Evaluation of pollution loading into Msimbazi river by rapid assessment and direct measurement methods

A rapid assessment (RA) methodology for environmental pollution was developed, evaluated and applied to the case of Msimbazi river. The selected parameters are BODs, Phosphorous and Nitrogen. The methodology is based on estimating waste loads from function variables and pollution intensities. The incorporation of penetration factors (PF) for waste loads reduction refines the assessment procedure . This has been shown after comparing RA results with Direct Measurement (DM) ones. The results show that all the three sources studied contribute to the pollution of the river with domestic being the leader 7600, 390 and 3200 tons/year for BODs, Phosphorou and nitrogen respectively. Industry is the second with high BOD discharge of 2500 tons/year. Direct measurement has been done to validate RA results and it is shown that the difference between the two methods is high when penetration factors (PFs) considerations were not incorporated into the RA model. At the point of discharge for instance, the difference observed is 23, 67 and 72% while after putting the concept of PFs into the model the difference is 4, 13 arid 8% for BOD5, P arid N respectively, which is encouraging. This is supported by regression equations. From this study the following can be recommended: RA is a useful tool for initial assessments of pollution sources. More studies should be done to develop more penetration factor(s) so as to refine the model, as the present ones do not consider other factors like the effect of phosphorous found in sediment. As the conversion factors for pollution and waste load used in the methodology are derived from models developed in more developed countries, in order to access pollution generation more accurately, a pollution index system for local situation should be developed. It is also recommended that RA assessment should be used if the need is to identify which some pollutes more followed by arialytical methods so as to reduce the cost of analysing sources with low amount of waste/pollutants.