Adsorption characteristics on sand and brick beds

Adsorption can be used to treat wastewater containing low levels of pollutants efficiently. In this work adsorption isotherms are first obtained for phosphates, nitrates, chlorides and detergents from batch experiments. The motivation for the choice of these solutes stems from the fact that they are present in grey water i.e., domestic wastewater. The sorbents used are sand, brick and a 1:1 mixture (by weight) of sand and brick. Langmuir isotherm was found to best fit the equilibrium data. Experiments were also carried out in fixed beds using the above material as adsorbent for the different solutes. The Langmuir isotherm obtained from batch experiments was confirmed using the continuous experiments.For each salt, four different feed concentrations were used for continuous experiments. Breakthrough curves were obtained by measurement of concentrations continuously at the exit using an on-line conductivity meter. A theoretical one-dimensional dynamic model (convection-dispersion equation) is used to understand the adsorption behavior in the fixed bed. The dispersion coefficient was obtained by minimizing the error between the experimental values and the predictions of the model using the method of least squares. This error was treated as an objective function and minimized for a set of operating conditions. The same dispersion coefficient was able to predict the breakthrough curves accurately for different operating conditions i.e., inlet concentrations.