Correlating Biochemical and Chemical Oxygen Demand of Effluents – A Case Study of Selected Industries in Kumasi, Ghana

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Abstract

 

This work aims at establishing an empirical correlation between Biochemical Oxygen Demand (BOD5) and Chemical Oxygen Demand (COD) of effluents from selected industries in the Kumasi Metropolis to facilitate speedy effluent quality assessment or optimal process control. Hourly effluent samples were collected for an eight-hour period three times per week for analysis of the principal parameters BOD5 and COD using the “Standard Methods for the Examination of Water and Wastewater”. Measured BOD5 and COD of the effluents were above the required discharged guideline of 50 mg/l and 250 mg/l respectively specified by the Environmental Protection Agency, Ghana. These levels of BOD5 and COD of the wastewaters could pose potential pollution to the waterbodies in which they are discharged since untreated.  Results also indicate that the degree of common variation between the two variables COD and BOD5 is highly positive for the effluents from Ghana Brewery Limited (GBL), Guinness Ghana Limited GGL) and The Coca-Cola Bottling Company of Ghana (Coca-Cola), thus the variables are said to be correlated. However, the degree of common variation between the variables was low for the effluent from the Kumasi Abattoir. The fitted equations were (GBL, y = 0.6558x – 270, r = 0.93; Coca-Cola, y = 0.3536x + 113.6, r = 0.81; GGL, y = 0.225x + 1343.7, r = 0.83; Kumasi Abattoir, y = 0.1331x + 54806, r = 0.22) with x and y representing COD and BOD5 respectively. The BOD5/COD ratio for the wastewater from the selected industries can also be approximated to the gradient of their respective fitted equations i.e. GBL, 0.66; Coca-Cola, 0.35; GGL, 0.23. The fitted equations for GBL, Coca-Cola and GGL can be used to facilitate rapid effluent assessment or optimal process control by these industries once the chemical oxygen demand is measured.

 

1. Introduction

Kumasi the capital city of Ashanti Region of Ghana is located in the south-central part of the country, about 250 km (by road) northwest of Accra and with an approximate size of 254km2. Lake Bosumtwi, the largest natural lake in Ghana, is located approximately 32 km south of Kumasi. With a population of 1,517,000 (2005, source: United Nations Population Division), Kumasi is the second-largest city in the country (http://en.wikipedia.org/wiki/kumasi).  Figure 1 shows the position of Ashanti Region and Kumasi the capital on the map of Ghana.

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