Optimization of Waste Discharge Points in Natural Streams

Ezeilo FE¹ and Agunwamba JC²*

Received: August 09, 2018;   Published: August 28, 2018

DOI: 10.32474/TCEIA.2018.02.000148

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Abstract

This paper reports on a study carried out to optimize the locations of multiple discharge points in a receiving stream, Amadi creek, so as to minimize the impact of oxygen demanding resources (BOD) on water quality. The study evaluated the water quality changes as a result of the increasing human and industrial activities around the creek. Water quality standards require the maintenance of dissolved oxygen (DO) concentration of 5mg/l or more at any time in streams. However practical analysis of the water samples from Amadi creek reveal a DO level as low as 2.3mg/l. The DO deficit was computed from data generated by sampling DO concentrations along the creek from various points of waste discharge downstream while the BOD of the stream was determined by monitoring BOD of samples obtained along the creek. The study also identified and quantified the amount of effluent entering the creek from various point sources. The DO deficit equations are solved by the methods of simple calculus (classical optimization), which simplifies the mathematical solution of the model equations by avoiding difficult to evaluate integrals Two scenarios were identified and used to investigate the effect of BOD on the DO level in the stream, using mathematical simulation techniques. Simulation results show that to ensure minimum impact of BOD on water quality waste discharge locations should be placed at the optimal locations of 10015.382m and 6992.282m upstream and downstream waste discharge points respectively, at an optimum DO deficit of 4.135mg/l for case 1.

For case2, the waste discharge locations are to be placed at optimal locations 40995.43m, 30665.17m, 41233.69m upstream and downstream waste discharge points respectively at an optimum DO deficit of 4.567mg/l. This means that if a new waste input is proposed for a stream its BOD input and its proposed location with respect to other inputs are important in order to determine the effect on the DO level in the stream Discharges from the second treatment plant would result in decreased dissolved oxygen level for a substantial distance downstream. This can have significant effects for streams and rivers with many influent waste streams over their course, as the dissolved oxygen (DO) will not have a chance to recover between each influent stream, resulting in significantly depressed oxygen levels .The dissolved oxygen (DO) deficit becomes zero at approximately the same distance downstream for both cases, though the two point source discharge case (case2) shows a higher short term DO deficit. This can cause problems if they DO concentration drops below the stipulated levels for the creek, leading to possible death of fish and other aquatic lives. It is therefore recommended that industrial establishments planning to site their treatment facilities along rivers or streams should be compelled to discharge their waste stream in compliance with the optimal locations with respect to any existing plant, so as to avoid undue dissolved oxygen (DO) depletion.

Keywords: Point Sources; Effluent; Discharge Point; Impact, Creek; Optimal Location; Sampling

Abstract| Introduction| Brief Description of the Study Area| Methodology| Effect of Flow conditions on Single Point Source Discharge| Effect of Flow Conditions on Two Sequential Point Source Discharge| Conclusions and Recommendations| References|