Advances in Water Treatment and Enviromental Management

210 WATER TREATMENTTABLE 1Design parameters for Stripping Volumes3.4 Case Study AThe performance of the Case A columns is shown in Fig 8. It can be seen that the concentrationin the raw water has been quite variable, ranging from 20 to 110 µg/l with an average of 93µg/1. The concentration of TCE in the aerated water was below the WHO Guideline level of 30µg/1 on all occasions. The peak, at day 165, is likely to be an erroneous result: it is extremelydifficult to maintain an adequate level of sample cleanliness when dealing with such lowconcentrations. The percentage removal graph. Fig 8 shows three such low points where thevalidity of the results must be questioned.Aside from these three points, the removal efficiency ranges from 87–98%. The average removalefficiency is 92.9%, or 93.8% omitting the three low points.If these removal rates are used in Equation (3) K L a can be shown to be 57.7.When mass transfer is liquid rate controlled K L a can be calculated from the following equation(Norman W S, 1961).The diffusivity of. K L a is therefore calculated to be 72.8. It can be seentherefore that the actual mass transfer rates achieved are 80% of theoretical values. This istypical in that about 0.5 m of tower packing is usually considered as ineffective since it isfunctioning primarily as a water distribution section (at the top) and an air distributor at thebottom.The removal efficiency for PCE averaged 93.6% when three apparently anomalous resultswere ignored.3.5 Case Study BIn Case B two packed towers were constructed to treat 500 m 3 /h of groundwater contaminatedwith TCE, PCE and low levels of CTC. The packing supplied by the Contractor was 94 ram(4)