Remediation potential of metalliferous soil by using extracts of composts and vermicomposts from Municipal Solid Waste

Accepted Manuscript Title: Remediation potential of metalliferous soil by using extracts of composts and vermicomposts from Municipal Solid Waste Author: Nuhaa Soobhany PII: DOI: Reference:

S0957-5820(18)30283-0 https://doi.org/10.1016/j.psep.2018.07.005 PSEP 1449

To appear in:

Process Safety and Environment Protection

Received date: Revised date: Accepted date:

11-6-2018 7-7-2018 8-7-2018

Please cite this article as: Soobhany, Nuhaa, Remediation potential of metalliferous soil by using extracts of composts and vermicomposts from Municipal Solid Waste.Process Safety and Environment Protection https://doi.org/10.1016/j.psep.2018.07.005 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Remediation potential of metalliferous soil by using extracts of composts and vermicomposts from Municipal Solid Waste

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Nuhaa Soobhany*

Department of Chemical & Environmental Engineering, Faculty of Engineering, University of Mauritius, Réduit 80837, Mauritius

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*Corresponding author. Tel.: +230 5914 59 75 E-mail addresses: [email protected]; [email protected] (N. Soobhany)

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Graphical abstract

Highlights 

Remediation of metalliferous soil by compost/vermicompost extract was examined 1

Vermicompost/compost extracts were exceptionally effective in Ni and Co remediation

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Remediation using extracts of vermicomposts outperformed to those of composts

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Treatment with vermicompost-extract from ground samples removed 79 – 92% of metals

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High RFs showed potential of using extracts for remediation of metalliferous soil

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ABSTRACT

The intervention management strategy to mitigate ecotoxicity in a heavy metal (HM)-contaminated soil was evaluated through a new soil remediation technique trial by using extracts of composts and

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vermicomposts from Municipal Solid Waste (MSW). The MSW composts and vermicomposts

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which were > 9.423 mm in size referred as coarse and those < 0.991 mm denoted as ground. The

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reduction percentage (R) for both compost-extracts and vermicompost-extracts from coarse samples

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was in the order of Ni > Co > Cu > Cd > Cr > Zn. Results showed that treatments with compost-

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extracts from ground samples removed 90.83% Ni, 90.45% Co, 84.64% Cu, 79.01% Cd, 76.85% Cr

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and 76.77% Zn from the contaminated soil. On the contrary, treatments with vermicompost-extracts from ground samples caused moderately higher reduction in Ni (91.52%), Co (90.69%), Cu

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(85.18%), Cd (81.42%), Cr (79.06%) and Zn (79.02%). The remediation factors (RFs) of the HMs from the ground vermicompost-extracts can be classified in the order: Ni (8.06 – 10.98) > Co (8.28

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– 10.61) > Cu (5.44 – 5.76) > Cd (2.82 – 4.41) > Zn (2.93 – 3.77) > Cr (1.37 – 2.11) whilst a lower RF value was obtained for the remediation treatments from the ground compost-extracts. Yet, in

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contrast of using compost-extracts from both coarse and ground samples to remediate metalliferous soil, data analysis revealed that vermicompost-extracts were more proficient in the mitigation of the concentration of HMs.

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Keywords: contaminated soil; remediation; vermicompost-extract; heavy metal; compost-extract; remediation factor

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1. Introduction The ever increasing human activities comprising of agricultural, urban or industrial are a major source of environmental pollution. Single or mixture of toxic metal pollution of soil is one of the potential problems that has threatened the sustainability of diverse agrarian ecosystems and is thus a matter of ever-growing concern for the public, mostly in developing countries. In a few instances,

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soil could be contaminated to such a degree that it may be categorized as a hazardous waste (Berti

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and Jacob, 1996). Tóth et al. (2016) evinced that approximately 6.24% or 137,000 km2 of the

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European agricultural soils are considered inappropriate with a relatively high concentrations of

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potentially harmful elements (PHEs), potentially toxic elements (PTEs) or trace elements (TEs) and thus requires eventual remediation action. The protection and rehabilitation of metal contaminated

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soils are extremely crucial so as to maintain the structural integrity and fertility of soil. The main

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sources of heavy metals (HMs) into soil environment are from various anthropogenic activities such

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as industrial processes (electroplating and metal extractive operations), atmospheric emissions, agrochemicals (Singh et al., 2010), sewage sludge (Antonkiewicz et al., 2017), waste disposal,

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metalliferous mining and smelting (Mohammed et al., 2011). Since the degradability and complete destruction of HMs are not possible, they become tenacious environmental contaminants and thus

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indefinitely cause pollution (Tomohito et al., 2010). However, the level of soil pollution by HMs relies on the soil retention capability, particularly on physicochemical properties which influence soil particle surfaces and also on the chemical properties of the metal. When HMs accumulate or deposit excessively in soils through atmospheric fallout, they pose a serious ecological,

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toxicological, critical threat to human health and render the soils unsuitable for agricultural use. Owing to leaching from contaminated soil, agricultural products, waste deposits or polluted drinking water, HMs are transferred into the food web (Martelli et al., 2006; Palmgren et al., 2008).

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Certain HMs like lead and cadmium which are potentially toxic to organisms are known to have long-term objectionable effects on human health when entering the body system through the digestive tract (Hovmond et al., 1983) and bio-accumulate over a period of time. To address these problems, numerous traditional remediation techniques have been designed and developed for the purpose of cleaning contaminated soils (McEldowney et al., 1993). These techniques comprise of

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bulk excavation, landfilling of contaminated materials (Begonia et al., 1998), acid washing and

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solidification (US-EPA, 1997). However, these technologies were found to be extremely costly,

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generate poor products, provide unacceptable solutions (Aleksandra, 2011) and very disruptive to

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the ecosystem (Gardea-Torresdey et al., 2004). Therefore, there is an imperative need to develop an alternate novel management practices, whether onsite or offsite, for the subsiding of contaminated

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soils, in order to reduce contaminants from entering the environment and risks to human health.

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Alternatively, environmentally benign treatment processes such as remediation have proved to be an

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inexpensive technology for remediating contaminated sites (Abou-Shanab, 2011). Remediation is a multidisciplinary strategy that employs biological systems to transform and/or to rid the

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contaminated soil into a less toxic or nontoxic compounds and can be subsequently applied over large areas. In order to be completely successful in producing high quality results, remediation

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techniques however depend upon the site characteristics, extent and nature of the pollutants. Numerous researches have been conducted where compost has been applied to soil thereby acting as a soil conditioner since it enhanced the soil organic matter, water contents and the cation exchange capacity (Paradelo and Barral, 2012; Ounia et al., 2014). While composts and

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vermicomposts have showed to represent a constantly bountiful supply of plant advantageous compounds (Soobhany et al., 2015a), increasing numbers in plant productivity for growers (Soobhany et al., 2017a) and some latest studies suggest that compost/vermicompost tea is also

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efficient which is an aqueous extract of compost/vermicompost (Islam et al., 2016). Extracts from composts and vermicomposts have been utilized extensively in horticultural and agricultural systems to enhance plant growth (Edwards et al., 2011) and to decrease pest or plant disease responses through an array of mechanisms (Noble and Coventry, 2005; Pane et al., 2011). Besides soil fertilizing capacity, composts may wield significant impacts on the mobility of HMs

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concentrations in contaminated field soils. Also, the stabilization of mine-combined soils is fully

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improved from the incorporation of soil amendments like composts, consequently decreasing sign

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of ecotoxicity (Tandy et al., 2009), even if these remediative outcomes may be reasonable or

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antithetical for certain types of composts containing high amount of toxic compounds (van Herwijnen et al., 2007a). Still, stabilization does not diminish the amount of contaminant but

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employs composts to improve the soil chemistry and sequester the pollutant into the matrix so as to

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lessen environmental risks (Burns et al., 1996). Organic constituents of vermicomposts exert high-

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metal remediation affinities (Pereira and Arruda, 2003; Carrasquero Duran et al., 2006) owing to the activity of earthworms in the process (Suthar, 2008; Soobhany et al., 2015b) and the employability

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of vermicomposts for extracting HMs from industrial effluents is a promising interest (Jordao et al., 2007, 2010). Since the heavy metal (HM)-scavenging properties of vermicomposts have

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demonstrated to be favourable, thus it is anticipated that the remediation of contaminated soil by using extracts from composts and vermicomposts will become an important prospective applied outlet for a clean environment. The focal matter of this research work was to perform an assessment on the remediation potential of metalliferous soils with a specific emphasis on the viability and

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applicability by using extracts of composts and vermicomposts from Municipal Solid Waste (MSW) with the aim of repairing metal-contaminated soil.

