In this study, we attempt to prospect potential bacterial isolates from mangrove sediments of Mangalavanam, Kerala, India, with positive carbonic anhydrase (CA) activity to sequester carbon dioxide by calcium precipitation process. Fifteen bacterial colonies (M1–M15) isolated were screened for their carbonic anhydrase enzyme production potential based on p-nitro phenol acetate assay. Based on the secondary screening, M3 and M8 were identified as the most potential for carbonic anhydrase production. The specific activity of the partially purified CA enzyme from M3 and M8 were 44 U mg⁻¹ and 76 U mg⁻¹ respectively. The enzyme activity increased by 1.6-fold upon precipitation by acetone (80%). The potential isolate which higher CA production, M8 was identified as Bacillus altitudinis based on 16S rDNA sequencing. Soil microcosm was established to study carbonic anhydrase production and CO₂ sequestration ability of B. altitudinis M8 strain. B. altitudinis M8 strain could reduce CO₂ by 75 ± 0.12% in microcosm composed of sterilized soil with bacteria (SSB) and by 97 ± 0.34% in microcosm with sterile soil with enzyme (SSE). Hence, the application of enzyme was found to be more effective in removing CO₂ when compared to bacterial inoculum. To further understand the bio-mineralization ability of this microbial isolate, calcium precipitation assay was conducted. There was a reduction of 42.22 ± 0.23% of free calcium in the medium through calcite precipitation. The carbonic anhydrase-mediated calcium precipitation by B. altitudinis M8 strain could be effectively employed in the process of carbon dioxide sequestration.

The mechanism of Cr(VI) immobilization in soils by organic substances are not well understood. In the present study, two crop residues (maize stalk and peanut shell) and their biochars obtained at various pyrolysis temperatures were prepared to investigate their influences on the immobilization of Cr(VI) in two contaminated soils via an incubation test and a bioassay. The results showed that Cr(VI) immobilization in soils was ascribed to dominant reduction (52–99%) coupled with secondary surface adsorption (1.2–48%) by organic substances. The maximum reduction capacity (Yₘ, 238 mg/kg) was found in an acidic brown soil with maize stalk amendment, secondly, with peanut shell amendment (Yₘ, 231 mg/kg). Their biochars presented a weaker capacity in reducing Cr(VI) to Cr(III) of soils than raw crop residues since carbonization accelerated the decomposition of oxygen-containing functional groups of organic substances. Soil properties, mainly soil pH, were negatively related to Cr(VI) reduction in soils remarkably, while concomitant anions in soils mainly the phosphate could compete with Cr(VI) for surfaces of soil particles and decrease Cr(VI) adsorption and subsequent reduction. The bioassay in pots with wheat seedlings further validated that maize stalk was a better organic substance for Cr(VI) immobilization and subsequent decrease of its bioavailability in contaminated soils than its biochar according to the results of wheat biomass and Cr contents in shoots and roots. Accordingly, to develop a cost-effective method for immobilizing Cr(VI) in contaminated soils, the raw maize stalk is more advantageous than the carbonaceous counterparts because no pyrolysis is required for the application.

It was investigated the potential of Rhodococcus erythropolis AW3 as a biosorbent for the removal of crystal violet (CV) dye from natural water and real effluents. The biosorbent was characterized by flow cytometry, Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), energy X-ray dispersive spectroscopy (EDS), and point of zero charge (pHZPC). Batch biosorption experiments were performed to optimize different parameters involved in the biosorption process. The equilibrium was reached at 90 min at the optimum biosorbent dose of 0.50 g L⁻¹ and pH of 9.0. Results indicated that Langmuir isotherm model was the most suitable to represent the experimental data, and the highest biosorption capacity was 289.8 mg g⁻¹. Kinetic data were well fitted with the pseudo-second-order model. The thermodynamic study showed that the process was favorable, exothermic, and associated with an increase of entropy. Finally, it was demonstrated that the biosorption process using Rhodococcus erythropolis AW3 could be successfully applied to remove CV from natural water and effluents derived from clinical and industrial activities.

