EVALUATION OF THE FACTORS AFFECTING THE SELF-PURIFICATION CAPACITY OF RIVER KADUNA, NIGERIA

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Department of Engineering

ABSTRACT
The study of the evaluation of the factors affecting the Self-Purification Capacity of River Kaduna, Nigeria in addition to developing an empirical relationship for the reaeration constant was investigated during the period of February, 2014 to July, 2014. The physico-chemical properties and river flow variables were collected bi-monthly. This was achieved by sourcing data within a pre-selected segment of the river. The river flow variables include: depth, width, time of travel and velocity, while the physico-chemical variables are Dissolved Oxygen (DO), Biological Oxygen Demand (BOD), pH and Temperature. Regression Analysis was carried out using Excel Spreadsheet and Matlab with the reaeration constant k2 (as a function of BOD, DO & Temperature) as the dependent variable while stream velocity and depth were the regressors. The mean monthly DO was between 4.1mg/l to 6.6mg/l which is within the range suitable for aquatic life. The pH value was found to be in the range of 6.1 to 7.3 with most of the points being in the 6.1 region thus showing the water as slightly acidic. The mean water temperature ranged between 20.4oC and 23.6oC during the study period which is ideal for aquatic life according to WHO. The mean BOD value for most of the months was found to be greater than 10mg/l which is higher than the WHO permissible value thus making the river unfit for human consumption without treatment because of high microbial activity. The coefficient of reaeration was developed and validated statistically having an R2 value of 0.814. The performance of this model was compared with six (6) well known reaeration coefficient models and it was found to compare favourably with the model for February having the closest fit. The average self-purification factor (f value) was found to be greater than unity in all the months studied which show that reaeration exceed deoxygenation with the months of March and April being the lowest and respectively 1.8 and 2.8. The average self-purification capacity of the month of June and July were higher because of the higher rate of transfer of oxygen from the atmosphere to the river and the values are 4.16 and 4.11 which shows the predominance of reaeration rate over deoxygenation rate.