Until now, the main point of interest in this book has been biological wastewater treatment. In this chapter we want to expand our perspective to the development of new production processes with reduced consumption levels of water and raw materials and with reduced production of wastewater. For this purpose, we have to direct our interest towards an entire production process and we have to consider new methods to save water and different, mostly non-biological ways to treat water.
Figure 13.1 provides a systematic view to make the following discussions in this chapter more readily understood.
It is necessary to limit the problem to a single state and it is also prudent to discuss the problem with respect to water while keeping in mind that water as well as all impurities may change their state.
Water pollution and wastewater treatment are typically divided into the two different fields of application, i.e. industrial and municipal wastewater. In this chapter, we will consider the production and treatment of industrial wastewater (Fig. 13.1).
Process integrated water management is characterized by three management procedures:
1. Minimization of water use may already be an important aim, but it may be that water reuse is not possible or the cases are restricted and the advantages are too small. Only if two or three processes have coupled, multiple use of water can offer a chance for considerable saving. Therefore, a separate discussion of point 1 is necessary.
2. The development of new processes and the optimization of existing or new ones with the aim of saving water, materials and energy must be the first step of water management. The price for fresh water, the costs for wastewater treatment and the charges for discharging into surface waters must be considered to find the best way for a sustainable development which is a balance of economical success, environmental protection and social acceptance (Fig. 13.2)
3. The regeneration and recycling of water should be taken into account where there is a short supply of fresh water, which makes it necessary to close water cycles at least partly. Point 3 should be discussed together with point 1.
economic problems Fig. 13.2 Sustainability (Christ 1996, 1999).
Decentralized effluent treatment systems can be divided in those with and those without reuse. There are two motivations to treat effluents in a decentralized manner:
• The water is only loaded by components which can be separated easily at low cost, which makes it possible to discharge the treated water directly into a river at no additional cost. The costs may be significantly lower than the amount which would have to be paid to the central WWTP. Another case may be applicable for a highly loaded effluent which can be treated anaerobically without significant sludge production and without aeration costs. It may be cheaper to treat this effluent anaerobically together with several similarly loaded effluents in comparison to a single aerobic stage.
• Following decentralized treatment, the water may be reused in further processes which do not need water with freshwater quality or it can be sent to a larger aerobic industrial or municipal WWTP.
In this chapter, we will explain what process integrated water management and decentralized effluent pretreatment are and how they can be applied in specific industries such as the chemical, pharmaceutical, food, textile, drinks, paper and cellulose, iron and steel industries. To these topics anual meetings take place at University Bremen, Germany (Rabiger 1999). We find the most examples for process integrated water management within the chemical industry. Therefore, this industry is suitable to give examples for the following discussion.
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