Tannins are special plant metabolites used in leather processing that act as pollutants. These substances are toxic to aquatic biota and can cause cell rupture. These harmful effects make the treatment of tannery wastewater difficult. Phytoplankton species are community components that are rarely considered in the biodegradation of organic compounds. However, in association with bacteria, these organisms can improve the biodegradation of pollutants by different mechanisms. The aim of the present study was to evaluate the potential of non-axenic cultures of Chlorella vulgaris containing Lactobacillus casei and Synechococcus sp. containing Rhizobium rosettiformans and Sphingomonas koreensis to biodegrade tannic acid (TA). Cultures in BG-11 medium containing TA (250 mg L⁻¹) were incubated under a photoperiod or in the dark and monitored for 96 h. The cultures with added TA grew more than the control cultures under both the photoperiod and dark conditions. A reduction in the TA concentration and the TA metabolite gallic acid was observed under both conditions. Ellagic acid was identified and demonstrated resistance to biodegradation under the evaluated conditions, and neither of the other metabolites was detected. BG-11 culture medium is poor in organic material; therefore, microalgae and cyanobacteria contribute to bacterial metabolism. Under experimental conditions, phytoplankton species seem to contribute to the biodegradation of tannin residues, and in natural environments, they may aid in the bioremediation of sites contaminated by these pollutants.

The field experiment of a rice–wheat rotation system was conducted on a coastal reclaimed farmland with different application rates of biogas slurry from a large-scale standardized hoggery. Crop yield, grain quality, and soil properties were examined to determine the appropriate application rate. At the slurry application rates of 480 m³ ha⁻¹ for rice and 9.00–11.25 m³ ha⁻¹ for wheat, grain yields of rice and wheat were 8.9 and 15.7% higher than those under conventional fertilization, respectively. When 840 m³ ha⁻¹ biogas slurry was applied to the rice field, the grain amino acid content was significantly higher than that of conventionally fertilized rice. In the rice–wheat rotation system, under biogas slurry treatments, soil pH and EC did not significantly increase; the contents of soil Pb, Cr, Cu, and Zn were within allowable limits; the contents of soil alkali-hydrolyzable nitrogen were greatly increased and significantly higher than those under conventional fertilization treatment; and the content of soil organic matter had no significant difference with that under no fertilization treatment. Therefore, the recommended application rate of biogas slurry on coastal reclaimed farmland should be 480 and 9.00–11.25 m³ ha⁻¹ for rice and wheat, respectively.

Degradation of humic acid (HA) in heterogeneous electro-Fenton/chlorine processes was investigated using a catalyst of Mn-Cu bimetallic oxides supported on Al-containing MCM-41. The catalyst was synthesized by co-precipitation method and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), N₂ adsorption–desorption, and X-ray photoelectron spectroscopy (XPS) techniques. The bimetallic oxide catalyst exhibited a higher activity compared to monometallic one. Adding Al in the bimetallic oxide catalyst enhanced the stability of the catalyst, reduced metal ion leaching, increased the initial ratio of Mn³⁺/Mn⁴⁺ and Cu⁺/Cu²⁺, and slightly enhanced the degradation efficiency of HA and corresponding chemical oxygen demand (COD). The effect of Mn and Cu content in MCM-41, catalyst dosage, pH value, and initial concentration of HA and salinity on degradation efficiency were investigated. A high COD reduction about 91.5% and general current efficiency (GCE) about 41.7% have been achieved under the optimal conditions of pH 6, salinity 1000 mg/L, catalyst dosage 0.5 g/L, HA sodium salt concentration 200 mg/L, and reaction time 60 min. A possible mechanism for the reaction was suggested. Kinetic analysis showed that HA degradation in the electro-Fenton/chlorine processes was fit with first-order kinetics.

