Activated carbon is used in many drinking water treatment plants and home water filters for the removal of unwanted dissolved compounds. Superfine powdered activated carbon (S-PAC) is a new material that has a much smaller particle size than traditional activated carbon. Due of its small size, S-PAC can remove contaminants faster and with less mass, but since S-PAC particles are very small they must be removed by membrane filtration before treated water is distributed. This filtration is not easy because S-PAC can block the membrane pores, negatively affecting the filter performance. One way around this might be to create larger particles through aggregation of S-PAC before it reaches the membranes. This study will evaluate various S-PAC aggregation techniques within a ceramic membrane filtration module for enhancing filter performance. This research will be carried out in collaboration with Dr. Matsui, an expert in combining S-PAC with ceramic membranes for contaminant removal, at Hokkaido University in Japan.
In previous work, S-PAC particles caused marked membrane pore blocking on 0.1 µm polymer-based membranes in dead-end filtration. Aggregation with chemical coagulation was shown to be successful at reducing the problem. This research will evaluate whether the results are similar with ceramic membranes instead of polymer ones. A ceramic membrane module will be operated with aggregated and disaggregated S-PAC to test the filter performance and compare with previous results. Additionally, the effects of natural organic matter (NOM) will be evaluated. Results of this study will contribute towards the understanding of S-PAC behavior and potential future applications for removal of trace contaminants in drinking water treatment. This NSF EAPSI award is funded in collaboration with the Japan Society for the Promotion of Science.
The primary goal of this project was to assess the interactions of aggregated superfine carbon particles with ultrafiltration membranes. As a first step, aggregation rates were measured for particles in ultrapure water and in salt water to determine the rate of background aggregation. The rate of aggregation was negligible except for very high particle and salt concentrations or salt solutions containing calcium. To achieve controlled aggregation, two chemical coagulants were used: ferric chloride and polyaluminum chloride (PACl). Jar tests were used to evaluate the balance of components on aggregation effects, including the amount of coagulant, amount of alkalinity, and the pH. PACl required more alkalinity than ferric chloride to aggregate the carbon particles. Aggregation with ferric chloride occurred at both pH 7 and pH 6, however, filtration performance changed drastically as a result. At pH 7, the flux was much above baseline, but at pH 6, the flux was lower than the baseline. Increasing the alkalinity did not affect the performance at pH 7. Aggregation with PACl also resulted in improved filtration performance, but only in the presence of agitation. Conversely, agitation did not affect results with ferric chloride. Natural organic matter (NOM) resulted in drastic fouling and the previously used coagulant recipe was not sufficient to mitigate the fouling. Further exploration of NOM-containing waters is necessary. Implications: The success of conventional chemical coagulants means that superfine carbon can be implemented easily into existing water treatment methods. The varying need for agitated filtration informs the design of superfine carbon contactors and choice of coagulant. Further work is necessary for understanding interactions with NOM, a component of all surface waters.
