Abstract
The use of phytoremediation to remove metals of contaminated soils is an interesting technique that is usually limited by adverse physical and chemical properties of this type of soils. The addition of biochar produced from manure waste could improve soil properties due to its nutrient content, high cation exchange capacity or water holding capacity. However, the high water content of manure wastes precludes its pyrolysis treatment use for biochar production, without a previous drying step. Indeed, hydrothermal carbonization (HTC) of manure wastes could be an adequate treatment method as it takes place in water solution. The product obtained after HTC of biomass, named hydrochar, exhibits different physiochemical properties than biochar that could affect their potential application. The objective of the present work is to study the effect of chars obtained by pyrolysis or HTC of manure wastes in mining soil phytoremediation with Sinapis alba. Two selected mining soils (PORT and GAM) were treated with two manure biochars prepared at 450 °C (BMW450) and 600 °C (BMW600), two hydrochars prepared by HTC of manure at 190 °C (HWM190) and 240 °C (HMW240) and raw manure waste (MW) at a rate of 10% in mass. Later, different soil samples were incubated with or without Sinapis alba growth. Experimental results shown that properties of chars have a great influence on the efficiency of the use of Sinapis alba in the phytoremediation of mining soils. The addition of BMW600 and raw material (MW) increased the production of aerial and root biomass for GAM soil. For PORT soil, HMW190, two biochars and MW increases root and aerial biomass whereas HMW240 only produces an increment on aerial biomass. Addition of two hydrochars and MW had a positive effect on the biochemical soil activities and the highest microbial biomass carbon of GAM and PORT soil samples was observed after addition of HMW190. Finally, the addition of biochars and hydrochars could improve the phytoremediation of mining soils by Sinapis alba. However, the heavy metal uptake greatly depends on the type of soil, the amendment and the target metal. The accumulation of As, Pb and Zn in the aerial part of Sinapis alba was very low. However, Sinapis alba acts as accumulator for As in the presence of BMW600 and HMW190, for Zn after amendment with HM190 and for Pb after BMW600 addition to PORT soil. For GAM soil, only the addition of BMW450 and BM600 improves the capacity of accumulation of As in roots.
Highlights
Over the years, mining and metallurgical activities have led to significant environmental damages
The addition of biochars and hydrochars could improve the phytoremediation of mining soils by Sinapis alba
These results show the great difficulty that still exists to generalize the use of biochar or hydrochar in the remediation of polluted soil
Summary
Over the years, mining and metallurgical activities have led to significant environmental damages. Soil metal pollution has a pernicious effect on soil microbial properties and on the taxonomic and functional diversity of soils that can difficult the growth of plants and the process of phytoremediation [3] For this reason, the addition of organic amendments as compost has been attempted for the improvement of soil properties as organic matter and nutrient content, cation exchange capacity, pH correction or water holding capacity could enhance the plant growth [4]. Despite of the interesting properties of manure wastes as raw material for the biochar preparation, their elevated water content can precluded its pyrolysis process being necessary an expensive and high-energetic drying process For this reason, hydrothermal carbonization (HTC) of wet manure wastes could be an interesting alternative to traditional pyrolysis for the preparation of improved carbon rich amendments, named hydrochars [11].
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