Annex I
AGENDA

1. Opening of the session

2. Election of the Chairman

3. Approval of the agenda and arrangements for the session

4. Report on intersessional activities

5. Scientific bases for organic pollution and its control in African inland waters

6. Future work programme

7. Approval of the report

8. Closing of the session

Annex II
LIST OF PARTICIPANTS

Anthony T. AMUZU
Head, Water Quality Division
Water Resources Institute
P.O. Box M.32
Accra
Ghana

Charles BINEY
Senior Research Officer
Institute of Aquatic Biology
P.O. Box 38
Achimota
Ghana

Davide CALAMARI (Convenor)
Professor of Zoology
Institute of Agricultural Entomology
University of Milan
Via Celoria 2
I-20133 Milan
Italy

Anthony M. IMEVBORE (Chairman)
Director
Institute of Ecology
Obafemi Awolowo University
Ile-Ife, Oyo State
Nigeria

Heiner C.F. NAEVE (Technical Secretary)
Senior Fishery Resources Officer
Fishery Resources and Environment Division
FAO
Via delle Terme di Caracalla
I-00100 Rome
Italy

Peter B.O. OCHUMBA
Research Officer
Kenya Marine and Fisheries Institute
P.O. Box 1881
Kisumu
Kenya

Massoud A.H. SAAD
Professor of Limnology
Department of Oceanography
University of Alexandria
Moharrem Bay
Alexandria
Egypt

Observers

Tom DOLA
Lake Basin Development Authority
P.O. Box 1516
Kisumu
Kenya

Paul N. GIKONYO
Fisheries Department
P.O. Box 58187
Nairobi
Kenya

James HEBRARD
Water and Lithosphere Unit
United Nations Environment Programme
P.O. Box 30552
Nairobi
Kenya

Annex III
DOCUMENTATION

Scientific bases for control of organic pollution in African inland waters
by Massoud A.H. Saad

Comments received from A.T. Amuzu, Accra, Ghana

Comments received from D.I. Anadu, Abakaliki, Nigeria

Comments received from C.A. Biney, Accra, Ghana

Comments received from F.M.M. Chale, Dar-es-Salaam, Tanzania

Comments received from A.M.A. Imevbore, Ile-Ife, Nigeria

Comments received from P.B.O. Ochumba, Kisumu, Kenya

Comments received from A.A. Oladimeji, Minna, Nigeria

Annex IV
SCIENTIFIC BASES FOR POLLUTION CONTROL IN AFRICAN INLAND WATERS
Domestic and Industrial Organic Loads

by

Massoud A.H. SAAD, Anthony T. AMUZU, Charles BINEY, Davide CALAMARI, Anthony M. IMEVBORE, Heiner C.F. NAEVE and Peter B.P. OCHUMBA

1. INTRODUCTION

Over the last years, in many African countries a considerable population growth has taken place, accompanied by a steep increase in urbanization, industrial and agricultural land use. This has entailed a tremendous increase in discharge of a wide diversity of pollutants to receiving water bodies and has caused undesirable effects on the different components of the aquatic environment and on fisheries.

Organic pollution of inland waters in Africa, in contrast to the situation in developed countries of the world, is often the result of extreme poverty and economic and social under-development. According to Tolba (1982), it is in these countries that the quality of water, and often the quantity, is lowest, sanitation and nutrition the worst and disease most prevalent.

Unfortunately, there are very few water quality studies for most African inland waters. In general, the available data come from scattered investigations which were carried out by individuals and by very few scientific projects concerned with African waters. Few reviews exist on the state of pollution of African inland waters, e.g. Dejoux et al. (1981), Dejoux (1988), Burgis and Symoens (1987) and Davies and Gasse (1988). Within the framework of the activities of the Committee for Inland Fisheries of Africa (CIFA), there reports were prepared. Two are on the state of inland water pollution in eleven countries from eastern, western and central Africa (Alabaster, 1981; Calamari, 1985), reviewing the existing sources of water pollution, the scientific investigations on the subject and the legislation enforced in the different countries. Both documents confirmed the existence of pollution problems at various levels in the different countries. The third report (Biney et al., 1987) concentrates on the scientific bases for the control of micro-pollutants (toxic substances, in particular pesticides). The CIFA Working Party on Pollution and Fisheries at its first session in Accra, Ghana, June 1986, agreed to prepare a review on the present state of organic pollution and its control in African inland waters.

2. IMPACT OF ORGANIC WASTES

Due to population and industrial growth, inland waters (rivers, lakes, etc.) become often the recipient of organic matter in amounts exceeding their natural purification capacity, while in the past natural purification and dilution were usually sufficient.

Sewage and other effluents rich in decomposable organic material, cause primary organic pollution. Secondary organic pollution is defined as the surplus of organic matter, which is the sum of undecomposed organic material introduced into the water body with primary pollution and of the material resulting from an extremely increased bioproductivity within the polluted ecosystem itself (Stirn, 1973). As stated by Dejoux et al. (1981), organic wastes mineralize in the receiving water bodies and the resulting nutritive elements stimulate plant production, leading to eutrophication. In this situation, the biomass increases considerably and goes beyond the assimilation limit by herbivores. This secondary organic pollution is considerably greater than the primary organic load. The excessive production of organic matter leads to the build up of “sludge” and the mineralization process consumes all dissolved oxygen from the water column, which causes fish kills. Consequently, organic pollutants are called oxygen-demanding wastes. The relatively high temperatures in tropical countries accelerate this process.

