Using hybrid packing materials in biofiltration systems takes advantage of both the inorganic and organic properties offered by the medium including structural stability and a source of available nutrients, respectively. In this study, hybrid mixtures of compost with either lava rock or biochar in four different mixture ratios were compared against 100% compost in a methane biofilter with active aeration at two ports along the height of the biofilter. Biochar outperformed lava rock as a packing material by providing the added benefit of participating in sorption reactions with CH4. This study provides evidence that a 7:1 volumetric mixture of biochar and compost can successfully remove up to 877 g CH4/m3·d with empty-bed residence times of 82.8 min. Low-affinity methanotrophs were responsible for the CH4 removal in these systems (KM(app) ranging from 5.7 to 42.7 µM CH4). Sequencing of 16S rRNA gene amplicons indicated that Gammaproteobacteria methanotrophs, especially members of the genus Methylobacter, were responsible for most of the CH4 removal. However, as the compost medium was replaced with more inert medium, there was a decline in CH4 removal efficiency coinciding with an increased dominance of Alphaproteobacteria methanotrophs like Methylocystis and Methylocella. As a biologically-active material, compost served as the sole source of nutrients and inoculum for the biofilters which greatly simplified the operation of the system. Higher elimination capacities may be possible with higher compost content such as a 1:1 ratio of either biochar or lava rock, while maintaining the empty-bed residence time at 82.8 min.

The environment is one of the main reservoirs of antibiotic resistance genes (ARGs) but multidrug resistant (MDR) environmental isolates are barely characterised. As suggested by the name, Pedobacter species have been predominantly isolated from soils, but are also recovered from water (including drinking water), chilled food, fish, compost, sludge, glaciers and other extreme environments. The susceptibility phenotype of Pedobacter lusitanus NL19 (isolated from a deactivated uranium mine), its closely related species and the genus type strain were investigated. All strains are MDR bacteria, resistant to β-lactams, colistin, aminoglycosides and ciprofloxacin. Therefore, Pedobacter spp. are likely intrinsically resistant to β-lactams (including ertapenem) and to other three classes of antibiotics. 6%–8% of their total protein-encoding genes encode a diverse collection of putative ARGs, including β-lactamases. These enzymes are highly abundant in all the other Pedobacter strains with sequenced genomes, especially class C, class B3 and class A. LUS-1 and PLN-1 were further characterised in E. coli. LUS-1 is a class A β-lactamase and it conferred an increase in the MIC of cefotaxime, albeit very low. PLN-1 is a class B3 β-lactamase with carbapenemase activity, conferring resistance to ertapenem and a 66x and 16x increase in the MIC of imipenem and meropenem, respectively. PLN-1 also hydrolyses ampicillin, 1st and 3rd generation cephalosporins, and at a lower extent cephamycins and 4th generation cephalosporins. Therefore, Pedobacter spp. encode a large and diverse arsenal of resistance mechanisms that make them environmental superbugs.

Trace elements (TEs) availability, biochemical activity and functional gene diversity was studied in a Cu-contaminated soil, revegetated for six years with a mixed stand of willow, black poplar, and false indigo-bush, and amended or not with compost plus dolomitic limestone (OMDL). The OMDL amendment significantly reduced Cu and As availability and soil toxicity, and increased the biochemical activity and microbial functional diversity assessed with the GEOCHIP technique, as compared to the unamended soil (Unt). The OMDL soil showed significantly higher abundance of 25 functional genes involved in decomposition organic compounds, and 11, 3 and 11 functional genes involved in the N, P and S biogeochemical cycles. Functional gene abundance was positively correlated with nutrient contents but negatively correlated with Cu availability and soil toxicity. The abundance of microbial functional genes encoding for resistance to various TEs also increased, possibly due to the microbial proliferation and lower Cu exposure in the presence of high total soil Cu concentration. Genes encoding for antibiotic resistance due to the co-occurrence of TEs and antibiotic resistant genes on genetic mobile elements. Overall, phytomanagement confirmed its potential to restore the biological fertility and diversity of a severely Cu-contaminated soil, but the increase of TEs and antibiotic resistant gene abundances deserve attention in future studies.

