Εκτίμηση της τοξικότητας διαφόρων σταδίων επεξεργασίας αποβλήτων τυροκομικών μονάδων με χρήση βιοδεικτών

Abstract

One of the major environmental hazard not only for the Achaia Prefecture, but also for many other regions of the Greek area has to deal with agro-industrial effluents which outfall to the countryside. Among the agro-industries, the units of milk treatment and cheese production are concerned as such of great environmental interest. Despite that the production of milk and dairy products is relatively limited in Achaia Prefecture, their scattered installation and their unlegal operation contribute considerably in the environmental pollution of the area. The most dairy units operate in periodical base, they are scattered in the countryside while they are relatively assessed as small units. Their effluents that have been considered as toxic. The basic aim of the present study is to estimate the toxicity of cheese whey effluents from dairy unit after their treatment for biogas production (hydrogen and methane) in anaerobic digestion reactors (H2-CSTR and CH4-CSTR respectively), aiming at the total estimation of their repercussions in the aquatic ecosystem. Initially, the ecological risk from the rejection of cheese-whey effluents in the river of Vouraikos has been estimated. The data drived to an annual forecast which gives critical levels of ecological risk during summertime, and remarkable level of risk during autumn. Integrated analysis proved that effluents concentration of the river smaller than 0,064% is prerequired in order to avoid the ecological risk of the aquatic fauna, while the present ecological situation of ecosystem is far from optimal, as the rejection of the untreated effluents into the water leads to concentrations 5 times higher than the above limit, approaching 0,32% during summertime. The toxicity estimation was achieved with the use of bioindicators from two trophic levels (freshwater invertebrates and fish): Daphnia magna and Thamnocephalus platyurus in the form of mikrobiotests Thamnotoxkit F and Daphtoxkit FTM magna, and the embryos of zebrafish (Danio rerio) according to the protocols of ISO and EPA. In total there have been taken 109 samples (4 duplicate samples of cheese whey, 55 duplicate samples from the reactor of hydrogen production and 50 duplicate samples from the reactor of methane production). In the toxicity tests applied (Thamnotoxkit F, Daphtoxkit FTM magna and zebrafish), L(E)C50 in 24h and 48h were calculated according to the tests protocols. It was found that mean LC50 values for the Thamnocephalus platyurus was 0.76 for the samples from H2-CSTR reactor and 1.33 for the samples from CH4-CSTR reactor. The corresponding values for Daphnia magna in the 48 hours was 1.82 and 2.26 while for the zebrafish 0.88 and 0.95 for the same period. The values resulted from the three tests classify the effluents from “very toxic” to “extremely toxic”. From the cross-correlation of physicochemical parameters with L(E)C50 results of Thamnocephalus platyurus, the samples of H2-CSTR reactor have positive correlation with the ammonium, nitrites and nitrates ions (R= 0.368, R=0.442 and R=0.362 respectively) and the samples of CH4-CSTR reactor have positive correlation only with TDS (R=0.860). Zebrafish correlates with phosphates (R= 0.542) and ammonium ions (R=0.562) for the samples of H2-CSTR, while for the samples of CH4-CSTR correlate with phosphates (R=0.963) and nitrites ions (R= 0.960). Daphnia magna does not show significant correlation. The highest values observed was for the samples of H2-CSTR with the ammonium ions (R= 0.316). According to the above results it is proved that Thamnocephalus platyurus and zebrafish are the most sensitive and suitable organisms for the toxicity estimation of the particular effluents. The observation of spinal malformations in a small percentage of zebrafish, led to the detection of heavy metals to all treated samples. Chromium, manganese, zinc and lead were detected, however the role of each one of them in the observed malformations could not be investigated in the frames of this study and further research is required. In ferentially, all the treated samples with both methods were toxic. They are not environmentally safe for direct disposal in the aquatic receiver and further treatment for the removal of the toxic factors as phosphates and the ions of nitrogen is needed. Finally, it must be noted that the present study is the first toxicity evaluation study of the dairy wastewaters after their treatment for biogas not only in the Greek area but worldwide. Since such a treatment constitutes an innovative and combined methodology that aims to the remediation of the wastewaters and the production of a beneficial by-product as biogas, the results of this study could constitute a useful tool, in one hand for the scientists concerning wastewater treatment provoking them to search methods for further remediation of these effluents from the remaining toxic factors and on the other hand for the officials in order to achieve monitoring and controlling of these particular units.