Coal fly ash enhanced planted-floating bed performance in phosphorus-contaminated water treatment

Despite the ability of fly ash (FA) to remove phosphorus (P) from water via sorption and precipitation, its use as a bedding material for planted floats has never been evaluated. This study was conducted to investigate the effects of FA on P removal and chlorophyll-a (an indicator of algal growth) reduction in P-contaminated water. Six different FA rates (0, 2.5, 5, 10, 25, and 50 w/w%; codes are FA0, FA2.5, FA5, FA10, FA25, and FA50, respectively) and two rice (Oryza sativa L.) treatments (unplanted and planted) were investigated. The floats containing FA were placed on P-enriched (4 mg P L−1) baths. Water samples were collected periodically and analyzed for the concentrations of total P (TP), soluble P (SP), and chlorophyll-a. Both SP and TP decreased (P < 0.05) as FA rate increased, and rice planting further enhanced (P < 0.05) P removal. The first-order rate constants of TP decrease in FA50 (0.143 and 0.192 day−1 for rice unplanted and planted, respectively) were two-fold greater than those (0.072 and 0.090 day−1, respectively) in FA0. Regardless of rice planting, chlorophyll-a concentration in the treatments with FA at 0-10% increased rapidly up to 0.65 mg L−1 within 10 days after treatment; however, those in FA25 and FA50 were consistently lower than 0.05 mg L−1, indicating suppression of algal growth, probably due to enhanced P removal by FA. However, increased salinity by FA mixing might further contribute to the suppression of algal growth.