This study examined the effects of effluent discharges from various point-loads on a
purposively selected receiving river, the self-recovery ability of the river and the
treatability of both the discharges and the receiving stream in a heavily industrialized
community.
The work involved field survey of industries producing and discharging effluents in
the study area (Ado Odo/ Otta industrial zone of Ogun State, Nigeria); determination
of the effluents‘ physico – chemical, biological and microbial characteristics, and the
impact of the discharged effluents on the receiving surface water using standard
methods. Primary data were also collected for analysis using structured questionnaires
and oral interviews to elicit the contribution of the industries to water pollution.
To advance analytical process various scenarios of improving water quality along the
river under study were examined. An array of computer based hydrogeometric and
water quality models were investigated. QUAL2K was operated as a one-dimensional
steady state and completely mixed system for hydrogeometric and water quality
analysis on the Atuwara River. The 10.81 km long stretch from upstream at Owode –
Ijako to Iju Water Works was mapped with geographical positioning systems (GPS)
and divided into 7 reaches with further segmentation of 0.3 km each from where grab
samples were collected routinely throughout the study period.
The research analyzed the effluent discharges from all industries along the river for
priority pollutants such as BOD, COD, TDS, TSS, and Heavy metals using standard
methods. The effluent samples were obtained and compared with river water samples
before and after receiving waste loads in the dry and wet seasons. Model result was
interfaced with geographical information systems (GIS) for clear display of model
outcome to demarcate polluted zones, limnographic points and wetlands of the
Atuwara watershed. The worst scenario of the effluent samples were obtained for
laboratory-scale treatability studies by applying electro – Fenton alone or with further
treatment by Granulated Activated Carbon (GAC) type BBC 945 to properly remove
traces of heavy metals.
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The result showed that the effluents were acidic in both seasons with range between
pH 5.4 - 6.7. The BOD and COD concentration were also very high especially at
immediate downstream of points of discharge. The level of dissolved oxygen (DO)
attained at points of discharge remain anoxic with the DO gradually increasing at
short distances downstream to each discharge point but much higher where tributaries
discharge into the river under study. The assimilative capacity of the river is very high
because of the contribution from the tributaries. Calculated worst scenario of BOD
discharge was about 12 metric tonnes per day. The heavy metals (cadmium, lead and
iron) were slightly above the FEPA standard at all sections of the river. All these
indicated that the river is impaired and should be declared polluted and not good for
human consumption without adequate treatment.
The study showed that the Atuwara River was grossly polluted. Treatment of the
worst scenario effluent collected from an industry showed that COD removal of more
than 66% was achieved with electro-Fenton treatment at a molar ratio of H2O2/Fe2+
between 150-250, using 0.3M H2O2 and 0.002M Fe2+ and when further treated with
the GAC 945 sample, the COD removal was 86%.
To achieve river water quality specified by regulatory authorities, it is therefore
recommended that substantial load curtailment from the firms discharging the
effluents be enforced by the government through mandatory provision of in-house
adequate treatment and at regulated flow rate to meet the National standards.