Effect of biochars with different particle sizes on fates of antibiotics and antibiotic resistance genes during composting of swine manure.

The impact of biochars with large particle sizes (LPB, 5-10 mm) and small particle sizes (SPB, <0.074 mm) on fates of antibiotics and antibiotic resistance genes (ARGs) during composting of swine manure with maize straw was explored. The results showed that antibiotics removal efficiencies were 40 %, 50 %, and 76 % for control treatment, control with LPB treatment, and control with SPB treatment after composting, respectively. The introduction of SPB reduced the total ARGs and mobile genetic elements (MGEs) levels by 28 % and 19 % after composting, respectively. The Mantel test results showed that organic matter, moisture content, and NH4+-N contributed the most to changes in antibiotics and ARGs. The significant effects of biochar specific surface area and antibiotics on MGEs further regulated the behavior of ARGs. Therefore, composting with SPB is more conducive to the removal of antibiotics and ARGs during composting of swine manure.

Degradation of ciprofloxacin by persulfate activated with pyrite: mechanism, acidification and tailwater reuse.

Residues of ciprofloxacin (CIP) in the environment pose a threat to human health and ecosystems. This study investigated the degradation of CIP by persulfate (PS) activated with pyrite (FeS2). Results showed that when [CIP] = 30 µM, [FeS2] = 2.0 g L-1, and [PS] = 1 mM, the CIP removal rate could reach 94.4% after 60 min, and CIP mineralization rate reached 34.9%. The main free radicals that degrade CIP were SO4˙- and HO˙, with contributions of 34.4% and 35.7%, respectively. Additionally, compared to the control (ultrapure water), CIP in both tap water and river water was not degraded. However, acidification could eliminate the inhibition of CIP degradation in tap water and river water. Furthermore, acidic tailwater from CIP degradation could be utilized to adjust the pH of untreated CIP, which could greatly promote the degradation of CIP and further reduce disposal costs. The reaction solution was not significantly biotoxic and three degradation pathways of CIP were investigated. Based on the above results and the characterization of FeS2, the mechanism of CIP degradation in the FeS2/PS system was that FeS2 activated PS to generate Fe(iii) and SO4˙-. The sulfide in FeS2 reduced Fe(iii) to Fe(ii), thus achieving an Fe(iii)/Fe(ii) cycle for CIP degradation.

Effect of biochar on antibiotics and antibiotic resistance genes variations during co-composting of pig manure and corn straw.

Pig manure is a reservoir of antibiotics and antibiotic resistance genes (ARGs). The effect of biochar on the variations in physicochemical properties, bacterial communities, antibiotics, ARGs, and mobile genetic elements (MGEs) of compost product during co-composting of pig manure and corn straw have been investigated in this study. Compared with the control treatment (CK), biochar addition accelerated the increase in pile temperature and prolonged the high temperature period (>55°C) for 2 days. Under biochar influence, organic matter degradation, NH4 +-N conversion and NO3 --N production was accelerated, and dissolved total organic carbon (DOC) and dissolved total nitrogen (DTN) utilization by microorganisms were enhanced. Biochar addition altered the microbial community and promoted the vital activity of Actinobacteria in the later composting stage. The antibiotics removal efficiency (except danofloxacin and enrofloxacin) was accelerated in the early composting stage (1-14 days) by biochar addition, the pile temperature had a positive effect on antibiotics removal, and the total antibiotics removal efficiency in CK and CK+Biochar treatments was 69.58% and 78.67% at the end of the composting process, respectively. The absolute abundance of most of the ARGs in the CK+Biochar treatment was lower than that in the CK treatment during composting, and the ARGs removal mainly occurred in the early (1-14 days) and later (28-50 days) stages. Biochar addition reduced the absolute abundance of MGEs (intI1, intI2) in the compost product, and most of the ARGs had a significant positive correlation with MGEs. Network analysis and redundancy analysis showed that ARGs and MGEs occurred in various host bacteria (Firmicutes, Actinobacteria, Bacteroidetes, Proteobacteria, and Halanaerobiaeota), and that DTN and NH4 +-N are the main factors regulating the changes in bacterial communities, antibiotics, ARGs, and MGEs during composting. Moreover, MGEs contributed the most to the variation in ARGs. In summary, biochar addition during composting accelerated antibiotics removal and inhibited accumulation and transmission of ARGs. The results of this study could provide theoretical and technical support for biochar application for antibiotics and ARGs removal during livestock and poultry manure composting.

