Abstract
Abstract Alum residuals were collected from a water treatment plant and used for improving the photocatalytic degradation of humic acid (HA) by combinations of zinc oxide (ZnO) and powdered residuals from a water purification plant (PRWPP). The influence of operating conditions such as initial humic acid concentration, pH, irradiation time, PRWPP to ZnO ratio, catalyst dose, and light illuminance have been investigated. The optimum PRWPP to ZnO ratio was 10:90. Using the prepared composites instead of bare ZnO raised the HA removal efficiency from 85.5% to 97.8%, and from 38% to 48.1% at catalyst doses of 1.2 g/l and 0.4 g/l, respectively. Moreover, it reduced energy consumption from 210.4 to 166.2 Wh per mg of HA. An artificial neural network model (ANN) was developed to predict the removal efficiency under different operating conditions. The optimum ANN structure yielded a coefficient of determination (R2 = 0.993). A modified Langmuir-Hinshelwood pseudo-first-order model was used for describing the degradation kinetics at different initial concentrations of HA.
Highlights
Coagulation followed by flocculation, sedimentation, and filtration is considered the conventional, most used technique in water treatment plants worldwide (Dassanayake et al 2015)
Humic substances can be subcategorized according to solubility properties into three main groups: humic acid (HA), which is soluble in water at pH . 2; fulvic acid (FA), which is soluble in water at all pH conditions; and humin that is insoluble in water at any pH level (Uyguner et al 2007)
The aim of this study is to investigate the possibility of adding powdered residuals from a water purification plant (PRWPP) as an enhancement to the zinc oxide (ZnO)-photocatalysis process for HA degradation
Summary
Coagulation followed by flocculation, sedimentation, and filtration is considered the conventional, most used technique in water treatment plants worldwide (Dassanayake et al 2015) In this process, a chemical coagulant, mostly aluminum salts, is added to help destabilize the electrical double-layered colloids and reduce the repulsive forces between the colloid particles; as a result, colloids agglomerate to form flocs and settle (Matilainen et al 2010). Humic substances are dark brown, structurally complex, and polyelectrolytic materials that represent the major percentage of natural organic matter (NOM) They comprise 40–80% of the dissolved organic carbon in natural waters. NOM is a major concern in water treatment for its ability to react with residual chlorine forming disinfection by-products (DBPs), such as trihalomethanes and haloacetic acids (Richardson et al 2007). Several approaches have been employed to remove humic acid or NOM, such as conventional or advanced coagulation, membrane filtration, ion exchange, adsorption using activated carbon, and advanced oxidation processes (AOPs) like ozonation, photo-Fenton, and heterogeneous photocatalysis (Liu et al 2008)
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