Patent Application
20080073290
Activated carbon (as received Filtrasorb400, 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 up 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 pre-determined, 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 in this particular example because it gave too much of a pH drop (down to 5.4 in the last example). However, 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. In an example of an embodiment of the present invention the carbon dioxide loading is within the range from about 0.1 to 1.0% 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 was 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
In addition to the laboratory-scale studies described in Examples 1, 2 and 3 above, a plant-scale trial was undertaken at the Haisthorpe Water Treatment Works (Yorkshire Water) to further demonstrate the effectiveness of carbon pre-treated with CO2 in water treatment according to examples of the present invention.
A trial was conducted during carbon filter bed commissioning operations. Thirty-three one-cubic meter quantity samples of activated carbon (33 m3 as-received base Chemviron F400 carbon) having moisture level notionally below 2% were treated with solid carbon dioxide to 0.5% w/w CO2 by intermittent mixing. In an example, the mixing was conducted during a tanker filling procedure. A weighed amount of solid CO2 (2.5 kg, in the form of dry ice pellets) to represent the required addition was evenly distributed by hand throughout each of the one-cubic meter increments of carbon as they were filled into the tanker. Quantities of treated and untreated carbon were used to fill one of each of the two Haisthorpe filter beds, respectively. Each of the beds was filled with 33 cubic metres of activated carbon, which corresponds to approximately 14.85 metric tons of F400 carbon each, and then contacted with Haisthorpe water. In an example, distribution was conducted to provide a generally homogeneous mixture of carbon dioxide and carbon. In another example of an embodiment of the present invention solid carbon dioxide was randomly or unevenly distributed into activated carbon.
The effluent waters during backwash commissioning of both filter beds were collected at various stages of bed-volumes flow-through and each was tested for pH property, and aluminium, manganese and iron content.
Previous laboratory studies using Haisthorpe water, detailed in Example 3, had indicated that 0.4% w/w CO2 pre-treatment of F400 carbon had achieved an effective nullification of the initial pH spike to within potable limits.
Additionally, metal leaching from contaminants in the water were generally minimized. Concentrations of aluminium and iron leach from the CO2 treated filter carbon were significantly lower than from the untreated carbon filter, and, also, levels of contamination were immediately, and markedly, below the respective Drinking Water Supply Limits. While the concentration of manganese from the CO2 pre-treated filter (4.5 μg/litre) was somewhat higher than that from the untreated carbon filter (as a direct consequence of the less alkaline water environment in the pre-treated filter) it was still significantly below the UK Drinking Water Supply Limit value of 50 μg/litre.
As an alternative to these methods of pre-treating carbon, in another example of an embodiment of the present invention, 0.5% w/w CO2-loaded carbon was achieved by direct blending of a weighed proportion of CO2-saturated F400 carbon with a weighed proportion of untreated F400 base carbon. The contact pH of the “blended” sample was determined and then compared with the contact pH of base untreated F400 carbon, and with a 0.5% w/w CO2 pre-treated F400 carbon prepared directly by the methods described previously. Ashton Towns water (pH 7.44) was used for the contact pH testing. The following four carbon samples were prepared and tested for contact pH property:
(i) Base F400 carbon having moisture level notionally below 2%;
(ii) CO2-saturated F400, prepared by placing a weighed amount of F400 base carbon in a glass container with dip-tube and exposing the carbon to a controlled flow of 100% CO2 gas for a sufficient amount of time to achieve a saturation CO2 uptake under ambient conditions, and re-weighed to indicate the saturated carbon sample had a CO2 uptake of 8.38 g per 100 g;
(iii) 0.5% w/w CO2 pre-treated F400, prepared by exposing a weighed quantity of F400 base carbon to a controlled flow of 100% CO2 for a governed adsorption time calculated to achieve the required 0.5% w/w CO2 loading—the actual CO2 loading was determined by the adsorption weight increase; and
(iv) Blended sample (representing 0.5% w/w CO2 loading), prepared from a weighed quantity of the CO2-saturated carbon (6.47 g) prepared in sample (ii) above that was blended by intermixing with a weighed amount of F400 base carbon (94.03 g) from sample (i) above to achieve a calculated 0.5% w/w CO2 loading of the carbon blend. In other examples, the carbon blend may be altered by varying the ratio of untreated carbon mixed with CO2-treated carbon.
The respective recorded test values were as shown in Table 1 below:
The method of blending a CO2 saturated carbon with a weighed proportion of untreated base carbon, by intermixing, gave a product equivalent to the method of direct loading of CO2 throughout all the carbon.