Degradation of methyl orange by pyrite activated persulfate oxidation: mechanism, pathway and influences of water substrates.

Degradation mechanism of methyl orange (MO), a typical azo dye, with pyrite (FeS2) activated persulfate (PS) was explored. The results showed that when the initial concentration of MO was 0.1 mM, FeS2 was 1.6 g/L and PS was 1.0 mM, the removal rate of MO could reach 92.9% in 150 min, and the removal rate of total organic carbon could reach 14.1%. In addition, both pH ≤ 2 and pH ≥ 10 could have an inhibitory effect in the FeS2/PS system. Furthermore, Cl- and low concentrations of HCO-3 had little effect on the degradation of MO with FeS2/PS. However, H2PO-4 and high concentrations of HCO-3 could inhibit the degradation of MO in the system. Besides, MO in river water and tap water were not degraded in FeS2/PS system, but acidification (pH = 4) would greatly promote the degradation. In addition, the removal rate of MO with FeS2/PS could still reach about 90% after five cycles of FeS2. Furthermore, the intermediates and possible degradation pathways were speculated by LC-MS, and the degradation mechanism of MO by FeS2/PS was that the cycle of Fe(III)/Fe(II) could continuously activate persulfate to produce SO4•-. The results could provide technical support for azo dye degradation in the FeS2/PS system.

Effect of pH regulation on the formation of biogenic schwertmannite driven by Acidithiobacillus ferrooxidans and its arsenic removal ability.

The effect of pH regulation on schwertmannite bio-synthesis and its As removal ability were investigated in this study. The total Fe precipitation efficiency in a conventional schwertmannite bio-synthesis system (CK) reached 26.5%, with a mineral weight of 5.21 g/L and a mineral specific surface area of 3.18 m2/g. The total Fe precipitation efficiency increased to 88.4-95.8%, the mineral weight increased to 17.10-18.62 g/L, and the specific surface area increased to 3.61-90.67 m2/g of five different treatments in which the system pH was continually adjusted to 2.50, 2.70, 2.90, 3.10, and 3.30 every 3 h, respectively. The very small amounts of schwertmannite were transformed to goethite when the system pH was periodically adjusted to 2.90, 3.10 and 3.30. The increased specific surface area of bio-schwertmannite was due to the contribution of mesopores, with most pores having a diameter of 2-20 nm. For actual As-containing groundwater (27.4 µg/L), the As removal rate was 52.9% for bio-schwertmannite collected from the CK system. However, the removal rate of As increased to 92.7-97.8% for minerals which were collected after five adjusted pH treatments. The outcomes of this study provide a fresh insight into the bio-synthesis regulation of schwertmannite, and have great significance for the treatment of As-containing groundwater.

The degradation of oxytetracycline with ferrous oxalate under different light irradiation.

Degradation of OTC under different light with Fe2+/C2O42- was investigated, and the reaction mechanism was also discussed. Although Fe(II/III)-C2O42- complex could weaken the inhibitory effect of Fe(II/III)-OTC complex on the detection of OTC by HPLC, the acidification could make inhibition become minimal. Response surface methodology was used to optimize the Fe2+/C2O42- dosage at low concentrations of Fe2+ and H2C2O4. When the OTC concentration was 0.04 mM, the optimal dosage was OTC:Fe2+:H2C2O4 = 1:1.25:2 to attain a removal rate of 80% after 60 min under simulated solar light, and HO• for degradation of OTC with Fe2+/C2O42+ could be 53%, furthermore, removal rate of OTC just increased 3 percentage points at 60 min when the simulated solar light changed into UV-254 nm, however, OTC could also be degraded for 48.89% removal rate after 3 h illumination of simulated visible light. The influence of Cl-, CO32-, HCO3-, NO3-, NO2-, or H2PO4- on the degradation of OTC with Fe2+/C2O42- under simulated solar light was studied. NO2- could inhibit degradation for NO2- could react with free radicals, but the reason of inhibition of degradation by HCO3-, or CO32- was its influence on pH, whereas Cl-, NO3- and H2PO4- had no influence on degradation. In addition, when the concentration of CO32- was higher than 4 mM, CO32- could promote the degradation for the direct photolysis of OTC at alkaline (pH > 10). Four products were detected by LC-MS, and the OTC degradation pathway was discussed.

