Fate of phthalic acid esters during composting of both lagooning and activated sludges

Abstract

Among the phthalic acid esters (PAEs) targeted by the United States Environmental Protection Agency (USEPA) as priority pollutants, diethyl-hexyl phthalate (DEHP) is the major pollutant identified at high concentration level in lagooning sludge (LS), at about 28.67 mg/kg, and in activated sludge (AS), at about 6.26 mg/kg. Other phthalic acid esters, such as di-butyl phthalate (DBP) and di-methyl phthalate (DMP) show very low concentrations. During sludge composting, after the stabilization phase, the subsequent appearance of DEP and then DMP occurred indicating that microbial metabolism begins by alkyl side-chain degradation before aromatic ring-cleavage. The appearance and accumulation of PAEs with a short alkyl side-chain in the last stages of AS and LS composting is suggested originating from the degradation of phthalates with a much long side-chain. The DEHP showed a rate of biodegradation that follows a first-order kinetic model during composting of both AS and LS. The calculated DEHP half-lives are 45.4 days for LS and 28.9 days for AS. The better DEHP biodegradation rate (2.4 Â 10 À2 day À1 ) have been observed in the case of AS composting compared to LS compost (1.53 Â 10 À2 day À1 ). The mono-ethylhexyl phthalates MEHP has been shown to follow the same order of biodegradation as DEHP indicating that the same mechanism is followed (hydrolysis or dealkylation of each DEHP side-chain). Composting could be suggested as a detoxification process for the removal of PAEs (mainly DEHP) from sludges after a sufficient time of treatment to provide a safe end product.

Isolation and identification of dibutyl phthalate-degrading bacteria from hydrospheres in Tokyo

“…Many clear-zone-forming cells were observed from bacteria isolated from both the fi rst and fourth activated sludge tanks, but no more than 10 cells/ml were observed in the infl ux water and the sludge drainage water. These results indicate that there were many DBP-degrading cells in the activated sludge, which confi rms previous studies about biodegradation of DBP using activated sludge (Amir et al, 2005;Roslev et al, 2007;Wang, 2004). Therefore, we suspect that samples of activated sludge from other locations also would likely contain Dibutyl phthalate-degrading bacteria from hydrospheres DBP-degrading bacteria.…”

Newly Identified Thermostable Esterase from Sulfobacillus acidophilus: Properties and Performance in Phthalate Ester Degradation

“…Another known example is the composting of both lagooning and activated sludges, which is a method often used to treat pollutants. Such a process is always done at relatively high temperatures to keep the reaction effective (18). Therefore, it is valuable to study the enzymes that are active and stable under such high-temperature circumstances.…”

Composting of wastewater treatment sludge with different bulking agents

“…Low pH during composting in R3 could be possibly explained by the acidic nature and high buffering capacity of corncob, which may have prevented increase of pH. In a study conducted by Amir et al (2005), similar values were observed for the final compost in composting studies that used wastewater treatment sludge. The EC can be used as an indirect method to evaluate the degree of salinity in the composting mixture, which indicates its possible phytotoxic/phytoinhibitory effects on plant growth after application to the soil (Lin, 2008).…”