Application of advanced adsorption processes for dissolved organic matter and heavy metal removal from water sources

Abstract

[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT AUTHOR'S REQUEST.] The main objective of this research was to develop an improved understanding of natural organic matter (NOM) and heavy metals removal from two water sources: the City of Columbia McBaine Water Treatment Plant and synthetic water samples prepared in the laboratory. Batch experiments were conducted to evaluate the feasibility of utilizing the adsorption process with magnetite, magnetic ion exchange resin (MIEX), and powdered activated carbon (PAC) as adsorbents to reduce the NOM found in natural groundwater. Control and treated samples were studied to determine the removal degree of dissolved organic matter (DOC) and to verify the impact to the formation potential of disinfection by-products (DBPs). There was no clear correlation found between DOC and disinfection byproducts formation potential (THMFP) over the range of DOC values examined in this study. For MIEX applications, this lack of correlation between DOC removal and DBP could be due to partial dissolution of organic components from MIEX itself. The research provides a framework for using adsorption for the removal of NOM and control of DBP. The presence of common groundwater constituents, such as iron, was found to adversely impact the adsorption capacity of NOM onto MIEX. Possible reasons may include- blocking of the ion-exchange sites on MIEX, and the formation of NOM-Fe complexes that may possess different sorption characteristics from pure NOM. The effects of iron in both Fe2+ and Fe3+ states on the adsorption of NOM onto MIEX were evaluated. The removals of TOCs were found to be higher in oxic conditions whereas the removals of UV254s were found to be higher in anoxic conditions. In oxic conditions, MIEX was capable of removing both NOM and iron effectively when coexisting in raw water. Iron could compete with NOM for exchange sites on MIEX at high dosages (>4 ml/L), which in turn could decrease the NOM removal rate. In anoxic conditions, similar removal patterns were observed as those in oxic conditions, except that MIEX adsorbed less iron with increasing iron content in the water samples. The extent of competitive adsorption was dependent on the initial concentration of trace compounds, the initial concentration of NOM, the molecular size of trace compounds, the molecular size distribution of NOM molecules, and the type and dosage of adsorbents. Experiments were also conducted to study the effects of pH, ionic strength and hematite nanoparticles dosage on the adsorptive removal of Co2+ from aqueous solution. It was observed that adsorption was enhanced in neutral pH conditions, comparing to acidic condition and irrespective of ionic strength. Freundlich models were capable of representing the data more satisfactorily than the Langmuir models. The co-ions removed Co in the order Pb2+> Cu2+ >HA. Hematite nanoparticles derived from ferroxane-AA were deposited on porous alumina tubes to develop tubular ceramic membrane for the removal of Co2+. Ferroane-AA loading on ceramic tube was found to be very low; 0.5 g of ferroxane-AA loaded only 1% and 2.0 g of ferroxane-AA loaded 0.7%. The regeneration process was tested for 4 washing cycles without membrane damage. The results of this study indicate that, with the adsorptive removal of cobalt ions from natural groundwater and the ability to adsorb multiple metal ions simultaneously, hematite nanoparticles may offer a potential and suitable remediation method for the removal of cobalt ions. The ferroxane-AA fabrication process takes place in an aqueous environment, does not involve the use of hazardous substances, and has low energy consumption due to the low firing temperature of the ceramic tube. Furthermore, the generation of liquid wastes on site can be avoided during operation. The membranes can be re-used after washing with a basic solution. The materials can be processed for regeneration in a centralized treatment facility for improved liquid waste management. Its compact and user-friendly design allows it to be deployed at the point of use, while it is also flexible to adapt to a larger scale, suitable for water treatment plants.