Arsenic pollution of drinking waters across the world is one of the most serious water-related problems due to its well-established consequences on human health even at very low concentrations in the lower µg/L range. Among different well-established options for arsenic remediation, the adsorption onto highly efficient commercial iron oxyhydroxide-based adsorbent such as granular ferric hydroxide (GFH) has proven to be effective and persuasive. However, GFH is a cost-extensive material. During the industrial production of granular fractions of conventional adsorbents, the fine-grained fraction (individual particle size of < 250 µm) is generated as by-product/waste as this fraction of granular adsorbents cannot be applied in fixed-bed adsorption filters because of high clogging potential in filter-bed.
In this doctoral thesis, an integrated water process combining the adsorption and submerged microfiltration (MF) unit (abbreviated as SMAHS) was investigated to employ fine-grained iron oxyhydroxides. Air bubbling was applied in the slurry reactor of a SMAHS to introduce shear at the membrane surface for fouling control. Moreover, the powdered-sized fractions (individual particle size of ~ 3 µm) of iron oxyhydroxides were applied to form the pre-deposited dynamic membrane (DM) and the effectiveness of the formed DM was assessed in MF process.
n addition to the fine fraction of the GFH, arsenic adsorption on µTMF (fine-grained tetravalent manganese feroxyhyte) was investigated through batch adsorption tests at pH 8 in three different water matrices and different adsorption isotherms were applied. The physical and chemical characteristics of the adsorbents were also fully investigated. The Freundlich isotherm describes the equilibrium isotherm data better than Langmuir isotherm, indicating a heterogeneous nature of the applied adsorbents. The isotherm data shows characteristics of favorable arsenic adsorption onto µGFH and µTMF. Further, adsorption efficiency of applied adsorbents depends strongly on the water quality parameters (pH and water matrix). Arsenic adsorption onto both adsorbents is mostly reversible, with a small proportion of irreversible adsorption.
The findings from SMAHS indicate that the arsenic adsorption efficiency is comparable to that found in a fixed-bed adsorption filter packed with conventional adsorbents of the same type, with potential benefits of simultaneous removal of micro-organisms and turbidity. The material cost is estimated to be as low as 0.30 €/m3 of product water when the arsenic concentration in the product water is below the drinking water regulation limit (10 µg/L). The outcomes further suggest that iron oxyhydroxides as forming materials of DMs may be applied in water treatment to achieve arsenic removal rates of greater than 90 % if operating conditions are well controlled. Moreover, arsenic removal rates of the SMAHS and DM can be predicted/modeled using a mathematical model based on a homogenous surface diffusion model (HSDM). In conclusion, it is expected that the new applications of fine-grained iron oxyhydroxides would not only increase the sustainable footprint of the conventional adsorbent production process as the by-product will be utilized but also be efficient solutions for arsenic remediation using the highly efficient low-cost adsorbents in water treatment.