Veterinary antibiotics like sulfonamides are frequently detected in arable lands and they can potentially contaminate food crops. It is thus of great importance to identify strategies to reduce food crops’ uptake of antibiotics. For the first time, using a pot culture experiment, sulfathiazole (STZ) uptake by lettuce (Lactuca sativa L.) grown in antibiotic-contaminated soils (10 and 100 mg STZ kg⁻¹ soil) and treated with (in)organic amendments, namely chemical fertilizer (NPK), compost, and hairy vetch, was investigated. Subsequent enhanced plant growth was witnessed when using hairy vetch treatment. The amount of antibiotic uptake was significantly reduced to 5 and 33% with hairy vetch application compared to compost or NPK application at 10 and 100 mg kg⁻¹ STZ, respectively. The total amounts of accumulated STZ in plant parts increased as the levels of STZ contaminated in soils were increased. STZ was much more abundant in the roots than the leaves. Within 30 days, the extractable STZ in the treated soils—especially with hairy vetch—diminished considerably to concentrations that are frequently detected in arable soils. We conclude that utilization of green manure (cover crop—hairy vetch) is a viable strategy for safer crop production in antibiotic-contaminated soils.

Polychlorinated biphenyls (PCBs) are ubiquitous and persistent organic pollutants generated exclusively from human sources and found in the environment as several congeners (e.g. Apirolio, produced in Italy and used for electrical transformers). To evaluate the ability of the natural microbial community of historically PCB-contaminated soil to transform or degrade PCBs after fresh contamination through the addition of Apirolio, a microcosm experiment was conducted in a greenhouse for approximately 8 months. Compost and Medicago sativa (alfalfa) were additionally used in the microcosms to stimulate microbial PCB degradation. Chemical analyses were performed to evaluate PCB concentrations in the soil and plant tissue. Changes in the microbial community under the different experimental conditions were evaluated in terms of total abundance, viability, diversity, and activity. Interestingly, the addition of Apirolio did not negatively affect the microbial community but did stimulate the degradation of the freshly added PCBs. The plant and compost co-presence did not substantially increase PCB degradation, but it increased the microbial abundance and activity and the occurrence of α-Proteobacteria and fungi.

Lead is one of the most potentially toxic metals present in soils. In situ Pb immobilization techniques reducing its bioavailability to soil organisms are of increasing interest. The present work compares the effectiveness of nanoscale zero-valent iron (nZVI), compost, and phosphate for Pb immobilization in an acidic, artificially polluted soil after different contact times (15 and 45 days). The availability and mobility of Pb were evaluated by the Tessier extraction procedure and the toxicity characteristics leaching procedure (TCLP). The impact on soil properties and soil phytotoxicity was also evaluated. The phosphate was the most effective treatment in all sampling times, reaching Pb reductions in more available fractions of 72%, followed by compost (40%) and nZVI (32%). Comparing the two sampling times, a significant reduction of available Pb in phosphate-treated soils was observed at a longer contact time. Soil properties changed depending on the treatment. In general, the application of compost improved the soil fertility, soils treated with nZVI showed an increase of pH and available sodium and iron concentration, and the treatment with phosphate increased available phosphorus concentration in soil, but was less than that obtained by the compost treatment. Regarding the soil phytotoxicity, Vicia sativa showed moderate phytotoxicity to untreated Pb-polluted soils, and the different treatments decreased it. In conclusion, at the experimental conditions, the use of phosphate resulted as more effective than compost and nZVI for reducing Pb availability in an acidic soil. Longer-term assays are necessary to evaluate the stability of the process.

Biochar as a soil amendment in street tree pits can be used to increase the soil’s ability to retain contaminants found in urban runoff. The increased retention can potentially decrease peak concentrations of soluble trace metals and de-icing salts in the soil solution, thereby decreasing the amounts taken up by tree roots or percolated out of the tree pits into the ground water. A leaching test measured the retention of trace metals (Cd, Zn, Cu, and Pb) and deicing salts (Na) by different kinds of biochar. The biochar was produced from hardwood (North American ash tree, Fraxinus americana) under different pyrolysis conditions, with three temperatures (350, 465 and 550 °C) and two residence times (10 and 30 min). Biochar pyrolyzed at 550 °C for 30 min significantly reduced the soluble concentrations of Zn, Cu, and Pb in the column leachate, most likely due to the its higher pH, surface area, and ash content. The pH of each treatment group was measured while the increase in ash content and surface area was inferred according to relevant literature. This biochar was then combined with soil and compost at rates ranging from 0 to 7.5% by dry weight to determine the proportion that optimally sorbed the contaminants. An application rate of 7.5% biochar by dry weight increased the soil mixture’s sorption capacity for Cd and Na while maintaining similar sorption of Cu, Zn, and Pb. The role of organic matter, such as that in compost, was especially important for the sorption of Zn and Cu. Hardwood biochar can thus improve the health of street trees and groundwater quality by sequestering trace metals and de-icing salts. Biochar can also be a useful tool to remediate contaminated soil, especially in urban environments.

