Adsorption of methylene blue dye from aqueous solution by sugar extracted spent rice biomass

Abstract

This study was aimed at using sugar extracted spent rice biomass (SRB) as a potential adsorbent to remove methylene blue (MB) dye from aqueous solution. The SRB was used without any modification. A three factor full factorial experimental design (2³) was employed to investigate the effect of factors (adsorbent dose, dye concentration, temperature) and their interaction on the adsorption capacity and color removal. Two levels for each factor were used; adsorbent dose (0.25–0.5 g/100 mL), dye concentration (25–50 mg/L), and temperature (25–45 °C). Initial dye concentration and adsorbent dosage were found as significant factors for the adsorption of MB dye. Langmuir isotherm (R² > 0.998) best explained the equilibrium of MB adsorption on SRB with monolayer adsorption capacity of 8.13 mg/g. The pseudo-second order model (R² > 0.999) was best fitted to explain the adsorption kinetics. Thermodynamic investigation revealed that the adsorption process was spontaneous, endothermic, and was feasible to treat dyeing wastewater.

Introduction

Global economy is confronted with the biggest challenges of energy insecurity and the consequences of environmental pollution. Lignocellulosic bioethanol (LCB) has emerged as an environment friendly and sustainable renewable fuel (Alvira, Tomás-Pejó, Ballesteros, & Negro, 2010). Besides its various advantages and cheap feedstock, the production of LCB is limited due to many technical and financial obstacles (Agbor et al., 2011, Lynd et al., 2008). The extraction of fermentable sugars from lignocellulosic biomass is hindered by its recalcitrant structure and the arrangement of polysaccharides (Geddes, Nieves, & Ingram, 2011). Several pretreatment techniques have been investigated to extract reducing sugars to be fermented into bioethanol. These pretreatments disrupt the biomass structure and make polysaccharides accessible for the subsequent hydrolysis step (Alvira et al., 2010). A substantial amount of biomass, however, is produced as waste after sugar extraction and/or fermentation. These biomass wastes require additional cost for their appropriate disposal. This disposal poses an additional financial liability for LCB industry which already faces market competitiveness against cheap fossil fuels. Thus, it is extremely important for any LCB facility to find out some economical and viable alternatives for the disposal of residual waste.

Wastewater treatment is a costly yet important task for process industries due to the straighten regulations in most of the countries. Various process industries use more than 10,000 synthetic dyes for different kind of applications (Ahmad & Rahman, 2011). These industries generate a huge volume of colored effluent carrying residual dyes which cannot be released without prior treatment due to its toxicity (Deng, Lu, Li, Zhang, & Wang, 2011). Several treatment approaches involving biological, physio-chemical, membrane filtration, and advanced oxidation (Ma et al., 2011, Madaeni et al., 2011, Verma et al., 2012, Whang et al., 2012) have been investigated to treat dye containing wastewater. However, performance of these treatments is constrained due to their operations, cost and production of sludge (Al-Anber, Al-Anber, Matouq, Al-Ayed, & Omari, 2011). Adsorption process has emerged as a feasible alternative for the treatment of such colored wastewater due to its simplicity and performance (Asgher and Bhatti, 2012, Mona et al., 2011). Different kinds of adsorbents have already been investigated for their application in colored wastewater treatment. Activated carbon, derived from various renewable and nonrenewable resources, has been found the most successful material for this task (Pavan, Lima, Dias, & Mazzocato, 2008). Although commercial activated carbon is highly efficient yet it is an expensive technology. Thus, a lot of studies have been carried out to search for low cost adsorbents especially renewable biomass (Ahmed and Dhedan, 2012, Dutta et al., 2011). Lignocellulosic biomass is a cheap and frequently available adsorbent; however, it inherits low efficiency when used without any pretreatment (Chowdhury et al., 2011, Low et al., 2011). The spent lignocellulosic biomass from LCB facility may offer several advantages as an adsorbent. It does not require any pretreatment and furthermore, it will economically manage the disposal of residue.

The objective of present study was to investigate the feasibility of sugar extracted spent rice biomass (SRB) as an adsorbent to remove methylene blue (MB) dye from the aqueous solution. MB is a cationic dye which is extensively used in dyeing industry. MB is a toxic dye and causes several health risks in humans upon exposure such as nausea, vomiting, eye injury, and methemoglobinemia (Al-Anber et al., 2011, Dutta et al., 2011, Vucurovic et al., 2012). A three factor full factorial experimental design was used for this investigation in order to evaluate the influence of operating factors (biosorbent dose, dye concentration, temperature). Adsorption dynamics, kinetics and thermodynamics of the adsorption process were also studied.