Denitrifying bioelectrochemical system provided an alternative technology for nitrogen removal, even power recovery from wastewater, and its nitrogen removal performance and intermediate accumulation were affected by the extracellular electron transfer modes and rate-limiting steps in denitrifying biocathodes. In the current study, the extracellular electron transfer modes and rate-limiting steps for nitrate reduction and nitrite reduction of denitrifying biocathode were investigated through cyclic voltammetry. When the cathode potential swept from 0.003 to − 0.897 V (vs. Ag/AgCl), denitrifiers were indispensable for electrochemical denitrification. Three peak potentials were found in the cyclic voltammogram of denitrifying biocathode, where E₁ (− 0.471 to − 0.465 V) and E₂ (− 0.412 to − 0.428 V) represented respectively nitrate reduction and nitrite oxidation while E₃ (− 0.822 to − 0.826 V) represented nitrite reduction. Nitrate reduction involved the direct electron transfer mode while nitrite reduction involved the mediated electron transfer mode. Intracellular catalytic reaction was the rate-limiting step for nitrate reduction, independent on the electrochemical activity of denitrifying biocathode and the nitrate supply. The nitrate supply posed an effect on the rate-limiting step for nitrite reduction. The mediator transfer was the rate-limiting step for nitrite reduction in the absence of nitrate. But both mediator transfer and intracellular catalytic reaction became the rate-limiting steps for nitrite reduction in the presence of sufficient nitrate.

1,3,5-Tris-(2,3-dibromopropyl)-1,3,5-triazine-2,4,6-trione (TDBP-TAZTO) is an emerging brominated flame retardant which is widely used in several plastic materials (electric and electronic equipment, musical instruments, automotive components). However, until today, no photochemical studies as well as the identification of possible phototransformation products (PTPs) were described in literature. Therefore, in this study, UV-(C) and simulated sunlight irradiation experiments were performed to investigate the photolytic degradation of TDBP-TAZTO and to identify relevant PTPs for the first time. The UV-(C) irradiation experiments show that the photolysis reaction follows a first-order kinetic model. Based on this, the photolysis rate constant k as well as the half-life time t₁/₂ were calculated to be k = (41 ± 5 × 10⁻³) min⁻¹ and t₁/₂ = (17 ± 2) min. In comparison, a minor degradation of TDBP-TAZTO and no formed phototransformation products were obtained under simulated sunlight. In order to clarify the photochemical behavior, different chemicals were added to investigate the influence on indirect photolysis: (i) H₂O₂ for generation of hydroxyl radicals and (ii) two quenchers (2-propanol, sodium azide) for scavenging oxygen species which were formed during the irradiation experiments. Herein, nine previously unknown PTPs of TDBP-TAZTO were detected under UV-(C) irradiation and identified by HPLC-(HR)MS. As a result, debromination, hydroxylation, and dehydrobromination reactions could be presumed as the main degradation pathways by high-resolution mass spectrometry. The direct as well as the OH radical-induced indirect photolysis were observed. Graphical abstract .

Huge amounts of natural bischofite (MgCl₂∙6H₂O) resulting from the mining process of salt lakes often cannot be utilized effectively and are discarded; techniques for reutilization of the discarded bischofite as magnesium resources are limited. The nano-magnesium hydroxide (nano-Mg(OH)₂) synthesized from natural bischofite was firstly used as catalyst for ozonation of antibiotics including sulfathiazole (ST), ofloxacin (OFL), and tetracycline (TC). Rapid ozonation of ST, OFL, and TC was achieved using nano-Mg(OH)₂ as catalyst. The removal rate constant of OFL in the catalytic ozonation treatment (kOFL = 0.512 min⁻¹) was nearly 2.1 times higher than the single ozonation (kOFL = 0.249 min⁻¹). The removal rate constant of ST and TC increased by 23.5% and 32.8% from 0.298 min⁻¹ and 0.384 min⁻¹ to 0.368 min⁻¹ and 0.510 min⁻¹, respectively, when the catalyst was added into the reaction system. The removal rate constant of ST sharply increased from 0.259 to 0.604 min⁻¹ when the reaction temperature increased from 15 to 35 °C while those of OFL and TC changes slightly. The removal efficiency sharply decreased when the initial concentration of ST, OFL, and TC increased from 10 to 500 mg L⁻¹. Both anions and cations could inhibit the removal of ST, OFL, and TC at relatively higher concentrations. The prepared nano-Mg(OH)₂ catalyst could maintain its catalytic activity in the repeated use process. High removal efficiency of typical antibiotics and heavy metals free indicated that nano-Mg(OH)₂ from natural bischofite is a promising ozonation catalyst in terms of antibiotics removal.

