Impact of cement effluent on water quality of rivers: A case study of Onyi river at Obajana, Nigeria

Physico-chemical characterisation of industrial effluent is of importance in view of its inherent toxic substances. Effluent from cement plant located in Nigeria was characterised and its impact on the receiving Onyi River was investigated in this study. Effluent, water samples from upstream, discharge point along the river course and downstream location were collected monthly. The river was monitored up to about 1 km downstream from the discharge point for a period of twelve months. The impact of the effluent on the water quality downstream was shown by reduced dissolved oxygen. With respect to upstream, the levels of pH, nitrate, phosphate, total solid, total suspended solids, total dissolved solids, turbidity and biological oxygen demand at downstream were much high, arising from the influx of cement effluent. The cement effluent significantly contributed to the levels of Zn (0.045 ± 0.003 mg/L) and Pb (0.016 ± 0.001 mg/L) downstream such that they exceeded the criteria set by USEPA and WHO respectively. Using Prati method of classification of surface water quality, the Onyi River fell in the class of slightly polluted water. Weight arithmetic water quality index of 85.2 and metal pollution index of 3.46 corroborated the classification. Hence, adequate treatment of downstream water prior to its use for beneficial purposes is required