Advances in Water Treatment and Enviromental Management

268 WATER TREATMENTsimultaneously. From these data and using the formula suggested in section7.1, the treatment efficiency of the SKO has been calculated and is shownin Table 1. The calculations have been based on the fundamental premisethat mass entering the device equals mass leaving the device.TABLE 1The analysis of the automatic and bulk samples from the SKO suggeststhat there is a considerable reduction in dissolved pollutants. However, theslight increase in suspended solids recorded by the outlet automatic sampleron 17/3/89 was due to some water decanting back through the machinefrom the sample bottle and leaving concentrated sediment in the bottom ofthe bottle.Two aesthetic studies have been carried out. On one occasion 53 objects ofsewage origin were recovered along a 50m stretch of river downstream ofthe overflow. On another occasion, 26 objects were found. One reason forthis could be that neutrally buoyant objects remain suspended within theSKO and when conditions are right (perhaps aided by leaves) escape withthe discharge. But, in the authors’ experience, this performance is good incomparison to the efficiency and effectiveness of conventional screens.9. CONCLUSIONSThe study commenced in October 1987 and is still continuing. Moreinvertebrate data are required to assess the long term trends of water quality