The California Department of Pesticide Regulation conducted indoor air monitoring to estimate sulfury fluoride (SO₂F₂) emissions that bystanders around fumigated houses were potentially exposed to during structural fumigation of residential houses. Monitoring was conducted for 23 fumigations between September 2014 and March 2015. The SO₂F₂ indoor concentrations were measured from four locations inside the fumigated houses once an hour. The decreases of indoor concentrations are due to gas leakage (treatment period) and aeration (aeration period) from the structure to the outdoor environment. Analysis on the monitoring data showed considerable variability of half loss time (11–60 h) and mass loss (22–81%) during treatment periods. The decline of indoor concentrations followed the first-order kinetics; therefore, the hourly flux (g/m²s) of a treatment period can be calculated using initial SO₂F₂ concentration, treatment period mass loss, and house height. Although the California Aeration Plan requires a minimum 12–24 h of aeration after a treatment, the monitoring data showed that 93 ± 5% of the mass at the end of the treatment periods was emitted through the ducting system within the first 2 h. The average ratio of the loss amount in the first hour to the loss in the second was 6:1. These monitoring results provided the critical input for the computer modeling to estimate bystander exposure during structural fumigations of residential houses.

For remediating polluted soils, phytoextraction of metals received considerable attention in recent years, although slow removal of metals remained a major constraint in this approach. We, therefore, studied the effect of selected organic and inorganic amendments on the solubility of zinc (Zn), cadmium (Cd), and lead (Pb) in polluted soil and enhancing the efficacy of phytoextraction of these metals by Indian mustard (Brassica juncea cv. Pusa Vijay). For this purpose, a greenhouse experiment was conducted using a metal-polluted soil to evaluate the effect of amendments, viz. green manure (T2), EDTA (T3), sulfur (S)+S oxidizing bacteria (Thiobacillus spp.) (T4), metal-solubilizing bacteria (Pseudomonas spp.) (T5), and green manure + metal-solubilizing bacteria (T6), on solubility and bioavailability of Zn, Cd, and Pb. Distribution of metals in different soil fractions revealed that Cd content in water soluble + exchangeable fraction increased to the extent of 34.1, 523, 133, 123, and 75.8% in T2, T3, T4, T5, and T6 treatments, respectively, over control (T1). Cadmium concentrations in soil solution as extracted by Rhizon sampler were recorded as 3.78, 88.1, 11.2, 6.29, and 4.27 μg L⁻¹in T2, T3, T4, T5, and T6, respectively, whereas soil solution concentration of Cd in T1 was 0.99 μg L⁻¹. Activities of Cd (pCd²⁺) in Baker soil extract were 12.2, 10.9, 6.72, 7.74, 7.67, and 7.05 for T1, T2, T3, T4, T5, and T6, respectively. Cadmium contents in shoot were recorded as 2.74, 3.12, 4.03, 4.55, 4.68, and 4.63 mg kg⁻¹ in T1, T2, T3, T4, T5, and T6 treatments, respectively. Similar trend in Zn and Pb content with different magnitude was also observed across the different amendments. Cadmium uptake by shoot of mustard was enhanced to the extent of 125, 62.5, 175, 175, and 212% grown on T2-, T3-, T4-, T5-, and T6-treated soil, respectively, over T1. By and large, free ion activity of metals as measured by Baker soil test proved to be the most effective index for predicting Zn, Cd, and Pb content in shoot of mustard, followed by EDTA and DTPA. Among the metal fractions, only water soluble + exchangeable metal contributed positively towards plant uptake, which explained the variation in shoot Zn, Cd, and Pb content to the extent of 74, 81, and 87%, respectively, along with other soil metal fractions. Risk to human health for intake of metals through the consumption of leafy vegetable (mustard) grown on polluted soil in terms of hazard quotient (HQ) ranged from 0.64 to 1.10 for Cd and 0.11 to 0.34 for Pb, thus rendering mustard unfit for the human consumption. Novelty of the study mainly consisted of the use of natural means and microorganisms for enhancing solubility of metals in soil with the ultimate aim of hastening the phytoremediation.

We used the community of benthic macroinvertebrates, alongside physical and chemical characteristics of the water, to verify the influence of an urbanized tributary on a Neotropical river. Specifically, our hypothesis is that urbanized tributaries are potentially able to simplify the biological diversity of the rivers where they flow. The collections were sampled in six sites every 2 weeks from April 2013 to March 2014, using artificial substrates. In conjunction with the benthic macroinvertebrate collections, the temperature, pH, and dissolved oxygen were measured using portable devices, as well as ammonia, total nitrogen, total phosphorus, and biochemical oxygen demand (BOD) in the laboratory. Rainfall values were also obtained. We observed a marked fall in the number of taxa and the values of richness, diversity equitability at the point located below the tributary mouth, with predominance of Chironomidae and Annelida. The high capture rates of a few groups considered tolerant and the high concentrations of total nitrogen, total phosphorus, and BOD confirm the alteration of the quality of the water at the sampling point located below the tributary mouth, leading to a local process of ecological simplification.

