Integrating environmental impact costs with engineering costs

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Membrane desalination process

Membrane desalination treatment is well established for many water and effluent applications. The technology requires some refinement and further development before it can be successfully applied to high sulphate containing mine water. The specific challenge has been to maximise water recovery and thereby reducing the brine/sludge volume production. The main stream membrane desalination process is fairly standardised for acid mine drainage and includes the unit treatment processes of:
• limestone/lime neutralisation;
• softening and excess gypsum crystallisation;
• micro/ultra filtration; and
• spiral reverse osmosis.
Different approaches are, however, implemented to further treat the first stage reverse osmosis (RO) brine stream as reflected in Figure 61 (p. Figure 61). The different brine treatment options include:
• Precipitation of gypsum and anhydrite using a hydro-thermal process, originally developed by Wren. Gypsum and anhydrite have an inverse solubility dependence on temperature. The hydrothermal process is based on sequential high temperature (140 – 160 °C) and high pressure (5 – 6 bar) vessels to progressively precipitate the sulphate salts in the form of a pure gypsum and pure anhydrite salt. The water product of the hydro-thermal brined treatment is after cooling blended back into the main reverse osmosis (RO) permeate product stream.
• De-saturation and secondary RO treatment involves the chemical treatment of the RO brine stream to destroy the anti-scalant effect and to precipitate the super saturated salts such as gypsum and calcite. The de-saturated brine stream is then treated in a secondary micro/ultra filtration and spiral RO process to increase the recovery of water. The de-saturation process can be repeated on the secondary RO brine stream to increase the water recovery even further.
• Thermal evaporation and crystallising technology can also be applied to the RO brine stream. This employs conventional technologies and has been applied to many industrial and mining effluents. The residue is concentrated brine or moist salt crystals. All three these brine treatment technologies have been successfully applied in Southern Africa and the achievable water recovery is as follows:
• hydrothermal brine treatment = > 98 % water recovery
• de-saturation and secondary RO treatment = > 95 % water recovery
• evaporation and crystallisation = > 90 % water recovery.

Economic feasibility of treatment processes

water is suitable for mine process water or to be discharged into surface water body or sewage network can be achieved by using either the:
• limestone/lime process;
• biological treatment process; or
• membrane desalination process.
The typical treatment costs of the different technologies considered are listed in Table 16. According to the table the treatment costs for the limestone process is the cheapest at R100 – R460/t sulphate removed. Also, it is evident that the running costs can range between R100 and R2500/t sulphate removed depending on the technology chosen. The capital cost varies between R88 250 and R5 million per tonne sulphates which would be removed per day. The preferred technology will not only depend on the bottom line cost but will also depend on factors such as the volume and quality of influent water, the required level of sulphate removal, and locality.

Waste discharge charge system

The Department of Water Affairs and Forestry (DWAF) is developing a waste discharge charge system (WDCS) to promote waste reduction and water conservation.
This system forms part of an overall pricing strategy being established under the National Water Act No. 36 of 1998 (NWA) and is based on the polluter-pays principle which aims to:
• promote the sustainable development and efficient use of water resources;
• promote the internalisation of environmental costs by those responsible for the pollution;
• create financial incentives for dischargers to reduce waste and use water resources in a more optimal way; and
• recover the costs of mitigating the impacts of waste discharge on water quality.
The WDCS is a response to a pollution problem that is already imposing a cost on society. The WDCS endeavours to shift some of the cost back to dischargers according to the polluter pays principle. The common perception that environmental charges are a trade-off against the economy for the sake of environmental benefits is shown in the literature to be largely false. Accordingly, a pollution charge should not be viewed as an additional burden on the economy. The result of pollution charges is often that overall pollution costs are reduced while the economy as a whole is more efficient and less wasteful, and generally more attractive to investors.
Water resource management in South Africa links the acceptable level of impact to the concept of resource quality objectives (RQOs), which balance the need to protect water resources with the need to develop and use them. The setting of RQOs is catchment specific, based on the social, economic and political drivers for development and utilisation of a specific water resource. RQOs are to be set as part of the classification system for water resources, through a process of consensus seeking among water users and other stakeholders, in which the government is responsible for ensuring that environmental interests are represented.

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CHAPTER ONE: INTRODUCTION 
1.1 The need for a more sustainable legacy for mine residue deposits
1.2 Problem statement
1.3 Hypothesis
1.4 Problem solution
1.5 Thesis organisation and structure
CHAPTER TWO: LITERATURE REVIEW 
2.1 Manmade landforms within the natural landscape
2.2 Minerals and mining
2.3 Tailings characterisation and disposal
2.4 Sphere of influence
2.5 Sustainable development
2.6 Decision making
2.7 Environmental planning and design
2.8 Environmental planning framework
2.9 Environmental impact estimation
2.10 Visual
2.11 Air
2.12 Water
2.13 Soil and landform
2.14 Concluding remarks
CHAPTER THREE: EXPERIMENTAL WORK AND MODELLING 
3.1 Introduction
3.2 Configurations modelled
3.3 Study site
3.4 Visual
3.5 Air
3.6 Water
3.7 Engineering cost model
3.8 Summary
CHAPTER FOUR: RESULTS 
4.1 Introduction
4.2 Visual perception
4.3 Visual perception zone of influence
4.4 Air quality zone of influence
4.5 Water quality influence
4.6 Engineering costs
4.7 Summary
CHAPTER FIVE: COMBINING ENVIRONMENTAL IMPACTS WITH ENGINEERING COSTS
5.1 Introduction
5.2 Engineering costs
5.3 Combining environmental impacts with engineering costs
CHAPTER SIX: INTEGRATING ENVIRONMENTAL IMPACT COSTS WITH ENGINEERING COSTS 
6.1 Introduction
6.2 Valuating environmental impacts
6.3 Integrating environmental impact costs and engineering costs
6.4 Total integrated environmental impact costs and engineering costs
CHAPTER SEVEN: INFLUENCE OF ENVIRONMENTAL IMPACTS ON TAILINGS IMPOUNDMENT DESIGN – DISCUSSION 
7.1 Introduction
7.2 Decision-making system
7.3 Valuation of environmental impacts
7.4 Sphere of influence
7.5 Sustainable development
7.6 Rehabilitation
7.7 Integrated environmental planning and design
7.8 Meeting legislative requirements
7.9 Summary
CHAPTER EIGHT: CONCLUSIONS 
8.1 Decision-making system
8.2 Engineering costs
8.3 Visual perception
8.4 Air quality
8.5 Water quality
8.6 Environmental impact valuation
8.7 Recommendations
List of references 
List of acronyms and abbreviations 
List of technical terms 
APPENDICES 

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