Magnetic susceptibility variation of MSW compost-amended soils: in-situ method for monitoring heavy metal contamination

Using magnetic susceptibility to evaluate pollution status of the sediment for a typical reservoir in northwestern China

Intensive anthropogenic activities may add to pollution risks to lakes and rivers, which can be revealed by the magnetic characteristics of sediments. The present study aims to assess the pollution status of the sediment of a typical reservoir in northwestern China by application of magnetic susceptibility. The values of magnetic susceptibility exhibited significant positive correlations with trace metals (Co, Cu, Mn, Ni, and V) and natural radionuclides (²³²Th and ⁴⁰K). Multivariate statistical analysis indicated common sources and similar deposition characteristics of magnetic particles and trace metals. It was conformed that magnetic susceptibility could be used as an indicator to identify industrial sources of trace metals, but was not suitable to indicate the traffic or natural sources. Linear regression equations between the low-frequency magnetic susceptibility and the integrated pollution index as well as annual effective dose rate indicated a potential for using magnetic susceptibility in semi-quantitative assessment of trace metal pollution and radiological hazard in sediments. A three-step procedure is proposed for the use of magnetic susceptibility in pollution monitoring, which provides a fast and effective method for estimating the pollution extent and tracing the major sources of trace metals in the sediment of lakes and rivers.

Distribution of 16 EPA-priority polycyclic aromatic hydrocarbons (PAHs) in sludges collected from nine Tunisian wastewater treatment plants

Polycyclic aromatic hydrocarbons (PAHs) are organic compounds which may be present as contaminants in wastewater sewage sludge. Due to their toxicity and persistence in the solid phase, information should be gathered relating to their presence in sewage sludge in order to determine their contamination risks after land application. In this study, sewage sludge samples from nine Tunisian wastewater treatment plants (WWTPs) were characterized for the total content in 16 EPA-priority PAHs using an optimized extraction protocol. These WWTPs differ in the type of applied treatment and the wastewater source. Through this first assessment of PAHs in Tunisian sludges, their total concentration varied from 96 to the highest level of 7718 ng g(-1). Regardless of the source of wastewater, the highest PAH content was found in sludges deriving from untreated wastewater (natural lagooning). In addition, some correlation was found between the distribution patterns of each PAH, the type of applied treatment on one hand and the wastewater source on other hand.

Scanning electron microscopy and magnetic characterization of iron oxides in solid waste landfill leachate

Leachate sludge samples were taken from two municipal solid waste sites of Jelekong and Sarimukti in Bandung, Indonesia. Their magnetic mineralogy and granulometry were analyzed to discriminate the sources of magnetic minerals using X-ray diffraction (XRD), scanning electron microscopy equipped with energy-dispersive X-ray spectroscopy (SEM-EDX) and rock magnetism. SEM-EDX analyses infer that the main magnetic minerals in the leachate sludge are iron oxides. In terms of their morphology, the grains from Jelekong are mostly octahedral and angular, which are similar to the general shapes of magnetic grains from the local soils. The grains from Sarimukti, on the other hand, are dominated by imperfect spherule shapes suggesting the product of combustion processes. Hysteresis parameters verify that the predominant magnetic mineral in leachate sludge is low coercivity ferrimagnetic mineral such as magnetite (Fe(3)O(4)). Furthermore, comparisons of rock magnetic parameters show that the magnetic minerals of soil samples from Jelekong have higher degree of magnetic pedogenesis indicating higher proportion of superparamagnetic/ultrafine particles than those of soil samples from Sarimukti. The plot of susceptibilities ratio versus coercive force has a great potential to be used as a discriminating tool for determining the source of magnetic minerals.

Study of the effects of urban organic residues on the distribution of culturable actinomycetes in a Tunisian agricultural soil

The main objective of this investigation was to identify a collection of actinomycetes isolates and to study the influence of amendment [municipal solid waste compost (MSWC) and farmyard manure (FM)] on their distribution in agricultural soil. For this purpose, a phenotypic and molecular characterization of 226 isolates collected from soil (with and without amendment) and 55 isolates from MSWC and FM was developed. The phenotypic study showed that the majority of strains isolated belong to the genus Streptomyces. By using the 16S rDNA polymerase chain reaction-restriction fragment length polymorphism method (restriction digest using six enzymes AluI, HhaI, MspI, TaqI, RsaI and HaeIII), two clusters were found: Streptomyces, dominant genus and Amycolatopsis, followed by Nocardioides. This result agreed with phylogeny revealed by 16S rDNA sequencing. The number of these actinomycetes in soil increased with FM or MSWC application. The studied soil is a potential source for isolation of actinomycetes, especially Streptomyces, and the application of organic amendment to the soil appeared to have an impact on the diversity of actinomycetes. Amendment of the soil with MSWC and FM significantly increased the number of actinomycetes due to the contribution of bacteria originally contained in biowastes and/or by stimulation of the endogenous soil micro-organisms.

Magnetic susceptibility as an indicator of heavy metal contamination in compost

One of the main restrictions to the agronomic use of compost is the excess of heavy metals, which are often present due to inadequate separation of biodegradable fractions from non-degradable or inert materials. Magnetic susceptibility (MS) measurements are a simple technique that has been reported as a useful tool for assessing anthropogenic pollution, especially heavy metal pollution on soil and sediment samples. The close relationship of MS with heavy metal contamination has been proved by combined analyses of chemical and magnetic data. In this study, the MS and total heavy metal concentrations of eight composts from different origins were determined; all composts were passed under a magnet to remove the magnetic material, and total heavy metals were determined again. In our work, high correlations were found between magnetic susceptibility and total Cd, Zn, Pb, Cr and Ni, thus confirming the applicability of MS measurement as a proxy for heavy metal contamination in compost quality assessments. The application of a magnet over the composts reduced the MS as well as the heavy metal content, the reduction of Fe and MS being the most significantly correlated. Thus, the inclusion of an additional magnetic separation step in the post-process compost finishing could be envisaged.

Microbiological parameters and maturity degree during composting of Posidonia oceanica residues mixed with vegetable wastes in semi-arid pedo-climatic condition

The aim of this study was to characterize the biological stability and maturity degree of compost during a controlled pile-composting trial of mixed vegetable residues (VR) collected from markets of Tunis City with residues of Posidonia oceanica (PoR), collected from Tunis beaches. The accumulation in beaches (as well as their removal) constitutes a serious environmental problem in all Mediterranean countries particularly in Tunisia. Aerobic-thermophilic composting is the most reasonable way to profit highly-valuable content of organic matter in these wastes for agricultural purposes. The physical, chemical, and biological parameters were monitored during composting over 150 d. The most appropriate parameters were selected to establish the maturity degree. The main result of this research was the deduction of the following maturity criterion: (a) C/N ratio < 15; (b) NH4+-N < 400 mg/kg; (c) CO2-C < 2000 mg CO2-C/kg; (d) dehydrogenase activity < 1 mg TPF/g dry matter; (e) germination index (GI) > 80%. These five parameters, considered jointly are indicative of a high maturity degree and thus of a high-quality organic amendment which employed in a rational way, may improve soil fertility and soil quality. The mature compost was relatively rich in N (13.0 g/kg), P (4.74 g/kg) and MgO (15.80 g/kg). Thus composting definitively constitutes the most optimal option to exploit these wastes.