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CHAPTER 6. TECHNOLOGICAL AND MANAGERIAL ASPECTS OF EUTROPHICATION

6.12. Conclusions and Recommendations

Today there are many examples of lakes that have recovered after the reduction of phosphorus discharge to the lakes and their tributaries. On the other hand, there are also many examples of no effect of an advanced wastewater treatment due to the presence of diffuse pollution sources, which were not reduced. It is therefore necessary to consider all sources of nutrients and organic matter in our efforts to solve the pollution problems properly.

A eutrophication and dissolved oxygen model of a lake or reservoir should always be developed with an indication of all sources of nutrients and organic matter and with possibilities to predict the effect of a certain reduction of the nutrient discharge from all sources. If the available data bank is poor, it should be considered to collect more data and/or at least to develop a static model with estimated mass balances for the most pertinent elements, such as nitrogen, phosphorus, and oxygen. Monitoring different parameters of water quality with respect to eutrophication provides data for modeling and useful information to decision-makers and managers of lakes and reservoirs.

Several countries in Western Europe apply advanced wastewater treatment but have also discovered that it is equally important to reduce the diffuse pollution of nutrients. Due to too high agriculture production in Western Europe, 10% of agricultural land is now fallow and it is converted, to a high extent, into constructed wetlands to apply the fallow land to achieve a higher reduction of the nutrient pollution originating from agriculture. The lesson learned is clear: a simultaneous abatement of point and non-point (diffuse) pollution is necessary to achieve acceptable results in management and control of eutrophication.

Many African states use WSPs and have obtained the experience that it is not sufficient to solve the pollution problems related to wastewater. Recent results (see Section 6.3. of this chapter) have clearly shown that the combination of WSPs and constructed wetlands offer a good cost-moderate solution in countries where the population density is relatively low. However, also in this case, the recommendations given in this chapter should be followed, which implies that the solution of diffuse pollution should also be considered and that the pattern of ecosystems in the landscape should be preserved. Increased eutrophication observed in Lake Victoria during the last decade is due to the lack of proper wastewater treatment. However, it is also caused by the drainage of valuable wetlands along the shoreline of Lake Victoria.

Many developing countries have still not invested in sewage systems. It opens for the possibilities to find non-traditional sanitary solutions based upon separation at the source of different types of wastewater. Industrial wastewater should be treated at the source and recycling should be considered. A separation of municipal wastewater into storm water, grey wastewater, urine and feces makes it possible to select:

• more cost-moderate treatment of storm water and grey water;
• recycling of urine; and,
• composting of feces.

This solution is, in most cases, ecologically more acceptable and more cost-moderate than that based on a sewage system. It is therefore recommended to include the sanitary system with consideration of an optimum solution.

The wastewater problem is not solved if the problem of the produced sludge is unsolved. Proper lake management also includes a solution to the solid waste problem. Non-treated urban waste can become a non-point source pollution of freshwater resources. All pollution problems are best solved by a reduction of the emission by reuse and recycling. This is particularly obvious in the abatement of solid waste pollution where glass, plastic, metals and paper can be reused or recycled. By composting the remaining waste, including the sludge, it becomes possible to recycle even the product of this process, the compost, as it may be used as a soil conditioner, provided that the concentrations of toxic material are lower than given standards and guidelines.

From the discussion in this chapter it can be concluded that a total, holistic lake and reservoir management, consists of:

• consideration of non-point and point sources,
• land use control of the entire watershed, and
• proper solution of the problems associated with the solid waste, such as the sludge from wastewater treatment and domestic garbage, is needed to ensure an ecologically sound solution, which can be realized with limited economic resources allocated to the solution of pollution problems.

A decision tree covering these aspects is shown in Figure 6.9. It contains reference to the previous decision trees in this chapter, which focus on the management of wastewater and solid waste.

Figure 6.9. Decision tree for the holistic management of lakes by focusing on the entire watershed.

Example of an artificial wetland constructed for treatment of liquid waste from a food producing company in Kenya is shown in Figure 6.10.

Figure 6.10. Artificial wetland for treatment of liquid waste from food producing company in Kenya.

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