Mass transfer kinetics of phosphate removal from sewage treatment plant effluent by waste mussel shell

Abstract

Excessive amount of phosphate (PO43-) released from sewage treatment plant effluent (STPE) may trigger eutrophication of water causing degradation of aquatic ecosystem and human health. Even though the presence of PO43- ions in aqueous solution can be removed using adsorption techniques, detailed description of adsorption kinetics is still not fully understood. In this study, the isotherm and kinetic adsorption of PO43- from aqueous solution onto porous material were conducted in batch experiments. A typical design of the hybrid plug flow column reactor (HPFCR) was used to remove PO43- from STPE. The kinetic models (i.e., pseudo-first-order (PFO) and pseudo-second-order (PSO)) and the isotherm models (i.e., Freundlich and Langmuir) were used to determine the adsorption kinetics and isotherms of PO43- from STPE onto waste mussel shell (WMS) and iron-coated waste mussel shell (ICWMS) adsorbents. The empirical models of bed depth service time (BDST), Thomas, and modified mass transfer factor (MMTF) were used to describe the adsorption kinetic processes of PO43- of WMS and ICWMS applied in the HPFCR. The experimental data for the adsorption of PO43- onto both WMS and ICWMS adsorbents fitted very well with the PSO kinetic model and Freundlich isotherm model, respectively. The dynamic adsorption capacity of WMS and ICWMS described by the BDST model has shown to increase with increase in the plug flow column (PFC) depth. The hydrodynamic behavior of PO43- global mass transfer can be described using the Thomas models for predicting the PFC performance. Employing the MMTF models enabled differentiation between the behavior of film mass transfer and porous diffusion. The resistance of PO43- mass transfer is dependent on porous diffusion and this contributes to the development of advanced WMS and ICWMS adsorbents in enhancing the performance of the HPFCR system in the future.