The sequestration of heavy metals (HMs) in sewage sludge (SS) caused by slow microwave pyrolysis (MP) treatment was studied.The MP was carried out using a full-scale unit working at 300°C and pressure 800 hPa with 3 kW magnetron at 2.45 GHz.To determine the efficiency of sequestration, a new methodology was used.The SS from three waste water treatment plants (WWTPs) differing in capacities, inflow and drying procedure were used to study the effect of pelletization and additives addition.The total HMs content in sludges and produced biochars was determined by extraction using Aqua Regia, while soluble fraction (bioavailable, potentially harmful fraction) was determined by extraction using deionized water.The analyses revealed significantly low concentration of biologically available HMs after MP process in biochars prepared by pelletization and with additives.Therefore, the slow MP showed its potential to immobilize most of HMs in biochar structure thereby preventing their fixation, solubilization, and bioavailability for plants and microorganisms and may enable its use in agriculture.We conclude that slow MP represents an eco-friendly way of SS disposal, which belongs among the important strategies of circular economy.
Abstract The overuse of synthetic fertilizers has been associated with negative environmental consequences. The use of biochar in this regard has been recommended as a win–win strategy. However, our understanding on the comparative influences of biochar prepared from various feedstocks mixed with other bulking agents on soil health and crop performance remained limited. Therefore, in the present study, three types of biochar produced from sewage sludge, food, and agricultural waste were analyzed and compared for their effects on soil enzymes (dehydrogenase, DHA; β-glucosidase, GLU; phosphatase, PHOS; urease, URE; N-acetyl-β-D-glucosaminidase, NAG; and arylsulphatase, ARS), soil basal, as well as substrate-induced respirations and plant growth and physiology characters. The results revealed that food waste-derived biochar co-pyrolyzed with zeolite and/or sawdust was more effective in improving soil physicochemical properties and carbon and phosphorous cycling enzyme (DHA, GLU, and PHOS) activities in addition to soil basal respiration. While the influence of wastewater sewage sludge-derived biochar was more pronounced on urease, N-acetyl-β-D-glucosaminidase, and arylsulphatase enzymes as well as plant biomass accumulation and physiological attributes. Moreover, agricultural waste-derived biochar was found to be effective in enhancing substrate-induced respirations. This study thus concluded that biochar derived from various feedstocks has the tendency to improve soil health and plant growth attributes which further depend on the type of modification prior to pyrolysis.
Abstract The rising prerequisite for developing novel green remediation methods for trace‐element‐contaminated lands is allied to the necessity to really mend the soil environs. The effectiveness of zeolite‐aided phytostabilization (AP) of soil contaminated with trace elements (TEs), from a scrap yard, using Lolium perenne as the plant for testing, was determined and discussed. The variability and activity of the rhizospheric bacterial community were also examined. The initial soil used in the AP experiment was characterized by especially high total contents of Zn, Pb, Cu and Cd. The TE total contents in roots and aboveground parts of L. perenne as well as in the phytostabilized soil materials were analyzed with flame atomic absorption spectrometry. The study revealed that the addition of natural zeolite into TE‐contaminated soil increased the relative plant biomass as well as the soil pH value as compared to the phytostabilized non‐amended series, whereas the total contents (with respect to an absolute value) of Zn, Pb, Cu and Cd were generally higher in roots than in the aboveground parts of L. perenne . In particular, the incorporation of zeolite to the soil contributed most significantly to the considerable relative decrease in the total contents of Cu, Pb, Cd and Zn in the soil, as well as the content of bioavailable and leachable speciations of Cd, Cu, Zn and Pb extracted from the soil using CaCl 2 solution as compared to the non‐amended series. In the phytostabilized zeolite‐amended soil, the overall bacterial diversity decreased but the presence of zeolite favoured the growth of microorganisms belonging to Gammaproteobacteria , Planctomycetia , and Thermomicrobia , in particular, the genera Mycobacterium , Williamsia , and Prochlorococcus .
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