3. SOURCES AND TRANSPORT OF ORGANIC LOADS

Rain water transports soil to streams, rivers and lakes by erosion processes, including dissolved and particulate organic matter. Decomposition of this organic matter continues during transport and in the sediments, giving new soluble organic and inorganic matter. The quantities of organic matter transported, its characteristics and composition vary from one region to another. A man-made transport mode of organic material to natural receiving waters are sewage pipes. Man himself is unable to use all the energy stored in food and his wastes are often discharged into the water without treatment. It is well known that untreated sewage creates a public health danger, being a potential for epidemics of water-borne diseases, such as typhoid fever, and also causes a serious loss of the recreational value of the inland waters (Stirn, 1973; Shuval, 1986). The present paper, however, is dealing with organic load only since public health problems resulting from sewage require separate attention and a specific strategy of their own.

In addition to the ever-increasing urbanization, industry and development of agriculture and forestry contribute considerably to the organic loads, which pose a hazard for inland waters and fisheries. Accordingly, domestic sewage and organic industrial wastes, as well as wastes from agricultural and forestry products are considered as main sources of organic pollution of African waters. Alabaster (1981) pointed out that agriculture is being further developed in some African countries, leading to an extension of existing industries involved in the processing of plant and animal products and to an increase in the highly oxidizable discharges.

3.1 Municipal Waste Water

According to Dejoux et al. (1981), urban pollution is generally organic in origin and is very dependent on the size of the urban development, on the existence of the effluent treatment systems and on the waste disposal habits of the inhabitants.

The principal physical, chemical and biological characteristics of traditional sewage are known. Mixed sewerage systems of modern municipalities, however, do add increasing levels of organic and inorganic material, some of them toxic (e.g. heavy metals), to municipal effluents from small industries. The rise in municipal BOD wastes is related to industrial effects rather than to the great changes in the habits of the population. The increase in the phosphorous compounds transported by wastewater constitutes a major problem. Many African towns have open drain systems, which are flooded during the rainy season, leading to high organic discharge to the receiving waters over short periods of time.

3.2 Organic Industrial Wastes

In most developed countries, industries produce a larger load of organic wastes than municipalities. Wastes with high BOD loads are produced by textile industries, paper and pulp mills, rubber production and chemical industries. Metal industries and mining contribute to a lesser degree to organic loads.

In Africa, food processing is a major industry; plants are mainly located inland, and consequently the discharged wastes create pollution problems in the inland waters (rivers, streams and lakes). Typical examples for such industries are meat processing and dairy plants, sugar refineries, breweries, distilleries and palm-oil industries. The quantities and characteristics of wastes from these sources vary, and the pollution caused by them has to be calculated on a case-by-case basis, especially when the organic load is considered. In general, BOD loads are higher than those of ordinary sewage.

4. PARAMETERS FOR MEASURING ORGANIC POLLUTION

BOD, COD and suspended solids are the traditional parameters for measuring organic pollution. However, parameters such as dissolved oxygen (DO), hydrogen sulphide (H₂S), pH, total dissolved solids (TDS) and nutrients are also important. The nutrients nitrogen (N) and phosphorus (P) have been identified as key factors in the eutrophication of inland water (Vollen veider, 1968). They are measured in their various organic and inorganic forms (e.g. NH₃, NO₂, NO₃, ).

The most relevant textbook on analytical methods is ‘Standard methods for the examination of water and waste water’ (APHA/AWWA/WPCF, 1980).

4.1 BOD (Biochemical Oxygen Demand), COD (Chemical Oxygen Demand) and Suspended Solids

The amount of oxygen necessary for the oxidative decomposition of a material by micro-organisms is known as the biochemical oxygen demand (BOD) of the material. The ultimate carbonaceous BOD of a water or a liquid waste is the amount of oxygen necessary for micro-organisms to decompose the carbonaceous materials that are subject to microbial decomposition (Warren, 1971).

The BOD value usually reported is the amount of oxygen consumed in milligrams per litre of water or waste water over a period of five days at 20°C under laboratory conditions. For domestic sewage the BOD value usually reported is about two-thirds of the ultimate carbonaceous BOD.

Domestic and industrial wastes often have BODs of several thousands of milligrams per litre; when inadequately diluted in receiving waters, these wastes can lead to severe oxygen depletion.

The chemical oxygen demand (COD) is a measure of the oxygen equivalent of the organic matter content of a sample that is susceptible to oxidation by a strong chemical oxidant under acidic conditions. For samples from a specific source, COD can be related empirically to BOD, organic carbon or organic matter content. The dichromate-reflux method is the most widely used for the determination of COD as it is easily applicable to a wide range of compounds (APHA/AWWA/WPCF, 1980). COD is an important, rapidly measured parameter for surface and wastewater investigations and for the control of waste treatment plant efficiency. As oxidation occurs under forced conditions, it is a more complete process than biological oxidation. Therefore, COD values (mg/l) are higher than BOD values.

