Variation of Al species during water treatment: correlation with treatment efficiency under varied hydraulic conditions

Chuang Wang,Xiaoshang Li,Guocheng Zhu,Wei Huang,Zhenghua Wang,Andrew Hursthouse,Zhaohui He

doi:10.2166/aqua.2021.144

Abstract

Abstract The concentration of hydrolyzed coagulant ion species is a key factor in determining drinking water treatment efficiency. Direct correlation of water treatment efficiency with changes in species during coagulation has not been addressed. We investigated the correlation under different hydraulic conditions and water treatment efficiencies including changes in removal of turbidity, ultraviolet adsorption at 254 nm (UV254) and dissolved organic carbon (DOC). Results highlighted that Al species (monomeric species as Ala, medium polymeric species as Alb and colloidal species as Alc) behaved differently during coagulation and treatment efficiencies were affected. When varying the mixing speed, the removal of Alc species had a strong negative correlation with water treatment efficiency but under other hydraulic conditions positive correlations were found. The removal of Ala species was positively correlated with water treatment efficiency, but under other hydraulic conditions the low abundance of Ala species meant the correlation was difficult to observe. The Alb species were significantly and positively correlated with water treatment efficiency with the highest correlation coefficient (R2) of 0.87. The correlation of metallic species with removal efficiencies of the DOC and the UV254 produced higher R2 values. Correlation of the rate of removal of Alb species with the removal efficiencies of the DOC or the UV254 was better than for Alc.

Highlights

With continuous population growth and industrialization, an inevitable increased demand for clean water creates challenges for its continual supply
We evaluated the variation of the poly aluminium chloride (PACl) species under different hydraulic conditions using the ferron method, and investigated the correlation between the changes in species abundance (%) in aquatic solution with water treatment efficiency, including the removal of turbidity (%), the ultraviolet adsorption at 254 nm (UV254) (%) and the dissolved organic carbon (DOC) (%)
Research on the correlation between the Al species removal and pollutants removal will help to understand the interaction between these species and pollutants including turbidity, DOC and UV254

Summary

Introduction

With continuous population growth and industrialization, an inevitable increased demand for clean water creates challenges for its continual supply. The use of traditional inorganic metallic salts such as (aluminum sulfate), is considered to have relatively low efficiency (Chang et al 1993) compared to pre-polymeric metallic salts. Widely used pre-polymeric metallic salts such as poly aluminium chloride (PACl) have been widely studied to improve the performance of water treatment prioritized due to their high molecular weight and charge and as a substitute for aluminum sulfate to avoid forming large quantities of Al(OH). A typical PACl is prepared using the following reactions: Al (OH) þ HCl → AlCl3 þ 3H2O, and 2mAlCl3 → (Al2Cln (OH)6Àn)m under alkaline conditions (Zheng et al 2011). The formation of PACl is a reaction converting Al3þ to

Methods

Results

Conclusion