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2. Materials and methods 2.1 Design and set-up of the remediation system

The mechanical sketch of the remediation system was drafted and blueprinted using Microsoft Office Visio 2007 software and set-up on a wooden table in the laboratory. The materials which were used were two glass beakers (1 L), peristaltic pump (ISMATEC- IDEX Corporation),

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transparent plastic tubing, glass column, cotton, metallic filter, metal stand and clamp. The internal

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diameter (I/D) and outer diameter (O/D) of the glass column was 5.0 and 5.5 cm respectively. The

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glass column was designed with an effective length of 39 cm so as to allow enough metalliferous

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soil (500 g) into it. A plastic tubing of a length of 3.5 cm was glued to the outlet of the glass column for filtrate passage and the schematic model of the remediation system set-up is presented in Fig 1.

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The peristaltic pump was initially calibrated for the determination of an adequate volume velocity

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and a constant volumetric flow rate of 33 mL/min was used in this study. It should however be

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noted that the density of soil samples (1088 ± 18 kg/m3 as calculated in this study) in the glass column may have an influence over the rate of compost/vermicompost extracts flow i.e overflowing

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of the aqueous extracts at the top of the glass column. A metallic filter with cotton on the upper side

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was inserted at the bottom of the glass column for the avoidance of soil particles into the filtrate.

2.2 Soil sampling and collection of composts and vermicomposts Original brown earth soil samples (around 30 kg), mature composts and vermicomposts samples were procured from the agrarian station of the University of Mauritius in Réduit. The soil samples

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were obtained from a depth of 0 – 10 cm, air dried and sieved manually through an opening mesh size of 2.362 mm metal hand sieve. These finely sieved soil samples (19.5 kg) were contaminated with salts (powdered form) of HMs (Cadmium (Cd), Chromium (Cr), Copper (Cu), Cobalt (Co),

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Zinc (Zn), Nickel (Ni)) and used for remediation experiments. The composts which were used in these experiments were previously generated from three organic constituents of MSW namely food, paper and yard wastes. The preliminary fundamental chemical properties (pH, electrical conductivity (EC), C/N ratio and particle size) of soils and the MSW-derived compost and vermicompost are characterized in Table A.1 (Supplementary material). The vermicomposts were

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also of the same MSW components and Eudrilus eugeniae were employed as earthworm specie for

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the vermicomposting process. The MSW components were earlier composted and vermicomposted

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as detailed by Soobhany et al. (2015b).

2.3 Experimental design

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2.3.1 Step I: Preparation of metalliferous soil

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The HMs content in the ground brown earth soil was at a natural level and thus, a synthetic

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contamination with HMs was opted for this study to obtain the metalliferous soil. Moreover, HMcontaminated soil could not be found naturally in the locality where the work has been conducted.

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The finely ground brown earth soil samples (< 2.362 mm) were contaminated with HMs using one large spoon of powdered salts of Cadmium (CdCl2.H2O, 99 % pure from AR grade), Chromium

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(CrCl3.6H2O, 96 % pure from AR grade), Copper (CuCl2.2H2O, 99 % pure from ACS reagent grade), Cobalt (CoCl2.6H2O, 98 % pure from ACS reagent grade), Zinc (ZnCl2, 98 % pure from ACS reagent grade), Nickel (NiCl2.6H2O, 98 % pure from puriss. grade ). HMs in the form of chloride salts were added since all these were readily available in the university laboratories. The

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prepared metalliferous soil was shaken for 3 hours through a mini drum rotator mixer for homogeneity. The HMs content of the original brown earth and synthetically contaminated soil were determined and characterized in Table 1.

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2.3.2 Step II: Preparation of aqueous extracts from composts and vermicomposts The as-received samples of MSW composts and vermicomposts (food, paper and yard) were sieved and particles which did not pass through the 9.423 mm metal hand sieve were labeled as coarse samples and utilized in the experiments. For, the second set of experiments, the composts and vermicomposts from MSW were finely grinded using a kitchen blender (Moulinex). The samples

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which passed through the 0.991 mm sieve were labeled as ground samples. The coarse and ground

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composts/vermicomposts generated from the three different organic constituents (food, paper, yard)

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were mixed with distilled water for aqueous extracts removal (compost-extracts and vermicompost-

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extracts). It was earlier found that ratios from 5% (1:20) to 20% (1:5) solid vermicompost to water showed efficient results in laboratory experiments (Edwards et al., 2011). In this study, a ratio of

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10% (1:10) was used, that is, 50 g of each compost and vermicompost sample was mixed with 500

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mL distilled water. The resulting mixture was homogenized for 2 hours using a shaker (Stuart Mini

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Orbital shaker) at 200 rpm. The mixture was then strained and the filtrate (compost-extracts and

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vermicompost-extracts) was used for remediation treatments of the metalliferous soil.

2.3.3 Step III: Remediation process

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The glass column of the remediation system was filled with 500 g of HM contaminated soil for each treatment using different aqueous extracts. A total of 13 remediation processes were experimented in this study. 6 sets in triplicate were run for the extracts generated from coarse samples of composts (3 sets) and vermicomposts (3 sets) to ascertain reproducibility of results. Another 6 sets

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in triplicate were run for the aqueous extracts produced from ground samples of composts (3 sets) and vermicomposts (3 sets). Another 1 set in triplicate was performed with distilled water therefore acting as control. These 13 remediation treatments which were replicated three times were labeled

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as C1 (extract from food waste compost), C2 (extract from paper waste compost), C3 (extract from yard waste compost), V4 (extract from food waste vermicompost), V5 (extract from paper waste vermicompost), V6 (extract from yard waste vermicompost) and Control (treatment with distilled water). The MSW compost and vermicomposts’ aqueous extracts were pumped at a flow rate of 33 mL/min through a peristaltic pump to the glass column containing the metalliferous soil as shown in

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Fig A.1 (Supplementary material). This process was repeated for each extracted solution from the

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composts and vermicompost samples. The treated soil after the remediation process by the aqueous

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extract from coarse sample was termed ‘treated soil CS’ and for the remediation treatment by the

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ground samples, it was denoted as ‘treated soil GS’. The resulting filtrate from the remediation system using coarse samples was termed ‘filtrated extract CS’ and for ground samples was termed

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as ‘filtrated extract GS’. The resulting filtrate from the remediation system using distilled water was

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denoted ‘filtrated water control’. The aqueous extracts for all the remediation experiments were

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collected for HMs analysis. After the remediation process, the remediated soil was dried at 60oC in an oven (OF-750G JEIO TECH) for 24 hr as per the TMECC (2001) for the determination of HMs

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content.

