Abstract
Increasing awareness on the detrimental effects of inorganic chemical coagulants and sustainable treatment have paved the way to develop environmentally-benign natural coagulants for water and wastewater treatment. In this research, brown, green, and red lentil (Lens culinaris) extracts have been evaluated as a natural coagulant for the turbidity reduction. The physicochemical characteristics properties of lentil extract were evaluated through field emission scanning electron microscopy (FESEM), Fourier-transform infrared spectroscopy (FTIR), zeta potential analysis, and energy-dispersive X-ray (EDX) analysis. Red lentil extract was found to be an anionic polymer with hydroxyl and carboxyl functional groups. The effects of three major operating parameters, pH, the concentration of coagulant, and settling time, were studied and optimized through response surface methodology (RSM) using the Box–Behnken Design (BBD). The red lentil extract as coagulant was outperformed alum in acidic wastewater treatment, which achieved up to 98.87% turbidity removal with an optimum concentration of 26.3 mg/L in 3 min. Besides, the red lentil extract as coagulant reduced 29.42% of material cost, generated 15.6% lower amount of sludge and produced flocs with better settling characteristic (SVI: 7.39) as compared to alum. Based on the experimental observation and characterization study, absorption and bridging mechanisms were proposed for red lentil extract as the coagulant in turbidity reduction.
Highlights
Over the years, the coagulation–flocculation process remains as a common and essential process for water and wastewater treatment due to its simple and cost-effectiveness properties
Apart from potential health impacts, the use of inorganic coagulant produces a large volume of aluminum-based sludges that caused ecotoxicological impact on the living organism
The dry brown, green, and red lentil extracts were characterized according to their surface morphologies, surface zeta potential, and element contents to establish a thorough understanding on the feasibility of different lentils as a natural coagulant for turbidity reduction
Summary
The coagulation–flocculation process remains as a common and essential process for water and wastewater treatment due to its simple and cost-effectiveness properties. Among all the available coagulants, inorganic coagulant, especially aluminum sulphate (alum) and iron (III) chloride were widely used in the coagulation–flocculation process. The inorganic coagulant used has raised controversial issues due to its toxicity which could potentially be hazardous to human health. Increasing studies have reported that the residual aluminum (from alum) retained in the water after the treatment may induce Alzheimer’s disease [1,2]. Apart from potential health impacts, the use of inorganic coagulant produces a large volume of aluminum-based sludges that caused ecotoxicological impact on the living organism. Certain developing countries cannot afford the costs of the imported chemicals for the coagulation–flocculation treatment
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