Accelerated degradation of PAHs using edaphic biostimulants obtained from sewage sludge and chicken feathers
Introduction
The technique of applying organic matter to soils contaminated with polycyclic aromatic hydrocarbons (PAHs) is widespread among scientists and engineers. It is a good environmental strategy which aims to eliminate or reduce the negative effects that these chemicals cause on soil microorganisms [1], [2], [3], [4], [5].
Because the microbial degradation is the most important process for these pollutants, for some authors this second role of organic matter has a greater importance than the first in the bioremediation of PAHs-polluted soils [6], [7], [8]. Organic matter mineralization releases nutrients continuously or intermittently over a period of time and therefore has been applied to PAH-contaminated soils to stimulate and maintain indigenous biodegradation rates. It is, however, a slow process that depends on several factors such as the PAH type, soil microorganisms tolerant to this PAH, and the quantity and chemical composition of the M.O. added to soil [4], [5], [9].
In recent years there has been increasing use of organic fertilizers or edaphic biostimulants (BS), obtained by hydrolysis from various organic materials, in the bioremediation of soils contaminated with organic xenobiotics such as PAHs and plaguicides. Unlike other sources of organic matter, these organic compounds are usually constituted by low-molecular-weight proteins and amino acids. This aspect is very important, since these compounds can be used directly by the soil microorganisms and therefore accelerates degradation of xenobiotic in soil. These products are also characterized by high polysaccharides content, and humic-like molecules that stimulate soil microorganisms, and thus, promote the degradation of the xenobiotic in soil [5], [10], [11], [12], [13].
Recently, the use of BS obtained from sewage sludge and chicken feathers has become very common in the degradation of plaguicides, mainly oxyfluorfen and chlorpyrifos [11], [13], with a notable increase in the degradation of the above xenobiotics after the applying both BS to the polluted soils.Since nostudies have been reported using these BS on PAH-contaminated soil, we hypothesize that both protein hydrolysates can be very useful in remedying different PAH-contaminated soils.
The objective of this study, therefore, was to investigate, under laboratory conditions, the influence of BS obtained from sewage sludge and chicken feathers in soils polluted with different PAH andits effect on soil biochemical properties and microbial community.
Section snippets
Soil, biostimulants and PAH characteristics
The soil used in this experiment is a Calcaric Regosol [14]. The main soil characteristics are reported elsewhere [11], [13], and summarized in Table 1, Table 2. The methodology used to the determine the physical and chemical parameters in soil and organic wastes is also described in Tejada et al. [11] and Rodriguez-Morgado et al. [13].
Three edaphic BS were used: (1) SS, derived from sewage sludge; (2) CF1, derived from chicken feathers provided by a poultry industry located in Murcia (Spain);
Evolution of PAH in soils
In non-organically amended soils, the degradation of Phe was higher than Py and BaP (Fig. 1). At the end of the experimental period, Phe was degraded to 49.6% of what had initially been added, followed by degradation levels of 31.9% and 12.3% for Py and BaP, respectively.
The application of the different BS to contaminated soil increased Phe Py and BaP degradation. However, this degradation depended on the BS type applied to the polluted soils. In this respect and at the end of the experiment,
Discussion
According to Tejada et al. [5], Zhang et al. [33], González et al. [34] and González-Paredes et al. [35], our results indicate that applying PAHs to soil induce adverse effects on biological properties. This toxicity was higher in BaP-contaminated soils, followed by Py and Phe suggesting that the number of aromatic hydrocarbon rings influences the toxicity caused on the soil’s biological properties. These results are in agreement with those obtained of Wammer et al. [36] and Toledo et al. [37].
Conclusions
It can be concluded that the application of BS decreased the toxic action of PAH on soil biological properties. However, this effect depended on the chemical composition of the BS that was applied to the soil. When CF1 was applied to PAH-polluted soils, a greater decrease in the inhibition of the soil’s biological properties occurred. This is probably due to their higher content of lower molecular weight peptides which are easily assimilated by soil microorganisms.
Acknowledgments
This work was supported by the Ministry of Science and Innovation (Spain), Plan Nacional I+DCTM2011-29930-01, CTM2011-29930-03 and by Proyecto Excelencia, Junta de Andalucía P11-RNM-7887.
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