Removal of arsenic(V) from water by filtration through immersed microfiltration membrane with prior adsorption

Cilj ovog rada bio je utvrditi mogućnost primjene uronjivih membrana pri uklanjanju arsena u pripremi vode za piće, putem adsorpcije na istaloženi željezov hidroksid te naknadne filtracije putem uronjenih mikrofiltracijskih membrana. Adsorpcijske karakteristike istaloženog Fe(OH)3 su uspoređene s drugim komercijalnim adsorbensima pomoću adsorpcijskih izotermi, a najveći kapacitet je primijećen kod istaloženog Fe(OH)3. Tijekom filtriranja različitih koncentracija suspenzija istaloženog Fe(OH)3 u demineraliziranoj vodi, određene su vrijednosti kritičnog fluksa pri čemu je najveća vrijednosti od 250 L/m2 h postignuta pri filtraciji suspenzije s koncentracijom dodanog Fe(III) od 0,344 g/L i protoku zraka za miješanje od 16,83 L/min. Tijekom kontinuiranog uklanjanja arsena(V) iz vodovodne vode u koju je dodano 100 μg/L As(V) uz dozu Fe(III) od 5,16 mg/L i filtracije kroz uronjive mikrofiltracijske membrane, koncentracija arsena u permeatu bila je uvijek ispod 10 μg/L. Tijekom kontinuiranog uklanjanja arsena(V) membrane nisu bile relaksirane ili čišćene, a fluks je iznosio 60 L/m2 h. Permeabilnost membrane na kraju pokusa se smanjila za 62%. Ukupnom otporu filtracije najviše je doprinio otpor začepljene membrane od 50% zbog istaloženog kamenca na površini i unutar pora membrane, a otpor kolača pridonio je 15% kada je koncentracija suspendirane tvari u reaktoru iznosila 8,85 g/L. Početna permeabilnost membrana postignuta je nakon pokusa filtracije pranjem u 1% oksalnoj kiselini.The aim of this study was to determine the possibility of using immersed membranes in removing arsenic from spiked tap water, through adsorption on precipitated iron hydroxide and subsequent filtration through immersed microfiltration membranes. Adsorption capacities of precipitated Fe(OH)3 were determined and compared with other adsorbents by calculating the adsorption isotherms, and the highest capacity was observed in precipitated Fe(OH)3. During filtration of precipitated Fe(OH)3 suspensions in demineralized water, critical fluxes were determined for a different suspended matter concentrations and mixing conditions. The highest value of 250 L/m2 h was achieved by filtrating suspension of 0.344 g Fe(III)/L and at airflow rate of 16.83 L/min. During a continuous experiment for 21 days in a reactor with an immersed membrane, tap water was spiked with 100 μg/L of As(V) and treated with 5.16 mg Fe(III)/L and the concentration of As(V) in treated water was always under 10 μg/L. The configuration of the membrane allowed the maintaining of a high permeate flux of 60 L/m2 h. Membrane fouling was mostly caused by the precipitation of scale on the membrane surface and into the membrane pores, which contributed 50% to the total resistance. Cake resistance contribution to total resistance was low and reached 15% at the end of the experiment when suspended matter in the reactor reached 8.85 g/L. The initial permeability of the membrane could be restored by chemical cleaning with oxalic acid