Concentration of phenols in waste waters and their adsorption by soils

Abstract

The concentration of phenols in the soils environment and their fate was studied as a function of five different soil types, six different monohydroxyphenols, and three different municipal landfill leachates media. Concentrations of naturally occurring phenols were also followed for a period of one year in young and old leachates. Methods for analysis of phenols were reviewed for quantitative and qualitative analysis of phenols in landfill leachates. To determine the adsorptive capabilities of the soils used in this study, the isotherm approach was used after the equilibration time of phenols in soils was determined to be five days. Concentrations of phenols varying from 5 ppm to 100 ppm were used to construct isotherm graphs. The soil-phenol isotherm curves conformed very well to the Freundlich equation, indicating multiple adsorption mechanisms and slow equilibration times in the soilsphenols reactions. A statistical analysis of the isotherm data showed %-free iron oxides to be the most important soil characteristic for the adsorption of phenols by all soils; followed by soil pH and % clay in order of significance. High solubility and moderate polarity of phenols also were found to be favorable factors in the adsorption of phenols by soils. Naturally occurring phenols such as cresols disappeared fastèr from soil solutions than synthetic phenols. The reactivities of phenols with MSW leachates increased with the age of the leachates. Very young leachates, having low pH and high TOC levels favored synthetic phenols over naturally occurring phenols to react with. All leachates studied demonstrated an ability to remove from solution one or more of the six phenols used in large quantities over a period of 15 days or less. The overall performance of the leachates used in this study seemed to be a function of the humic acid levels found in them. Levels of naturally occurring phenols in leachates varied from several ppbs to more than 9000 ppbs for a year's period. The highest phenol levels were found in the young phenols and the lowest levels in the old phenols; indicating that pH and TOC concentration determine the amounts of phenols in solution. In column studies of perfusion of leachates through 10 cm of soil materials packed at field densities, no soil was able to stop the migration of phenols for more than 5 to 10 pore volume displacements. Low pH and high TOC levels seemed to play a much larger role in the migration of phenols through soils than the levels of phenols found in the leachates used. The use of phenol enriched deionized water passed through soil columns showed the fact that there is a clear dependency of adsorption of phenol on the flow rate. Slow rates favored adsorption of phenol by all soils studied. The TOC analysis of the effluents from the phenol enriched water-soil columns studies indicated that some mechanisms for the disappearance of phenol from soil solution may have been transformation reactions as well as adsorption reactions. Varying TOC levels with flux seemed to indicate that these reactions are much slower than the adsorption reactions. The use of Cu⁺² saturated soils in an attempt to correlate transformation reactions of phenol with transition metal catalytic properties failed to increase the adsorption and/or transformation of phenol in the soil media. The 4-aminoantipyrine colorimetric method performed well in the analysis of phenols in air unstable leachates. Gas-liquid chromatography using NPGSB+H₃PO₄ on Anakrom A 90/100 mesh was used for the quantitative and qualitative analysis of phenols in leachates.