摘要
Recently,the application of plant-based coagulants in wastewater/effluent treatment has drawn much attention due to their many advantages over chemical agents in terms of biodegradability,toxicity,residual sludge production,and cost.In this study,plant-based extract from Cassia fistula seed(CFSE)was experimentally evaluated for its efficiency in treating wastewater from smallscale gold mining operation(SSGM)as a coagulant.The coagulation tests were conducted in 1 L graduated cylinders following manual homogenisation,with interface height measurements at 0,5,10,15,20,25,and 30 min.Particularly,the efficiency of reducing the levels of physicochemical parameters(pH,Turbidity,Total Suspended Solids-TSS,Total Dissolved Solid-TDS,and Electrical conductivity-EC)and the heavy metal ions(Arsenic-As,Cadmium-Cd,Chromium-Cr,Copper-Cu,Iron-Fe,Mercury-Hg)concentrations in the SSGM wastewater was explored in relation to coagulant dosage,settling behaviour and kinetics.The physicochemical parameters were analysed using a Crison pH meter,HACH DR/2000 spectrophotometer,Hydro Test HT 1000,Hanna RODI EC/TDS meter and Crison Conductometer Basic C30 whilst the heavy metal ions concentrations were measured using A Varian AA240FS Fast Sequential Atomic Absorption Spectrometer.The settling behaviour results showed a three-phase settling patterns that aligned with charge neutralisation mechanisms dominant in plant-based coagulants.For physicochemical parameters and heavy metals,a drastic removal/reduction was observed:turbidity(93.4%-97.7% reduction),TDS(80.4%-90% reduction),EC(80.3%-93% reduction),TSS(95.9%-97.5% reduction),As(45%-75% removal),Cd(25%-75% removal),Cr(6.98%-65.12% removal),Cu(59.35%-95.65% removal),Fe(19.06%-53.24%)and Hg(11.54%-23.08%).The pH of the wastewater also experienced an alkaline shift which influenced the cationic activity of the CFSE.Generally,CFSE demonstrated optimal performance for treating SSGM wastewater at 10 g/L dosage,where peak initial settling rate(3.03 cm/min)and the most compact sludge was obtained.Overall,the findings have demonstrated that CFSE offers a sustainable alternative to chemical coagulants for SSGM effluent treatment,though the results represent preliminary or screening-level efficiency under simulated field conditions.
