Patent Application
20080073289
Activated carbon (as received F400, 12×40 US mesh) was transferred to a glass container fitted with a dip pipe and exposed to a flow of various quantities of carbon dioxide to give carbon dioxide loadings varying from 0.1 to 10% by weight. For a preferred example, the loadings vary from 0.2 to 5%. The latter representing the maximum amount of carbon dioxide that can be taken tip by the carbon. Depending upon the selected carbon, it may be excessive for this application, resulting in carbons that would impart too much acidity to the water and be below the potable pH value. Appropriate loadings are determined by applying a convenient flow rate of carbon dioxide based on the weight of the gas for the required amount of time−ml/min×total minutes gives total volume. The carbon is weighed before and after the gas is flowed through and the weight uptake is confirmation of the final loading. Untreated activated carbons were used as the control, and a carbon prepared by the method of U.S. Pat. No. 5,876,607 was used for comparison. Additional work was carried out using reactivated carbon (as received F400 React, 12×40 US mesh, ex. Feluy) loaded with carbon dioxide at approximately 0.3 and 0.5% w/w, respectively, as further described below.
Samples of untreated carbon and carbon treated as described above in amounts of 100 cm3 were added, in turn, to two bed volumes of water locally supplied by Ashton-in-Makerfield Township with stirring. The initial pH of the local water was 7.44. The contact pH was recorded after 30 minutes. The water was then decanted and two bed volumes of fresh Township water were added. This process was repeated a number of times to represent the effect of additional bed volumes. The contact pH was plotted as a function of the number of water bed volumes. Results are shown in
All experiments were conducted at the laboratory ambient temperature and pressure. The laboratory bed volume measured 200 cubic centimetres (i.e. two bed volumes stated above).
Addition of two bed volumes of the town's water to untreated F400 activated carbon resulted in the anticipated pH spike as illustrated in
Samples of F400 activated carbon were treated with varying quantities of carbon dioxide. Each sample was contacted with two bed volumes of water from Ashton-in-Makerfield Township. The water had an initial pH of 7.44. The contacted water experienced an immediate decrease in the effluent water's pH. The degree to which the decrease occurred was noted to be a function of the amount of carbon dioxide added. For example, F400 carbon saturated with carbon dioxide (corresponding to a loading of 7.52%) gave the biggest fall, to about 5.4 pH. A loading of only 0.5% carbon dioxide gave a drop in pH to about 6.4. The influence of carbon dioxide loading on initial contact pH is illustrated in
The contact pH corresponding to 0% carbon dioxide loading is that resulting from exposure of the water to untreated carbon. Knowledge of this value together with the other experimental points illustrated in
The contact pH of F400 carbon with 0.3% carbon dioxide loading is illustrated in
According to the patented method, F400 carbon was soaked in an unspecified quantity of water for 16 hours before being drained and subsequently treated with carbon dioxide, and this procedure was followed here. Two bed volumes of soak water were added to the F400 and left for 16 hours. The drained soak water had a pH of 9.27. The wetted carbon was then treated with carbon dioxide and a further two bed volumes of water were added to give a contact pH of about 7.6. This value rose above the upper potable range of 8.5 after the subsequent addition of 12 bed volumes of water, as observed in
The dry 0.3% carbon dioxide-treated carbon delivered water with a pH in the standard, potable range throughout the course of the washings. Use of 0.5% carbon dioxide-treated carbon for this carbon-water system would likely result with a water pH that would be too acidic. Increasing the dry carbon dioxide loading to 1.16%, however, produced initially acidic water which was below the pH 6.5 threshold up to about 10 bed volumes.
The ideal loading of carbon dioxide varies depending upon the selected carbon and the water to be treated. For the best results in a particular situation a suitable amount of loading should be determined up-front, especially before conducting large scale water treatment. This determination may be aided with extrapolation from related tests or graph interpolation. As exemplified above, a 7.52% loading was excessive because it gave too much of a pH drop (down to 5.4 in the last example). The appropriate amount of carbon dioxide for most situations involving carbon pre-treatment is expected to range from about 0.1 to 10% by weight of the carbon.
Data for reactivated F400 carbon is illustrated in
It is notable that the untreated, reactivated carbon required about 80 bed volumes to bring the water pH into the potable range whereas both the carbon dioxide-treated carbons are consistently and immediately within the potable range.
Activated carbon (as received F400 carbon) was treated by exposing it to a flow of carbon dioxide gas to give a loading of 0.4% weight carbon dioxide by weight of the carbon. A loading of 0.4% carbon dioxide was pre-selected based on anticipated condition similarities with the prior example. A sample of treated carbon was used to contact raw feed waters from Nutwell Water Treatment Works (Yorkshire Water). For comparison, a sample of untreated carbon was also contacted with the feed water. Each sample contacted water contained in a laboratory bed column measuring 200 cubic centimetres. A notional contact time of 45 minutes was used. The pH of each treated effluent was measured at one bed-volume intervals over 30 bed volumes. Results of the two samples show a comparison of the effluent pH property of F400 carbon both with and without CO2 pre-treatment as illustrated in
Additional samples of untreated carbon and carbon treated as described in Example 2, and contacted with water from the Haisthorpe Water Treatment Works (Yorkshire water). Results of water treatment with the carbon samples are illustrated in
Neither of the Nutwell or Haisthorpe waters tested appeared to be particularly troublesome, indicating that only a minimal number of washes would be required during commissioning to bring the pH of the water to within the potable range. Nevertheless, treatment of the Filtrasorb 400 carbon with 0.4% w/w carbon dioxide gas produced effective nullification of the initial pH spike for both water samples, which were immediately measured to be within the potable limits, indicated by the dotted lines in
While the foregoing has been set forth in considerable detail, it is to be understood that the detailed embodiments and Figures are presented for elucidation and not limitation. Process variations may be made, but remain within the principles of the invention. Those skilled in the art will realize that such variations, modifications, or changes therein are still within the scope of the invention as defined in the appended claims.