Effect of microbial nutrients supply on coal bio-desulfurization.

Research on coal desulfurization is very important for economic, social, and environmentally sustainable development. In this study, three batches of shake flask experiments were conducted for coal bio-desulfurization using Acidithiobacillus ferrooxidans to explore the relationship between microbial nutrients (iron-free M9 K medium) supply and coal bio-desulfurization efficiency. The results showed that the removal rates of pyritic sulfur and total sulfur from coal effectively increased following reintroduction of coal into the filtrate from previous batch. The removal rates of pyritic sulfur and total sulfur were 55.6% and 10.0%, 77.1% and 16.1%, and 86.5% and 28.2%, respectively, in the three batch experiments without iron-free M9 K medium addition. In contrast, the removal rates of pyritic sulfur and total sulfur reached 87.5% and 28.2%, 89.1% and 31.6%, and 92.0% and 29.1%, respectively, in the three batch experiments with 6.7% iron-free M9 K medium addition. However, addition of excessive iron-free M9 K medium was detrimental to coal bio-desulfurization because of the synthesis of jarosite (MFe3(SO4)2(OH)6, M = K+, NH4+) and gypsum (CaSO4·2H2O), which further declined the pyritic sulfur bio-oxidation efficiency and total sulfur removal efficiency.

Effects of Acid Mine Drainage on Calcareous Soil Characteristics and Lolium perenne L. Germination.

Acid mine drainage (AMD) is a serious environmental problem resulting from extensive sulfide mining activities. There is a lack of more comprehensive and detailed studies on the effect of AMD on calcareous soil characteristics and seed germination. In this study, five calcareous soil samples, collected from Xiaoyi, Taigu, Xiangning, Hejin, and Xixian counties in Shanxi Province, China, were used to investigate the effects of acid AMD on soil characteristics and Lolium perenne L. germination through laboratory culture experiments. The results showed that the increase in the total soil calcium oxide and magnesium oxide (CaO + MgO) contents led to a rise in the amount of Fe2+ in AMD converted into Fe3+, and that major ions (H⁺, Fe, SO42-) in AMD were trapped in the soil. The total Cao + MgO contents in the soil collected from Hejin and Taigu counties were 14.23% and 6.42%, the pH of AMD-polluted soil decreased to 7.24 and 3.10, and 98.7% and 54.0% of the Fe2+, 99.9% and 58.6% of the total Fe, and 76.0% and 26.4% of the SO42-, respectively, were trapped in the soil when the AMD volume to soil mass ratio was 10 mL/g. The results for the soil from Taigu County showed that when the soil had an AMD volume to soil mass ratio of 10 mL/g, the organic matter, available phosphorus (available P), available potassium (available K), Cr, and Cd contents in soil decreased by 16.2%, 63.0%, 97.1%, 7.8%, and 73.2%, respectively; the total phosphorus (total P) and total potassium (total K) did not significantly change; whereas the available nitrogen (available N) and total nitrogen (total N) increased to 16.1 times and 1.76 times, respectively. Compared to the initial soil collected from Taigu County, the Lolium perenne L. germination rate decreased by 81.1%, and the cumulative amount of Cr in the Lolium perenne L. increased by 7.24 times in the AMD-polluted soil when the AMD volume to soil mass ratio was 6 mL/g. The soil conditions could not support Lolium perenne L. germination when the AMD volume to soil mass ratio was 10 mL/g. The outcomes of this study could have important implication in understanding the hydrological/geochemical-behaviour of major ions of AMD in calcareous soil. The findings also have great significance in predicting plant growth behavior in AMD-polluted calcareous soil.

Photodegradation of carbamazepine with BiOCl/Fe3O4 catalyst under simulated solar light irradiation.