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2.3.4 Step IV: Mass balance within the remediation system To search for the flow source of HMs tested and sequestered level of HMs in compost-extracts and vermicompost-extracts, a mass balance in heavy metal (HM) was followed for the remediation treatments in C1, C2, C3, V4, V5 and V6 for both coarse and ground samples. The equation for

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mass balance in HM was as designated by Azizi et al. (2011) but modified literally in Eq. (1) and applied to this remediation context: Input content (HM in metalliferous soil) = Output content (HM in treated soil + HM in filtrate)

(1)

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2.3.5 Step V: Remediation factor (RF) and reduction percentage Remediation factor (RF) was calculated as an indication of metal accumulation in the extracts. RF value greater than 1.0 indicates high remediation capacity of metal in extracts. The RF for HMs in the metalliferous soil was calculated using the formula in Eq. (2): RF = Ce /Cr

(2)

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where Ce is the total concentrations of metals in filtrated extract (mg/L) and Cf is the total

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concentrations of metals in remediated soil (mg/L).

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The reduction percentage (R) which is the percentage of metal remediated by ‘compost-extract’ and

R = [(Cc – Cr)/ Cc] * 100

(3)

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and used by Taiwo et al. (2016):

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‘vermicompost-extract’ at each treatment in the contaminated soil was determined as per Eq. (3)

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where Cc is the concentrations of HM in contaminated soil (m/L) and Cr is the concentrations of

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HM in remediated soil (mg/L).

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2.4 Experimental analysis: Determination of HMs The aqua regia treatment was adopted for the remediated soil in the finding of Cd, Cr, Cu, Co, Zn

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and Ni. The digestions of the samples which were in line with Method TMECC 04.12-B Nitric acid digestion, SW-846 US EPA 3050B Modified as per the TMECC (2001) was followed. About 5 g of oven-dried ground solid particles (<0.25 mm) was weighed to the proximate 0.001 g on the Mettler PM400 top balance into the reaction vessel and 18 mL of concentrated HCl were poured and after

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which, 6 mL of HNO3 conc were added. Before rendering the solution more soluble by light boiling under reflux, the content in the reaction vessel was allowed to stand for 12 h. When cooled, the condenser was partly rinsed with 2 M dilute nitric acid and transferred into a 200 mL volumetric

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flask wherein it is filled to the brim with dilute HNO3. Subsequent to careful mixing, the content of the volumetric flask was filtered and determined by Atomic Absorption Spectrophotometer (GBC Avanta AAS). For the analysis of HMs in the filtrated extract CS and filtrated extract GS after the remediation process, the extracts were similarly found by GBC Avanta AAS. The sample experimental determination procedure which was in compliance with Method TMECC 04.13-B

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Atomic Absorption Spectrophotometry as per the TMECC (2001) was followed.

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2.5 Statistical analysis

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The remediation trials were conducted in triplicate to ensure reproducibility of results. All results reported in this study were the means and standard deviations of values noted on 9 samples (3

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samples from each triplicate experiment). An independent two-sample t-test was carried out among

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experimental values prior to the use of the Levene’s Test for Equality of Variances to determine the

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statistical significance analysis of the aforesaid replicates obtained using threshold p-value of 0.05. The two-sample t-test for independent samples using IBM SPSS Statistics 20.0 software was used

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for hypothesis testing that is; to examine the significant difference for concentration of HMs among remediation trials between compost-extracts and vermicompost-extracts. Results were considered

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significant when p < 0.05 for the HMs analyses performed.

3. Results and discussion 3.1 Cadmium

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Fig 2 illustrated the Cd content (mg/L) in contaminated and treated soil for the remediation techniques by using extracts from composts and vermicomposts which were derived by both coarse and ground samples. Generally, remediation treatments with extracts from all sets of ground MSW

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composts and vermicomposts removed Cd content in the contaminated soil to a higher extent when compared to treatments with extracts from coarse MSW composts and vermicomposts. The reduction in Cd level during the remediation treatments might be owing to the apparent decrease of toxic metal ions by the compost-extracts and vermicompost-extracts as reported by other authors (Pant et al., 2009; Chatterjee et al., 2013). This decrease in Cd content might be caused by the

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mature, cured compost-extracts and vermicompost-extracts in absorbing down HMs in soil. Similar

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decrease in Cd was reported by Mora et al. (2005) in the remediation of HM-contaminated soil

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using MSW composts and biosolid compost as amendments. The contaminated soil had a more or

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less neutral pH as presented in Table A.1 and it could be possible that this physicochemical property; pH of the contaminated soil was augmented by the relatively high pH value of these

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composts and vermicomposts extracts (Table A.2: Supplementary material) with an effect in

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diminishing Cd content. From Fig 2, the total Cd content in the contaminated soil at the start of the

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experiments was 18.18 ± 0.02 mg/L and the total Cd content in the treated soil CS was 6.27 ± 0.34 mg/L for C1, 6.28 ± 0.66 mg/L for C2, 5.88 ± 0.02 mg/L for C3, 5.30 ± 0.37 mg/L for V4, 5.49 ±

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0.66 mg/L for V5, and 4.19 ± 0.48 mg/L for V6. Whilst, the Cd content in the treated soil GS was 5.42 ± 0.39 mg/L, 4.71 ± 0.21 mg/L, 3.82 ± 0.30 mg/L, 3.38 ± 0.34 mg/L, 4.78 ± 0.38 mg/L, and

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4.06 ± 0.17 mg/L for C1, C2, C3, V4, V5 and V6 respectively. Remediation treatment of the contaminated soil with distilled water (control) showed high concentration of Cd (14.70 ± 0.71 mg/L) which implied that treatment with extracts were more effective than the control. The possible presence of sequestering agents in the extracted solutions exerted better remediation capacity of the

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metalliferous soil as compared to distilled water which might have a ring-like center for the formation of bonds with the metal ion allowing it to be excreted. Cd did not demonstrate any significant disparity between treatments of C1 and V4 (t-test; p = 0.058). Among C2 and V5, the

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contrariety was statistically insignificant with regard to Cd concentration (t-test; p = 0.554). Similarly, the change of Cd concentration denoted a statistically insignificant dissimilarity between C3 and V6 (t-test; p = 0.288). It could also be noted that the Cd content in the filtrated extract GS was a little bit higher compared to filtrated extract CS, which indicated effectiveness in terms of Cd removal when using extracts from the ground samples. From Fig 2, when comparing the

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remediation treatment between extracts from vermicomposts and composts, it could be seen that the

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Cd content was much less in soil treated with vermicompost-extracts (V4, V5, V6) than

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contaminated soil treated with compost-extracts (C1, C2, C3). The larger decrease in total Cd in soil

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treated with vermicompost-extracts might be attributed to the fact that vermicomposts are much finer particles than composts (Atiyeh et al., 2000) with strong HMs remediation capacity (Suthar,

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2010; Soobhany et al., 2015b). Thus, to some extent, this reasoning could define the characteristics

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of the vermicompost-extracts which might possess absorption cells that could eventually decrease

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the Cd content in the contaminated soil. This reasoning was also justified by Singh et al. (2011) who delineated that composts present a risk of HMs whilst in vermicomposts, HMs are destroyed and

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hold within worm bodies. These results somewhat agree with previous research study conducted by van Herwijnen et al. (2007b) who reported a decrease in Cd concentration on the efficiency of soil

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organic and inorganic amendments on the remediation of a metal contaminated soil.

