Physicochemical Characterization and the Effect of Flow-Distance on Correlation between Chemical and Biochemical Oxygen Demands of Industrial Wastewaters

This work was carried out to establish the effects of the activities of a cluster of industries in Jos-South
Local Government Area of Plateau State, Nigeria, on the environmental quality of the industrial area.
Some physicochemical parameters – temperature, pH, turbidity, suspended solids (SS), total solids
(TS), total hardness, alkalinity, biological oxygen demand (BOD), chemical oxygen demand (COD),
heavy metals (Cu2+, Co2+, Fe2+ & Zn2+), phosphates, nitrates, sulphates and chlorides – of the
wastewaters from the various industries were investigated using standard protocols. Also, the
influence of flow-distance on the empirical correlation between biochemical oxygen demand (BOD)
and chemical oxygen demand (COD) of the wastewaters was investigated. Wastewater samples were
collected at point-sources and at 25, 50, 75 and 100 m distances from the point-sources. Sampling
was done twice a week for a full seasonal cycle at peak production period (morning and evening). The
samples’ pH was adjusted to 7 using 0.5 M acid for basic samples and 1.0 M alkali for acidic samples,
de-chlorinated using 0.0125 M Na2S2O3 and seeded when necessary and then diluted with de-ionized
water. The ranges of the parameters were as follows: temperature: 22 – 32°C, pH: 5.5 – 10.4, SS: 0 –
1,300 mg/L, TS: 200 – 1.400 mg/L, sulphate: 0.37 – 1.37 mg/L, nitrites: 0.10 – 1.09 mg/L and
phosphate: 14.80 – 21.83 mg/L. The phosphate values, especially, were in excess of the maximum
contamination limit specified by Federal Environmental Protection Agency (FEPA) and World Health
Organization (WHO); and are capable of triggering eutrophication, which will in turn increase
BOD/COD values. Concentrations of heavy metals, determined by Atomic Absorption
Spectrophotometry (AAS), ranged as follows: 0.07 – 2.01 mg/L for Cu2+, 0.58 – 3.27 mg/L for Fe2+,
0.01 – 3.18 mg/L for Zn2+ and 0.11 – 0.18 mg/L for Co2+ whose specified standard is not available.
BOD5 values ranged between 5.34 – 25.88 mg/L while COD values ranged from 727.30 –8,308.66
mg/L. Some BOD5 values were in excess of the allowable limit while all COD values were observed
to be very high. This implies an appreciable level of pollution exists here and recipient water bodies of
these wastewaters are at risk of being polluted. COD and BOD5 of the wastewaters from different
sources highly correlated with correlation coefficients ranging 0.9396-0.9985. The empirical
correlation between COD and BOD5 was generally maintained despite the distance of flow of the
wastewater from point-source and contributions of washings from farmlands and other human
activities i.e. the correlation between COD and BOD5 for wastewaters was not affected by flow
distance. The correlation equations for the industries may, therefore, be used to deduce rapid effluent
quality from chemical oxygen demand (COD) of sample from any point along the effluent flow path.