Assessment of urban and industrial effluents on a receiving stream using statistical and quality indices

Abstract

Discharging untreated effluents into surface water bodies is a widespread practice that degrades surface water, thereby jeopardizing public health in several African countries, including Nigeria. Due to a lack of access to clean drinking water, many users rely exclusively on stream water, making stream quality monitoring very important. The Arobieye stream in Ota, Nigeria, is one such stream that is impacted by effluent discharge from an urban centre and an alcoholic beverage factory. Stream and effluent samples were obtained from known intervals for physicochemical and faecal contamination analysis. Some of the pollutants from the urban and industrial effluents that exceeded the maximum contaminant limit included COD (78.6 mg/l and 8192 mg/l), phosphate (5.087 mg/l and 6.91 mg/l), cadmium (0.016 mg/l and 0.079 mg/l), total coliform (40,000 cfu/100 ml and 180,000 cfu/100 ml), and Escherichia coliform (25,000 cfu/100 ml and 110,000 cfu/100 ml). Pearson’s correlation matrix revealed strong positive correlations between the total coliform and nitrate (0.976), between the copper and nitrite (0.989), and between the Escherichia coli and zinc (0.910) concentrations. The stream arithmetic weighted mean water quality index (WQI_A) test also revealed that the stream depreciated from a test score of 74.13 (good) to 37.83 (bad). Pollution discharge into streams occurs year-round without any regulatory checks. Therefore, regulatory authorities need to increase their enforcement drive to protect the stream and downstream users. Additionally, a public advocacy programme should be initiated to educate downstream users on the dangers of ingesting untreated water from streams.