Solid materials finding their way into natural waters may have some undesirable effects while carried in suspension and can also have other undesirable effects after settling on the bottom. These effects include turbidity (decreasing photosynthetic activity) and oxygen depletion. These solids are generally classified as total, suspended and dissolved. Total solids are measured as residue left in a container after evaporation and drying of a wastewater sample at a fixed temperature in an oven. Total solids include filtrable and non-filtrable residues, corresponding to dissolved and suspended matter respectively.

4.2 Nutrients

Phosphorus is essential for the growth of autotrophic organisms, and in a number of cases is the nutrient that limits the primary productivity of a water body. Phosphorus is in particulate, organic or dissolved form, in the majority of cases as orthophosphate, which is the form utilized by the organisms. Organic phosphorus is released by enzymatic activity, while particulate phosphorus constitutes a reservoir; after precipitation to the bottom sediments, it can be released as soluble orthophosphate according to the redox conditions, determined mainly by the presence of oxygen.

Dissolved nitrogen compounds include ammonia nitrogen, nitrite, nitrate and various organic compounds. In contrast to the phosphorus cycle, which involves a very important physico-chemical component, the nitrogen cycle is controlled mainly by microbiological processes. Dissolved oxygen has a decisive influence on the cycle, determining the rates of the processes.

Nitrate is an essential nutrient for many photosynthetic organisms and in some cases it constitutes the growth limiting factor. It is present only in small quantities in fresh water but it has a high concentration in effluents from treatment plants; it is frequently a contaminant of ground water.

Nitrite is an intermediate oxidation state of nitrogen, both in the reduction of nitrate and in the oxidation of ammonia. It has the highest toxicological significance for human health.

Ammonia is naturally produced but its concentration is frequently increased by contamination resulting mainly from deamination of organic substances. It is highly toxic to aquatic animals, although it can be utilized directly as nutrient by several algal species.

All the forms of nutrients can be analysed after various treatments of the samples by means of spectrophotometric methods.

5. CALCULATION OF ORGANIC AND NUTRIENT LOADS

The assessment of nutrient loading and of the relative contribution of the different sources of nutrients to surface waters is of critical importance for the implementation of pollution control measures to prevent or reverse eutrophication.

Analyses provide a precise measurement of nutrient loads but they are very costly and time-consuming and they fail to give adequate information regarding the contribution from different sources. The only possible approach to a large-scale evaluation is a theoretical estimate by means of quantification of the various sources, by collecting data on land use, population, agricultural and industrial activities and by applying appropriate and specific coefficients.

This method has been extensively used in developed temperate countries, and suitable coefficient are available. For tropical countries some modifications are necessary and extrapolations would have to be made. Most of the following information is taken from a review by Vighi and Chiaudani (1987).

5.1 The Evaluation of Point Sources

The quantity of nutrients and organic matter discharged to surface waters from point sources can be estimated on the basis of some general assumptions without major difficulties; some practical problems, however, can arise with collection of the data needed.

A higher degree of uncertainty is connected with losses of nutrients in rivers before reaching eutrophic water bodies. According to different authors, a 50 percent loss can be assumed as a mean value.

5.1.1 Domestic point loadings

Domestic point loadings of phosphorus can be calculated by estimating both the metabolic contribution and the contribution from polyphosphates in synthetic detergents. Detergent phosphorus is one of the main factors responsible for increased eutrophication since the fifties. As for the metabolic contribution, a phosphorus load of 0.58 kg per capita per year is generally assumed.

In developed countries phosphorus contribution from detergents has decreased from 0.7 to 0.2 kg P per capita per year, due to the legislation concerning the reduction of phosphorus content in detergents.

Nitrogen contributions depend on the dietary habits and can range from 3.5 to 5.8 kg per year.

In developed countries organic matter, expressed as BOD, is generally assumed to be 20 kg BOD per capita per year.

5.1.2 Industrial loadings

According to OECD, the contribution of phosphorus from industrial loadings is only one tenth of that from domestic loadings. It is restricted to industries such as food processing, phosphoric acid production, etc. Although the phosphorus content of different industrial waste waters has been measured, a precise evaluation of phosphorus loadings is rather difficult to make and could only be arrived at by means of detailed surveys. More important is the industrial contribution of nitrogen compounds and organic matter. Table 1 shows the nitrogen contribution from some industrial activities (Provini et al., 1978).

Table 1

Nitrogen content in effluents from different industrial activities

As discussed in chapter 4, BOD loads can cause oxygen depletion and other deterioration of water quality.

The BOD value for some industrial activities is also reported in inhabitant equivalents (i.e. by multiplying the number of workers in the industry by the conversion factor, for instance 20 kg BOD per person per year × conversion factor × number of workers in a given industry). See Table 2 for conversion factors.

Table 2

BOD conversion factors for different industrial activities
(ISTAT, 1963)

Conversion factors for most other industrial activities are around 1.

The potential nutrient loads - in kg per capita per year - from different animals are as follows:

5.1.4 Evaluation of diffuse sources

Nutrient loads from diffuse sources are undoubtedly more difficult to evaluate. Non-point loadings at present can be only partially quantified.

To estimate losses from uncultivated land, a classification of soils has been proposed by Vollenweider and, on the basis of a wide review of data, the following loss coefficients - in kg/ha/year - have been established:

Losses from cultivated land depend on fertilizer applications. Phosphate leaching is relatively small; the formulation of fertilizers (mineral fertilizers, organic manure), amount and techniques of application largely influence the release of phosphorus from agricultural runoff, mainly through erosion. The release is highest from animal manure.

