The use of ultrasound-assisted anaerobic compost tea washing to remove poly-chlorinated dibenzo-p-dioxins (PCDDs), dibenzo-furans (PCDFs) from highly contaminated field soils

The remediation of dioxin-contaminated soil of a specific coastal area previously employed for the manufacture of pentachlorophenol (PCP) in southern Taiwan’s Tainan City has attracted much attention of researchers there. This work addresses the possibility of providing an effective and environmentally friendly option for removing PCDD/Fs from soil in that field. Soil screening/sieving was first conducted to assess particle distribution. Fine sand was observed to be the major component of the soil, accounting for more than 60% of the total mass. A combination of ultrasonification and mechanical double-blade agitation was used to facilitate the washing of the soil using the biosurfactant anaerobic compost tea. More than 85 and 95% of total removal efficiencies were achieved for moderately and highly contaminated soils after 6 and 10 washing cycles, respectively, under ambient temperature, a soil/liquid ratio 1:2.5, 700 rpm, and over a relatively short duration. These results were achieved through the collision and penetration effects of this combined treatment as well as PCDD/F partitioning between the particles and anaerobic compost tea. This study represents the first to report the use of anaerobic compost tea solvent to wash soil highly contaminated by dioxin. It was concluded that anaerobic compost tea, rich in non-toxic bio-surfactants (e.g., alcohols, humic acids), can be used to improve bioavailability and bioactivity of the soil making bio-attenuation and full remediation more efficient.     

Assessment and potential sources of metals in the surface sediments of the Yellow River Delta,Eastern China

The Yellow River Delta is the most intact estuary wetland in China and suffers from great pressure of metals. Seventy-seven surface sediment samples were collected in the delta, and contents of Cu, Pb, Cd, Cr, Zn, Ni, and Mn were analyzed by inductively coupled plasma spectrometry and those of Hg and As by atomic fluorescence spectrometry. The results showed that means of metal contents (ppm, dry weight) were as follows: Hg, 0.04; Cr, 61.72; Cu, 20.97; Zn, 60.73; As, 9.47; Pb, 21.91; Cd, 0.12; Ni, 27.24; and Mn, 540.48. 43.8% of Hg and 14.3% of Cd were from the allogenic source while others from the authigenic source. The results of the geoaccumulation indexes appeared that 6.5% of sites from the estuarine and the Gudao areas were moderately polluted by Hg. All ecological risk index values of Hg and 37.7% of Cd were more than 40, which were the main factors of strongly and moderately potential ecological risks of 37.7% of sites in the delta. High Cd contents may be due to the alkaline conditions of the delta and the unreasonable management of the farmland, while the abnormal distribution of Hg to the wet or dry deposition and the erosion of the seawater. It was suggested to monitor Hg content in the atmosphere of the Yellow River Delta. The results were expected to update the pollution status of metals in the delta and created awareness of preserving the sound condition of the Yellow River Delta.     

Arsenic sorption by red mud-modified biochar produced from rice straw

Red mud-modified biochar (RM-BC) has been produced to be utilized as a novel adsorbent to remove As because it can effectively combine the beneficial features of red mud (rich metal oxide composition and porous structure) and biochar (large surface area and porous structure properties). SEM-EDS and XRD analyses demonstrated that red mud had loaded successfully on the surface of biochar. With the increasing of pH in solution, arsenate (As(V)) adsorption on RM-BC decreased while arsenite (As(III)) increased. Arsenate adsorption kinetics process on RM-BC fitted the pseudo-second-order model, while that of As(III) favored the Elovich model. All sorption isotherms produced superior fits with the Langmuir model. RM-BC exhibited improved As removal capabilities, with a maximum adsorption capacity (Q_max) for As(V) of 5923 μg g^?1, approximately ten times greater than that of the untreated BC (552.0 μg g^?1). Furthermore, it has been indicated that the adsorption of As(V) on RM-BC may be strongly associated with iron oxides (hematite and magnetite) and aluminum oxides (gibbsite) by X-ray absorption near-edge spectroscopy (XANES), which was possibly because of surface complexation and electrostatic interactions. RM-BC may be used as a valuable adsorbent for removing As in the environment due to the waste materials being relatively abundant.     