Temporal–spatial distribution of synthetic pyrethroids (SPs) in overlying water and surface sediments and ecological risk to aquatic systems were investigated, where paired water and surface sediments were collected during dry and wet periods in Guangzhou urban waterways. Eight target SPs (i.e., tefluthrin, bifenthrin, cyhalothrin, permethrin, cyfluthrin, cypermethrin, esfenvalerate, and deltamethrin), with cypermethrin and permethrin as major components, were ubiquitously detected in both water (dissolved and particle phases, separately) and sediments. Significant increases of ΣSP (sum of eight SPs) concentrations were observed in both water and sediment from the dry period to the wet period. The spatial distribution of SPs was mostly impacted by land-use type, with the highest ΣSP concentrations in the residential areas, which indicates the massive application of pyrethroids in household mosquito control. It is demonstrated that SPs preferred to be adsorbed to the particles, and rainfall-induced runoff was suggested as an important mechanism that moved SPs to the receiving waterways. A rising trend on sediment concentrations of SPs in the Guangzhou area in the last decade implied increasing application of pyrethroid insecticides, with cypermethrin and permethrin as the dominant components, where the contamination of SPs was positively related with urbanization rate (e.g., resident population and green coverage area). A special emphasis was placed on the potential effects of both individual SPs and their mixtures in three trophic levels (i.e., algae, daphnia, and fish) using toxic units (TUs) and risk quotients (RQs) for water and sediments. In spite of no acute effects due to SPs in the sediments, the toxic units showed daphnia as the most sensitive species in water, with acute risks to daphnia exhibited in several sampling sites. The risk assessment points out that a chronic toxicity (RQ index) caused by SPs in three trophic levels (algae, daphnia, and fish) exists, especially in Daphnia magna. Graphical abstract

The purpose of this piece of work is to study the process of adsorption of paracetamol on activated carbon, silica and alumina and their degradation using UV radiation. The results demonstrate a higher adsorption of paracetamol on alumina and activated carbon, while a minor value was observed in the case of silica. The H-bonding and π-stacking interactions between paracetamol and supports can be explained by the variation in the adsorption capacity values. When the paracetamol adsorbed was irradiated with two different UV irradiance values (59.78 mW cm⁻² and 119.56 mW cm⁻²) for 120 min, the higher degradation percentage was observed on activated carbon with a value of 79%. In the case of alumina and silica, the maximum percentages obtained were 65% and 77%, respectively. The incorporation of H₂O₂ in the reaction medium increases the rate of degradation, mainly at higher irradiance, reaching the maximum values in less time.

Tailings and waste rocks can be used to build covers with capillary barrier effects (CCBE) for the purposes of reclaiming acid-generating waste storage facilities while enhancing the value of the materials available on site. The efficiency of non-acid generating tailings, desulfurized tailings, and non-reactive waste rocks as cover materials was demonstrated in previous laboratory and field studies. However, acid-generating waste rocks are usually not considered for cover construction because of the risk of contamination. Nonetheless, using acid-generating waste rocks as the bottom capillary break layer in a CCBE could have economic and logistical benefits for companies, including helping to reduce the volume of waste rock piles and to valorize material that are generally considered to be problematic. In this study, laboratory column tests were performed to evaluate cover scenarios using acid-generating waste rocks from Westwood-Doyon mine (Québec, Canada). These waste rocks were placed under a moisture-retaining layer made of desulfurized tailings. A column test with non-acid-generating waste rocks was also performed for comparison purposes. Columns were submitted to eight wetting/drainage cycles. The performance of these systems was assessed by monitoring the volumetric water content in the different layers and by analyzing the water quality of the leachates. Significant reductions in contamination were observed when covers were added on the reactive waste rocks. These results suggest that it could be possible to valorize acid-generating waste rocks in cover systems.

A range of different studies has been performed in order to design and develop photocatalysts that work efficiently under visible (and near-infrared) irradiation as well as to improve photons absorption with improved reactor design. While there is consensus on the importance of photocatalysis for environmental applications and the necessity to utilized solar irradiation (or visible-light) as driving force for these processes, it is not yet clear how to get there. Discussion on the future steps towards visible-light photocatalysis for environmental application is of great interest to scientific and industrial communities and the present paper reviews and discusses the two main approaches, band-gap engineering for efficient solar-activated catalysts and reactor designs for improved photons absorption. Common misconceptions and drawbacks of each technology are also examined together with insights for future progress.