3.2 Chromium

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The comparison in total Cr content (mg/L) of the remediation techniques by treating with extracts from composts and vermicomposts, both by coarse and ground samples is shown in Fig 3. At the start of the experiments, from Fig 3, the total Cr content in the contaminated soil was 16.83 ± 0.02

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mg/L and at the end of the experiments, the total Cr content in the treated soil CS for C1 was 6.61 ± 0.37 mg/L whilst V4 was 6.27 ± 0.03 mg/L and the total Cr content in the treated soil GS was 5.21 ± 0.56 mg/L and 3.87 ± 0.47 mg/L for C1 and V4 respectively. The total Cr content in the treated soil CS for C2 was 6.18 ± 0.30 mg/L whilst V5 was 3.88 ± 0.10 mg/L and the total Cr content in the treated soil GS was 3.90 ± 0.28 mg/L and 3.52 ± 0.52 mg/L for C2 and V5 respectively. From Fig

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3, the treated soil with extracts from coarse samples showed a total Cr content of 6.51 ± 0.04 mg/L

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for C3 whilst 5.64 ± 0.35 mg/L was found in V6 and the total Cr content in the treated soil GS was

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5.36 ± 0.49 mg/L and 4.53 ± 0.05 mg/L for C3 and V6 respectively. A high concentration of Cr

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(12.76 ± 0.79 mg/L) was obtained after the remediation treatment with distilled water (control) as compared to the extracts. The low level of Cr in the soils treated with the compost-extracts and

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vermicompost-extracts might be due to the presence of sequestering agents which wielded superior

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remediation capacity of the metalliferous soil. Contaminated soil which has been treated with

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extracts of composts and vermicomposts produced a treated soil with a lower Cr content as compared to control. It could be observed that the remediation treatments using extracts from

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ground MSW composts/vermicomposts effectively removed Cr in the contaminated soil to a much higher level as compared to treatments using extracts from coarse MSW composts/vermicomposts.

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The decrease in Cr content during the remediation technique was generally due to the evident absorption of toxic Cr ions by the compost-extracts (Chatterjee et al., 2013) and vermicompostextracts as reported by Pant et al. (2009). The mechanism behind this decrease in HM might be explained by the presence of the cured compost-extracts and vermicompost-extracts which helped

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in the absorption of Cr in soil. Statistically, Cr showed insignificant difference among each pair of remediation treatments by employing extracts from composts/vermicomposts (both coarse and ground) (t-test; p = 0.353 between C1 and V4; p = 0.403 between C2 and V5; p = 0.103 between C3

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and V6). The Cr content in the filtrated extract GS was higher compared to the filtrated extract CS which indicated that Cr remediation was more successful when using extracts from the ground MSW composts/vermicomposts samples. From the results obtained in Fig 3, it could be inferred that the remediation experiment by using vermicompost-extracts from MSW was exceptionally proficient in the activity of Cr accumulation compared to the use of compost-extracts since Cr

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content was much less in soil treated with vermicompost-extracts. Earthworms have been

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scientifically researched as crucial bio-accumulators and bio-indexes of environmental

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contamination of tenacious HMs like Cr (Wang et al., 2009; Soobhany et al., 2015a). This

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justification could still define the characteristics of the vermicompost-extracts in possessing

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3.3 Copper

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absorption cells that could ultimately decrease the Cr content in the contaminated soil.

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The Cu content in each of the remediation systems of the contaminated and treated soil, filtrated

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extracts from both ground and coarse samples was presented in Fig 4. The total Cu content in the contaminated soil at the start of the experiments was 14.07 ± 0.01 mg/L. The average total Cu

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content in the treated soil CS at the end of the experiments were 3.09 ± 0.36 mg/L, 3.29 ± 0.34 mg/L and 3.19 ± 0.39 mg/L for C1, C2 and C3 respectively. Whilst, treatment with compostextracts from ground samples produced a treated soil GS with Cu content of 2.16 ± 0.00 mg/L, 2.39 ± 0.03 mg/L and 2.59 ± 0.17 mg/L for C1, C2 and C3 respectively. For the remediation treatments of V4, V5 and V6 by vermicompost-extracts from coarse samples, the final average Cu in the 15

treated soil CS were 2.78 ± 0.35 mg/L, 3.13 ± 0.14 mg/L and 3.11 ± 0.09 mg/L respectively. While, the final average Cu content for the remediation treatments of V4, V5 and V6 by vermicompostextracts from ground samples were 2.09 ± 0.10 mg/L, 2.15 ± 0.04 mg/L and 2.19 ± 0.07 mg/L

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respectively. Cu did not prove any significant difference (t-test; p = 0.620 among C1 and V4; p = 0.630 among C2 and V5; p = 0.503 among C3 and V6) between all pairs of remediation treatments of the contaminated soil in respect of using compost-extracts and vermicompost-extracts. As shown from Fig 4, the remediation treatments using extracts of composts/vermicomposts resulted in lower Cu concentrations than the control (9.29 ± 0.47 mg/L) which could be due to the occurrence of

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sequestering agents in the extracts with a ring-like center for the formation of bonds with the metal

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ion allowing it to be exuded. The reduction in total Cu level in all the remediation systems could be

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attributed to the evident reduction of toxic Cu ions by both types of extracts as pointed out by

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previous researchers (Pant et al., 2009; Chatterjee et al., 2013). This decline in Cu content might be caused by the extracts (both types) in absorbing HMs in soil. It might also be likely that the more or

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less neutral pH value of the contaminated soil (Table A.1) has been raised by the high pH value of

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these composts and vermicomposts extracts (Table A.2: Supplementary material) with an effect in

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diminishing Cu content. Quite alike reduction in Cu was reported by other workers (Mora et al., 2005; van Herwijnen et al., 2007b; Farrell and Jones, 2010) in the enhancement of HM-

CC

contaminated soil through the use of mature MSW composts and by Tandy et al. (2009) for the cocomposting of contaminated soil with organic wastes. Comparing the remediation treatment

A

between the use of extracts from vermicomposts and composts (both coarse and ground), it could be seen that the Cu content was much less in soil treated with vermicompost-extracts than in soil treated with compost-extracts. The larger decrease in total Cu in soil treated with vermicompostextracts might be attributed to the fact that vermicomposts are much finer particles than composts

16

(Atiyeh et al., 2000) with strong HMs remediation capacity (Suthar, 2010; Soobhany et al., 2015b). Thus, to some extent, this reasoning could delineate the characteristics of the vermicompost-extracts which might contain absorption cells whereby Cu are concentrated in the filtrated extract CS and

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filtrated extract GS from the contaminated soil.

3.4 Cobalt

The level of total Co content (mg/L) for the remediation treatments of the contaminated and treated soil, filtrated extracts from both ground and coarse samples is shown in Fig 5. From Fig 5, the total

U

Co content at the start of the experiments for the contaminated soil was 19.48 ± 0.20 mg/L. The Co

N

content in the treated soil CS for C1 was 4.08 ± 0.97 mg/L whilst V4 was 2.74 ± 0.38 mg/L and in

A

the treated soil GS was 1.86 ± 0.12 mg/L and 1.81 ± 0.70 mg/L for C1 and V4 respectively. The

M

total Co content at the end of the experiments in the treated soil CS for C2 was 3.89 ± 0.19 mg/L whilst V5 was 3.51 ± 0.62 mg/L and in treated soil GS was 2.86 ± 0.47 mg/L and 1.89 ± 0.20 mg/L

D

for C2 and V5 respectively. The total Co content in the treated soil CS before the remediation

TE

process for C3 was 3.83 ± 0.66 mg/L whilst V6 was 3.58 ± 0.74 mg/L. The Co content was 2.88 ±

EP

0.43 mg/L and 2.10 ± 0.09 mg/L for C3 and V6 respectively in treated soil GS. On the whole, it was observed that remediation treatments in terms of Co removal by using extracts were more effective

CC

when compared to the control (9.29 ± 0.47 mg/L). The possible reason for this low content of Co by using extracts might be owing to the occurrence of sequestering agents which put forth enhanced

A

remediation capacity of the metalliferous soil. The remediation treatments using extracts from ground MSW composts/vermicomposts effectively removed Co in the contaminated soil to a much higher level as compared to treatment using extracts from coarse MSW composts/vermicomposts. The explanation behind this decrease in Co might be due to the presence of the cured compost-

17

extracts and vermicompost-extracts which contributed in the absorption of HM in soil. Comparing remediation treatments of the extracts from MSW composts and vermicomposts (both coarse and ground) in processing contaminated soil, it could be seen that remediation using vermicompost-

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extracts was more effective since Co content was much of a lesser amount in the treated soil. Wang et al. (2009) stated that earthworms have been researched as essential bio-accumulators and bioindicators of environmental contamination of persistent HMs like Co. In this study, this justification could delineate the characteristics of the vermicompost-extracts in possessing absorption cells which consistently remediate the pertinacious Co from the contaminated soil during remediation

U

process. It could be deduced from Fig 5 that the filtrated extract GS demonstrated higher level in Co

N

compared to filtrated extract CS, which indicated that the remediation technique of the

A

contaminated soil was outstandingly efficient in terms of Co removal. Statistically, Co showed

M

insignificant difference between each pair of remediation processes (t-test; p = 0.306 among C1 and

D

V4; p = 0.657 among C2 and V5; t-test; p = 0.309 among C3 and V6).

