Composted sewage sludge utilization in phytostabilization of heavy metals contaminated soils

Abstract

In phytostabilization, heavy metal-tolerant plants (e.g.,grasses) can be used to reduce the mobility of heavy metals in soils. The most important step in phytostabilization is the selection of the suitable plant species, in which growth and development can be supported by soil amendments. Sewage sludge compost could be a suitable additive, which provides nutrients for the plant species used for phytostabilization and contributes to an alternative solution for sewage sludge utilization. The aim of the study was to examine the potential of sewage sludge compost in phytostabilization for heavy metal contaminated matrices: identify the optimal ratio of sewage sludge compost to decrease phytotoxicity of the matrices, and assessment of feasible plant species for phytostabilization based on its bioaccumulation properties. In this research, perennial ryegrass (Lolium perenne), broad-leaved sorrel sorrel (Rumex acetosa), lettuce (Lactuca sativa) and cabbage (Brassica oleracea var. capitata) were used for phytotoxicity experiments as well as for testing sewage sludge compost amended phytostabilization of polluted flotation sludge and mine tailings. Sewage sludge compost increased the pH and electric conductivity of the matrices. High salt content and low acidity, altogether with heavy metals caused harmful physiological effects on plant species grown without any compost addition. In the root development test, as in the germination test, the application of 5% sewage sludge compost proved to be optimal. The lower translocation factors of broad-leaved sorrel and perennial ryegrass showed a higher rate of heavy metal accumulation in the roots. Perennial ryegrass, cabbage, and lettuce plant species reached their maximum biomass by adding 5% of sewage sludge compost. Based on the bioaccumulation, translocation and biomass properties, application of perennial ryegrass is recommended for phytostabilization of heavy metal contaminated sites. Furthermore, composted sewage sludge also had a significant effect on the reduction of heavy metal uptake by cabbage and lettuce, which highlights their role as indicator plants in ecotoxicological measurements.

NOVELTY STATEMENT

The effects of sewage sludge compost added to the heavy metals contaminated flotation sludge and mine tailings (pH = 4.8) were examined. The applicability of broad-leaved sorrel and perennial ryegrass that can be found under natural conditions in the study area was assessed as a function of sewage sludge compost ratio for phytostabilization purposes. Moreover, ecotoxicological tests had been performed with cabbage and lettuce on sewage sludge compost + flotation sludge and mine tailings mixtures. Based on the results, it was proved that the phytostabilization is feasible with the investigated plant species by adding 5% of sewage sludge compost to the flotation sludge and mine tailings.

Keywords:

• Bioaccumulation
• ecotoxicology
• heavy metals
• phytostabilization
• translocation

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

The research was financed by the Thematic Excellence Programme of the Ministry for Innovation and Technology in Hungary [ED_18-1-2019-0028], within the framework of the Space Sciences thematic programme of the University of Debrecen.