Investigation of Plausible Mechanism of the Synthesized Inorganic Polymeric Coagulant and Its Application toward Fluoride Removal from Drinking Water

Abstract

Fluoride, an anionic pollutant, existing in concentrations exceeding the allowed limit of 1.5 mg/L in drinking water, has been reported to cause detrimental impact on human health. The traditionally employed methods for water defluoridation mostly involve Al-based coagulants, which however face some limitations, such as requirement of relatively high dosage and production of excessive amounts of chemical sludge posing a problem of its safe disposal. In this study, two inorganic polymeric coagulants of medium (IPC-M) and ultrahigh basicity (IPC-UH) were synthesized using polymerization of aluminum trihydrate (Al 2 O 3 •3H 2 O) with an aqueous solution of 32% hydrochloric acid. The basicity of coagulants was increased by manipulating the redox reaction of the product with the aluminum metal. The synthetic coagulants were analyzed using various characterization techniques, viz., Fourier transform infrared spectroscopy, electrospray ionization−mass spectrometry, and field emission scanning electron microscopy with electron-dispersive X-ray spectroscopy, and the main physicochemical properties such as % Al 2 O 3 , relative basicity, and % chloride. The aluminum species distribution was assessed by the ferron assay, and their electrochemical properties such as dissolved charge, conductivity, acidity, and pH were also measured. The application of IPCs was explored for their fluoride removal efficacy using jar tests. The outcome showed that IPC-M was the most efficient when applied in a pH range relevant to fluoride-containing water as it was the only coagulant that showed increasing efficiency at pH values > 7. The uptake capacity of coagulants for using synthetic samples prepared in Milli-Q water containing 9 mg/L of raw fluoride concentrations to achieve residual concentration of less than 1.5 mg F/L at the pH value 6.5 ± 0.1 was calculated as 87.68 and 68.48 mg F/g Al 2 O 3 for IPC-M and IPC-UH, respectively, which were higher than the reported values of 37.42 and 37.75 mg F/g Al 2 O 3 for alum and polyaluminum chloride in an earlier published paper. The residual aluminum concentration in these experiments ranged at 30 ± 5 and 20 ± 5 μg Al/L, respectively, for IPL-M and IPL-UH, which were well within the WHO norm for drinking water (<200 μg/L), indicating their immense application in the field.

Development of an integrating coagulation and reverse osmosis system to treat highly turbid water using synthesized coagulants

“…The dose required in the case of both the IPC is 1/3 to that of the dose required in the case of Alum. This may be due to the formation of more polymeric to the monomeric species (Al 2 (OH) 5 .2H 2 O) in case of IPC-UH (Solanki et al 2020a). Moreover, polymeric species present in IPC show the net structure and bridging flocs formation during the coagulation process.…”

“…There are three major Al species formed in the coagulation process: monomeric, oligomeric, and polymeric species (Dubey et al 2018a). The monomeric, oligomeric, and polymeric Al species are dominant in the case of alum, IPC-M, and IPC-UH, respectively (Solanki et al 2020a). The monomeric species leads to sweeping flocculation, resulting in various sized flocs, both big and small (Dubey et al 2018b(Dubey et al , 2018a.…”

“…All of the chemicals utilized in the investigation, including aluminium sulphate (Al 2 (SO 4 ) 3 .16H 2 O), calcium carbonate (CaCO 3 ), and hydrochloric acid (HCl), were purchased from Merck which were of analytical grade. Inorganic Polymeric Coagulants were synthesized using polymerization of aluminium tri-hydrate (Al 2 O 3 .3H 2 O) with an aqueous solution of 32% hydrochloric acid as per our earlier publication (Solanki et al 2020a). Same coagulants were used in this study for a removal of turbidity.…”

“…Therefore, the present article proposes integrating coagulation and RO systems to treat highly turbid water using synthesized coagulants. The coagulants synthesized in the previous research work (Solanki et al 2020a) were implemented in the present article for removing turbidity of water collected from the Bisalpur dam, which is the major source of drinking water in Jaipur Rajasthan (India). All the physicochemical properties were determined for the collected dam water sample and coagulant treated water stream and outlet stream of the RO system.…”