Abstract
The main objective of the present study is to effectively utilize the de-oiled algal biomass (DAB) to minimize the waste streams from algal biofuel by using it as an adsorbent. Methylene blue (MB) was used as a sorbate for evaluating the potential of DAB as a biosorbent. The DAB was characterized by SEM, FTIR, pHPZC, particle size, pore volume and pore diameter to understand the biosorption mechanism. The equilibrium studies were carried out by variation in different parameters, i.e., pH (2–9), temperature (293.16–323.16 K), biosorbent dosage (1–10 g L−1), contact time (0–1,440 min), agitation speed (0–150 rpm) and dye concentration (25–2,500 mg L−1). MB removal was greater than 90% in both acidic and basic pH. The optimum result of MB removal was found at 5–7 g L−1 DAB concentration. DAB removes 86% dye in 5 minutes under static conditions and nearly 100% in 24 hours when agitated at 150 rpm. The highest adsorption capacity was found 139.11 mg g−1 at 2,000 mg L−1 initial MB concentration. The process attained equilibrium in 24 hours. It is an endothermic process whose spontaneity increases with temperature. MB biosorption by DAB follows pseudo-second order kinetics. Artificial neural network (ANN) model also validates the experimental dye removal efficiency (R2 = 0.97) corresponding with theoretically predicted values. Sensitivity analysis suggests that temperature and agitation speed affect the process most with 23.62% and 21.08% influence on MB biosorption, respectively. Dye adsorption capacity of DAB in fixed bed column was 107.57 mg g−1 in preliminary study while it went up to 139.11 mg g−1 in batch studies. The probable mechanism for biosorption in this study is chemisorptions via surface active charges in the initial phase followed by physical sorption by occupying pores of DAB.
Highlights
Treatment of wastewater streams has always been an important and challenging area of research and several physico-chemical and biological processes exist for colour removal from various effluents
Algal biodiesel production generates a large amount of waste de-oiled algal biomass (DAB), which is still the subject of numerous studies including its use as a substrate for bioethanol, biogas in addition to be used as animal/poultry/fish feed, fertilizer, and remediation of dyes & heavy metals [18,15]
The DAB (10 g L21) removes 86% of the dye (50 mg L21) in 5 minutes under static condition and nearly 100% in 24-hours with agitation at 150 rpm, which indicates the Methylene blue (MB) removal by DAB in static conditions is more feasible as it requires lesser energy input
Summary
Treatment of wastewater streams has always been an important and challenging area of research and several physico-chemical and biological processes exist for colour removal from various effluents. Common methods for colour removal are coagulation and flocculation [2], biological oxidation and chemical precipitation [3] and activated carbon adsorption [4]; the latter is the preferred method for removing, recovering and recycling of dyes from wastewaters due to its simplicity. It is not without its limitations due to the costs involved as well as difficulties in regeneration of the substrate [5,6]. Algal biodiesel production generates a large amount of waste de-oiled algal biomass (DAB), which is still the subject of numerous studies including its use as a substrate for bioethanol, biogas in addition to be used as animal/poultry/fish feed, fertilizer, and remediation of dyes & heavy metals [18,15]
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