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3.5 Zinc

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The data for the change in Zn (mg/L) in the contaminated and treated soil through the remediation

CC

treatments could be compared from Fig 6. The Zn content in the contaminated soil at the start of the experiments was 19.74 ± 0.22 mg/L as shown in Fig 6. The Zn content in the treated soil CS

A

derived from MSW composts for C1, C2 and C3 was 9.03 ± 0.67 mg/L, 7.30 ± 1.38 mg/L and 8.27 ± 0.31 mg/L respectively. For the remediation processes of V4, V5 and V6, the Zn content in the treated soil CS was 5.97 ± 0.13 mg/L, 4.64 ± 0.02 mg/L and 6.68 ± 0.58 mg/L respectively. For the remediation treatment with extracts from ground composts samples, the Zn content in the treated soil GS for C1, C2 and C3 was 4.59 ± 0.13 mg/L, 4.67 ± 0.14 mg/L and 5.70 ± 0.14 mg/L 18

respectively whilst for remediation treatment of treated soil GS for V4, V5 and V6 was 4.14 ± 0.00 mg/L, 5.03 ± 0.01 mg/L and 4.57 ± 0.02 mg/L respectively. Statistically, there was no significant disparity (t-test; p = 0.258 among C1 and V4; p = 0.230 among C2 and V5; p = 0.215 among C3

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and V6) in Zn among each pair of remediation processes i.e using extracts from vermicomposts and its paired controls irrespective of coarse or ground samples. Fig 6 depicted that treated soil which has been remediated with extracts of composts and vermicomposts generated low-Zn soil as compared to control (distilled water) with a value of 23.20 ± 1.89 mg/L. The low content of Zn in the treated soil might be due to the presence of sequestering agents in the extracts of composts and

It

could

be

observed

that

treatments

with

extracts

from

ground

MSW

N

control.

U

vermicomposts which exerted better remediation capacity of the metalliferous soil as compared to

A

composts/vermicomposts successfully removed Zn in the contaminated soil as much as compared to

M

treatment using extracts from coarse MSW composts/vermicomposts. Remediation of contaminated soil of (C1, C2, C3, V4, V5 and V6) demonstrated a decrease in total metal concentration which

D

could be explained by the evident absorption of toxic Zn by the compost-extracts (Chatterjee et al.,

TE

2013) and vermicompost-extracts as reported by Pant et al. (2009). This decrease in Zn content

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might be caused by both types of extracts in absorbing down HMs in soil. The decrease in Zn during this experiment somewhat corresponded with the research made by other researchers (Mora

CC

et al., 2005; Farrell and Jones, 2010) in the remediation of HM-contaminated soil using conventional incorporation of mature MSW composts. The contaminated soil had a more or less

A

neutral pH (Table A.1) and it might be probable that this physicochemical property of the contaminated soil has been raised by the high pH value of these composts and vermicomposts extracts (Table A.2) with an effect in diminishing Zn content. From Fig 6, when comparing the remediation treatment between extracts from vermicomposts and composts, irrespective of coarse or

19

ground samples, it could be observed that the Zn content was lesser in soil treated with vermicompost-extracts (V4, V5, V6) than contaminated soil treated with compost-extracts (C1, C2, C3). The larger decrease in total Zn in soil treated with vermicompost-extracts might be regarded as

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being caused by the fact that vermicomposts are much finer particles than composts (Atiyeh et al., 2000) with strong HMs remediation potential owing to the activity of earthworms during the vermicomposting process (Soobhany et al., 2015b). Thus, to some extent, this reasoning could describe the characteristics of the vermicompost-extracts which might possess absorption cells that

U

could ultimately decrease the high level of Zn content in the contaminated soil.

N

3.6 Nickel

and

treated

soil,

filtrated

extracts

from

both

ground

and

coarse

M

contaminated

A

Fig 7 illustrated the presence of Ni content (mg/L) for all the remediation treatments of the

composts/vermicomposts. The total Ni content in the contaminated soil at the start of the

D

experiments was 13.71 ± 0.68 mg/L. From Fig 7, the total Ni content in the treated soil CS for C1

TE

was 2.24 ± 0.57 mg/L whilst V4 was 2.09 ± 0.32 mg/L and the total Ni content in the treated soil

EP

GS was 1.58 ± 0.35 mg/L and 1.16 ± 0.01 mg/L for C1 and V4 respectively. The total Ni content in the treated soil CS for C2 was 2.40 ± 0.52 mg/L whilst V5 was 2.28 ± 0.10 mg/L and the Ni content

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in the treated soil GS was 1.26 ± 0.34 mg/L and 1.54 ± 0.27 mg/L for C2 and V5 respectively. The total Ni content in the treated soil CS for C3 was 2.41 ± 0.07 mg/L whilst for V6 was 1.68 ± 0.53

A

mg/L and in the treated soil GS was 1.73 ± 0.08 mg/L and 1.16 ± 0.21 mg/L for C3 and V6 respectively. The variation of Ni content showed a statistically insignificant difference among C1 and V4 (t-test; p = 0.497) among C3 and V6 (t-test; p = 0.866) and among C2 and V5 (t-test; p = 0.074). Similarly as to the other metals tested in this study, remediation of the contaminated soil

20

with distilled water still showed high concentration of Ni (54.49 ± 6.34 mg/L) which denoted that treatment with extracts were more effective than the control and eventually could be explained by the presence of possible sequestering agents in the extracted solutions. From Fig 7, a decrease in

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total Ni was obtained for both types of remediation treatments (i.e. using extracts from both compost and vermicomposts samples) which might be due to the possible slow release in Ni throughout the remediation process. The reasoning behind this reduction in Ni might be owing to the presence of the extracts (both types) which contributed in the absorption of HM in soil. It could be found from Fig 7 that the filtrated extract GS demonstrated higher level in Ni as compared to the

U

filtrated extract CS, which designated the effectual removal of Ni when using extracts from the

N

ground samples. However, when comparing the remediation treatments between extracts from

A

vermicomposts and composts (both coarse and ground), it could be highlighted that the Ni content

M

was much less in soil treated with vermicompost-extracts than in soil treated with compost-extracts. The larger decrease in total Ni in soil treated with vermicompost-extracts might be due to the fact

D

that vermicomposts are much finer particles than composts with strong HMs remediation potential

TE

and comparable intellectualizing was corroborated by many researchers (Atiyeh et al., 2000; Suthar

EP

2010; Soobhany et al., 2015b). Still, to some extent, this reasoning could elucidate on the characteristics of the vermicompost-extracts which might contain absorption cells wherein the Ni

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are concentrated in the filtrated extracts from the contaminated soil. From this study, it could be observed that extracts from ground vermicomposts were outstandingly efficient in Ni remediation

A

during remediation of metalliferous soil.

