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Chapter 7 Conclusions and Recommendations
7.1. Conclusions
This chapter summarises the main findings of this study and presents the recommendations for future research. The limitations and errors are also discussed. Sustainable development is the overarching concept of this study. This concept aims to re-direct development onto a path in which industrial expansion and advancement are done in such a way so as to protect humans and the environment. Cleaner production is one way of striving for a more sustainable path for industry and business. Cleaner production is based on the principle more with less and it promotes the increase of overall efficiency and the reduction of risks to people and the environment by the continuous application of a preventive environmental strategy to industrial and business activities in general. There are a number of tools employed in cleaner production and LCA is one of them. LCA is a technique for assessing the environmental aspects and potential impacts associated with a product, service or activity over its entire life cycle (i.e. from cradle-to-grave). It takes into account releases to all media (water, soil and air) and the consumption of raw materials. This tool has definite advantages, most notably its holistic quantitative and comparative approach from a cradle-to-grave perspective. It also detects the shifting of pollution between media or processes. In the last decade a series of applications emerged for LCA in the water industry and this research is such an application.
The overall objective of this study was to generate information on the environmental life cycle of water in an urban context. This included the abstraction and treatment of raw water, the distribution of potable water, the collection and treatment of wastewater, the disposal to sea of effluents and the recycling of water. Of particular interest was the environmental efficiency of recycling water for industrial use and to examine the net effect of recycling.
7.1.1. The main findings of the study
The LCA impact analysis in Chapter 3 of each individual unit provided some valuable insights into where the major environmental impacts lie in a water and sanitation system. By breaking up the system into sub-systems and then further analysing these subsystems as individual processes one could easily identify the units which could be targeted for environmental improvement. By studying the construction, operation and decommissioning phase of each sub-system separately
we were able to confirm the literature findings that the operations phase was responsible for the majority of the impacts.
The results showed that the operations phase was responsible for over 90 percent of the environmental load for all the studied impact categories. This result is in line with many other LCA studies on water and wastewater treatment processes (Emmerson et al., 1995, Meijers et al., 1998, Grabski et al., 1996). This lead to a streamlining of the study and for some of the units, detailed calculations to assess the environmental impact of the construction and decommissioning phase were not carried out. This resulted in a large time saving without a significant loss in accuracy.
One of the unexpected findings was the low environmental impact of the dam for the LCA categories. Although the dam is a major emitter of greenhouse gases, per kilolitre however, the impact of the dam are small compared to the other treatment processes. Most of the impacts occur during the construction stage, many of which are not encompassed by traditional LCA impact assessment methodology. The impact analysis of the dam was completed by undertaking a social analysis. This was necessary as in some cases, the social impact of dam construction outweighs the environmental impacts.
A closer examination of the operations phase revealed that with the exception of the human ecotoxicity category, the use of electricity resulted in almost 80 percent of the burdens of the other impact categories. It must be noted that this is specific to water and wastewater treatment processes, where the chemical input is small in comparison to the electrical input. This resulted in the development of an electricity index as a performance indicator. This is one of the major outcomes of this thesis as it allows for a simple measurement of environmental performance by monitoring electricity consumption.
The results from the LCAs of each unit in Chapter 3 directed the study to two areas; how to minimise the electricity use of the system and secondly to examine more closely the generation of electricity in South Africa and the impact model used.
With regard to the first, the two highest electricity using processes were targeted for an improvement analysis. These were the activated sludge treatment process and the ozonation process at Wiggins Waterworks, which uses 9700 and 4300 kWh/ day respectively. These processes were analysed in detail in order to ascertain exactly where and how the electricity was being used. Different improvement measures were suggested and in some cases tested. The
improvement analysis showed that the electricity use of the ozonators at Wiggins Waterworks could be reduced by as much as 80 % by limiting the air flow to the thermal destruct unit, used to destroy excess ozone.
A detailed analysis of the activated sludge unit was conducted. Various methods of reducing the electricity usage of the system were considered. These included; alternate aeration methods, varying the operating conditions and using a chemical pre-treatment step. The possibilities for reducing the electricity consumption for this unit are large with the possibility of an order of magnitude reduction. However due to the sensitive nature of the process trials were not able to be carried out. It must be stated that electricity efficiency measures are not a priority in the South African water industry due to the relatively low cost of electricity. Rather the focus is on reducing the chemical consumption which contributes to a large proportion of the operating expenses.
