The interaction between different volatile organic compounds (VOCs) is a critical issue associated with bioremediation of co-contaminated sites. Contradictory results have been reported on the effects of co-existence of VOCs on biodegradation of each VOC. These contradictions are thought to be caused by inter-study variability in microbial diversity. To examine the effects of co-existing VOCs on biodegradation of each VOC, a series of biodegradation tests were carried out with a microcosm capable of degrading all three VOCs: dichloromethane (DCM), benzene, and toluene. We added different combinations of the VOCs to the microcosm while monitoring VOC concentration and microbial community diversity. Degradation of DCM and benzene was minimally influenced by co-existence of other VOCs; however, degradation of toluene was dramatically enhanced by the co-existence of benzene. Propioniferax was identified in cultures exposed to benzene alone and cultures simultaneously exposed to benzene, toluene, and DCM. Propioniferax was dominant, but prior to this study, it was not known to degrade benzene, toluene, and DCM. In the cultures exposed to only toluene, Rhodanobacter, Mycobacterium, Bradyrhizobium, and Intrasporangium increased during the biodegradation. The former three bacteria increased more rapidly when benzene and DCM were also included. These results suggest that co-existence of benzene and DCM can enhance the activity of Rhodanobacter, Mycobacterium, and Bradyrhizobium and consequently accelerate the degradation of toluene.

Biochars from two different feedstocks (peanut shell-PB; wheat straw-WB) were used in this study to understand the sorption mechanisms of atrazine (ATR), 17α-ethinyl estradiol (EE2), and phenanthrene (PHEN) to help minimize the bioavailability of the organic pollutants in the environment. Sorption isotherms of ATR, EE2, and PHEN by WB and PB biochars followed the Freundlich model where the sorption parameter (n) shows the trend: ATR > EE2 and PHEN, while the sorption capacity (log K ₒc) increases from ATR < EE2 < PHEN and indicate that the most hydrophobic and planar organic pollutant (PHEN) is the most easily adsorbed organic compound on PB and WB. The higher H/C and (O + N)/C ratios of WB (0.099 and 0.525, respectively) suggest its stronger aliphaticity and polarity than PB (0.078 and 0.352, respectively) that induced stronger sorption affinity for ATR and PHEN. Higher specific surface area (m² g⁻¹) of PB (19.7) may be responsible for the higher sorption capacity for EE2 than WB (8.8) because it can accommodate the large molecule of EE2. Results from this study may be helpful to predict the bioavailability of organic pollutants when soils contaminated with pollutants are remediated with biochars produced from wheat straw and peanut shells.

Hexavalent chromium (VI) in wastewater is a great risk to human health and to the quality of water sources. However, adapted microorganisms can rapidly reduce this chemical species to the trivalent form (III) and make it less active. Our objective was to evaluate the capacity of bacterial isolates for Cr (VI) reduction in nutrient medium and in effluent and to compare indigenous microorganisms with those isolated from wastewater contaminated with Cr (VI). Cr (VI) reduction was also tested with different sources of carbon, nitrogen, and phosphorus at two temperatures (10 and 30 °C). Initially, the resistant microorganisms were isolated from the solution with 100 mg L⁻¹ of Cr (VI). Subsequently, we evaluated the effectiveness of the isolates in reducing Cr (VI) I in culture medium under temperature-controlled conditions, with concentrations of 10 and 100 mg L⁻¹ of Cr (VI). In the subsequent step, we studied the isolates and autochthonous microorganism efficiency to reduce Cr (VI) present in contaminated effluent, with the addition of nutrients and at different temperatures (10 and 30 °C). In the culture medium containing 10 mg L⁻¹ of Cr (VI), isolates were reduced by 100 % in 48 h. When tested against 100 mg L⁻¹ of Cr (VI), the decrease was 70 and 40 % at 120 h of incubation of the isolates 6 and 11, respectively. In the effluent, there was no significant reduction without nutritional biostimulation. When carbon and phosphorus were applied, isolates 6, 11, and indigenous microorganisms reduced 100 % of the Cr (VI) in 72 h. Nitrogen was not limited in terms of effluent characteristics. At 10 °C incubation temperature, Cr (VI) was completely reduced but slower compared to incubation at 30 °C. The results demonstrate that nutritional biostimulation aided by bioremediation is an excellent tool for reducing hexavalent chromium in wastewater.