Hexabromocyclododecanes in soils and plants from a plastic waste treatment area in North China: occurrence,diastereomer- and enantiomer-specific profiles,and metabolization

Plastic waste is a source of organic contaminants such as hexabromocyclododecanes (HBCDs). HBCDs have been found to cause developmental and reproductive toxicity; it is important to investigate the occurrence and metabolization of HBCDs in the soil environments with plastic waste contamination. This work analyzed HBCDs and their metabolites in soil and plant samples collected from Xinle and Dingzhou—the major plastic waste recycling centers in North China. Results showed that total HBCD concentrations in soils followed the order: plastic waste treatment site (11.0–624 ng/g) > roadside (2.96–85.4 ng/g) ≥ farmland (8.69–55.5 ng/g). HBCDs were detected in all the plant samples with total concentrations ranging from 3.47 to 23.4 ng/g. γ-HBCD was the dominant congener in soils, while α-HBCD was preferentially accumulated in plants. Compositions of HBCD isomers in soils and plants were significantly different (P < 0.05) among sampling sites and among plant species. HBCDs in farmland soil and all plant samples exhibited high enantio-selectivity based on the enantiomeric fractions (EFs). Furthermore, metabolites of pentabromocyclododecenes (PBCDEs) were frequently identified in soils, and mono-OH-HBCDs were the most common ones in plants. This study for the first time provides evidences of HBCD contamination in the soil-plant system caused by plastic waste, their stereo-selectivity, and metabolization behavior, improving our understanding of the environmental behavior and fate of HBCDs.     

Heavy metal (Cu,Cd, Pb,Cr) washing from river sediment using biosurfactant rhamnolipid

Heavy metal-contaminated sediments posed a serious threat to both human beings and environment. A biosurfactant, rhamnolipid, was employed as the washing agent to remove heavy metals in river sediment. Batch experiments were conducted to test the removal capability. The effects of rhamnolipid concentration, washing time, solution pH, and liquid/solid ratio were investigated. The speciation of heavy metals before and after washing in sediment was also analyzed. Heavy metal washing was favored at high concentration, long washing time, and high pH. In addition, the efficiency of washing was closely related to the original speciation of heavy metals in sediment. Rhamnolipid mainly targeted metals in exchangeable, carbonate-bound or Fe-Mn oxide-bound fractions. Overall, rhamnolipid biosurfactant as a washing agent could effectively remove heavy metals from sediment.

     

Individual and combined inhibition of phenol and thiocyanate on microbial activity of partial nitritation

This study evaluated the individual and interactive effect of phenol and thiocyanate (SCN⁻) on partial nitritation (PN) activity using batch test and response surface methodology. The IC₅₀ of phenol and SCN⁻ on PN sludge were 5.6 and 351 mg L⁻¹, respectively. The PN sludge was insensitive to phenol and SCN⁻ at levels lower than 1.77 and 43.3 mg L⁻¹, respectively. A regression model equation was developed and validated to predict the relative specific respiration rate (RSRR) of PN sludge exposed to different phenol and SCN⁻ concentrations. In the range of independent variables, the most severe inhibition was observed with a valley value (17%) for RSRR, when the phenol and SCN⁻ concentrations were 4.08 and 198 mg L⁻¹, respectively. An isobole plot was used to judge the combined toxicity of phenol and SCN⁻, and the joint inhibitory effect was variable depending on the composition and concentration of the toxic components. Furthermore, the toxic compounds showed independent effects, which is the most common type of combined toxicity.

     

Physiological mechanisms of a wetland plant (Echinodorus osiris Rataj) to cadmium detoxification

Environmental Science and Pollution Research - Physiological responses of Echinodorus osiris Rataj plant under cadmium (Cd) stress (5 and 15&nbsp;mg&nbsp;L?1) were studied by...     

Spatial variation and toxicity assessment for heavy metals in sediments of intertidal zone in a typical subtropical estuary (Min River) of China

Environmental Science and Pollution Research - Sediment samples were collected in five marshes (C1, Phragmites australis marsh; C2, P. australis and Cyperus malaccensis marsh; C3, C. malaccensis...     

Effect of chlorination and ultraviolet disinfection on tetA-mediated tetracycline resistance of Escherichia coli

Antibiotic-resistant bacteria are an emerging threat to public health during drinking water consumption and reclaimed water reuse. Several studies have shown that the proportions of antibiotic-resistant bacteria in waters may increase when exposed to low doses of UV light or chlorine. In this study, inactivation of tetracycline-resistant Escherichia coli and antibiotic-sensitive E. coli by UV disinfection and chlorination was compared to determine the tolerance of tetracycline-resistant E. coli to UV light and chlorine, and tetracycline resistance of a tetracycline-resistant E. coli population was studied under different doses of the disinfectants. Our results showed that relative to antibiotic-sensitive E. coli, tetracycline-resistant E. coli had the same tolerance to UV light and a potentially higher tolerance to chlorination. The mortality frequency distributions of tetracycline-resistant E. coli exposed to tetracycline were shifted by both chlorination and UV disinfection. When compared to the hemi-inhibitory concentrations (IC₅₀) of tetracycline-resistant E. coli with no exposure to UV or chlorination, the IC₅₀ of tetracycline-resistant E. coli treated with tetracycline was 40% lower when inactivation by UV light or chlorination reached 3-log but was 1.18 times greater when inactivation by chlorination reached 4.3-log. Chlorination applied to drinking water or reclaimed water treatment may increase the risk of selection for highly tetracycline-resistant E. coli.