Copper ion removal by Acer saccharum leaves in a regenerable continuous-flow column

Highlights

• Ability of Acer saccharum leaves to adsorb Cu (II) was studied in continuous mode.

• Performance of column was evaluated in eight sorption–desorption cycles.

• Sorption process was simulated by a non-linear local equilibrium model.

• Maple leaves are low-cost and locally available biomass for metal removal.

Abstract

Waste leaves from Acer saccharum (maple tree) were used for continuous removal of Cu (II) ions from aqueous solutions in a packed-bed column. Inlet metal concentrations of 15–110 mg/l and flowrates 5–30 ml/min were investigated in continuous column operations resulting in effluent concentration of 1 mg/l of Cu (II), which meets the Canadian drinking water standards. Eight adsorption–desorption cycles were carried out with regeneration efficiencies of 98% using 0.1 N H₂SO₄. Adsorption capacity of the biosorbent remained fairly constant at 18.3 mg/g over eight cycles. The adsorption performance of the column was successfully predicted using a model based on non-linear local equilibrium and mass balance equations. The results showed that maple leaves can be employed as an easily accessible, abundant, and low cost biosorbent for the removal of metals from wastewater in continuous operations.

Introduction

Among the emerging technologies for the removal of heavy metals from various effluents, biosorption of metals using natural biomass or agro-industrial wastes and by-products is known to be a feasible and efficient alternative [38], [1]. Varieties of biosorbents have been tested for their metal removal capacities; nevertheless, biosorption as a remediation process has not been utilized yet for large scale industrial effluent treatment [41], [25], [9]. Although numerous batch sorption studies had been conducted evaluating various biosorbents, very seldom the same biosorbents were tested in continuous column operation. Continuous column operation is an effective and economic process engineering method for maximum capacity utilization of the sorbents, and for design and scale up of the system [40], [2], [30]. Another important factor for successful application of biosorption is selection of the best biomass for a certain metal adsorption, in which, other than adsorption effectiveness, availability and cost should be taken into consideration [18]. In this work, maple leaves as a natural waste biomass found in abundance in temperate regions like Canada were selected for copper ion removal. The main objective of this work was to examine the applicability and efficacy of maple tree leaves (MTL) to remove copper ions in a flow-through column in continuous mode.

A deciduous species, sugar maple or Acer saccharum is native to Canada and one of the most common maple trees in North America, known for its valuable sap and wood. Centralized composting programs are being implemented in some communities across Canada for organic waste management including fallen leaves and yard wastes. However, an alternative way of using the large volume of waste leaves could reduce the cost of disposal and also result in resource recovery.

Batch adsorption studies involving heavy metals and maple tree waste residues, such as maple wood sawdust and leaves have been studied earlier: Yu et al. [47] investigated chromium adsorption with maple sawdust, [29] studied the biosorption of Cu (II) by maple wood sawdust, and Krishna and Gilbert [21] tested maple leaves for removal of Ni (II) from aqueous solutions. Furthermore, batch biosorption of cationic dyes with Norway maple leaves was tested by Witek-Krowiak et al. [44]. However, to the best of our knowledge, performance of maple leaves in continuous configurations was not adequately evaluated. In this study, we investigate the use of fallen maple leaves for metal adsorption as an important, environment-friendly waste management method. Copper removal from industrial wastewater is of great importance due to its abundance in the effluents of metal industry sources [17] and toxicity at high doses [46]. Although MTL is in abundance in Canada, desorption of Cu (II) from the exhausted MTL adds additional value to the biosorption process economy, which was conducted in this work.

Performance estimation, design, and optimization of a fixed-bed biosorption column can be conducted by appropriate mathematical modeling [39], [6]. Such modeling approach for column biosorption is normally complicated; therefore, to achieve an analytical solution, it is desirable to use simplified assumptions and explicit mass transfer expressions [2], [8]. In this work, a mathematical model was developed to describe the column biosorption process based on material balance equations involving solute movement by bulk flow, diffusion, and a non-linear local equilibrium sorption model.