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AGROIWATECH Informe resumido

Project ID: ICA2-CT-2002-10010
Financiado con arreglo a: FP5-INCO 2
País: Germany

Feasibility of post ozonation of treated agro-industrial wastewater

Processes in the agro-industry need much process water for eg. cleaning processes. This has to be considered, when regarding an integrated process management. Waters of such industries are highly loaded with organic contents, which lead to extensive eutrophication if discharged uncleaned into ecosystems. They undergo (e.g. in Germany) several processes for cleaning, reuse of these substances in the water and for disposal or recycling.

An example is the water treatment process in the potato-industry, which has been used for this work. The excess water of this process is treated by several processes to use the contents of this water for production of fertiliser and energy. After these steps, the water has to be cleaned biologically to reach the limits of official regulations for discharge, such as the concentration of COD, nitrogen concentrations or CFU. Since the biological processes only can alter the biological degradable contents of the waster water, recalcitrant contents have to be treated in a different way.

The regulations and needs for the excess water differ strongly from the regulations and needs for process waters. Process water in the agro-industry has to be useable according to regulations for food processing. This means eg. nearly germ-free and free of harmful contents for the human organism. So it has to be distinguished between the discharge of excess water to municipal receiving system and the reuse of excess water for the process itself.

Commonly, the last step of such water treatment processes is the reverse osmosis (RO) to retain contents like recalcitrant COD, salt or germs. Ozonation is a well-known application for drinking-water disinfection. It is a conventional treatment process for treating difficult wastewaters as landfill-leachate in order to remove COD among other contents, too.

Thus, it should be possible to treat excess water from the agro-industry to enable a reuse of the water or at least to enable a discharge into further treatment processes such as municipal wastewater treatment. But since the production of ozone is expensive and energy intensive, enhancements of this technique is needed. And the ozonation of wastewater has to compete with techniques as the RO, UV-disinfection or common processes as chlorination. The wastewater examined was taken from a MBR, treating effluent water from the potato-industry.

The process and fruit water is processed through several unit operation steps, which produce energy, fertiliser and proteins. The remaining water is treated by a membrane bio-reactor (MBR) with micro filtration for inlet into the municipal receiving system. A partial stream is processed via reverse osmosis for industrial water recycle. The volumetric flow rate of the water is 55 cbm/h, during campaign approx 110 cbm/h with a COD of 250 - 300 mg/l, (This is less during campaign due to the higher flow rate). The concentrations of ammonia and nitrate are 1-2 mg/l resp. 5-6 mg/l. The samples for the tests of the ozonation efficiency are taken between the MBR and the RO.

The wastewater was analysed regarding the dissolved COD and the CFU. Measurements of TS or VSS have not been done, because the micro filtration is capable to hold back the micro organisms in the biological treatment process. Samples of 250 mL were taken from the ozonsation-reactor prior to the ozonation and several times during the ozonation itself. The ozonation of the water containing 1.500 mg/L COD showed a degradation of COD of 20%. By adding H2O2, the degradation rate was improved up to 70% after one hour of operation. The number of CFU could be eliminated after 3 minutes of ozonation. Summarising, it can be stated, that disinfection ad degradation of recalcitrant substances for the reuse of wastewater at least in the potato industry is possible by polishing the effluents of a MBR by oxidation processes. If this can be done by ozone itself, or if an additional activation of the ozone and the water to a radical reaction system (AOP) is needed has to be shown regarding the specific wastewater, which the application is to be designed for and the official regulations for process water in the specific industry on site.

Moreover, the use of the processed water as water for the direct food-production of the use as washing water has to be focused. Additionally, the efficiency of the post-ozonation of wastewater with other treatment processes as eg. reverse osmosis has to be viewed at regarding economic and environmental impacts on site.

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