Irrigation water quality influences heavy metal uptake by willows in biosolids

Abstract

Phytoextraction is an effective method to remediate heavy metal contaminated landscapes but is often applied for single metal contaminants. Plants used for phytoextraction may not always be able to grow in drier environments without irrigation. This study investigated if willows (Salix x reichardtii A. Kerner) can be used for phytoextraction of multiple metals in biosolids, an end-product of the wastewater treatment process, and if irrigation with reclaimed and freshwater influences the extraction process. A plantation of willows was established directly onto a tilled stockpile of metal-contaminated biosolids and irrigated with slightly saline reclaimed water (EC ∼2 dS/cm) at a wastewater processing plant in Victoria, Australia. Biomass was harvested annually and analysed for heavy metal content. Phytoextraction of cadmium, copper, nickel and zinc was benchmarked against freshwater irrigated willows. The minimum irrigation rate of 700 mm per growing season was sufficient for willows to grow and extract metals. Increasing irrigation rates produced no differences in total biomass and also no differences in the extraction of heavy metals. The reclaimed water reduced both the salinity and the acidity of the biosolids significantly within the first 12 months after irrigation commenced and after three seasons the salinity of the biosolids had dropped to <15% of initial values. A flushing treatment to remove excess salts was therefore not necessary. Irrigation had an impact on biosolids attributes such as salinity and pH, and that this had an influence on metal extraction. Reclaimed water irrigation reduced the biosolid pH and this was associated with reductions of the extraction of Ni and Zn, it did not influence the extraction of Cu and enhanced the phytoextraction of Cd, which was probably related to the high chloride content of the reclaimed water. Our results demonstrate that flood-irrigation with reclaimed water was a successful treatment to grow willows in a dry climate. However, the reclaimed water can also change biosolids properties, which will influence the effectiveness of willows to extract different metals.

Potential of Energy Willow Plantations for Biological Reclamation of Soils Polluted by 137Cs and Heavy Metals, and for Control of Nutrients Leaking into Water Systems

“…Concentration of Ni in willow leaves in our experiments was 1-2 mg/kg. In accordance with results of other researchers it varied from 1.97 mg/kg [45], to 10 and more mg/kg [46]. Thus, our results are closer to the lowest limits of heavy metals contents in willow biomass.…”

Using Jerusalem Artichoke to Extract Heavy Metals from Municipal Sewage Sludge Amended Soil

“…The research shows that, compared to Rubik, Albik cleaned the substrate more effectively. Research conducted by Laidlaw et al [23] confirms that energy crops, including willow, can be used for phytoextraction of heavy metals from substrate polluted with heavy metals. The cited authors [23] showed that willow, out of all heavy metals, extracts cadmium from the substrate most efficiently.…”

“…Research conducted by Laidlaw et al [23] confirms that energy crops, including willow, can be used for phytoextraction of heavy metals from substrate polluted with heavy metals. The cited authors [23] showed that willow, out of all heavy metals, extracts cadmium from the substrate most efficiently. Our own research also shows that Jerusalem artichoke, as an energy crop, also efficiently extracts Cd from the substrate.…”

“…Research on the suitability of willow for remediation of sewage sludge showed that there are differences in heavy metal uptake between clones of the same species [21,47], which is why not only selection of appropriate plant species but also selection of proper variety or clone appear to be important in heavy metals phytoextraction [21,23,47,49].…”

“…Plants with a high phytoextraction potential include, among other things, Jerusalem artichoke, miscanthus, and spartina [21][22]. Using the process of phytoextraction of heavy metals from sewage sludge is an alternative method of soil cleaning [2,5,23]. Scientific literature indicates that there is little research on assessing the applicability of different Jerusalem artichoke varieties for phytoextraction of heavy metals from municipal sewage sludge used on landfills or in reclaiming postindustrial areas.…”