Saccharification of newspaper waste after ammonia fiber expansion or extractive ammonia.

Salvatore Montella,Venkatesh Balan,Christa Gunawan,Vincenza Faraco,Leonardo Da Costa Sousa,Olimpia Pepe,Simona Giacobbe

doi:10.1186/s13568-016-0189-9

Salvatore Montella, Venkatesh Balan + Show 5 more

Open Access

https://doi.org/10.1186/s13568-016-0189-9

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Abstract

The lignocellulosic fractions of municipal solid waste (MSW) can be used as renewable resources due to the widespread availability, predictable and low pricing and suitability for most conversion technologies. In particular, after the typical paper recycling loop, the newspaper waste (NW) could be further valorized as feedstock in biorefinering industry since it still contains up to 70 % polysaccharides. In this study, two different physicochemical methods—ammonia fiber expansion (AFEX) and extractive ammonia (EA) were tested for the pretraetment of NW. Furthermore, based on the previously demonstrated ability of the recombinant enzymes endocellulase rCelStrep, α-l-arabinofuranosidase rPoAbf and its evolved variant rPoAbf F435Y/Y446F to improve the saccharification of different lignocellulosic pretreated biomasses (such as corn stover and Arundo donax), in this study these enzymes were tested for the hydrolysis of pretreated NW, with the aim of valorizing the lignocellulosic fractions of the MSW. In particular, a mixture of purified enzymes containing cellulases, xylanases and accessory hemicellulases, was chosen as reference mix and rCelStrep and rPoAbf or its variant were replaced to EGI and Larb. The results showed that these enzymatic mixes are not suitable for the hydrolysis of NW after AFEX or EA pretreatment. On the other hand, when the enzymes rCelStrep, rPoAbf and rPoAbf F435Y/Y446F were tested for their effect in hydrolysis of pretreated NW by addition to a commercial enzyme mixture, it was shown that the total polysaccharides conversion yield reached 37.32 % for AFEX pretreated NW by adding rPoAbf to the mix whilst the maximum sugars conversion yield for EA pretreated NW was achieved 40.80 % by adding rCelStrep. The maximum glucan conversion yield obtained (45.61 % for EA pretreated NW by adding rCelStrep to the commercial mix) is higher than or comparable to those reported in recent manuscripts adopting hydrolysis conditions similar to those used in this study.

Highlights

The world municipal solid waste (MSW) volume is expected to reach 2.2 billion tonnes by 2025, due to the increase of urban residents to 4.3 billion
The macromolecular composition of ammonia fiber expansion (AFEX) pretreated newspaper waste (NW) is assumed to have the same composition of untreated NW (Table 1), due to the fact that, as previously reported, the AFEX pretreatement preserves the macrostructure of the lignocellulosic biomasses, reducing the degree of polymerization ofcellulose minimizing the degradation of the original carbohydrates (Holtzapple et al 1991; Kumar et al 2009)
The cellulose percentage after acid pretreatment, reported by Guerfali et al (2015), and the holocellulose percentage, after alkaline pretreatment, reported by Wu et al (2014), were comparable to data obtained after AFEX or extractive ammonia (EA) method; contrariwise, the alpha cellulose and holocellulose percentage, reported by Sangkharak (2011), after pretreatment by using NaOH are both higher than those reported in this study, but the reaction conditions used for AFEX reaction are milder (65 versus 100 °C and residence time 15 min versus 4 h for AFEX and basic pretreatment respectively)

Summary

Introduction

The world municipal solid waste (MSW) volume is expected to reach 2.2 billion tonnes by 2025, due to the increase of urban residents to 4.3 billion. Managed urban solid waste is one of the main causes of environmental pollution and a serious health hazard, due to contamination of groundwater and surface. The lignocellulosic fractions from MSW are more suitable to achieve this objective than dedicated agricultural crops (avoiding the displacement of food crops and minimizing the conflict food versus fuel) or forest resources (avoiding the issues concerning a massive deforestation). The newspaper waste (NW) alone constitutes up to 14 % of MSW (Subhedar et al 2015), and it can be recycled fewer times that office paper due to the fact that it is usually made by shorter fibers. After the typical paper recycling loop, the NW can be further valorized as feedstock in biorefinering industry since it still contains up to 70 % polysaccharides which can be hydrolysed to fermentable sugars (Wang et al 2012a)

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