A magnetic BiOCl/Fe3O4 catalyst with simulated solar light response was successfully prepared through a precipitation process and characterized by X-ray diffraction, scanning electron microscopy, UV-vis diffuse reflectance spectroscopy, VSM, Brunauer-Emmett-Teller, X-ray photoelectron spectroscopy. The photocatalytic activity of BiOCl/Fe3O4 nanocomposites was further investigated through the photodegradation efficiency of carbamazepine (CBZ). In this study, 90.3% of CBZ was removed after 60min irradiation in the presence of the BiOCl/Fe3O4 catalyst. Three reactive species were identified; the contribution of h+, HO, and O2- to CBZ degradation was approximately 94.98%, 3.25%, and 1.06%, respectively. The pH value had a significant effect on the CBZ degradation, and the best performance was achieved at pH 2.68. The presence of common anions (NO3-, Cl-, CO32-, and SO42-) also affected the CBZ degradation. The inhibiting effect followed the order of CO32->SO42->Cl-. However, NO3- weakly favored the photodegradation of CBZ. Moreover, the BiOCl/Fe3O4 photocatalyst could be easily recollected from the solution by applying an external magnetic field. This type of magnetic photocatalyst, which is characterized by ease of separation, may have application potential in wastewater treatment. The disappearance of CBZ as well as the formation of its products were determined by liquid chromatography mass spectroscopy and the possible photocatalytic degradation pathways were proposed.

Reaction Mechanism of 4-Chlorobiphenyl and the NO3 Radical: An Experimental and Theoretical Study.

Experiment and theoretical chemistry calculations were conducted to elucidate the mechanism of the reaction between 4-chlorobiphenyl (4-CB) and the NO3 radical. The degradation of PCBs was investigated mechanistically through transient absorption spectroscopy technology and high-accuracy theoretical calculation by using 4-CB as the model. Laser flash photolysis (LFP) experiments were performed at 355 nm. The main intermediate was analyzed through transient absorption spectroscopy and identified to be a charge transfer complex (CTC). The final products were identified through GC-MS analysis. The ground states and excited states of the reactants were calculated through density functional theory (DFT) method. The absorption bands at 400 and 700 nm show good agreement with the experimental results. The ratio of absorbance at 400 and 700 nm is 1.6, and the experimental value is 1.8. Analysis of the charge population indicated that one unit charge transfer from 4-CB to NO3. The entire reaction process was divided into two phases. In the first phase, the CTC intermediate was formed by electrostatic attraction between 4-CB and the NO3 radical. In the second phase, the most important channel of subsequent reactions is the σ-complex as an intermediate formed by N-C coupling. The final product 4-chloro,2-nitrobiphenyl was generated with the breakage of BC-H and BN-O, and benzene derivatives were formed by other channels.

Degradation of sunscreen agent p-aminobenzoic acid using a combination system of UV irradiation, persulphate and iron(II).

Increased usage and discharge of sunscreens have led to ecological safety crisis, and people are developing the advanced oxidation processes (AOPs) to treat them. The present study aimed to determine the degradation efficiency and mechanism of the sunscreen agent p-aminobenzoic acid (PABA) using the UV/Fe(2+)/persulphate (PS) method. A series of irradiation experiments were conducted to optimise the system conditions and to study the impacts of the natural anion. Free radicals and degradation products were identified in order to clarify the degradation mechanism. Initial PS and Fe(2+) concentrations showed significant impacts on PABA degradation. Natural anions, such as Cl(-), NO3 (-), H2PO4 (-) and HCO3 (-), impeded PABA degradation because of ion (Fe(2+)) capture, radical scavenging or pH effects. Hydroxyl (HO·) and sulphate (SO4 (·-)) radicals were two main radicals observed in the UV/Fe(2+)/PS system; of these, SO4 (·-) showed greater effects on PABA degradation. Over 99 % of the available PABA was completely degraded into carbon dioxide (CO2) and water (H2O) by the UV/Fe(2+)/PS system, and the remaining PABA participated in complex radical reactions. By-products were identified by total ion chromatography and mass spectrometry. Our research provides a treatment process for PABA with high degradation efficiency and environmental safety and introduces a new strategy for sunscreen degradation.