Pollution problems and an engineering approach to the management and control of industrial effluents

ABSTRACT

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.

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CHAPTER ONE

1.         INTRODUCTION

1.1      Background to the Study

Water is life and the quality and adequacy of water is an essential measure of the quality of life or rather the existence of life. Consequently water quality management is (or should be) one of the most important activities of mankind, so as to protect and save human life. The management of water quality, or the protection of the aquatic ecosystem in a broader sense, means the control of pollution. Water pollution originates from point and non-point (diffuse) sources and is mostly anthropogenic activities.

A crucial aspect in the series of complex activities of planning and implementing water pollution control actions is the quantitative determination and description of the relationship between human activities and the state of the aquatic system. These activities are essential for the modelling of aquatic systems (hydrological, hydrodynamics, hydraulic, and water quality modelling) (Jolankai, 1997).

Planning and management activities require the assessment of hydraulic and water quality conditions often beyond the range of observed field data. In this context, both hydraulic and water quality models need be made that are general enough to (1) describe observed conditions and (2) predict planning scenarios that may be substantially different from observed conditions. In stream water pollution control the main objective is to assess if the system complies with the maximum pollutant release allowed from point and non-point source pollution, so that pollutant levels in the receiving streams meet water quality standards. Water quality models for in – stream water pollution control have been calibrated and verified with data collected prior to model development during surveys designed to check basin wide water quality for regulatory compliance (Radwan et al, 2003).

1.2    Statement of the Problem

A lot of environmental degradation is generated during the planning, developmental stage including construction and final occupation of engineering projects.

The problems include deforestation, land and water pollution, and contamination of ground water, poor environmental sanitation, poorly planned road network, air and noise pollution, destruction of natural food chain, toxicity and radioactivity within the eco-system, etc. Others are:

–        Rapidly increasing generation of industrial effluents and discharge into the available water courses

–        Increasing difficulty of industries to comply and meet regional and national water quality standards and limits

–        Increasing occurrence of water- borne diseases as a result of pollutions from indiscriminate industrial effluents discharge into water courses

–        Deterioration of water quality standards and its effects on water supply, aquatic ecosystems and public health due to river pollution in populated areas

–        Service delivery standards: Many existing national environmental standards and environmental management practices are based on those developed in industrialized countries, under conditions totally different from those existing in developing countries.

These standards are often inappropriate, even where they are in theory appropriate they often cannot be applied due to high cost.

1.3    Aims of the Research

The aims of this research include the:

i.            Determination of the dilution power and self- recovery ability of a purposively selected river in Ado-Odo/Otta District after receiving industrial effluents, and

ii.             Assessment of the industrial waste management capability of the treatment facilities of selected industries.

1.4      Specific Objectives of the Study

The specific objectives of this study are to:

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1.      Characterize selected industrial effluents and determine their impacts on a purposively selected receiving water courses;

2.      Use an existing model to determine the ability of the selected receiving stream to recover from the environmental impacts of the industrial activities, and

3.      Determine the treatability of the effluents and recommend an engineering solution to the impacts.

1.5    Justification for the Research

Existing literature showed that there has been no detailed scientific and engineering study of industrial impact on the rivers in Ado-Odo/Otta Industrial Zones. Presently there exists a global focus on sustainable consumption and production activities by industries. There is the need therefore to determine conformity by the industries with the Federal Environmental Protection Agency (FEPA) of Nigeria other national and international regulations.

The findings of this work will be useful to Engineers in the design and management of industrial wastes.

1.6      Scope of the Study

i.            The scope of this study was limited to a field survey of selected industries which discharges industrial effluents into River Atuwara.

ii.             Laboratory scale modelling of the pollution impacts, using QUAL2K developed by the United States Environmental Protection Agency (USEPA), to determine the hydrodynamics and water quality of the receiving river; and

iii.             Laboratory bench – scale treatability study and analysis of the identified pollutants of concerns in the effluents from the selected industries

1.7      Delimitation of the Study

The study covered River Atuwara in Otta Municipal Districts. The major polluting industries in the industrial layouts will be determined in the three major industrial areas in Otta viz: Idiroko road, Ijoko road and Lagos-Abeokuta expressway. A model

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