.nr-68) has shown great enzymatic bio-deinking activity towards a laser jet printed paper with deinkability brightness test of 55%, a value that was slightly lower than the value showed by a commercial lipase from Sigma (63%). In regards of this quality, Lip.nr-68 was purified and characterized to obtain the pure biological characteristic of this catalyst. Airlift fermenter system was used with optimum parameters of 65°C, pH of 6.8, and air flow rate of 1.00 L/min and inoculum size at 7.0% (v/v) in a cultivation medium containing; glucose of 1.25% (w/v); yeast extract of 1.25% (w/v); NaCl 0.75% (w/v) and olive oil of 0.10% (v/v) for 24 hours. The extracted extracellular crude lipase was purified to homogeneity by using four-step procedures: acetone precipitation, Sephadex G-100 filtration chromatography and twice of DEAE Sefarose CL-6B anion exchange chromatography by 22.1 times with a final yield of 25%. The molecular weight of the purified enzyme was estimated to be 33.5 kDa after SDS-PAGE analysis.
Fouling induced enzyme immobilization on polymer membrane with controlled variables can retain enzyme stability and performance. In this study, the effect of enzyme concentration towards the fouling-induced enzyme immobilization was investigated. Alcohol dehydrogenase (ADH) was used as model enzyme to be immobilized on poly(ether) sulfone (PES) membrane at different concentration (0.05, 0.10 and 0.20 g/L). The transmembrane pressure and pH were fixed at 2 bar and pH 7 respectively during the process takes place. The result shows that higher enzyme concentration gives higher loading efficiency with 83.95%. Hermia’s model predicted that standard and intermediate blocking dominating the fouling mechanism at all enzyme concentration tested.
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