The assessment and modelling of depletion of dissolved oxygen in Woji/Okujagu Stream
Date
2021-05
Authors
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Publisher
Federal University of Technology, Owerri
Abstract
This research work presents the study of the depletion of dissolved oxygen in Woji/Okujagu River in Port Harcourt Local Government Area of STREAM State,
Nigeria. The study was carried out between February, 2017 (dry season) and August, 2017 (wet season). The sampling exercise was done on six (6) selected stations (stations A, B, C, D, E and F) along the river located at progressive distances 200m upstream and downstream from the point of influent discharge. Sampling was done three times during the dry season (February) and during wet season (August) 2017. The physical and chemical properties of the river samples such as Temperature, Total Suspended Solids (TSS), Electrical Conductivity (EC), pH, Nitrates, Biochemical Oxygen Demand (BOD5), and Dissolved Oxygen (DO) were analysed using standard methods. The parameters were then compared to ascertain their conformity with national and international standards set by the Nigerian Environmental Standard and Regulation Enforcement Agency (NESREA) and the World Health Organisation (WHO). Further analysis was carried out by the application of extended version of Thomas slope and O′Connor re-aeration and Streeter-Phelps models to determine the
depletion of dissolved oxygen in the River by the decomposition characteristics of the discharged effluents. The results of the analysis showed that the temperature ranged from 25.4 - 29.50C, TSS ranged from 145.6 – 484.4mg/L, EC ranged from 422.7 - 982.2 µS/cm, pH ranged from 6.0 - 7.3, Nitrates ranged from 12.5 - 97.3mg/L, BOD ranged from 22.5 – 75.2mg/L and DO ranged from 2.2 – 6.5mg/L. Only pH values were within the recommended NESREA and WHO standards. The pollution index for all the stations was 2.7081. The critical time tc was 6250 sec (0.0353 day). Deoxygenation constant Kd and ultimate BOD Lo were 0.744 and 79.2mg/l, respectively. The re-aeration constant Kr was 0.0282. The values of DO obtained from laboratory analysis were plotted against time. The DO curve generated showed that the minimum DO level of the River is 2.7mg/l. From the curve, the measured and simulated DO showed that the DO reduction rate tends to be greater than self-purification rate which can contribute greatly to the degradation of the quality of the river ecosystem and human/aquatic life. It is therefore recommended that relevant authorities should embark on regular monitoring activities of receiving STREAM in STREAM State to ensure the safety of human and aquatic population and the environment.
Description
This thesis is for the award of Master of Engineering (M.ENG) degree in Civil Engineering (Water Resources Engineering Option)
Keywords
Influent discharge, river pollution, physicochemical parameters, dissolved oxygen, models., Department of Civil Engineering
Citation
Owor, A. A. (2021). The assessment and modelling of depletion of dissolved oxygen in woji/Okujagu Stream (Unpublished Master's Thesis). Federal University of Technology, owerri, Nigeria