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Natlenianie zanieczyszczonych osadów dennych podczas tymczasowego składowania

Malina G., Vermeulen J., Kromer M.

Inżynieria i Ochrona Środowiska

2004

T. 7, nr 3/4

401-419

Dla badanych osadów określono indeks dojrzewania, stopień kurczenia, współczynnik dyfuzji oraz dystrybucję tlenu. W celu odwodnienia osadów i uzyskania różnych etapów fizycznego dojrzewania osadów zastosowano potencjały matrycowe w zakresie od -100 do -1 000 000 hPa. Sprawdzono wpływ zastosowanego potencjału matrycy na występowanie miejsc pozbawionych tlenu w agregatach osadowych. Przeprowadzone badania pozwoliły na wypracowanie efektywnej metody pomiaru centrów tlenowych w osadach dennych. Dostarczyły one danych o wpływie kurczenia się agregatów na wzrost współczynnika dyfuzji tlenu, a w konsekwencji na wzrost natlenienia, co ma istotne znaczenie dla bioremediacji osadów zanieczyszczonych substancjami organicznymi (np. substancje ropopochodne, WWA) podczas ich tymczasowego składowania.

Temporary disposal is the most widely adopted alternative for sediments dredged annually in some countries (e.g. the Netherlands) for both maintenance and environmental reasons. For good management of disposal sites, knowledge is required about controlling the behaviour of sediments during disposal. A short overview was made about processes that take place during temporary disposal, and how they can affect the biodegradation of organic contaminants. The method of oxygenation measurements within sediments aggregates was developed and improved in order to evaluate the bioremediation potentials during temporary disposal of sediments contaminated with organic compounds. The parameters determined for three studied sediments (I, II and III) included: the ripening index, shrinkage, diffusion coefficient and oxygen distribution in sediment aggregates. To enhance dewatering and to simulate diverse stages of sediment ripening, matrix potentials from -100 to -1,000,000 hPa were applied. The effect of diverse matrix potentials on the formation of oxic and anoxic zones within the aggregates was also determined. The complete transformation of sediments into soil was taking place at matrix potentials between -1000 and -2000 hPa when the ripening indexes for all sediments dropped below 0.7. For lower ripening indexes an increase of pore volumes filled with air was observed. The highest ripening index of 0.5 was for sediment III, in which the highest organic matter content was found. Decreasing matrix potentials resulted in an increase of the O2 penetration depths in sediment aggregates. At the matrix potential of -16,000 and lower, the whole aggregates were fully aerated. Increased organic matter contents limited the depth of O2 penetration. The diffusion coefficients were higher proportionally to the decreased matrix potentials. Shrinkage of aggregates affected the diffusion coefficients and oxygenation, which is an important factor to be considered for bioremediation of sediments contaminated with organic substances (oil hydrocarbons, PAHs) during temporary disposal. Thus, the physical ripening of dredged sediments is a promising technique to enhance aerobic bioremediation of polluted sediments.