Manufacture of fly ash based coagulants for use in water treatment

Abstract

Fly ash was explored as a raw material for the production of three fly ash-based coagulants being raw, calcined and calcined– sodium hydroxide complex coagulants. Calcined fly ash and calcined fly ash – sodium hydroxide complex coagulants were prepared by calcining raw fly ash at a temperature of 800ºC and all three were acid washed with hydrochloric acid before being used as coagulants. A fly ash sample from a local coal fired power plant was characterization by means of an XRD and FTIR. The characterization results revealed the presence of various compounds which included quartz, hematite, magnetite, anhydrite, and ettringite with a large characteristic peak showing quartz at approximately 26º ≈ 2θ. The behaviour of the prepared coagulants in treating waste water was investigated at different turbidity ranges of low (19 NTU), medium (49 NTU) and high (80 NTU) in jar test experiments. Coagulant doses were also varied at these different turbidity levels to determine the dosage that gives the lowest turbidity for all the three coagulants. From this study, we observed that an increase in coagulant dose from 0.05 to 0.25g/l led to a decrease in residual turbidity. Calcined fly ash was more effective at low and medium turbidity at a dosage of 0.20 g/l whereas Calcined fly ash – sodium hydroxide complex coagulant was found to be more effective with the highest % reduction of 99.8% at a higher turbidity for the same dose.