title: Improving phosphate removal of sand infiltration system using alkaline fly ash.
abstract: Septic tank effluent is customarily disposed of by soil infiltration. Coarse, sandy soil such as those found in Perth, Western Australia, exhibit low attenuation capabilities for phosphate (PO4(3-)) during effluent infiltration. Amendment of such soil with different amounts of alkaline precipitator and lagoon fly ashes was investigated as a means of reducing phosphorus (P) leakage to ground water. Alkaline precipitator fly ash possessed the highest P sorption capacity in terms of its Langmuir and Freundlich isotherm parameters during initial batch tests. The test materials were repeatedly contacted with fresh PO4(3-) solutions over 90 contacting cycles to gain a better indication of long-term P sorption capability. Again, precipitator fly ash exhibited higher P sorption capacity than lagoon fly ash and Spearwood sand. Column studies assessed the influence of various application rates of alkaline precipitator and lagoon fly ashes on the P removal of septic tank effluent. Septic tank effluent was applied at the rate of 4 cm/day to the column for 12 weeks. Concentrations of P were monitored in the column effluent. All the fly ash columns were more efficient in reducing P migration compared to the sand column. Increased levels of fly ash in the soil columns resulted in increased P attenuation. Lagoon fly ash was inferior to precipitator fly ash for P removal; high application rates of fly ash caused clogging of the infiltration bed apparently due to their lower permeability. It is reasoned that 5-15% precipitator fly ash, and less than 30% lagoon fly ash could be added to coarse sands to produce an infiltration bed, which would result in a better quality effluent than can be obtained with untreated sand alone.
authors.affiliation: Institute for Natural Resources and Waste Management, Hong Kong Baptist University, Hong Kong SAR, People's Republic of China.
authors.forename: K C
authors.initials: KC
authors.lastname: Cheung
authors.forename: T H
authors.initials: TH
authors.lastname: Venkitachalam
mesh_terms: D002244:Carbon / Q000737:chemistry*; D060729:Coal Ash; D008673:Metals, Alkaline Earth / Q000737:chemistry*; D052638:Particulate Matter; D010710:Phosphates / Q000493:pharmacokinetics*; D012722:Sewage; D012989:Soil Pollutants / Q000493:pharmacokinetics; D014877:Water Pollution, Chemical / Q000517:prevention & control*
chemical_list: D060729:Coal Ash; D008673:Metals, Alkaline Earth; D052638:Particulate Matter; D010710:Phosphates; D012722:Sewage; D012989:Soil Pollutants; D002244:Carbon