Hydraulic ram pumps and Sling Pumps

F WATER QUALITY AND SUPPLY: McCONNACHIE, WARHURST, POLLARD and CHIPOFYAwhile the container was further cooled with tap wateron the outside. The resultant carbon was moist and toavoid any resulting irreproducible ash removal it wasdecided to improve and simplify the procedure bystopping the steam injection when the temperaturefell to 200 o C.Carbon characterisationTwo adsorbates, phenol and methylene blue, were usedto establish the porosity characteristics of the Moringacarbons. Two commercial carbons, Acticarbone andEurocarb, were also phenol tested. Conventionally thepores of activated carbon are divided into three groups,micropores of less than 2 nano-metres in “width”,mesopores of 2-50 nm and macropores of greater than 50nm. Phenol molecules can penetrate down to the lowerrange of micropores whereas methylene blue requirespores of about 1.3nm so can only enter the largestmicropores and the mesopores.For the adsorption tests, carbon samples (0.5 or 0.2g -see Figure 2) were added to 100mL of 0.01M solution ofthe methylene blue or the phenol adsorbate in 250mLErlenmeyer flasks, sealed with Suba-seals, then shaken at90 strokes per minute in a temperature controlled shakerbath at 25 o C for 24 hours. The flask contents were thenvacuum filtered through Whatman No. 542 filter paper,acidified with a drop of 1M HCl and the residual adsorbateconcentrations found by ultra-violet spectrophotometryat 665 nm for the methylene blue and 270nm for thephenol. All determinations were at least duplicated.For the Edinburgh carbons, in addition to the phenoland methylene blue tests, nitrogen adsorption analysisfor surface area characterisation and pore size distributionwas carried out as well as iodine number determinationto assess each carbon’s ability to remove low molecularweight compounds (Warhurst, McConnachie et al., inpress), (Warhurst, McConnachie et al., in press).ResultsThe results of the tests are given in Figures 1 and 2. Eachcarbon has been identified as, for example, EH700/30which is carbon derived from husk material used atEdinburgh and heated at 700 o C for 30 minutes; M denotescarbon from husk material used at Malawi, and P iscarbon from pods.The process of steam pyrolysis gives reproducible yieldswith duplicate runs differing by less than 1 per cent. Yieldtends to reduce as the heating temperature increases. Theduration of heating (soak time) has little effect on yield at500 or 600 o C but tends to give reduced yield for longertimes at the higher temperatures. The pods were turnedto ash at temperatures >700 o C whereas the husks ashedabove 800 o C and also at 800 o C when the time was 120minutes.Both the methylene blue and the phenol results showthat the capacity for a carbon to adsorb impurities willtend to improve as the temperature and the soak time ofproduction are increased. A compromise must be reachedbetween obtaining a high yield and maximising theadsorptive capacity and these are compared in Figure 2.The cost of production of the carbon is likely to be thegoverning factor which requires assessment of the powerrequirements of the particular furnace used.One difficulty which arose when carbon which hadbeen produced from the pods at 500 and 600 o C was usedin the adsorption tests was that a brown colour wasimparted to the sample which prevented reliable spectrophotometerreadings. Acid washing of the carbon coun-Figure 1. Activated carbon yield as percentage of original mass.280