Organic substances in woodchip aqueous leachates and their ecotoxicity

Organic substances in woodchip aqueous leachates and their ecotoxicity

en

Woodchip material is one of the most promising fill media for denitrifying bioreactors. Woodchip denitrifying bioreactors are used for nitrate reduction in the outlets of drainage systems, shallow groundwaters, etc. Despite their overall positive effect, undesirable leaching of organic compounds from the fill medium can occur during a bioreactor’s start-up phase. The released organic compounds can cause oxygen depletion and some of them can have a toxic effect on biota. The paper presents the quality of leachates of five wood-based materials which can be used as denitrifying bioreactor media, i.e. oak, poplar, beech, spruce, and a mixture of pine+larch. The leachates were prepared on a rotating shaker. The quality of the leachates varied according to the wood species both in their physicochemical parameters – pH, dissolved oxygen (DO), oxidation-reduction potential (ORP), chemical oxygen demand (COD), biochemical oxygen demand (BOD), dissolved organic carbon (DOC), phenolic compounds, and in their toxicity. Oak showed the highest leachability of organic compounds (COD 3,370 mg/L, BOD 750 mg/L, DOC 1,435 mg/L), followed by spruce (COD 1,930 mg/L, BOD 570 mg/L, DOC 770 mg/L). The leachability of organics from poplar and beech was similar and reached medium values, while the leachate of pine+larch contained the lowest concentration of organic compounds. Overall leachability of organic substances corresponded with the leachability of low-molecular phenolic compounds. In the leachates of oak and spruce phenol, o-, m-, and p-cresol, thymol, p-ethylphenol, and p-valerylphenol were found. The chemical composition of leachates led to expected toxicity levels. The highest toxicities were determined for oak and spruce leachates with a sensitive response from both test organisms, Sinapis alba and Thamnocephalus platyurus. The leachates of poplar and beech showed moderate toxicity for crustaceans, while for higher plants they were non-toxic. The leachate of pine+larch was non-toxic for both test organisms.

Woodchip material is one of the most promising fill media for denitrifying bioreactors. Woodchip denitrifying bioreactors are used for nitrate reduction in the outlets of drainage systems, shallow groundwaters, etc. Despite their overall positive effect, undesirable leaching of organic compounds from the fill medium can occur during a bioreactor’s start-up phase. The released organic compounds can cause oxygen depletion and some of them can have a toxic effect on biota. The paper presents the quality of leachates of five wood-based materials which can be used as denitrifying bioreactor media, i.e. oak, poplar, beech, spruce, and a mixture of pine+larch. The leachates were prepared on a rotating shaker. The quality of the leachates varied according to the wood species both in their physicochemical parameters – pH, dissolved oxygen (DO), oxidation-reduction potential (ORP), chemical oxygen demand (COD), biochemical oxygen demand (BOD), dissolved organic carbon (DOC), phenolic compounds, and in their toxicity. Oak showed the highest leachability of organic compounds (COD 3,370 mg/L, BOD 750 mg/L, DOC 1,435 mg/L), followed by spruce (COD 1,930 mg/L, BOD 570 mg/L, DOC 770 mg/L). The leachability of organics from poplar and beech was similar and reached medium values, while the leachate of pine+larch contained the lowest concentration of organic compounds. Overall leachability of organic substances corresponded with the leachability of low-molecular phenolic compounds. In the leachates of oak and spruce phenol, o-, m-, and p-cresol, thymol, p-ethylphenol, and p-valerylphenol were found. The chemical composition of leachates led to expected toxicity levels. The highest toxicities were determined for oak and spruce leachates with a sensitive response from both test organisms, Sinapis alba and Thamnocephalus platyurus. The leachates of poplar and beech showed moderate toxicity for crustaceans, while for higher plants they were non-toxic. The leachate of pine+larch was non-toxic for both test organisms.