Nitrogen, on the contrary, is highly mobilized in soil. When in inorganic form, it can be present in very large amounts both in runoff water, resulting in contamination of surface waters, and in percolating water, arousing concern for groundwater contamination.

Due to the large variability of geopedological features, land use, agricultural practices, etc., the quantification of nutrients in runoff water can only be approximative. The release of phosphorus, in relation to the phosphorus applied on cultivated land (in kg/ha/year), is estimated to be as follows:

These values must be added to the background loadings, depending on the characteristics of the soil.

To evaluate nitrogen runoff in agricultural areas, a N/P ratio of about 100 is assumed.

6. SELECTED AFRICAN EXPERIENCES

The two major sources of organic matter and nutrients are domestic discharges and food processing industries. The increase in African population is exponential, especially in towns; the population of Bujumbura, for example, has tripled in twenty years. The populations of Abidjan and Lagos have increased by twenty times in forty years. Cairo, according to the last census, has more than 10 million inhabitants. Similar trends can be observed everywhere in Africa.

Despite the fact that in many situations the organic load has not been properly quantified, one should stress the relevance of food processing industry in all African countries in contributing to the BOD load, especially of big rivers. Dejoux (1988) gives the following examples: Wastes from fruit juice production and breweries are discharged to the Niger at Bamako, to the Maraohué in Côte d'Ivoire, to the Logone in Tchad, as well as to the Abidjan and Lagos Lagoon and to the coastal lake Nokoué in Benin.

Wastes are seasonally discharged from sugar-cane processing at Ferkéssedougou to the Bandama River, at Banfora to the Comoé (Burkina Faso) and to the Sabi-Lundi River in Zimbabwe, from coffee processing at Bouaflé to the Bandama, and to River Nyando in Kenya. Palm oil factories, milk processing industries, sisal, etc., are other important sources for wastes with a high BOD.

Alabaster (1981) and Calamari (1985) have reviewed the state of aquatic pollution in Burundi, Cameroon, Côte d'Ivoire, Ghana, Kenya, Mali, Malawi, Nigeria, Sudan, Tanzania and Zambia. Both reviews reported on the research activities and publications in these countries. Some of this research deals with the organic wastes and their effects on the receiving inland waters.

In the following part, selected African experiences are reported, illustrating situations in which water bodies suffer from organic loads and referring to research conducted and effects observed.

6.1 Northern Africa

In North Africa, the delta lakes in Egypt are influenced by organic pollution to various degrees, depending mainly on the discharge rates and the dilution capacity. The depths of these water bodies (Nozha Hydrodrome, Lake Mariut, Lake Edku, Lake Brollus and Lake Manzalah) range from 1 to 1.5 m. Lake Mariut, which was once a highly productive lake, is now considered as the most polluted delta lake, severely affected by domestic sewage from the southern part of Alexandria, by industrial wastes from several factories constructed close to the northern side of the lake and by agricultural runoss. Next in order of pollution is the Nozha Hydrodrome. Because of their considerable size, Lake Edku, Lake Brollus and Lake Manzalah show a pollution gradient from regions further away from the direct effect of discharges to those near the waste outfalls.

A considerable part of the allochthonous organic matter in the form of sewage and the autochthonous organic substances resulting from the subsequent increase in bioproductivity, decomposes, consuming dissolved oxygen and causing deoxygenation of the water. The biota, particularly fish, may be asphyxiated. After depletion of dissolved oxygen, anaerobic decomposition of organic matter continues (the stagnating water turns septic) and decomposition gases are produced. Among them is the toxic hydrogen sulphide, which is recognized by its unpleasant smell. Suspended materials deposit on the bottom and thus blanket it. This affects the spawning of fish and reduces the numbers of bottom fauna, important for the food chain. In Lake Mariut, fisheries have been affected since about 30 years. Some fish species have decreased in number or disappeared. Tilapia species, relatively unaffected by pollution, now account for about 80% of the fish production in this lake.

Organic pollution of Lake Mariut and its effects have been widely studied by Saad (1972, 1972a, 1973, 1974, 1980, 1985), Saad et al. (1984), Wahby and Abdel-Mouniem (1979) and Wahby et al. (1978). Sediments in different delta lakes were analysed by Saad (1978, 1979, 1980a, 1980b). Saad (1978a, 1985a) also describes the dissolved organic matter content of Lake Edku. Changes in the blood of fish due to pollution were found by Saad et al. (1973).

The Nile in Egypt, being the lower part of the river, contains considerable concentrations of organic matter resulting from allochthonous supply (mainly domestic wastes) and autochthonous production (Saad, 1980c; Saad and Abbas, 1985). Levels of organic matter in Aswan Lake are not so high as to cause pollution in this second largest man-made lake in the world. Obviously, part of the organic matter in this lake originates from the inflowing Nile water, which receives this matter mainly from discharges of the countries upstream.

The Lake of Tunis suffers much from organic pollution (Stirn, 1967, 1968, 1972, 1973). In certain areas dissolved oxygen is depleted and hydrogen sulphide is produced as a result of anaerobic decomposition of organic matter; the unpleasant odour of this gas can be smelled near these septic zones.