A series of carbon test samples was prepared to determine the effect of initial moisture content on the contact pH property of a CO2 modified F400C grade carbon. Various weighed amounts of water were added to weighed quantities of oven dried F400C carbon. Water and dried carbon weights for each sample were calculated to produce various moisture contents of the carbon ranging from nil to x %. After completion of water addition each prepared carbon sample was quickly stirred and then carefully transferred respectively to a labelled plastic bottle with screw-top fitment. The series of moisturized carbon samples was left to equilibrate for 16 hours at ambient conditions.
After equilibration, each of the moisturized test samples was further treated with a measured flow of 100% carbon dioxide gas (via a dip-tube assembly) for a flow time calculated to achieve a CO2 loading of 0.5% w/w. The actual loading of CO2 achieved was determined by sample weight increase, and, if required, an additional exposure to the CO2 gas flow was effected.
The resulting ‘carbon/moisture/CO2’ samples were allowed to re-equilibrate for 16 hours at ambient conditions.
For comparison purposes, a sample of the oven dried F400C carbon was also included in the test series (i.e. dried carbon base with no moisture or CO2 additions).
The composition weights of the prepared test samples are detailed in Table 2 below:
For each of the eight ‘carbon/moisture/CO2’ F400C carbon samples, a 100 cm3 quantity was measured and was added to 100 cm3 (i.e. 1 bed-volume) of water, locally supplied by Ashton-in-Malcerfield Township, with stirring. The initial pH of the local water was 7.35. After 15 minutes contact time the pH of the carbon/water system was recorded.
The excess water was then carefully decanted from the wetted carbon and an additional 1 bed volume of fresh Township water was added. The pH was again measured after 15 minutes contact time. This procedure was repeated twenty times to represent the effect of washing the carbon with additional bed volumes. The contact pH values obtained are shown plotted as a function of the number of water bed volumes in
As an extension to the contact pH studies reported in Example 6, a further experimental study was undertaken to determine the effects of even higher loadings of initial water content on the contact pH property of a CO2 modified carbon. Moisture levels ranging from 20% to 60% on a CO2 modified F400C grade carbon were investigated.
A series of five carbon test samples was prepared for the study by variously adding a weighed amount of water to a weighed quantity of an oven dried F400C carbon. Water and dried carbon weights for each test sample were calculated to thus produce the required moisture contents of 20, 30, 40, 50 and 60%. After completion of water addition each prepared carbon sample was quickly stirred and then carefully transferred respectively to a labelled plastic bottle with screw-top fitment. The moisturized carbon samples were then left to equilibrate for 16 hours at ambient conditions.
After equilibration, each of the moisturized test samples was CO2 treated with a measured, flow of 100% carbon dioxide gas (via a dip-tube assembly) for a flow time calculated to achieve a CO2 loading of 0.5% w/w. The actual loading of CO2 achieved was determined by sample weight increase, and, if required, an additional exposure to the CO2 gas flow was effected.
The ‘carbon/moisture/CO2’ samples were allowed to re-equilibrate for 16 hours at ambient conditions.
The five prepared samples were designated as Samples 9 to 13 and their composition weights are detailed in Table 3 below.
For contact pH testing of each moisturized sample prepared above, a 100 cm3 quantity was measured and was added to 100 cm3 (i.e. 1 Bed-volume) of water locally supplied by Ashton-in-Makerfield Township. The initial pH of the local township water was 7.35. The pH of the carbon/water system was recorded after 15 minutes of contact time.
The excess water was then carefully decanted from the wetted test carbon and an additional 1 bed volume of fresh Township water was added. The contact pH was again measured after 15 minutes. This procedure was repeated twenty times to represent the effect of carbon washing with the additional water bed volumes.
The contact pH values obtained for the additional five test samples are included in Table 4 and the contact pH values for are plotted as a function of the number of water bed volumes in
For comparison purposes, also included in the result are the respective contact pH values determined previously in Example 6 for both Sample 1 an untreated oven dried F400C carbon with no pre-moisture or CO2 additions, and for the previous Sample 7 which represented 10% initial moisture addition before CO2 modification.
As demonstrated by the various examples, addition of carbon dioxide to carbon improved the carbon's water treatment capabilities. In further examples, the drier the carbon was prior to addition the greater the carbon performance results.
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.
This application claims priority to and is a continuation-in-part of U.S. application Ser. No. 11/534,817, filed Sep. 25, 2006.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 11534817 | Sep 2006 | US |
| Child | 11754401 | US |