3.9 Remediation factor (RF) and reduction percentage in HMs

21

The attributes of the extracts used from the composts and vermicomposts samples, contamination and type of earthworms employed for processing the vermicomposts nearly correlates with RF value which is defined as the ratio of the metal concentration in filtrated extract to the

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concentrations of metals in remediated soil. RF was a predominant point affecting the concentration of HMs in metalliferous soil as reported by the quantity of metal concentration in the filtrated extracts. Table 2 represented the RFs values and reduction percentage (R) in HMs obtained for the remediation treatments using extracts from coarse samples. From this study, composts and vermicompost-extracts were proved to potentially remediate toxic HMs; hence they are essential to

U

RFs which revealed that remediation using extracts from coarse composts/vermicomposts can

N

productively remove HMs. Dissimilar values of RFs were found for the different HMs which might

A

be due by the certitude that different type of extracts from the samples exerted different remediation

M

capacity. The results somewhat differed with the findings as researched by Sung et al. (2011) who outlined low metal concentrations in treated silt loams which resulted in very low bioaccumulation

D

coefficients of metals during the combined mild soil washing and compost-assisted phytoextraction.

TE

Using RFs values to compose the treatment of contaminated soil using vermicompost-extracts from

EP

coarse samples, the HMs can be orderly arranged as follows: Ni (5.03 – 7.57) > Co (4.55 – 6.17) > Cu (3.51 – 4.10) > Cd (2.33 – 3.37) > Zn (1.97 – 3.26) > Cr (0.85 – 1.64). Whilst for the treatment

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with compost-extracts from coarse samples, the RFs values can be arranged in the order: Ni (4.70 – 5.32) > Co (3.92 – 4.17) > Cu (3.30 – 3.59) > Cd (1.90 – 2.09) > Zn (1.19 – 1.75) > Cr (0.80 –

A

0.89). The distinction in the percentage decrease of Cd, Cr, Cu, Co, Zn and Ni might be for the reason of the competition aspect between HMs and filtrated extracts’ absorption. The sequence for the average reduction percentage (R) in metal concentration (as analyzed before the remediation

22

treatment) for the 6 sets of experiments using both vermicomposts and composts extracts from coarse samples was Ni > Co > Cu > Cd > Cr > Zn.

The RFs values and R in HMs obtained for the remediation treatments using extracts from ground

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samples of composts and vermicomposts is shown in Table 3. Table 3 delineated that compostextracts and vermicompost-extracts were found to have the potential to mitigate toxic HMs, therefore they are largely indispensable to RFs which showed that remediation using extracts from ground composts/vermicomposts can efficiently remove HMs. It could be found that disparate values of RFs were attained for different HMs and this might be due by the certitude that these type

U

of extracts from the samples exerted different remediation capacity. Quite high efficiency of

N

remediation factors were obtained in this research which differed from the very low

A

bioaccumulation coefficients (< 1) obtained by Sung et al. (2011) during the integrated mild soil

M

washing and compost-aided phytoextraction in the remediation of HM silt loams. Also, it could be

D

figured out from this experimental remediation option that low metal concentrations in treated soil

TE

induced high RF values of metals in the extracting medium. To compile the treatment of contaminated soil by employing vermicompost-extracts from ground samples, the RFs values of the

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HMs can be orderly arranged as follows: Ni (8.06 – 10.98) > Co (8.28 – 10.61) > Cu (5.44 – 5.76) >

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Cd (2.82 – 4.41) > Zn (2.93 – 3.77) > Cr (1.37 – 2.11). On the other hand, the treatment with compost-extracts from ground samples, the RFs values can be arranged in the order: Ni (6.94 –

A

10.33) > Co (5.84 – 9.49) > Cu (4.44 – 5.51) > Cd (2.36 – 3.78) > Zn (2.46 – 3.31) > Cr (1.14 – 1.58). The dissimilarity in the percentage decline of Cd, Cr, Cu, Co, Zn and Ni might be mostly owing to the antagonism facet between HMs and filtrated extracts’ absorption. The arrangement of the average reduction percentage (R) in metal concentration (as determined initially) for all

23

remediation treatments using both compost-extracts and vermicompost-extracts from ground samples was Ni > Co > Cu > Cd > Cr > Zn.

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3.10 Mechanisms of beneficial effects in using extracts for remediation technique In this study, extracts of compost and vermicompost derived from MSW stimulated better remediation capacity of metalliferous soil in contrast with distilled water (control). Nevertheless, it is shown to have focal disparities among the effects of the use of extracts of vermicomposts and extracts of composts whereby the addition of vermicompost-extracts derived from MSW constantly

U

outperformed the treatments with all the three types of compost-extracts as a remediation technique.

N

Prior from the vermicomposting process, data analysis clearly suggested that the maturity of the

A

MSW vermicomposts was fully enhanced by the earthworms, thereby producing vermicompost-

M

extracts with strong HMs remediation capacity. Thus, to some extent, this reasoning could define the characteristics of the vermicompost-extracts which might possess absorption cells or more

D

sequestering agents than the compost-extracts that could eventually decrease the Cd, Cr, Cu, Co, Zn

TE

and Ni contents in the contaminated soil. Therefore, remediation treatments of metal-contaminated

EP

soil with extracts from V4, V5 and V6, irrespective from either being generated from coarse or ground samples, decreased Cd, Cr, Cu, Co, Zn, Ni compared to treatments with compost-extracts.

CC

Moreover, the basic differences between composting and vermicomposting processes which employ reasonably different microbial communities and the further beneficial physicochemical

A

characteristics like pH of the processed waste (Soobhany, 2018a) and its generating extracts might contribute to difference in the remediation capacity of the HMs. However, the complex structure of acids that are generated as a result of the augmentation in microbial communities in earthworm cast (Arancon et al., 2004; Soobhany et al., 2017b; Soobhany, 2018b) during the precedent

24

vermicomposting process of the MSW, could produce supposedly an extract with a complex structure of acids which might have reacted in combination for the improvement in remediating

3.11 Large-scale applicability of this remediation treatment

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HM-contaminated soil.

Since the metal-scavenging properties of metalliferous soil proved favorable by using extracts of composts and vermicomposts from MSW, this newly-devised study could effectively be applied to a real-world context for the treatment of metalliferous soil, that is, on a large-scale basis by

U

adopting the same remediation technique as described in this study. But, the arrangement of the

N

experimental remediation system should be designed and constructed in such a way that it could

A

treat a larger load of HM-contaminated soil for one intake i.e much more than 500 g. For the need

M

of a large-scale applicability of this treatment, bigger and sophisticated resource materials might be used, that is, big pumps instead of peristaltic pumps, plastic (Polyvinyl Chloride: PVC) pipes

D

instead of plastic tubing, large metallic columns instead of glass column. The resulting filtrate

TE

(filtrated extract) from the remediation system could be treated and further utilized by farmers in

EP

horticultural and agricultural systems to enhance plant growth and to decrease plant disease responses. For the large scale remediation process, the ex situ (excavation of contaminated soils for

CC

treatment) or in situ (on-site treatment) treatments could be adopted, which will eventually depend on the production costs and environmental conditions. For the on-site treatment, the metalliferous

A

soil could be remediated environmentally exactly in place where the contaminated soil is found (i.e without excavating it to some other location). As such, the set-up of the experimental remediation system should be constructed on the metal-contaminated site, which will depend on land availability at the most basic level. Thus, using compost/vermicompost-extracts for contaminated soil

25

remediation could be referred as a “tailored” technique which could specially make to treat metalliferous soil at specific sites.