6.2 West and Central Africa

Of the total population of Côte d'Ivoire, estimated at 7.9 million in mid 1979, about 1.5 million are concentrated in and around Abidjan. Of these, only about 350 000 are serviced by the sewage system discharging into Ebrié Lagoon. Pagès and Citeau (1978) analysed the concentrations of faecal coliforms in the central part of the lagoon over a year cycle and found several heavily contaminated areas. Environmental degradation is also reflected in low concentrations or even absence of oxygen at the bottom, i.e. in Coccody, Marcory and Bietry bays and in subsequent changes in the benthos fauna. In fact the benthic populations in the bays are now dominated by certain species of oligochaetes, considered as indicators of heavy pollution. The area suffers also from industrial discharges from light industry.

In Ghana, Biney (1982) classified all areas of the country according to the BOD level into three categories: "unpolluted and recovering from pollution (<4 mg/l), “doubtful and poor quality” (4–12 mg/l) and “grossly polluted” (>12 mg/l). Of the 16 lagoons investigated by Biney (1982), 12 were found polluted in varying degrees; grossly polluted are Korle (Accra) and Chemu (near Tema), serving as receptacles of industrial and domestic wastes. Lake Barekese, a man-made lake in the Ashanti region of Ghana which is used as a water supply reservoir, has been extensively studied (Amuzu, 1973, 1975).

In Mali most of the activities depend on the Niger and its tributaries. According to the information obtained by Calamari (1985), pollution problems are not too critical and could easily be managed; most of the wastes consist of oxidizable matter.

In Cameroon, several mass mortalities were recorded in partially-managed river areas near Bafussam, caused by oxygen depletion due to the large organic load (Calamari, 1985).

Except for a few regions, in Nigeria urban areas do not have any central sewerage system or sanitary excreta disposal system. The waste water from most parts of more than 186 urban centres is carried in open drains into streams and rivers, a characteristic feature of many developing countries (Sridhar et al., 1981). According to Calamari (1985), analytical data on the lagoon of Lagos (the largest town in Nigeria) do not exist. However, this lagoon, once very productive in fish, is now considered as a bad place for fishing (Adeyanju, 1979). Ekundayo (1977) reported that the eutrophication of Lagos Lagoon was due primarily to extensive pollution by large quantities of industrial and domestic wastes. In Ibadan, the chemical and microbiological characteristics of the waste water flowing in open drains has been investigated by Sridhar et al. (1981). These open drains, carrying various pollutants, contribute to the pollution of streams, since they travel short distances and consequently offer only limited self-purification of the waste water. In densely populated areas the waste water showed higher values of turbidity, total and suspended solids, oxidizable organic matter, BOD and ammonia nitrogen, with negligible concentrations of dissolved oxygen. The waste water finally enters three major streams, which could be considered open sewers, with water colour ranging from greyish to black, devoid of fish. The water quality in one of these streams can be compared to that of partly treated waste water, turbid and with considerable amounts of total and suspended solids, oxidizable organic matter, BOD and ammonia nitrogen (Sridhar et al., 1981).

The effects of sewage pollution on the distribution and abundance of some organisms, including insects, algae and crustaceans have been studied (Oladimeji and Wade, 1984). In the anaerobic zones of the study area only a few tolerant invertebrate species such as Eristalis and Psychoda were found. The number of organisms increased as conditions such as dissolved oxygen concentration and electrical conductivity improved. Fishes such as Epiplatys sp. and Barilius niloticus were abundant in areas with high dissolved oxygen concentrations.

The seasonal variations in the sediment phosphate relative to the water column of Lake Asejire in the Oyo State of Nigeria were studied by Egborge (1981). Ninety percent of the available phosphate was associated with the bottom sediments, which acted as a sink.

According to Beecroft et al. (1987) and Awanda (1987), the bulk of the organic load discharged into the Kaduna River comes from the breweries (NBL and IBBI). Waste water discharge from these sources originates fom liquors extracted from grains and yeast and have the characteristic smell of malt. They are slightly acidic (pH 5–6), with high particulate and soluble organic content. Effluents from the textile industries have been shown to contain fibres, toxic organic chemicals and heavy metals. The phytoplankton density is lower in points of the Kaduna receiving heavy loads of organic pollutants. The lower number of species of flora and fauna below the Kakuri drain, which carries the effluents from the textile mills and breweries to the river, are attributable to organic pollution. Awanda (1987) noted that the higher density of certain dominant groups of chironomid (midge) larvae and nematodes at some of these heavily polluted points may be an indication that only these species, tolerant of low dissolved concentrations, are able to survive.

6.3 Eastern Africa

East African inland water systems have undergone successive changes since the mid-fifties due to intensive selective fisheries, modification of the drainage area, invasion by introduced species and the increasing physico-chemical changes in the environment. In Kenya, organic pollution and eutrophication of inland waters is to be attributed to the increase in population, urban and industrial activities and agricultural production (Kallquist and Meadows, 1977; Meadows, 1980; Alabaster, 1981; Ochumba, 1985). Indicative of the deterioration of water quality in Lake Victoria are algal blooms and fish mortality (Ochumba, 1987; Ochumba and Kibaara, 1989) and species reduction (Okemwa, 1984; Barel et al., 1985). The rift valley lakes (Baringo, Turkana, Naivasha, Nakuru and Elementaita) are threatened by receding lake levels due to drought and by industrial and riparian agriculture (Meadows, 1978; Harper, 1984).

