REMOVAL OF PHOSPHATES FROM WASTEWATER USING MODIFIED COAL FLY ASH

Abstract

Phosphates act as primary nutrients for aquatic life and may lead to overgrowth of algae (Eutrophication) in stagnant water bodies like lakes and ponds. An elevated level of phosphate in a water system stimulates the growth of photosynthetic algae and toxic cyanobacteria. This affects the water quality through consumption of dissolved oxygen, destroys aquatic life. Removal of phosphate from wastewater is therefore necessary to meet the discharge limit to control eutrophication. Removal of phosphate from wastewater by chemical treatment and biological treatment has been widely investigated. Among numbers of removing techniques, adsorption is known more useful and economical. Coal fly ash (CFA) has been given great attention as a potential adsorption material for phosphate removal in recent years since it is easily available and cost-effective. The presence of various active constituents in fly ash like oxides of aluminium, iron, and calcium makes it one of the most suitable materials for phosphate sorption. In the present study laboratory scale experiments were carried out using the coal fly ash (CFA) and modified coal fly ash (MCFA) for the removal of phosphate. Batch experiments were performed to study the adsorption of phosphate ions on coal fly ash and modified coal fly ash adsorbents. Characterization of both the adsorbents was carried out using various techniques such as Proximate analysis, FTIR, FE-SEM and Particle size analysis. Effects of process parameters like adsorbent concentration, contact time, pH, and temperature on the removal of phosphate from wastewater have been investigated to determine the optimum process conditions for maximum removal of phosphate. Effects of initial phosphate concentration on the removal of phosphate have also been investigated. Results showed that the removal of phosphate by fly ash was rapid. The removal percentage of phosphate in the first 5-15 min reached 95 % of the maximum removal of phosphate by fly ash. The optimum coal fly ash (CFA) and modified coal fly ash (MCFA) doses were found to be 36 g/l and 10 g/l respectively. The parameters of Pseudo-First order and Pseudo-Second order kinetics have been found. Adsorption of phosphate on both the adsorbents has been found to follow pseudo second order kinetic model. Adsorption data of phosphate by the modified fly ash and untreated coal fly ash fitted better with Langmuir model.