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4. Conclusions This study revealed that compost-extracts and vermicompost-extracts from coarse samples of composts/vermicomposts exerted high remediation capacity which helped in subsiding metalliferous soils and in reducing contaminants from entering the environment. Vermicompostextracts from coarse samples exhibited higher metal scavenging properties in contrast to compost-

U

extracts derived from coarse samples. Different values of remediation factors (RFs) were calculated

N

for the various HMs and this revealed that extracts from the samples exerted different remediation

A

capacity. Data analyses advocated the viability and employability of utilizing extracts from coarse

M

and ground composts/vermicomposts as a suitable management strategy to reduce toxic HMs in contaminated soil (soil ecotoxicity) which might be useful in gaining a hygienic environment and risks

to

human

health.

Besides

D

fewer

to

reducing toxic

HMs,

the

utilization

of

TE

compost/vermicompost-extracts in the remediation of metalliferous soil could advance this goal by

EP

aiding plant growth. Yet, this novel-devised study necessitates further scientific investigation to corroborate the experiences of remediation techniques and to expand on this reporting study on the

CC

use of compost-extracts and vermicompost-extracts to treat HM-contaminated soil.

A

Acknowledgements The author expresses infinite thanks to all researchers whose scientific findings and suggestions were of fundamental supply and valuable in putting on reliability to this first-ever devised

26

experimental analysis. Special thanks to the anonymous reviewers for their instructive comments

A

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EP

TE

D

M

A

N

U

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and suggestions.

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metals via dietary intake of foodstuffs from the wastewater irrigated site of a dry tropical area of India. Food Chem. Toxicol. 48, 611–619. Singh, R.P., Singh, P., Araujo, A.S.F., Ibrahim, M.H., Sulaiman, O., 2011. Management of urban solid waste: Vermicomposting a sustainable option. Resour. Conserv. Recycl. 55, 719–729.

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Soobhany, N., Mohee, R., Garg, V.K., 2015a. Recovery of nutrient from municipal solid waste by composting and vermicomposting using earthworm Eudrilus eugeniae. J. Environ. Chem. Eng. 3, 2931–2942.

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Soobhany, N., Mohee, R., Garg, V.K., 2015b. Comparative assessment of heavy metals content

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during the composting and vermicomposting of Municipal Solid Waste employing Eudrilus

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eugeniae. Waste Manage. 39, 130–145.

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Soobhany, N., Mohee, R., Garg, V.K., 2017a. A comparative analysis of composts and vermicomposts derived from Municipal Solid Waste for the growth and yield of green bean

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Soobhany, N., Mohee, R., Garg, V.K., 2017b. Inactivation of bacterial pathogenic load in compost

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Sung, M., Lee, C.Y., Lee, S.Z., 2011. Combined mild soil washing and compost-assisted phytoremediation in treatment of silt loams contaminated with copper, nickel, and chromium. J.

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Hazard. Mater. 190, 744–754. Suthar, S., 2008. Metal remediation from partially composted distillery sludge using composting earthworm Eisenia fetida. J. Environ. Monit. 10, 1099–1106.

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Test Methods for the examination of compost and composting, 2001 [Online]. Available from:

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Wang, Q., Zhou, D., Cang, L., Li, L., Zhu, H., 2009. Indication of soil heavy metal pollution with earthworms and soil microbial biomass carbon in the vicinity of an abandoned copper mine in

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M

A

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Eastern Nanjing, China. Eur. J. Soil Biol. 45, 229–234.

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O/D 5.5 cm I/D 5 cm Metal Stand

Clamp

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Metalliferous soil

39 cm

Glass column

Plastic tubing

Peristaltic pump

Extracts from composts/ vermicomposts

Cotton

N

3.5 cm

U

Metallic filter

M

A

Filtrate

40 11.67

30 20 10

6.27

C1

A

14.36

14.80

13.40

14.12

11.90

12.30

12.88

12.69

13.99

3.48

4.71

3.82 5.88

3.38 5.30

4.78 5.49

4.06 4.19

14.70

6.28

18.18

18.18

18.18

18.18

18.18

18.18

C2

C3

V4

V5

V6

Control

13.47

18.18

CC

0

5.42

D

12.76

TE

50

EP

Cadmium content (mg/L)

Fig 1: Schematic diagram for the arrangement of the experimental remediation system 60

Contaminated soil Filtrated extract GS

Bioremediation treatments Treated soil CS Treated soil GS Treated soil control Filtrated water control

Fig 2: Cd content (mg/L) in contaminated and treated soil

35

Filtrated extract CS

50 11.62

12.93

10.22

10.65

11.47

12.30

12.96

13.31

10.56

12.95

SC RI PT

Chromium content (mg/L)

60

40 30

10.32

5.21

3.90

5.36

3.87

20

6.61

6.18

6.51

6.27

10

16.83

16.83

16.83

16.83

C1

C2

C3

V4

3.52 3.88

0

N

11.91

11.68

10.98

10.78

2.16 3.09

2.39 3.29

11.48

15 10 5 0

14.07

C1

CC

Contaminated soil Filtrated extract GS

16.83

V5

V6

Control

14.07

C2

Filtrated extract CS

11.92

11.88

10.88

11.29

10.94

10.96

4.78

2.59 3.19

2.09 2.78

2.15 3.13

2.19 3.11

9.29

14.07

14.07

14.07

14.07

14.07

C3

V4

V5

V6

Control

D

20

TE

25

16.83

11.99

M

30

12.76

5.64

A

35

EP

Copper content (mg/L)

40

4.53

U

Fig 3: Cr content (mg/L) in contaminated and treated soil 45

4.07

16.83

Bioremediation treatments Treated soil CS Treated soil GS Treated soil control Filtrated water control

Contaminated soil Filtrated extract GS

11.19

Bioremediation treatments Treated soil CS Treated soil GS Treated soil control Filtrated water control

A

Fig 4: Cu content (mg/L) in contaminated and treated soil

36

Filtrated extract CS

50

17.62

16.62

16.60

17.67

17.59

17.38

15.40

15.59

15.65

16.74

15.97

15.90

10.19

1.86 4.08

2.86 3.89

2.88 3.83

1.81 2.74

1.89 3.51

2.10 3.58

9.29

19.48

19.48

19.48

19.48

C1

C2

C3

V4

40 30 20 10

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Cobalt content (mg/L)

60

0

19.48

19.48

19.48

V5

V6

Control

Bioremediation treatments Contaminated soil Filtrated extract GS

Treated soil CS Treated soil control

Treated soil GS Filtrated water control

U

Fig 5: Co content (mg/L) in contaminated and treated soil

40

10.71

12.44

30

4.59

19.74

0

C2

EP

C1

Contaminated soil Filtrated extract GS

14.71

15.17

13.77

15.10

13.06

4.58

4.14

5.03

4.57

15.16

5.70 8.27

5.97

4.64

6.68

19.74

19.74

19.74

19.74

19.74

C3

V4

V5

V6

Control

D

19.74

20 10

11.47

TE

Zinc content (mg/L)

7.30

15.60

14.04

4.67

9.03

N

15.07

M

15.16

A

60 50

Filtrated extract CS

Bioremediation treatments Treated soil CS Treated soil GS Treated soil control Filtrated water control

A

CC

Fig 6: Zn content (mg/L) in contaminated and treated soil

37

Filtrated extract CS

45 40 12.14

12.45

11.98

12.55

12.17

12.55

11.47

11.31

11.30

11.62

11.43

12.03

7.47

1.58 2.24

1.26 2.40

1.73 2.41

1.16 2.09

1.54 2.28

1.16 1.68

6.24

13.71

13.71

13.71

13.71

13.71

13.71

13.71

C1

C2

C3

V4

V5

V6

Control

30 25 20 15

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Nickel content (mg/L)

35

10 5 0

Contaminated soil Filtrated extract GS

Bioremediation treatments Treated soil CS Treated soil GS Treated soil control Filtrated water control

A

CC

EP

TE

D

M

A

N

U

Fig 7: Ni content (mg/L) in contaminated and treated soil

38

Filtrated extract CS

Table 1: Original and metalliferous soil characterization

Cd (mg/L)

1.74 ± 0.23

18.18 ± 0.02

Cr (mg/L)

3.71 ± 0.77

16.83 ± 0.02

Cu (mg/L)

2.12 ± 0.06

14.07 ± 0.01

Co (mg/L)

0.00 ± 0.00

19.48 ± 0.20

Zn (mg/L)

6.23 ± 1.10

Ni (mg/L)

2.69 ± 0.02

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Metalliferous soila

19.74 ± 0.22 13.71 ± 0.68

Values designate mean ± standard deviation based on 3 samples.