Titania/silica nanomaterials have many possible applications; however, they can be toxic to living organisms, particularly if the material accumulates in niche environments, e.g. areas colonised by actinomycetes. This study therefore investigated the effect of non-activated and UV light-activated titania/silica nanospheres on an environmental Streptomyces strain. The bacteria were incubated with the nanospheres and subsequently cultured on solid medium. The morphology and elemental composition were analysed using optical and electron microscopy (TEM, STEM) and energy-dispersive X-ray spectroscopy (EDX). The appearance of Streptomyces sp. in the experimental and control samples demonstrated that the nanospheres did not have bactericidal properties in the used dose. Furthermore, the observed strain not only survived in the presence of the nanomaterial but also appeared to play a role in its dissolution with an accumulation of the titanium in the intracellular globules of polyphosphate (volutin). Additionally, it was discovered that the UV light-activated titanium dioxide altered the ability of the bacteria to secrete humic acid. The reported phenomenon might be made possible through an accumulation of titanium in the volutin compounds. These findings suggest that streptomycetes could be employed to participate in the dissolution of nanomaterials which enter the natural environment.

The use of poultry waste (without proper treatment) as a potential fertilizer in agricultural soils have great concern to environment and human health, due to high levels of organic and inorganic toxicants, including heavy metals. Thus, the aim of this study was to monitor and assess bio-accumulation of heavy metals, cadmium (Cd), copper (Cu), Iron (Fe), lead (Pb), and zinc (Zn) contained in soil amended with poultry waste (SPW) and compared with controls. The physico-chemical parameters and heavy metal concentration in control soil (CS), poultry waste (PW), and SPW samples was also determined. The comparison study between the test vegetables and controls showed that the concentrations of Cd, Cu, Fe, Pb, and Zn in edible parts of chili pepper were found to be 0.057, 38.0, 61.9, 1.02, and 51.1 mg kg⁻¹, respectively, while the levels of Cd, Cu, Fe, Pb, and Zn were 0.14, 28.7, 138, 3.67, and 64.7 mg kg⁻¹, respectively, in coriander grown on SPW. The uptakes of heavy metals in test vegetables were found to be 35.7 to 95.6 % higher as compared with control vegetables. Soil-to-vegetable transfer factor values for all heavy metals in test samples were higher than control samples (p < 0.05). The enrichment factor values were >1.05, which indicated that the source of heavy metal contamination in the studied area was anthropogenic. Graphical Abstract Fate of heavy metals from poultry manure to agricultural soil

Styrene-divinylbenzene copolymer beads with ionic liquid-like functionalities (ILLF) covalently immobilised on the surface were synthesised and used to remove Cd(II) and Pb(II) from aqueous solutions. The dependence of adsorption behaviour on initial pH and metal ion concentration of solution was established. Higher ILLF content causes improved adsorption performance as ILLF are involved in coordination with metal ions. Experimental data were analysed by several isotherm models using non-linear and linear regressions, the goodness of fit being assessed by various error functions. Langmuir and Temkin models successfully describe Cd(II) and Pb(II) adsorption, respectively, whereas Freundlich model provides the poorest fit for adsorption of the two metal ion species. For a particular isotherm model, the best fit is offered by its non-linear or linear forms or by both of them. The adsorption of Cd(II) and Pb(II) is favourable and spontaneous. The synthesised adsorbents have potential applications in wastewater treatment.

The removal of As(V) from aqueous solutions by leonardite loaded with ferric ions (Fe-leonardite) has been investigated. The influence of pH, contact time, and arsenate concentration on the adsorption process were evaluated. Batch kinetic studies showed that equilibrium time was reached at 24 h of contact time. Equilibrium data obtained with low initial arsenate concentrations (10–400 ppb) were fitted to both Langmuir and Freundlich models, and the maximum adsorption capacity was estimated to be 322 μg g⁻¹. Arsenic sorption was evaluated in continuous mode to reproduce industrial applications and to determine the conditions where the process was controlled by either mass transfer or reaction rate. A maximum sorption capacity of 905 μg g⁻¹ was obtained in continuous experiments. These results indicate that Fe-leonardite is a great potential material for removing arsenate at low initial concentrations from contaminated water.

