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

2021

Sci Rep

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Removal of heavy metals (HMs) from soil is a priority in soil washing/soil flushing. However, for further management of remediated soil, it should be characterized in detail. This study presents, for the first time, an evaluation of soil quality after column flushing with new-generation washing agents (WAs) recovered from municipal sewage sludge (dissolved organic matter, DOM; soluble humic-like substances, HLS; soluble humic substances, SHS) and Na2EDTA as a standard benchmark. Sandy loam soil was spiked with industrial levels of Cu, Pb and Zn, then flushed in a column reactor at two WA flow rates (0.5 and 1.0 ml/min). Soil quality was assessed by determining both physico-chemical (pH, total HMs and their mobility, soil organic matter, OM, humic substances, HS and their fractions, macroelements) and biological indicators (dehydrogenase activity, DHA; germination rate, GR; and inhibition factors for roots and shoots of Triticum aestivum). Total residual HMs contents and HMs contents in the mobile fraction were significantly lower in soil flushed at 1.0 ml/min than in soil flushed at 0.5 ml/min. With all WAs, the decrease in Cu content was larger than that of the other HMs, however this HM most effectively was removed with DOM. In contrast, Pb most effectively was removed by HLS and Na2EDTA, and DOM should not be used to remediate Pb-contaminated soil, due to its very low effectiveness. Flow rate did not appear to affect the fertilizing properties of the soil, DHA activity or soil toxicity indicators. Soil flushing with all SS_WAs increased OM, HS, and exchangeable P, K and Na content in remediated soils, but decreased exchangeable Ca content, and in most cases, exchangeable Mg content. Soil flushing substantially improved DHA activity and GR, but only slightly improved the shoot and root inhibition factors.

Section: Introductionmentioning

confidence: 99%

Quality of heavy metal-contaminated soil before and after column flushing with washing agents derived from municipal sewage sludge

2021

Sci Rep

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“…HLS contains both low-molecular-weight organics and macromolecular compounds (fulvic and humic acids), whereas SHS are mainly consist of fulvic and humic acids 3 Among different organic functional groups, carboxyl (carboxyl-C) and amino (N-alkyl-C) groups readily interact with metals 47 . In all washing agents derived from sewage sludge, carboxyl (dissociated and undissociated) and unprotonated amino groups were the most abundant and the intensities in the infrared spectra for these groups decreased in the order DOM > HLS > SHS 30 . This can explain higher DOM efficiency in metal removal, especially Cu and Zn.…”

Section: Resultsmentioning

confidence: 99%

“…As SS_WAs, three different washing solutions were used: DOM, HLS and SHS. The previous study presented a detailed extraction procedure and characteristics of the used washing solutions 18,30 . Briefly, WAs were extracted (1:10 ratio (w/v)) with water (DOM) and 0.1 M NaOH (HLS and SHS) from the dried sewage sludge (105 °C).…”

Section: Methodsmentioning

confidence: 99%

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Suitability of environmental indices in assessment of soil remediation with conventional and next generation washing agents

2020

Sci Rep

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Remediation of soils contaminated with metal must ensure high efficiency of metals removal, reduce bioavailability of residual metals and decrease ecological risk. Thus, for comprehensive environmental soil quality assessment, different indices must be used. In this study, suitability of 8 indices was used for soil highly contaminated with Cu (7874.5 mg kg−1), moderately with Pb (1414.3 mg kg−1) and low with Zn (566.1 mg kg−1), washed in batch and dynamic conditions with both conventional and next-generation washing agents. The following indices were used: modified contamination factor (mCf), modified contamination factor degree (mCdeg), mobility factor (MF), reduced partition index (IR), potential ecological risk factor (Er,Z), modified potential ecological risk factor (Er,m), potential ecological risk index (RIZ) and modified ecological risk index (RIm). For mCf,mCdeg and IR own classification scale was proposed. It was proven that most useful indices for assessment of soil pollution with metals were mCf and mCdeg. The mCf together with the IR allow to simultaneous assessment of soil pollution and stability for individual metals. These indices were appropriate for soil contaminated with different concentrations of metals, washed under both hydrodynamic conditions using various washing agents and different effectiveness of metals removal. Thus, they may be considered as most useful for evaluation of remediation method, feasibility of washing agent and assessing soil quality after washing.

“…Sewage sludge can be a source of dissolved organic matter (DOM), soluble humic-like substances (HLS), and soluble humic substances (SHS) [ 46 , 48 ]. These WAs might simultaneously remove HMs and improve soil fertility after remediation [ 48 ].…”

Section: Novel Was and Their Applicability For Hms Removal From Somentioning

confidence: 99%

New-Generation Washing Agents in Remediation of Metal-Polluted Soils and Methods for Washing Effluent Treatment: A Review

2020

IJERPH

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Soil quality is seriously reduced due to chemical pollution, including heavy metal (HM) pollution. To meet quality standards, polluted soils must be remediated. Soil washing/soil flushing offers efficient removal of heavy metals and decreases environmental risk in polluted areas. These goals can be obtained by using proper washing agents to remove HMs from soil. These washing agents should not pose unacceptable threats to humans and ecosystems, including soil composition. Currently, it is desirable to use more environmentally and economically attractive washing agents instead of synthetic, environmentally problematic chemicals (e.g., ethylenediaminetetraacetic acid (EDTA)). The usefulness of novel washing agents for treatment of heavy metal-contaminated soils is being intensively developed, in terms of the efficiency of HM removal and properties of washed soils. Despite the unquestionable effectiveness of soil washing/flushing, it should be remembered that both methods generate secondary fluid waste (spent washing solution), and the final stage of the process should be treatment of the contaminated spent washing solution. This paper reviews information on soil contamination with heavy metals. This review examines the principles and status of soil washing and soil flushing. The novel contribution of this review is a presentation of the sources and characteristics of novel washing agents and chemical substitutes for EDTA, with their potential for heavy metal removal. Methods for treating spent washing solution are discussed separately.