As water is a basic need, it is in most cases directly or indirectly subsidized. For recycled water that can be used in agriculture, the price should be adapted to the possibilities of the users. For the effluent of the depicted treatment process, the price includes not only the water but also the nutrients dissolved in the water that can be used to substitute fertilizers. The costs of the transport of the water and the treatment process can be covered by fees for wastewater purification paid by the original users of the water, the revenues from biogas utilization, and the price paid by the users of the treated water. Depending on the economic situation, additional subsidies might be necessary to cover the costs of the treatment process. For a sustainable operation, it would be valuable if at least the costs for operation could be covered by the users, making the operation independent from decisions of external sponsors.
Irrespective of these considerations, the benefits of such a system for the overall economy are immense: Most important, the wastewater is treated and pathogenic microorganisms that can be spread by the wastewater are retained, being a crucial prerequisite for health care. Additionally, this concept helps to build up local small scale economies by utilizing the water for growing fruit and vegetables in the vicinity of settlements. Inhabitants can benefit from a healthier diet and a better supply with vitamins as well as by employment and an extra income by selling the products on local markets. This semi-centralised approach can lead to a system of almost closed cycles of water, nutrients, and energy.
7.5 HUMAN DIMENSION OF WATER REUSE
Essential precondition for the successful realization of water reuse according to the concept DEUS 21 is the early involvement of the affected stakeholders: inhabitants, regional and local authorities, infrastructure planners, construction enterprises, land owners, and future users of the treated water. The early determination of tariffs and prices is important to ensure acceptance by the users and to prevent annoyance. In Knittlingen, several meetings with the town’s administration, the town council, the inhabitants, and the involved planners and constructors have been organized, before and during the implementation of the project. During the project, the acceptance of the new infrastructure system has been checked by interviewing the inhabitants of the development area, by visiting them, and by questionnaires. The public attitudes were predominantly positive.
Especially for the implementation of a water reuse scheme, the communication between the users of the recycled water, that is, the farmers, the authorities, and the operators of the wastewater treatment plant is important to ensure a safe utilization of the
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recycled water. Potential problems in operation have to be communicated to the end users, if the quality of the effluent could be affected. It is also important to keep in mind that a sound irrigation and fertilization management is necessary to guarantee that the water is used in the right way. This helps prevent problems with over-fertilization and salinization. The initial users of the water, the inhabitants, have to be informed about substances that must not be added to the sewage like leftovers of pharmaceuticals and of cleaning agents, and other chemicals used in households. The awareness to add as little chemicals as possible to the sewage will be higher when the inhabitants are involved in the utilization of their treated sewage and profit from their correct behaviour.
If a concept like DEUS 21 is realized in a certain region for the first time, a research institution located in the region with specialists in social and agricultural sciences should be involved to adapt the concept to the local culture and biogeographic conditions like climate, soil characteristics, and local plant species.
7.6 CONCLUSIONS
In the research project DEUS 21 in Knittlingen, a semi-centralised water management concept has been demonstrated. The effluent of the wastewater treatment plant, operated according to the AnMBR process, is characterized by a relatively low concentration of organic substances (COD), no particles, almost no pathogenic microorganisms, and a relatively high concentration of the nutrients ammonium and phosphate. This quality, which has not been achieved before with an anaerobic process at low temperatures and a comparable influent quality, makes the recycling of the water and the nutrients in agriculture a feasible option. This could lead to a change in wastewater management and an increase in reuse applications.
As the concentrations of ammonium are relatively high, ammonium-free water, for example, rain water, and phosphorous have to be added and the irrigation and fertilization has to be realized according to a management scheme, taking into account the different growth stages of the plants.
The following aspects are relevant for a sustainable implementation of the concept:
The specific water consumption should be low and rainwater should be collected separately, as the necessary membrane area correlates with the amount of water to be treated and has a significant impact on investment costs, operation costs and energy demand.
High temperatures lead to higher growth rates of the anaerobic microorganisms and therefore allow the operation with lower solid concentrations, and increase the filterability of the sludge. This results in higher fluxes and a reduction of the necessary membrane area as well.
A demand for the produced biogas, for example, for cooking, or the waste heat of electricity production close to the treatment plant saves fossil energy resources. The utilization of the effluent in agriculture saves water and nutrients and substitutes a process to eliminate the nutrients, which would be necessary for a discharge into receiving waters.
A further optimization of the treatment process should aim at generating sludge with a higher ratio of methanogens, allowing a lower concentration of solids. The operation of the filtration should be optimized to achieve a higher sustainable flux. Both measures would reduce the necessary membrane area. The rotating disk filter itself is currently refined, reducing its investment and operational costs as well as the energy demand.
All in all, with minor optimization of the treatment process, the concept DEUS 21 is suited best for the implementation in regions with warm climate and a demand for irrigation water, in which no wastewater treatment exists yet. This semi-centralised approach with water reuse can help to build up sustainable water infrastructures and local markets for fruit and vegetables and decrease the dependency of regions on the world markets.
REFERENCES AND FURTHER READING
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Bacchin P., Aimar P. and Field R. W. (2006). Critical and sustainable fluxes: theory, experiments and applications.Journal of Membrane Science,281, 42–69.
Beringer T., Lucht W. and Schaphoff S. (2011). Bioenergy production potential of global biomass plantations under environmental and agricultural constraints.GCB Bioenergy,3(4), 299–312.
Lettinga G., Rebac S. and Zeeman G. (2001). Challenge of psychrophilic anaerobic wastewater treatment.Trends in Biotechnology,19(9), 363–370.
Liao B. Q., Kraemer J. T. and Bagley D. M. (2006). Anaerobic membrane bioreactors: applications and research directions.Critical Reviews in Environmental Science and Technology,36, 489–530.
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Mohr M. (2011). Betrieb eines anaeroben Membranbioreaktors vor dem Hintergrund der Zielstellung des vollständigen Recyclings kommunalen Abwassers und seiner Inhaltsstoffe (Operation of an Anaerobic Membrane Bioreactor in the Context of the Objective of Complete Recycling of Municipal Wastewater and its Contents). Ph.D. thesis. In: Berichte aus Forschung und Entwicklung, Vol.40, Fraunhofer Verlag, Stuttgart.
Sutton P. M., Bérubé P. and Hall E. R. (2004).Membrane Bioreactors for Anaerobic Treatment of Wastewaters. Water Environmental Research Foundation, University of British Columbia, Canada.
UNESCO (2009).The 3rd United Nations World Water Development Report: Water in a Changing World (WWDR-3). United Nations Educational, Scientific and Cultural Organization, UNESCO Publishing, Paris, France. http://www.unesco.org/new/en/ natural-sciences/environment/water/wwap/wwdr/wwdr3-2009/downloads-wwdr3/.
Zech T., Mohr M., Sternad W. and Trösch W. (2011). Comparison between aerobic and anaerobic wastewater treatment with a ceramic membrane filtration system. In: Proceedings to 6th IWA Specialist Conference on Membrane Technology for Water and Wastewater Treatment, Aachen, Germany.
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