Chemical cross-linking and the high molecular weight of superabsorbent copolymers (SAPs) are the two main causes of their resistance to biodegradation. However, SAP particles are colonized by microorganisms. For the purposes of this study, the dry technical copolymer of acrylamide and potassium acrylate containing 5.28 % of unpolymerized monomers was wrapped in a geotextile and incubated in unsterile Haplic Luvisol soil as a water absorbing geocomposite. The highest number of soil bacteria that colonized the hydrated SAP and utilized it as the sole carbon and energy source was found after the first month of incubation in soil. It was equal to 7.21–7.49 log₁₀ cfu g⁻¹ of water absorbed by the SAP and decreased by 1.35–1.61 log₁₀ units within the next 8 months. During this time, the initial SAP water holding capacity of 1665.8 g has decreased by 24.40 %. Moreover, the 5 g of SAP dry mass has declined by 31.70 %. Two bacteria, Rhizobium radiobacter 28SG and Bacillus aryabhattai 31SG isolated from the watered SAP were found to be able to biodegrade this SAP in pure cultures. They destroyed 25.07 and 41.85 mg of 300 mg of the technical SAP during the 60-day growth in mineral Burk’s salt medium, and biodegradation activity was equal to 2.95 and 6.72 μg of SAP μg⁻¹ of protein, respectively. B. aryabhattai 31SG and R. radiobacter 28SG were also able to degrade 9.99 and 29.70 mg of 82 mg of the ultra-pure SAP in synthetic root exudate medium during the 30-day growth, respectively.

The olive oil industry produces a highly complex wastewater, known as olive oil mill wastewater (OOMW), which represents a relevant environmental problem for the Mediterranean region. Several physicochemical, biological and combined treatments have been tested to deal with this industrial externality but none was totally effective in reducing its toxicity for species inhabiting the receiving freshwater systems. Within this framework, nanotechnology appears as a promising research area, offering new approaches for the treatment of wastewaters based on the enhanced physical and chemical properties of nanomaterials (NMs). In this context, this work aimed to investigate the treatability of OOMW through several treatments involving advanced oxidation processes plus the use of two nanomaterials as catalysts (UV/H₂O₂, UV/TiO₂, UV/Fe₂O₃, UV/TiO₂/H₂O₂ and UV/Fe₂O₃/H₂O₂). The concentrations of the catalyst and of the oxidant agent were also investigated. The results obtained showed that photodegradation treatments combining TiO₂ or Fe₂O₃ NMs with H₂O₂ were the most efficient. Regarding the OOMW toxicity to Vibrio fischeri, it was significantly reduced with the following treatments: UV/TiO₂/H₂O₂ and UV/Fe₂O₃/H₂O₂. However, the highest reduction recorded for this parameter was obtained in the treatment with UV/H₂O₂. The use of NMs combined with H₂O₂ showed a great potential for removing phenols from OOMW, which have been pointed out as the major toxic compounds of this wastewater.

The content and speciation of heavy metals can fundamentally affect the hydrolysis of sludge. This research study investigates the migration and transformation rule of heavy metals during the hydrolysis process by measuring the content of exchangeables (F1), bound to carbonates (F2), bound to Fe-Mn oxides (F3), bound to organic matter (F4), and residuals (F5) under different periods of time undergoing hydrolysis. The results show that the hydrolysis process generally stabilized Cu, Zn, Mn, Ni, Pb, Cr, and As by transforming the unstable states into structurally stable states. Such transformations and stabilization were primarily caused by the changes in local metal ion environment and bonding structure, oxidation of sulfides, pyrolyzation of organic matter, and evaporation of resulting volatile materials. An X-ray diffractometry (XRD) of the residuals conducted after hydrolysis indicated that hydrolysis did have a significant influence on the transportation and transformation of heavy metals.