Kinetic modelling of high turbid water flocculation using native and surface functionalized coagulants prepared from shed-leaves of Avicennia marina plants

Abstract

Coagulation performance of shed-leaves of Avicennia marina plants collected from Alang coastline, Gujarat (India) was scrutinized for the treatment of mud and starch water suspensions. For which, native, hydrochloric acid, sodium hydroxide and sodium chloride treated A. marina shed-leaves were processed with minimum environmental impact. Experiments were accomplished for the concentration of water suspensions (10-50 g/L) at the range of pH 7.0-8.0. The performances of these coagulants were assessed in terms of reduction in turbidity, pH, alkalinity, hardness, electrical conductivity and solids from water suspensions. The removal of bulk impurities was noted due to the floc formation of coagulant through hydrolysing salts, thus, resulted in the highest settlement at pH 7.82, 7.90 for mud and starch water, accordingly. Native and functionalized A. marina coagulants (AMCs) were characterized and interpreted using scanning electron microscopy, elemental analyses, energy dispersive and Fourier transform infrared spectroscopy. HCl treated AMC was relatively effective with good coagulation performance (96.76%), when compared with native and other treated AMCs. The turbidity removal by all AMCs obeyed with World Health Organization (WHO) acceptable limit of finished water, where HCl treated AMC clarified 15.15 and 16.36 NTU of mud and starch water suspensions to produce a clear water of 0.92 and 1.61 NTU, respectively. The proficiency of prepared AMCs were compared with other natural coagulants and surface functionalized (HCl > NaOH > NaCl) AMCs prepared in this study exerted better performance than the native AMC. The critical coagulation rate from the second-order kinetics were evaluated and the results were highly satisfying. Other physico-chemical parameters of water suspensions were evident for the adequate removal of impurities by non-toxic plant-based coagulants.

Keywords: Avicennia marina; Critical coagulation; Flocculation; Surface functionalized; Turbidity; Water quality.