The social impacts of the provision of water and sanitation were investigated in order to create a more complete picture. The results from the social impact analysis differed from the environmental analysis in that the impact of the construction phase was found to be significant.
The construction of Inanda Dam was shown to have the largest impact of any of the studied sub- systems due to the forced removal of the residents in the dam's floodplain. Another area, which is often neglected in social impact assessments, was the impact of electricity use during the operations phase. Here the advantage of using the LCA methodology is clear and the impact of electricity generation, although occurring hundreds of kilometres away, is included. The highly localised nature of the power stations result in a concentration of the pollution effects. An increase in respiratory illnesses in the area of the power stations has been noted. However no scientific studies have been carried out to validate these claims.
In Chapter 6 scenarios were considered to investigate how best the water and sanitation supply levels in the eThekwini Municipality could be increased. The results of the LCA study in chapter 3 provided a base case. The options investigated were, maximising the use of existing assets, water recycling and the construction of new infrastructure. In order to quantify the total impact of each option and thereafter rank them, a service based functional unit was chosen. The functional unit was the provision of a basic level of water and sanitation services to 200 000 new customers. The scenarios considered customers in both rural and urban areas. A number of interesting findings arose. These are summarised here;
• The first step for any municipality needing to expand its water and sanitation service levels is to examine how well the present infrastructure is being utilised. This includes a waste minimisation program, leak detection and a water demand management program.
Existing assets should also be individually investigated to determine the potential scope for improvement.
• When seeking to reduce the environmental impact of a water and sanitation system an energy audit is preferable to a detailed LCA. This is quicker to perform and this study has shown that electricity is responsible for the majority of the environmental impacts.
Friedrich and Pillay (2005) proposed the use of an electricity index as a measure of environmental performance for urban water systems in South Africa. The amount of energy expressed as kWh/kl of water (potable or wastewater) is enough to simplistically judge the overall environmental performance of existing water systems. It is also a relatively easy index to use from the point of view of the technical staff involved in operating water plants and pumping stations and which usually are not familiar with global warming and C02 equivalents. The use of an electricity index would be a good measure, as long as the underlying data (i.e. electricity consumption) can be measured reliably and assigned to different operations or processes
• Alternate methods of sewage treatment should be considered if possible. On-site treatment systems such as the urine diversion toilet being used by the eThekwini Municipality have a low environmental impact provided they are operated correctly.
This is dependent on the location of new customers as on-site sanitation methods can only be used in rural or peri-urban areas.
• By using all existing assets at their maximum design capacity, a reduction in the total environmental burden can be achieved. Dams need to be operated at their design abstraction limits otherwise they act as large greenhouse gas emitters for no return. The use of the LCA technique resulted in a quantification of the environmental impacts from the dam.
• Although the recycling of water is energy intensive, it has a net positive environmental impact. It is important therefore, to ascertain the quality of water required by the customer. If only an industrial grade is required then only that should be supplied. This is not a blanket generalisation as was found when analysing the impact of providing
bottled water. In that instance it was better to provide a potable water supply to all consumers than to separately provide bottled water for drinking purposes only. This was due mainly to the large burden associated with the production of the bottles.
One of the most important outcomes of this thesis is the development of a framework for the sustainable expansion of a water and sanitation system. This framework serves as an addition to the existing framework for 'Appropriate Solutions For Water Supply and Sanitation'. This addition allows decision makers to include sustainability criteria when considering expansion options.
7.1.2. Important limitations of these conclusions
While LCA is a valuable environmental tool it is not the right tool for evaluating all environmental impacts. For the analysis of the dam environmental impact assessment is probably a better tool as LCA neglects impacts such as changes in bio-diversity and downstream river morphological effects. For the other water and wastewater treatment process LCA provides a good representation of their environmental impact. The use of LCA in water treatment processes is well documented and its focussing ability is a valuable tool.
The use of a non South African database to calculate the magnitude of the impacts results in some inaccuracies. However for the important emissions from the generation of power these measurements are close enough to the GaBi database to be used.