The potential problems of organic pollution in Tanzania's inland waters are described by Ngoile et al. (1978), Alkbrant (1979), and McAuslan (1980); main threats to Lake Tanganyika are riparian agriculture and oil prospecting. In Burundi, the main concerns are the discharge of sewage and industrial wastes to Lake Tanganyika (REGIDESO, 1980) and agricultural inputs to the Rizizi River (Autrique, 1977). Internal overturns in the rift valley lakes in Uganda and Ethiopia have been associated with fish kills and algal blooms (Burgis, 1978; Belay and Wood, 1984) due to nutrient enrichment and oxygen depletion. Magasa (1978) concluded that organic pollution in Malawi is centered around Blantyre City and the Shire River, which receives agriculture-based wastes. In Zambia, Mumba et al. (1978) have indicated that water pollution is mainly a problem with the Kafue River due to industrial and urban development; fish kills in the river (Kaoma and Salter, 1979) were due to excessive levels of nitrogen compounds.

6.4 Southern Africa

Marshall reported limnological data for 33 Zimbabwean lakes and used them to predict their fish yields. Except for eutrophic lakes such as the McIlwaine, phosphorus was found to be the major limiting nutrient.

Since the early sixties, several algal blooms occurred in Lake McIlwaine due to nutrient enrichment through urban discharges from the town of Harare. Measures had been taken to reduce eutrophication, e.g. some of the effluents were used to fertilize the farmland around the town, particularly during the rainy season. However, such measures were considered insufficient (Wells, 1975).

A review of the more recent situation of this lake is given by Thornton (1981) with a self-explanatory title, ‘Lake McIlwaine: an ecological disaster averted’. He describes the recovery of the lake after severe measures had been taken to reduce the total load of nutrients. In the same area, Harare region, Thornton and Nduku (1982) showed that drainage waters from heavily urbanized areas had nutrient contents two to twenty times higher than waters from forest and savannah areas.

7. ORGANIC POLLUTION CONTROL

The above review of effects of organic pollution on inland waters evidentiates the need for control of this type of pollution, which is best achieved by control at its source. As many sources of organic pollution are at the same time generating other pollutants, their control resolves a number of pollution problems.

Although organic matter is the most important source of African inland water pollution, discharges of limited quantities of organic pollutants are unlikely to have harmful effects on large lakes or even small water bodies. In fact, each environment has the capacity to accommodate limited, quantifiable loads of pollutants, defined as Environmental Capacity (GESAMP, 1986). Furthermore, large amounts of organic wastes can be controlled by the introduction of more economical technologies which may even facilitate constructive use of the nutrients. However, not only primary consequences but also processes of secondary organic pollution have to be kept under control as they may lead to irreversible damage of the ecosystems.

Legal, administrative and technical measures are necessary to reduce or eliminate the undesirable effects of organic loads, e.g. unacceptable physical, chemical and biological changes in the receiving inland waters. Consequently, multi-disciplinary team work is needed for water pollution control.

7.1 National Responsibilities toward Aquatic Pollution Control

At national level, as stated by Lesaca (1978), control of aquatic pollution is achieved by:

1. formulation of national policy for pollution control;

2. enactment of appropriate legislation, and

3. establishment of appropriate institutional arrangements (administrative and technical) for monitoring, implementing and regulating pollution control.

7.1.1 National policy

A country must define objectives for the control of existing sources of pollution and prevention of new ones. In developed countries and in some developing nations such policies are part of the legislation. Lesaca (1978) reported on the different aspects of national environmental policy, e.g. evolution of environmental policy, political will of governments, policy on environment and development and on pollution prevention, protection and enhancement strategies.

7.1.2 Legislation

After determination of a national policy this has to be transformed into appropriate legislation for the protection of the aquatic environment aiming at pollution control and prevention.

Most developed and also some developing countries have enacted environmental legislation. Alabaster (1981) and Calamari (1985) reviewed the existing situation in eleven countries in Eastern, Western and Central Africa. According to Alabaster (1981), water pollution control legislation has evolved rapidly in several countries but is still under review in others. In a few cases environmental legislation is already being used effectively for pollution control.

It is hoped that each African country will achieve its own environmental legislation in the near future, taking into consideration the experience of developed countries in order to avoid the mistakes made there. It is important that such legislation includes requirements for environmental impact assessment, a process for incorporating environmental considerations into all development activities already at the planning stage. Also, legislation must provide mechanisms for the enforcement of aquatic pollution control laws, ideally with the support of local and provincial offices.

7.1.3 Implementation of procedures

7.1.3.1 Standards and criteria

The formulation of standards is of special interest. For the quality of waters, two different types of standards exist: water quality standards, defining characteristics a water body should have depending on its dominant use, and effluent standards, limiting the pollution loads that a point source could discharge into the receiving waters. Considering organic pollution, the most important parameters which must be controlled through standards are pH, colour and turbidity, nutrients (P and N), suspended and total solids, COD and BOD (Lesaca, 1978).

The terms “standards” and “criteria”, used in water pollution control and often treated as synonyms and interrelated, are clearly distinct. Standards are limiting values laid down in legislation and arrived at by compromise between competing demands. Criteria are quantitative evaluations arrived at by scientific research using defined analytical methods. A wider discussion on this argument is given by Biney et al. (1987). Accordingly, a criterion is defined for a single parameter and one utilization of water (e.g. a criterion for COD or BOD in water used for aquaculture). Consequently, specific criteria will exist for the various uses for each parameter; a general criterion will therefore have to adopt the most restrictive value.