Perchlorate, a pervasive water pollutant, poses a threat to some aquatic environments. Antibiotics, as an emerging contaminant, have increasingly been found in aquatic environments in recent years. As a special co-contaminant, antibiotics modify the composition and function of microbial communities, and the biodegradation rate of perchlorate is changed in the environment. In this study, three typical antibiotics widely found in aquatic ecosystems (lincomycin (LIN), erythromycin (ETM), and sulfadiazine (SDZ)) and two input modes (once and multiple times) were selected to reveal the effects of antibiotics on perchlorate degradation and changes in the microbial community. Additionally, antibiotic resistance gene (ARG) abundance and microbial community composition were analyzed to illustrate the response of bacteria to antibiotic types and input methods by QPCR and high-throughput sequencing. The perchlorate degradation rate was inhibited by three antibiotics (LIN > ETM > SDZ) in this study. LIN and ETM had stronger inhibitory effects on perchlorate degradation, and the abundances of their ARGs increased with increasing antibiotic concentrations. With the continuous culturing and multiple inputs of antibiotics, the percentage of ARGs decreased after crossing a threshold. Additionally, the dominant degradation bacteria were different under pressure from different antibiotics. The type of the antibiotic, the background level of ARGs, and the dissemination of ARGs between bacteria were the main factors influencing the degradation system. The results presented herein will help us understand the modifications of microbial communities that occur in persistent pollutant systems contaminated with antibiotics.

Reverse osmosis (RO) technique plays an important role in the treatment of secondary biochemical effluent. However, the reverse osmosis concentrate (ROC) with high salinity and organic pollutants generated from this process remains a challenge to be tackled. The O₃-assisted UV-Fenton advanced oxidation process (AOP) as a pretreatment for the nanofiltration (NF) was used to treat the ROC of industrial wastewater. The optimal removal rates of COD and UV₂₅₄ were 80.4 and 77.4%, respectively. In the NF process, four types of commercial NF membranes (NF90 (Dow, USA), DK (GE, USA), NT101, and NT103 (NADIR, Germany)) were used to treat the AOP effluent. The effects of operating pressure and feed temperature on ion rejection were investigated. The results show that NF90 and NT103 membranes had better rejections to monovalent ions, while DK and NT101 membranes could effectively separate monovalent and divalent ions and their ion rejections decreased with the increase of feed temperature. With the NF90 membrane, the highest TDS removal rate of 89.65% was obtained at the operating pressure of 1.2 MPa.

Conventional air pollutants (PM₁₀, CO, NOₓ) gradually increased from fall to winter during 2015 in Istanbul. Several air pollution episodes were observed during this period. This study was made in order to determine polycyclic aromatic hydrocarbon (PAH) levels, identify the sources of air pollution, and make toxicity assessment based on Benzo(a)pyrene equivalent concentrations. The sampling took 14 sequential days during winter. High-pressure weather conditions prevailed at the start of the sampling. The conditions were then changed to low-pressure condition towards the end of the sampling. Strong inversion was effective on the onset of the sampling. Strong inversion was effective at the onset of the sampling. A high-volume sampler was used to collect gas and particle phase samples. Total suspended particle concentrations were between 27 and 252 μg m⁻³. Sixteen PAH species were investigated. Total (gas + particle) PAH concentrations were between 76.4 and 1280.3 ng m⁻³, with an average of 301.4 ng m⁻³. Individual PAH concentrations were between not detected (n.d.) and 99.2 ng m⁻³ in the gaseous phase, and between n.d. and 11.5 ng m⁻³ in the particle phase. Phenanthrene had the highest share among 16 PAH compounds. Benzo(a)pyrene was not detected in 8 days. On the remaining days, its concentration ranged between 5.5 and 14.8 ng m⁻³ with an average of 3.7 ng m⁻³. Low-molecular-weight PAHs dominated gaseous phase; inversely, high-molecular-weight PAHs dominated particle phase. Possible sources were identified by diagnostic ratios. These ratios suggested that coal combustion and diesel vehicle exhaust emissions had a substantial impact on ambient air quality. Benzo(a)pyrene equivalencies were calculated for each PAH compound in order to make toxicity assessment. Total benzo(a)pyrene equivalencies ranged between 0.4 and 30.0 ng m⁻³ with an average of 7.2 ng m⁻³.