A

CC

EP

TE

D

M

A

N

U

a

Original brown earth soila

39

Table 2: Remediation factor (RF) and reduction (%) in HMs using extracts from coarse samples Cd Cr Cu Co Zn

Ni

C1 (extract from food waste compost) RF 1.90 ± 0.16 0.81 ± 1.14

3.59 ± 0.54

3.92 ± 1.17

1.19 ± 0.16

5.32 ± 1.62

Reduction (%)

78.05 ± 2.57

79.08 ± 4.99

54.25 ± 3.42

83.64 ± 4.19

65.52 ± 1.88

60.73 ± 2.23

C2 (extract from paper waste compost) 1.91 ± 0.30

0.89 ± 1.26

3.30 ± 0.44

4.01 ± 0.25

1.75 ± 0.52

4.84 ± 1.27

Reduction (%)

65.44 ± 3.61

63.30 ± 1.80

76.61 ± 2.40

80.03 ± 0.99

62.99 ± 7.00

82.47 ± 3.81

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RF

C3 (extract from yard waste compost) RF

2.09 ± 0.01

0.80 ± 1.13

3.45 ± 0.55

4.17 ± 0.89

1.39 ± 0.09

4.70 ± 0.16

Reduction (%)

67.64 ± 0.13

61.34 ± 0.24

77.35 ± 2.80

80.36 ± 3.40

58.08 ± 1.55

82.44 ± 0.49

V4 (extract from food waste vermicompost) RF

2.44 ± 0.24

0.85 ± 1.20

4.10 ± 0.64

6.17 ± 1.00

2.31 ± 0.07

5.65 ± 1.03

Reduction (%)

70.84 ± 2.02

62.76 ± 0.20

80.23 ± 2.48

85.91 ± 1.97

69.76 ± 0.67

84.78 ± 2.36

4.64 ± 1.00

3.26 ± 0.01

5.03 ± 0.27

81.99 ± 3.18

76.51 ± 0.08

83.38 ± 0.74

4.55 ± 1.15

1.97 ± 0.26

7.57 ± 2.69

81.60 ± 3.82

66.14 ± 2.96

87.72 ± 3.86

RF

2.33 ± 0.40

1.64 ± 2.31

3.51 ± 0.20

Reduction (%)

69.80 ± 3.64

76.94 ± 0.61

77.79 ± 1.01

N

V6 (extract from yard waste vermicompost) 3.37 ± 0.50

1.04 ± 1.47

3.53 ± 0.13

Reduction (%)

76.96 ± 2.62

66.47 ± 2.07

77.91 ± 0.64

M

A

RF

Control (distilled water)

U

V5 (extract from paper waste vermicompost)

0.24 ± 0.06

0.17 ± 0.24

0.52 ± 0.08

1.10 ± 0.11

0.30 ± 0.03

1.22 ± 0.31

Reduction (%)

19.15 ± 3.89

24.18 ± 4.72

33.97 ± 3.31

52.31 ± 2.39

23.20 ± 1.89

54.49 ± 6.34

Overall estimated range in reduction from compost-extracts Reduction range (%) 65.44 – 67.64 60.73 – 63.30 76.61 – 78.05

79.08 – 80.36

54.25 – 62.99

82.44 – 83.64

Overall estimated range in reduction from vermicompost-extracts Reduction range (%) 69.80 – 76.96 62.76 – 76.94 77.79 – 80.23

81.60 – 85.91

66.14 – 76.51

83.38 – 87.72

EP

TE

D

RF

A

CC

Values designate mean ± standard deviation based on values over 9 samples (3 samples from each triplicate experiment)

40

Table 3: Remediation factor (RF) and reduction (%) in HMs using extracts from ground samples Cd Cr Cu Co Zn

Ni

C1 (extract from food waste compost) RF

2.36 ± 0.24

1.21 ± 1.70

5.51 ± 0.00

9.49 ± 0.67

3.31 ± 0.12

7.92 ± 1.95

Reduction (%)

70.19 ± 2.15

69.02 ± 3.33

84.64 ± 0.01

90.45 ± 0.61

76.77 ± 0.67

88.51 ± 2.52

3.22 ± 0.13

10.33 ± 3.07

C2 (extract from paper waste compost) 2.86 ± 0.17

1.58 ± 2.23

4.89 ± 0.08

5.91 ± 1.14

Reduction (%)

74.09 ± 1.13

76.85 ± 1.64

83.02 ± 0.24

85.32 ± 2.42

76.32 ± 0.73

90.83 ± 2.48

4.44 ± 0.35 81.57 ± 1.18

5.84 ± 1.01 85.23 ± 2.18

2.46 ± 0.09 71.12 ± 0.72

6.94 ± 0.35 87.40 ± 0.55

SC RI PT

RF

C3 (extract from yard waste compost) RF Reduction (%)

3.78 ± 0.38 79.01 ± 1.66

1.14 ± 1.62 68.15 ± 2.92

V4 (extract from food waste vermicompost) RF

4.41 ± 0.55

1.54 ± 2.18

5.76 ± 0.33

10.61 ± 4.48

3.77 ± 0.00

10.77 ± 0.08

Reduction (%)

81.42 ± 1.87

76.99 ± 2.80

85.18 ± 0.73

90.69 ± 3.60

79.02 ± 0.00

91.50 ± 0.06

9.35 ± 1.07

2.93 ± 0.00

8.06 ± 1.60

90.29 ± 1.01

74.53 ± 0.03

88.78 ± 1.98

2.82 ± 0.30

2.11 ± 2.98

5.54 ± 0.13

Reduction (%)

73.73 ± 2.10

79.06 ± 3.08

84.70 ± 0.30

N

RF

U

V5 (extract from paper waste vermicompost)

V6 (extract from yard waste vermicompost) 3.48 ± 0.19

1.37 ± 1.93

5.44 ± 0.21

8.28 ± 0.41

3.32 ± 0.02

10.98 ± 2.13

Reduction (%)

77.67 ± 0.95

73.09 ± 0.30

84.45 ± 0.52

76.84 ± 0.09

91.52 ± 1.51

89.21 ± 0.48

0.17 ± 0.24

0.52 ± 0.08

1.10 ± 0.11

0.30 ± 0.03

1.22 ± 0.31

24.18 ± 4.72

33.97 ± 3.31

52.31 ± 2.39

23.20 ± 1.89

54.49 ± 6.34

Overall estimated range in reduction from compost-extracts Reduction range (%) 70.19 – 79.01 68.15 – 76.85 81.57 – 84.64

85.23 – 90.45

71.12 – 76.77

87.40 – 90.83

Overall estimated range in reduction from vermicompost-extracts Reduction range (%) 73.73 – 81.42 73.09 – 79.06 84.45 – 85.18

89.21 - 90.69

74.53 – 79.02

88.78 - 91.52

Control (distilled water) 0.24 ± 0.06 RF 19.15 ± 3.89

EP

TE

D

Reduction (%)

M

A

RF

A

CC

Values designate mean ± standard deviation based on values over 9 samples (3 samples from each triplicate experiment)

41