Enhanced degradation of organic micro-pollutants in aerobic post-treatment of digested sludge
Author
Furgal, Karolina
Term
10. term
Publication year
2009
Pages
74
Abstract
Organiske mikroforureninger (fx dufte, baktericider, lægemidler og flammehæmmere) findes i overfladevand, udløb fra renseanlæg og i slam, hvilket viser, at nuværende rensning ofte ikke fjerner dem. Disse stoffer bruges bredt i personlige plejeprodukter, plast og tekstiler; nogle er klassificeret som prioriterede forureninger med mistænkte mutagene, kræftfremkaldende eller toksiske effekter. I renseanlæg fjernes de ofte ved sorption til slam, fordi mange har høj oktanol-vand fordelingskoefficient (Kow), dvs. de binder sig hellere til slam end bliver i vandet. Deres tilstedeværelse i slam skaber bekymring for sikker bortskaffelse. Dette studie undersøgte, om biologisk nedbrydning kan øges i udrådnet slam under aerobe (med ilt), anokse (lavt/næsten ingen ilt) og anaerobe (uden ilt) forhold ved brug af laboratoriereaktorer. Vi vurderede også en ekstra aerob behandling af udrådnet slam fra Ejby Mølle renseanlæg for at sænke niveauerne af mikroforureninger, reducere slammængden og spare bortskaffelsesomkostninger. Stofferne blev udtaget fra slam ved væske-væske-ekstraktion (LLE), koncentreret i toluen til 1 mL og kvantificeret med gaskromatografi-massespektrometri (GC-MS). Med ilt til stede blev de fleste målte mikroforureninger fjernet hurtigst. Højeste fjernelsesrater blev set for lette PAH’er (polyaromatiske kulbrinter), OTNE, TnBP og DEHP; middel for triclosan, HHCB og nogle tungere PAH’er; og lav eller ingen fjernelse for AHTN, nonylfenoler samt transformationsprodukterne HHCB-lacton og triclosan-methyl i både aktiveret og udrådnet slam. Beregninger for en eksisterende aerob tank på Ejby Mølle viste, at efter den tilgængelige opholdstid ville alle forbindelser ligge under grænsen bortset fra nonylfenol-isomerer, som lå langt over den danske grænseværdi.
Organic micro-pollutants (such as fragrances, bactericides, pharmaceuticals, and flame retardants) are found in surface waters, wastewater treatment plant effluent, and sludge, showing that current treatment often fails to remove them. These compounds are widely used in personal care products, plastics, and textiles; some are classified as priority pollutants with suspected mutagenic, carcinogenic, or toxic effects. In treatment plants, removal commonly occurs by sorption to sludge because many have a high octanol–water partition coefficient (Kow), meaning they tend to bind to sludge rather than stay in water. Their presence in sludge raises concerns about safe disposal. This study investigated whether biodegradation can be enhanced in digested sludge under aerobic (with oxygen), anoxic (low/no oxygen), and anaerobic (no oxygen) conditions using lab-scale sludge reactors. We also assessed an additional aerobic treatment of digested sludge from the Ejby Mølle WWTP to lower micro-pollutant levels, reduce sludge volume, and save disposal costs. Compounds were extracted from sludge by liquid–liquid extraction (LLE), concentrated in toluene to 1 mL, and quantified by gas chromatography–mass spectrometry (GC–MS). With oxygen present, most target micro-pollutants were eliminated fastest. Highest removal rates were observed for lighter PAHs (polycyclic aromatic hydrocarbons), OTNE, TnBP, and DEHP; intermediate rates for triclosan, HHCB, and some heavier PAHs; and low or no removal for AHTN, nonylphenols, and the transformation products HHCB-lactone and triclosan-methyl in both activated and digested sludge. Calculations for an existing aerobic tank at Ejby Mølle indicated that after the available retention time, concentrations of all compounds would be below the limit except nonylphenol isomers, which would remain far above the Danish cut-off value.
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