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AGROIWATECH Sintesi della relazione

Project ID: ICA2-CT-2002-10010
Finanziato nell'ambito di: FP5-INCO 2
Paese: Germany

Estimation of costs and ecological impact of agro-industrial wastewater treatment

There are water pollution problems due to inadequate agricultural practices in the CEE countries by intensive use of fertilisers and pesticides. Since there has been a huge load of pollution led into ecosystems, he demands implementation plants for water quality management. Resident fertilisers and pesticides on the agricultural products could be arriving in the food chain or the off water of agro-industries.

Several methods for the economic and ecological evaluation of processes are introduced in literature. Among them Life Cycle Assessment (LCA), Life Cycle Costing (LCC) methods as well as input-output analysis, social matrices, change analysis and many other, Some of them can be calculated mathematically, some of them are argumentative. Mixtures of methods are always possible.

Common to all techniques is that a more or less complex model of the process, the streams inclusive up- and down-streams and the plant has to be made with respect to different scenarios of possible processing options. After doing so, the environmental pressures (e.g. CO2 or energy) should be determined.

One of the methods, the Simple Additive Weighting (SAW) method is viewed at. The ecological impact in was focused the green-house-effect and the energy-consumption in terms of carbon dioxide emissions. The economical impact was considered to be dependent on the investment and the costs for energy. The factors given for the evaluation are the emissions in the sense of aggravating green-house-effect, the energy consumption and the ability to save process water. The evaluation of the impacts was done with respect of the process itself. It was shown, that the reverse osmosis uses less energy than the ozonation, but the retentate has to be disposed.

A calculation of the energy consumption and the transport of retentate for disposal in terms of CO2 emission showed, that the use of ozone for polishing the effluent of the model plant emits 65 % less carbon dioxide than the treatment by RO. The reuse of the water has to be viewed at from the point of official regulations on site and the purpose, the water should be used for. For example, water for cleaning-up purposes and for flushing procedures or for transportation of the fruits can be reused at a higher level of contamination than water for the direct contact with food production depending on the specific regulations.

The emission of carbon dioxide (or equivalents) is only viewed from the point of additional production. Thus not regarding the emissions of the treatment process, since the overall balance of such processes is zero, because all CO2 is produced with natural non-fossil resources. The overall energy production of a lagoon is zero whereas the energy production of other processes as UASB and the investigated plant could reach from 297 to 1,471 MWh/a for the model treatment plant, depending on the type of waste or wastewater and the treatment process. Regarding the waste, it is important to consider the space needed for disposal in landfills or the reusability in the agriculture.

Certain types of organic wastes can be used as fertiliser, if they have a high organic content and they can be used for improving the quality of the soil. The eutrophication of the waste or wastewater was expressed as output of nitrogen from the processes. The results show that the raw water (sugar factory) as well as the effluent of an UASB reactor does not diminish the oxygen demand of the water. If a MBR-system were attached, the oxygen demand goes towards 0. If a lagoon was used for water treatment, there would be still a non-neclectable oxygen demand. Additionally, the emissions of a lagoon cannot be specified since the processes happen parallel and simultaneously.

Moreover, an energy recovery or the production of green energy is not possible by a lagoon. In contrast the reduction of nitrogen, a German plant produces products as fertilisers and proteins, which can be sold. The calculation of the overall costs shows, that, if only the RO and the ozonation are regarded, the costs for the ozonation are 61 % of the costs for the ozonation. But is the whole process including the anaerobic treatment and the MBR into account, the option using the RO is only 75 % of the costs for the option with the ozonation. The degree of water-reclamation depends on the intended purpose and the local regulations. The consequence is, that if the water is needed for flushing no polishing could be of need.

The use of water for irrigation as well depends no the matrix of the waste or water, since there are influences to the soil or groundwater aquifer and has to be evaluated for a specific need. A comprehensive definition of technology should be done with a holistic approach instead with a fixed set of criteria. This is to be done with concepts and sets of definitions, which agree with the site-specific circumstances especially, when the irrigation of wastewater or treated wastewater is considered for the reuse of water.

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