The European Inland Fisheries Advisory Commission (EIFAC) has undertaken to determine water quality criteria for freshwater fish in Europe. Criteria have been formulated for different parameters, some of which relevant for the control of organic pollution, e.g. suspended solids, pH and ammonia (Alabaster and Lloyd, 1982). However, criteria for the European region are based on the climatic conditions and the fish species there and, consequently, cannot be applied indiscriminately in other regions. Criteria for Europe and other regions could, however, be adapted for organic water pollution control in Africa, taking into consideration the particular climatic conditions and geographic situation in this continent. This could be a first step, but work needs to be initiated on specific criteria to provide a scientific basis for water pollution control in Africa.

7.1.3.2 Monitoring programmes

Monitoring systems have to be established to check on the health of the aquatic environments and the effects of large loads of organic wastes on the biota, especially the commercially important species. In African countries, the steps indicated below are proposed for a monitoring programme.

A survey should be carried out to identify the principal pollution sources. According to Calamari (1985), a register of point sources has been completed or is at an advance stage of preparation in the five countries he visited in West and Central Africa. For each water body, calculations are made of the BOD and other water quality characteristics of the organic wastes, discharged untreated or from municipal and industrial treatment plants. The organic loads of the receiving waters should also be investigated, taking into consideration seasonal changes of runoff and biological activities.

A map of the receiving waters based on the survey is then prepared, showing for each water body the organic pollution load in BOD and its different sources, as well as the number of treatment plants for domestic and industrial wastes. On the basis of this map, certain areas in which organic pollution is serious can be selected. Special attention should be given to these areas, and the different compartments (water, sediments and organisms) should be monitored over a suitable period (one to two years).

Biological monitoring uses living organisms as sensors for environmental quality; species composition and diversity, as well as population density, normally decrease with lowering of the water quality. Methodology comprises sample collection and processing, identification and counting of aquatic organisms as well as biomass measurements. Since sample collection and observations are performed in the field and analyses are carried out in the laboratory, research stations are needed, preferably near the polluted areas.

The results obtained from the selected heavily polluted areas are useful for the design of a continuous monitoring programme, which could cover all polluted inland waters in a country. Such large-scale monitoring activities necessitate a number of suitable laboratories in well-equipped research institutes and fishery departments, as well as a sufficient number of trained technical and scientific personnel. In some African countries water pollution laboratories do exist, but with insufficient means. Therefore, improvement of the equipment and structure of the existing laboratories, as well as the establishment of new laboratories, is highly recommended.

7.2 Remedial Measures

7.2.1 Treatment of organic wastes

A considerable portion of the African population lives in rural areas; accordingly, the wastewater treatment technologies applied in Africa vary from simple systems to modern ones. Industries such as food and textile are mostly located in urban centres. These industries generally discharge their waste water through the sewage system to the municipal treatment plant. Hence, industrial wastes are treated in the same way as sewage, i.e. by sedimentation, biological methods and, recently, also by chemical precipitation. This treatment is quite appropriate for organic wastes from these industries. However, in order to reduce the load on the community treatment plant, industrial organic wastes should be reduced internally, i.e. subjected to treatment inside the factory. The principles of current methods for sewage treatment are discussed in detail by Zain-ul-Abedin (1978). They are also summarized by Bruneau (1974) and Landner (1978), who concentrate on the aspects pertinent to industrial wastes. These two authors provided an illustration showing the different types of waste treatment (Fig.1).

The simplest biological treatment method is to use a small lagoon and to leave the problem of decomposition to nature. When this lagoon emanates an unpleasant odour after becoming anaerobic, it should be followed by a second lagoon working under aerobic condition (Fig.1). This aerated lagoon can be loaded more heavily (Fig.1.2). Both these treatments are not recommended in densely populated areas. A more effective method is the use of sedimentation tanks (Fig.1.3). One of their advantages is that they can be continuously cleared of sedimented sludge and floating materials. Two kinds of biological processes exist for treatment of large amounts of water in a short time. The oldest is the trickling filter system, in which the water passes over stones or plastic on which the micro-organisms form a surface coating where biological degradation takes place (Fig.1.4). The second method is activated sludge, in which the micro-organisms are suspended in the water to be treated (Fig. 1.5). This system can be loaded more heavily than trickling filters. In the above treatment facilities, the nutrients in the waste water, especially phosphorus, are not reduced. Also, some of the sludge may escape with the effluent into the recipient water. Consequently, in certain cases, the activated sludge method has to be supplemented by chemical precipitation of nutrients (Fig. 1.6).

1. LAGOONS
2. AERATED LAGOONS
3. SEDIMENTATION
4. BIOLOGICAL TREATMENT, TRICKLING FILTER
5. BIOLOGICAL TREATMENT, ACTIVATED SLUDGE
6. CHEMICAL TREATMENT

Fig. 1 Types of waste treatment

The most popular sewage treatment process in Nigeria is the Imhoff septic tank system, which allows for the anaerobic decomposition and settlement of sewage in confined dug-out pits. These pits are sealed with concrete to prevent obnoxious odour and spread of wastewater-borne bacteria.

