Washing agents from sewage sludge: efficiency of Cd removal from highly contaminated soils and effect on soil organic balance

Barbara Klik,Zygmunt M Gusiatin,Dorota Kulikowska,Sylwia Pasieczna-Patkowska

doi:10.1007/s11368-019-02367-7

Abstract

PurposeTo compare Cd removal from different soils with three washing agents recovered from sewage sludge (dissolved organic matter (DOM), soluble humic-like substances (HLS), soluble humic substances (SHS)). Also, to investigate how washing with these agents changes soil organic-matter composition (OM).Materials and methodsSandy clay loam (S1) and clay (S2) highly contaminated with Cd (300 mg kg−1) were washed with DOM, HLS, or SHS solutions at various pHs, and with various washing times and washing modes (single or double). Cd distribution and OM composition were determined (including content of humic substances (HS), fulvic fraction (FF), labile humic acids (L-HA), and stable humic acids (S-HA)).Results and discussionCd removal proceeded with pseudo-second-order kinetics. Equilibrium was reached in 30 min (S1) and 60 min (S2). DOM, HLS, and SHS removed 75–82% of Cd from S1, and 80–87% from S2. The most mobile fraction of Cd was removed after one wash. S2 retained more OM, including HS, than S1. Although washing did not change the HA/FF ratio in most variants, washing with DOM and HLS increased the percentage of L-HA in both soils. Washing with SHS increased S-HA content in both soils, but the percent content of S-HA was similar to that in the unwashed soil.ConclusionsDOM, HLS, and SHS derived from sewage sludge can effectively remediate clay and sandy clay soils highly contaminated with Cd. Washing with an SHS solution can increase the content of the most stable carbon forms (HA), which is beneficial for carbon sequestration in remediated soils.

Highlights

Remediation of contaminated soils via chemical extraction with both conventional and unconventional washing agents (WAs) has been frequently studied and is still considered a Responsible editor: Kitae Baek a relatively large amount of information is available about removal of heavy metals (HMs), including Cd, with acids (Gu et al 2018) and chelating agents (Wang et al 2016; Wei et al 2018), some of these WAs harm soil properties
dissolved organic matter (DOM), humic-like substances (HLS), and soluble humic substances (SHS) derived from sewage sludge can effectively remediate clay and sandy clay soils highly contaminated with Cd
The WAs extracted from sewage sludge had different pHs, which was related to the type of extractant used

Summary

Introduction

Remediation of contaminated soils via chemical extraction with both conventional and unconventional washing agents (WAs) has been frequently studied and is still considered a Responsible editor: Kitae Baek a relatively large amount of information is available about removal of HMs, including Cd, with acids (Gu et al 2018) and chelating agents (Wang et al 2016; Wei et al 2018), some of these WAs harm soil properties. EDTA removed 46–82% Cd from contaminated soil (Chen et al 2015; Wang et al 2017), but it can cause some ecological problems in the soil environment due to its persistence or slow degradation. Natural plant biosurfactants (e.g., saponin) can be used to remediate soil without the negative effects of EDTA They are relatively expensive, and their availability is limited because only a few plant species contain saponins at concentrations high enough to make their recovery profitable.

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