Enzymatic hydrolysis of office paper and newspaper to reducing sugars.

Abstract

Abundant lignocellulosic biomass from municipal solid waste (MSW) is comprised of 40 % waste paper, which can be utilised to produce bioethanol, a renewable energy resource to reduce fossil fuel use. Eventhough lignocellulosic biomass provides a low cost resource, it is very difficult to convert into bioethanol and this results in the cost of bioethanol production being commercially unfeasible. Production of bioethanol from lignocellulosic biomass consists of two steps. The first step converts the biomass to fermentable sugars by hydrolysis. This is followed by microbial fermentation of the sugars to bioethanol. The objective of this study was to investigate hydrolysis of two types of waste paper, namely, office paper and newspaper, to produce fermentable sugars using the enzyme cellulase.

Enzymatic hydrolysis of waste paper is affected by numerous factors such as reaction time, enzyme/paper ratio, pretreatment and smfactant addition. A type of statistical design, i.e. Low Cost Response Smface Method (LCRSM) was used to study the main and interactive effects among the four significant factors of reaction time (4-20 h), enzyme/paper ratio (2-18 % ), H₃PO₄ pretreatment (0-8 g/L), smfactant concentration (0-8 g/L for office paper and 0-12 g/L for newspaper) on sugar production efficiency. This method was proposed because it is comparable to other conventional experimental design methods with much lesser time, cost and effort in optimising the four variables to give the maximum sugar yield. The optimum conditions for office paper were obtained as follows: reaction time = 20 hours, enzyme/paper ratio = 18 %, H₃PO₄ = 8 g/L, surfactant = 4.2 g/L and predicted sugar yield = 86.6 %. For newspaper, the optimum conditions were: reaction time= 20 hours, enzyme/paper ratio= 18 %, H₃PO₄ = 8 g/L, surfactant= 6.8 g/L and predicted sugar yield= 18 %.The predicted sugar yields obtained with a commercial software package are similar to those predicted using Genetic Algorithms (GAs) and in good agreement with experimental sugar yields of 82.2 % and 17 .13 % measured under the predicted optimum conditions for office paper and newspaper respectively.

Reaction time is a dominant factor as longer time periods are required for efficient interaction between cellulase and cellulose. Enzyme/paper ratio is another important factor because cellulase breaks down cellulose into reducing sugars. However, the rate of reaction is influenced by the strnctural features of cellulose. The structural features that govern the susceptibility of cellulose to enzymatic attack include: (1) the amount of lignin content, (2) the degree of crystalline portion, (3) moisture content of cellulose and (4) the accessible areas between the microfibrils for cellulase molecules to penetrate through. Pretreatment has to be applied prior to hydrolysis. H₃PO₄ pretreatment was not so effective with substrate containing lignin, but is able to reduce the level of crystallinity of cellulose and further increase the accessible area. Therefore, both substrates experienced different extent of saccharification yield. Smfactant addition depends on the amount of lignin exposed to the environment solution surface and works effectively in preventing unspecific binding of cellulose onto lignin smfaces.