| Abstract |
For the past few years, in Greece, there has been a remarkable development in decentralized wastewater installations in small communities. The increasing tendency of manufacturing such installations is due to the low cost of manufacture and operation, as well as in the direct possibility of re-use of the processed effluents for irrigation of agricultural units, considering the decreased water availability in certain areas.
In the current work and for the time interval of nine months, the efficiency of two small decentralized wastewater systems was studied and evaluated in the Prefecture of Heraklion. The aim was mainly the quality evaluation of the processed effluent for disposal and re-use, according to the permissible legislation limits. These decentralized wastewater systems are found in the communities “Stavrakia” – “Voutes” and in the community “Dafnes”, serving roughly 1800 equivalent residents.
The evaluation of the efficiency of decentralized wastewater system was carried out on the basis of a carefully organized program of samplings, where various physicochemical parameters for wastewater were measured such as: Total Suspended Solids (TSS), Biochemical Oxygen Demand (BOD5), Chemical Oxygen Demand (COD), Total Organic Carbon (TOC) etc. In the frame of this work, an attempt was also made applying heterogeneous photocatalysis, as one important among the advanced oxidation processes (AOP’s), for the pretreatment of urban wastewater waste, aiming to degrade the refractory, non-biodegradable organic compounds that inhibits the biological activities. For the needs of the experiment, the application involved influent samples, sampled at position just before their entry to the trickling bio-filters, using catalyst Degussa P25 TiO2 in concentrations 200 mg/L, 500 mg/L and 1000 mg/L. The experiment was carried out under the exposure of UV-A radiation, for the time interval of eight hours.
Overall, the results in decentralized wastewater system in the settlements “Stavrakia” – “Voutes” present efficient results. Almost the 100% for the BOD5 and the COD was removed, and the effluent of processed sewages was shown to be suitable for re-use (limited and unlimited irrigation) according always to the permissible legislation limits. On the contrary, the installation of treatment of sewages in the settlement “Dafnes” does not give satisfactory results, rendering the effluents in this case totally inadequate for re-use. Finally, the process of heterogeneous photocatalysis was found to be efficient for catalyst loading of 1000 mg/L, leading to a reduction of TOC of up to 42%. Further work is of course required in this area, studying and setting the critical parameters (e.g. pH, conductivity, organic load, irradiation exposure, etc.) for improvement of the photocatalytic efficiency. In addition, the system may well be tested to be activated under the presence of sunlight, with the purpose of a wide-range application with low operational cost for the integration of the photocatalytic technology in open biological treatment units.
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Τριτοβάθμια επεξεργασία λυμάτων μικρών οικισμών με τη χρήση χαλικόφιλτρων με ανακυκλοφορία