Mining activities often cause important impacts on soil and water quality. The main objective of this study was to evaluate the effect of amendments (compost and technosol made from waste) on metal concentrations in a mine soil planted with Brassica juncea. A greenhouse experiment with cylinder pots was carried out during 11 months. The mine soil was collected from the settling pond of the depleted copper mine of Touro (Galicia, Northwest Spain). A series of characteristics were analysed including soil pseudototal metal concentrations, soil CaCl₂-extractable (phytoavailable) metal concentrations and metal concentrations in soil pore water. The results showed that at depth 0–15 cm SCP (mine soil + compost, grown with B. juncea) had a significantly lower CaCl₂-extractable Cu, Pb, Ni and Zn concentration than STP (mine soil + technosol, grown with B. juncea) over the time (P < 0.05). At depths 15, 30 and 45 cm, STP and SCP had lower Cu pore water concentration than S over the time. The highest translocation factor (TF) values for all metals (Cu, Pb, Ni and Zn) were observed at time 1 (3 months) in the settling pond soils treated with technosol and B. juncea L. The conclusions of this experiment revealed that SCP compared to STP caused a higher reduction on Cu, Pb, Ni and Zn phytoavailable concentrations in the first depths.

Municipal sludge compost (MSC) is commonly used as fertilizer or an amendment in barren soils. However, MSC-borne Cd is of great concern in food safety because of its toxicity. Loess subsoil (LS) is barren and lacks nutrients, but it has a strong ability to absorb and stabilize heavy metals. Hence, LS may be amended with MSC and may reduce the bioavailability of Cd. To simulate the dose effect of the accumulated MSC-borne Cd in amended LS, pot experiments were conducted to study the bioavailability of Cd and other mineral nutrition elements in broad bean (Vicia faba L.) under Cd stress. Plant height and dry biomass remarkably increased as the physicochemical properties of LS were significantly improved; however, they were not significantly influenced by the added Cd. The Cd in the plants grown in MSC amended-LS (P2) mainly accumulated in roots (32.12 mg kg⁻¹) and then in stems and leaves (6.00 mg kg⁻¹). Less Cd (0.74 mg kg⁻¹) accumulated in the edible parts, where the Cd concentration was 53% lower than that in the edible parts of plants grown in LS (P1). The decreased Cd concentrations in the P2 beans may be due to the biomass dilution effect. Notably, the Cd concentrations in the beans exceeded the national safety limit value (0.2 mg kg⁻¹) when the Cd treatment levels exceeded 2 mg kg⁻¹ in LS and 6 mg kg⁻¹ in amended LS. The MgCl₂ extraction procedures can be used to assess Cd bioavailability in amended soil-plant systems. The potential antagonism of Zn and Cu against Cd toxicity in the soil-plant system may explain why this plant can tolerate higher Cd concentrations after MSC application.

Methane biofilter (MBF) technology, a cost effective method to control atmospheric emission of CH₄, is usually developed as a passively aerated system to control low-volume point-source emissions such as those from landfills with gas collection systems. Actively aerated high-rate methane biofilter (HMBF) systems are designed to overcome the shortcomings of passively aerated systems by ensuring the entire filter bed is utilized for CH₄ oxidation. Flow-through column experiments point to the fact that CH₄ oxidation rates of actively aerated systems could be several times higher than that of passively aerated systems. However, reports of the performance of field HMBF systems are not available in literature. Furthermore, there are no studies that demonstrate the possibility of using laboratory data in the design and operation of field systems. The current study was conducted to fill this research gap and involve a comparative study of the performance of laboratory columns to field performance of a HMBF system using solution gas produced at an oil battery site as the CH₄ source. The actively aerated column studies confirmed past results with high CH₄ oxidation rates; one column received air at two injection points and achieved an oxidation rate of 1417 g/m³/d, which is the highest reported value to date for compost-filled columns. Subsequent studies at a specially designed field HMBF filled with compost showed a higher oxidation rate of 1919 g/m³/d, indicating the possibility of exceeding the high CH₄ oxidation rates observed in the laboratory. The achievement of observed field oxidation rates being higher than those in the laboratory is attributed to the capability of maintaining higher temperatures in field HMBFs. Furthermore, results show that field HMBFs could operate at lower than stoichiometric air to CH₄ ratios, and lower retention times than that of laboratory columns. Results indicated that laboratory columns may not truly represent field behavior, and said results could only be used in the preliminary design of field HMBFs.