The Evaluation of Modified Clays as a Coagulant For Water and Wastewater Treatment.

Coagulation is one of the standard processes in potable water and wastewater treatment, for destabilising colloidal and dissolved pollutants and. producing large flocs which can be removed from the water in subsequent solid/liquid separation processes. Aluminium and iron ferric salts are common water treatment coagulating chemicals. The natural mineral clays have attracted a great deal of research interest; the potential use of natural and modified clays as adsorbents for treating heavy metals and organic pollutants, or as coagulants for enhancing the settling performance and chemical oxygen demand (COD) removal in wastewater treatment have been investigated and applied practically. Nevertheless, the application of modified clays as coagulants has not been studied thoroughly. In particular, there are no published research results of using modified clay coagulants for sedimenting natural organic matter removal, algae control and car-washing wastewater treatment. This study aims to examine the comparative performance of modified clay coagulants for water and car-washing wastewater treatment. And the objectives of this study were: 1) to characterise the physicochemical properties of various raw clays and Al/Fe-modified clay coagulants by the analysis of various property parameters, 2) to optimise the PAC preparation for the preparation of Al-modified clays, 3) to isolate and purify the sedimentary natural organic matter from the Daecheung lake in Korea by using acid-base method, and to characterise the resulting NOM, 4) to evaluate the comparative performance of metal-based coagulants and Al/Fe-modified clays in the removal of humic and fulvic acids in terms of the reduction of turbidity, UV254, and colour (UV420-abs), 5) to evaluate the removal efficiency of algae (Microcystis aeruginosa) by coagulation with conventional coagulants and Al/Fe-modified clays in terms of reduction of chlorophyll-a and turbidity, and 6) to evaluate the treatment performance of car washing wastewater with various modified and raw clays in comparison with conventional metal-based coagulants. The main findings arising from the work detailed in this thesis are as follows: Raw-montmorillonite KSF makes a lower pH level (pH 1.8) than the other raw and modified clays when it is put into water. This results in a high leaching of Al3+ concentrations, when it was used as coagulant in water treatment. This limits its use in practice for drinking water treatment. The characteristics of humic substances obtained from the Daecheung lake sediment were consistent with those from other aquatic and sedimentary humic substance sources. In the removal of humic and fulvic acids by coagulation, for all types of coagulants, coagulation at initial pH 6.5 was more favourable than at initial pH 7.5. The comparative performance demonstrated at initial pH 6.5 and 7.5 that raw-KSF had the biggest effect on the final pH level drop down while P-KSF and raw-K10 showed the smallest drop in pH level. The order of turbidity removal could be expressed as: Al/Fe-KSF>PAC=Fe-KSF>Raw-KSF>AS>FS>Al/Fe-K10>Fe-K10. Overall, in the treatment of humic acid water, the order of the removal of UV254 and VIS420-abs was Raw-KSF (with great pH decreasing > AS ~ Al/Fe-KSF ~Fe-KSF>PAC ~Fe-K10>A1/Fe-KSF>FS, and in the treatment of fulvic acid, the order of the UV254-abs and VIS420-abs removal was Raw-KSF~AS > FS > Fe-K10 > Al/Fe-KSF~Fe-KSF > PAC > Al/Fe-K10. Obviously, modified clays (e. g. , Al/Fe-KSF) improved the turbidity removal but did not improve the UV254-abs and UV-Vis420-abs removal. Comparative coagulation results in the treatment of algae-containing model waters demonstrated that AS and PFS achieved 95% turbidity removal and PAC and PFS achieved more than 90% Chl-a removal. For KSF clay-based coagulants, the order of turbidity removal was P-KSF > raw-KSF > Fe-KSF > Al-KSF > Al/Fe-KSF and the order of Chl-a removal was Al-KSF > raw-KSF = Al/Fe-KSF > all others. For K10 based clays, the order of turbidity removal was Fe-K10 = P-K10 > all others. Raw-K10 was found to have no turbidity removal function. In terms of the Chl-a removal, almost all the coagulants showed 81% or higher efficiency. In particular, P-K10 showed 96% Chl-a removal over the entire dosages. Overall, P-KSF and raw-KSF demonstrated the best Chl-a removal. In the treatment of car washing wastewater, Fe-KSF and Fe- or A1-K10 can achieve the highest oil removal efficiency. For a low dose of clay, 200 mg/L (equivalent to a metal dose of 0.06 mM as metal), the Fe-KSF and Fe- or Al-K10 can remove 95% of oil but for the same metal dose, PAC can only remove about 80%. P-KSF coagulant can achieve the greatest removals of suspended solids and COD in comparison with the PAC and other clay-based coagulants. From this study, it can be concluded that montmorillonite can be modified with the acid, mixing polymeric Al/Fe species or a cationic polymer. And the resulting modified clay coagulants possess the specific properties to react with particles, organic constitutes and oils, and can be used as coagulants for treating NOM, controlling algae and remediation of car-washing wastewater. The modified clay coagulants thus represent a new type of coagulant having high potential in the treatment of various water and wastewaters over and above conventional coagulants