Introduction to Soil Treatment with Digestate PDF

Soils contaminated with petroleum products is a well-recognized worldwide problem (Lu et al., 2014). Among soil treatment methods, bioremediation constitutes a promising and economical approach (Beškoski et al., 2011; Coulon et al., 2010). A body of literature exists on the topic of total petroleum...

Soils contaminated with petroleum products is a well-recognized worldwide problem (Lu et al., 2014). Among soil treatment methods, bioremediation constitutes a promising and economical approach (Beškoski et al., 2011; Coulon et al., 2010). A body of literature exists on the topic of total petroleum hydrocarbons (TPH) bioremediation analysing various biostimulation (addition of nutrients) and bioaugmentation (application of cultivable degrading agents) strategies (Masy et al., 2016; Safdari et al., 2018; Sayara et al., 2010a). Application of organic matter to soil is known to improve soil quality by e.g. stabilization of pH and enrichment in soil organic matter, which supports microbial growth (Nardi et al., 2004; Tambone et al., 2010). However, not much attention is paid on the use of organic amendments (e.g. organic wastes) for soil treatment. Reasonable practice of waste management encourages recycling of organic waste by soil application (Tampio et al., 2016). Digestate is a by-product of anaerobic digestion processes which constitutes a valuable organic amendment with several advantages over mineral fertilizers (Gómez-brandón et al., 2016; Walsh et al., 2012). First of all, digestate contains high density and diversity of microorganisms with wide catabolic capacities (Wang et al., 2018). Secondly, during anaerobic digestion nutrients become concentrated in bioavailable form (Gómez-brandón et al., 2016; Kataki et al., 2017) and easily biodegradable organic carbon quantity is reduced (Risberg et al., 2017). Moreover, itwas observed that humic acidswhich are present in digestate can support desorption of organic contaminants from soil matrix increasing their bioavailability (Liang et al., 2007; Sayara et al., 2010b). However, despite the promising physico-chemical and microbial properties of digestate, to the best of our knowledge it has never been tested before as an amendment in soil bioremediation. Thus, the influence of the application of digestate on soil microbial activity is not known. Particularly, to better understand the role of digestate in the process, its influence on microbial diversity and on the concentration of functional genes need to be addressed. Organic matter present in digestate may be degraded by monooxygenases encoded by alkB genes (Sutton et al., 2013). Interestingly, the same enzymes are crucial formetabolismof alkanes and other TPH constituents and could thus play a key role in the process (Sutton et al., 2013). The final effect of digestate on soil microbial activitymay be affected by factors like soil texture, physico-chemical and hydraulic properties as well as contaminants concentration, composition andweathering stage. For example in clay rich soils low permeability limits fluid flow and can affect oxygen transfer due to the formation of soil aggregates (Yeh and Young, 2003) which may be enhanced after digestate application. Thus, the influence of soil composition and texture on the treatment efficiency and on the microbial activity needs to be addressed. The main objectives of this study were i) to assess the value of digestate as microbial inoculum for the remediation of TPH contaminated weathered soils, ii) to study the effect of digestate on activity and diversity of soil microflora, and iii) to evaluate the impact of soil composition and texture on the efficiency of microbial respiration. In order to study how soil particle size affects microbial activity after digestate application we have examined two common types of industrial TPH contaminated soils, a clay rich soil and a sandy soil. Together with digestate application, bioaugmentationwas performed by addition of soil indigenous TPH degrading bacteria immobilized on biochar. The bacterial diversity was monitored through high throughput sequencing of 16S rDNA (Illumina MiSeq). The functional property of the bacterial communities in these conditions was assessed through quantification of alkB genes (qPCR).