Polycyclic aromatic hydrocarbons degradation by composting in a soot-contaminated alkaline soil

Abstract

This study deals with the biodegradation of the polycyclic aromatic hydrocarbons (PAH)s present in a soil contaminated by soot waste, characterised by a total PAHs content in the 200 mg kg −1 range. A challenging characteristic of the waste soil treated was its high alkalinity, with a pH of about 12.8. The waste came from a soot-contaminated area located in the industrial zone of Porto Marghera, Venice (Italy). The biodegradation process employed was the composting of the waste with sewage sludge and yard waste. The process was carried out on a pilot scale using a closed tank with forced aeration for a period of 60 days, followed by 70 days with natural aeration. The time evolution of the process was monitored by following the time change in the concentration of the 16 US-EPA PAHs, as well as temperature, pH, electrical conductivity, C and N contents. Also phytotoxicity parameters, such as the growth and respiration indexes, were monitored. An induction time of about 30 days was observed, which corresponded to the time required before observing a significant self-drop in the waste pH and an increase in mass temperature. Afterward, a progressive drop in the PAHs concentration was observed, up to reaching after 130 days an overall degradation percentage in the order of 68%. The degradation was more effective on rather low molecular weight PAHs (2-4 rings).

Bioremediation of heavily hydrocarbon-contaminated drilling wastes by composting

“…Bioremediation of contaminated soils by composting has been extensively reported in scientific literature, and these methods have proven to be effective in petroleum hydrocarbons degradation (Van Gestel et al 2003;Antizar-Ladislao et al 2004;Moretto et al 2005;Joo et al 2007;Zhang et al 2011;Laos et al 2012;Chen et al 2015). However, drilling cuttings composting bioremediation reports are scarce in scientific literature.…”

The use of biosolids in the composting of a crude oil and salt contaminated clay soil.

“…Despite mixing all o f the compost bins prior to sampling and using the same sampling procedure on all o f the bins, the replicate samples often varied significantly from each other. Moretto et al (2005) reported a similar problem when composting PAH contaminated soil. Compost construction, although carefully planned, can be heterogeneous due to the number o f feedstocks used and unique variations in rate o f organic matter decomposition (Miller 1993).…”

“…Huang et al (2004) reported that EC values follow a trend similar to pH values. Moretto et al (2005) reported an initial large decrease followed by a stabilization o f the EC. As with the other physiochemical properties o f compost, the values presented in literature vary greatly due to differences in the feedstocks used.…”

“…These compounds have properties that can be toxic, mutagenic, and/or carcinogenic to humans (Moretto et al 2005) …”

“…Huang et al (2004) experienced thermophilic periods o f 32 days (maximum temperature o f 60°C) and 40 days (maximum temperature o f 69°C) during windrow composting. Moretto et al (2005) reported temperature data in the thermophilic range (>45°C) for approximately 30 days for their pilot-scale reactor. Tiquia et al (2002) reported temperatures in the thermophilic range for over 40 days in six o f their windrows.…”