The classical treatment methods summarized above remove only part of the critical nutrients (nitrogen and phosphorus). Consequently, even treated waste water has often impaired the quality of receiving waters due to the increase in the nutrient content and the consequent growth of algae (eutrophication) (Stirn, 1973; Zain-ul-Abedin, 1978). This problem has to be solved to protect the aquatic environment. In a laboratory pilot plant, ion exchange resins have proved to be an effective means to treat effluents from a municipal secondary-treatment plant and to prevent eutrophication in the receiving waters (Liberti et al., 1981).

Good methods for treatment of sewage and industrial organic wastes nowadays are available and are continuously improved. Proper wastewater treatment, however, produces increasing amounts of sludge, the disposal of which constitutes already in some countries a major waste problem. Cillié (1979) has reported on prospects for sludge treatment, utilization and disposal.

Focussing on waste treatment alone, however, is unsatisfactory since such practice often merely transfers a pollutant from one environment medium to another. A more appropriate approach is to reduce wastes at their sources, that is to limit their production as much as possible by the use of Low and Non-Waste Technologies (LNWT). Such technologies employ concepts like resource recovery, waste recycling and residue utilization. The aim is to circumvent the need for treatment, discharge or disposal of large volumes of wastes and to reduce demand for raw materials, energy and water.

7.2.2 Utilization of effluents

Reuse of domestic and industrial waste water is not a new concept. Use of waste water for irrigation purposes is at the same time a practical treatment process since agricultural and forest soils have proved efficient “living filters” for the removal of pollutants from waste water. A review of the literature regarding application of waste water on mineral soils was published by Bouwer and Chaney (1974). According to Wightman et al. (1983), overland flow is a viable process for treating municipal and industrial waste water. A properly designed and operated overland flow system can achieve more than 90% reduction of BOD and suspended solids and about 70–90% reduction of nitrogen. According to Terry and Tate (1981), the organic soil they have studied can be effectively used to remove the major portion of nitrogen and phosphorus from effluents of secondary treatment plants. Purification is greatly enhanced by the presence of a crop.

Water reuse in agriculture is highly recommended for arid areas and countries suffering from drought problems. However, Sridhar et al. (1981) concluded that the discharge of untreated waste water on soils on which vegetable crops are grown affects soil productivity and the vegetables grown in the soil become infected with pathogenic organisms and are rendered unfit for human consumption, especially when consumed raw (Pillai, 1955; Sridhar and Pillai, 1973).

The utilization of fish ponds for wastewater treatment and protein production holds much promise for the future. The use of domestic sewage as a fertilizer for fish culture was recognized in several countries and gave good results. It is, however, preferable to treat the wastewater before application to fish ponds in order to reduce the organic load. Primary treated sewage, containing less organic material than raw sewage but more nutrients than secondary treated sewage, is preferred for fish ponds where no feeds or fertilizers are provided. However, the use of sewage in fish ponds can result in a higher incidence of intestinal parasites and humans can be infected by eating contaminated raw or insufficiently cooked fish.

7.3 Training, Education and Public Information

Education and training of technical and professional staff are required, since the lack of trained personnel is a major obstacle for efficient water pollution control. Training can be achieved either by sending chemists, biologists and limnologists abroad or by initiating national training programmes under the supervision of experienced national and foreign experts. Training should cover sampling and analytical techniques, biological monitoring, biology and ecology of commercially important fish species and wastewater treatment technology.

It is equally important to ensure public support for water pollution control through inclusion of environmental topics in school curricula and increasing public awareness through the media.

7.4 Regional Cooperation in the Use of Shared Water Resources

Several agreements have been stipulated by African governments to cooperate in the development of their common river or lake resources in an environmentally sound and sustainable manner. Some of these agreements led to the establishment of Commissions such as those for Lake Chad, the Niger River and the Senegal River, and Action Plans such as the Zambezi Action Plan (United Nations, 1970; Alabaster, 1981; David, 1988). For joint management of fishery resources, CIFA established sub-committees for Lake Victoria and Lake Tanganyika. While these agreements promote the use of shared water resources for socio-economic development, the threat to water quality arising from pollution caused by domestic sewage, industrial wastes and agricultural development within water sheds now deserves urgent attention. Water pollution is increasing in many countries, and developments upstream of a river are often adversely influencing water quality downstream. Bernacsek (1984) reviewed the ecological effects of large dams in Africa and pointed out that downstream of the Kainji Dam in Nigeria, the Roseires Dam on the Blue Nile, and Akosombo Dam on the Volta River in Ghana deoxygenated water caused fish mortalities.

As the demand for water use grows, countries sharing water resources must include comprehensive plans to control and monitor pollution, if the water quality impairment within one territory is not to create conflicts elsewhere.

8. CONCLUSIONS

• Pollution from organic matter and nutrients is of considerable importance in African inland waters and fisheries. Remedial actions should be undertaken.

• A lot of information is still missing, and specific research programmes at national and regional level are needed; this entails the need for a network of adequately equipped laboratories.

• Exchange of data and experience between African countries concerning organic pollution and its control is necessary, in particular on self-purification processes under African climatic conditions and on waste treatment processes for domestic and industrial organic wastes appropriate for Africa.

• An increase in the number of experts on the subject and intensification of training and education are called for.

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