Delignification of pineapple peel waste by sodium hydroxide pre-treatment

Abstract

Agriculture-based economies have caused the amount of lignocellulosic biomass wastes to be gradually increasing. It has been a major concern to all nations on the disposal method because it can cause major environmental problems. One of the largest agriculture residues contributing to this issue is pineapple waste. Pineapple waste especially the peels are the major by-product obtained during pineapple processing which contribute about 20 - 40 % of the total weight of the fruit. Since, pineapple peels rich in cellulose, it has huge potential use as substrate to develop into valuable bio-based materials. However, pre-treatment is required to overcome the complex structure of lignocellulosic biomass and make it accessible for enzymatic and microbial hydrolysis. In this study, chemical pre-treatment method was performed using alkaline solution, sodium hydroxide (NaOH) on pineapple peels waste. The first stage was the evaluation of the influence of NaOH concentration, temperature and retention time on degradation of lignin content using design of experiment, Box-Behnken and response surface methodology. Based from the Design-Expert software, the maximum lignin degradation was 55.5 % with the pre-treatment performed at 3 % NaOH concentration, 35.3 oC with 120 hr exposure time. The second stage of the study was evaluating the delignification kinetic. Kinetic data of the pre-treatment were evaluated at different temperatures (20 oC, 30 oC and 40 oC) at constant NaOH concentration, 3 % for 120 hr. Delignification by NaOH pre-treatment was possible at all levels of temperature in the bulk phase, however, results were more significant at temperatures 30 oC. The kinetic constant at 20 oC, 30 oC and 40 oC were 0.0093 h-1, 0.1467 h-1 and 0.1649 h-1 respectively and the activation energy was 21.63 kJ/mol. The delignification was highly dependent on temperature and duration of pre-treatment.