Continual discharge of textile wastewaters loaded with a variety of synthetic dyes and metals is considered as a huge threat to surrounding ecosystems. In order to treat these undesirable pollutants, microbial bioremediation is considered as an efficient and economical technique. This study was conducted to evaluate the use of bacterial strains for simultaneous removal of azo dyes and hexavalent chromium [Cr(VI)]. Fifty-eight bacterial strains were isolated from Paharang drain wastewater and tested for their potential to decolorize reactive red-120 (RR-120) in the presence of 25 mg L⁻¹of Cr(VI). Among the tested isolates, FA10 decolorized the RR-120 most efficiently and was identified as Acinetobacter junii strain FA10. Based on quadratic polynomial equation and response surfaces given by the response surface methodology (RSM), Cr concentration and pH were found to be the main factors governing the RR-120 decolorization by FA10. The strain FA10 also exhibited a substantial salt resistance since it showed a considerable decolorization of RR-120 even in the presence of 150 g L⁻¹of NaCl. Moreover, the strain FA10 also showed the potential to simultaneously remove the Cr(VI) and the selected azo dyes in the same medium. More than 80 % of the initially added Cr(VI) was removed over 72 h of incubation along with the appreciable decolorization efficiency. The strain FA10 also exhibited good tolerance to considerable levels of different heavy metals. The findings of this study suggest that the strain FA10 might serve as an efficient bioresource to develop the biotechnological approaches for simultaneous removal of different azo dyes and heavy metals including Cr(VI).

Washing-down parlours and standing areas, following milking on dairy farms, produce dairy soiled water (DSW) that contains variable concentrations of nutrients. Aerobic woodchip filters can remove organic matter, nutrients and suspended solids (SS) in DSW, but the effluent exiting the filters may have to be further treated before it is suitable for re-use for washing yard areas. The performance of a single-layer sand filter (SF) and a stratified SF, loaded at 20 L m⁻² day⁻¹, to polish effluent from a woodchip filter was investigated over 82 days. Average influent unfiltered chemical oxygen demand (CODT), total nitrogen (TN), ammonium–N (NH₄–N), ortho-phosphorus (PO₄–P) and SS concentrations of 1,991 ± 296, 163 ± 40, 42.3 ± 16.9, 27.2 ± 6.9 and 84 ± 30 mg L⁻¹ were recorded. The single-layer SF decreased the influent concentration of CODT, TN, NH₄–N, PO₄–P and SS by 39, 36, 34, 58 and 52 %, respectively. Influent concentrations of CODT, TNT, NH₄–N, PO₄–P and SS were decreased by 56, 57, 41, 74 and 62 % in the stratified SF. The single-layer SF and the stratified SF were capable of reducing the influent concentration of total coliforms by 96 and 95 %, respectively. Although a limited amount of biomass accumulated in the uppermost layers of both SFs, organic and particulate matter deposition within both filters affected rates of nitrification. Both types of SFs produced final water quality in excess of the standards for re-use in the washing of milking parlours.

A mesocosm experiment was established to evaluate the effect of two organic wastes: fermented sugar beet residue (SBR) and urban waste compost on the stimulation of plant growth, phytoaccumulation of heavy metals (HM) and soil biological quality and their possible use in phytostabilization tasks with native (Piptatherum miliaceum, Retama sphaerocarpa, Bituminaria bituminosa, Coronilla juncea and Anthyllis cytisoides) and non-native (Lolium perenne) plants in a heavy metal-contaminated semiarid soil. Except R. sphaerocarpa, SBR increased the contents of shoot N, P and K and shoot biomass of all plants. The percentage of mycorrhizal colonization was not affected by the organic amendments. The highest increase in dehydrogenase and β-glucosidase activities was recorded in SBR-amended P. miliaceum. SBR decreased toxic levels of HM in shoot of P. miliaceum, mainly decreasing Fe and Pb uptake to plants. This study pointed out that the SBR was the most effective amendment for enhancing the plant performance and for improving soil quality. The combination of SBR and P. miliaceum can be regarded the most effective strategy for being employed in phytostabilization projects of this contaminated site.

Pesticide biodegradation was studied in soil samples of a representative small periurban production unit (Moreno District, Argentina). The mean periods required for the 50 % dissipation of chlorpyrifos (16 days ± 1 day), procymidone (3.7 days ± 0.6 day), and trifluralin (3.6 days ± 0.6 day) were significantly lower than those measured for reference soil samples of a close location, using doses similar to the manufacturer’s recommendation. A preliminary screening scheme for pesticide-degrading bacteria on horticultural soil allowed the isolation of nine culturable bacterial strains, eight of which belonged to Pseudomonas genus. In order to consider the influence of the variability of soil properties on the biodegradation results, humidity, organic matter, conductivity, pH, water retention volume, density, respiration, and total phosphorous content were studied for different soil samples, finding no significant differences in the performed analysis. Overall, although the horticultural activity alters the natural soil, pesticide contamination effects could be reversed by the autochthonous microbial community.

Phosphorus (P) loss from non-point sources is a main cause of freshwater eutrophication in agricultural regions. Knowledge-based watershed management plans, aimed at reducing the diffuse flux of phosphorus from specific land-use and site characteristics to freshwater resources, are needed in order to curb eutrophication in agriculture regions. In this context, the use of a phosphorus index provides a simple and practical method for identifying hot-spot source areas and to estimate their potential for contributing a flux of P to the surface waters. However, as a semi-quantitative tool, the P index is usually difficult to validate due to inadequate data representation relative to large spatial and temporal variation in P fluxes. An amended P index scheme is therefore developed and validated, based on comprehensive synoptic soil study and stream water monitoring as well as a previous study that had applied the former P index in the studied watershed in northern China (Zhang et al. 2003). The amendments include the use of data from the individual village units (mean area, ca. 30.6 ha), use of the degree of P saturation (DPS) in the source factor scheme, adoption of flow length factor and modified water course erosion factor into the P transportation scheme, and an adjustment of the organization structure of the P index scheme. The validation of the amended P schemes was performed by comparing the modeled average P index values with the corresponding measured P fluxes for 12 different sub-catchments. The results indicate an improved precision in the simulated potential for P loss using the refined P index scheme. Measured fluxes of total P (r = 0.825), particulate P (r = 0.867), and less-studied yet more relevant dissolved P (r = 0.627) all showed significant correlations with the modeled P index values in the amended P scheme. The primary direct finding of the current research is that the areas with close proximity to rivers and the reservoir, as well agricultural land around villages, are found to be the main hot-spot sources for P loss to the reservoir.

Drought conditions should magnify the effect of wastewater treatment plant (WWTP) effluent on river biogeochemistry. This study examined the impact of WWTP effluent on the Enoree River in the piedmont region of South Carolina during a period of significant drought. The Enoree River lacks impoundments, upstream agricultural runoff, and significant industrial point sources, so the single most important human influence on river chemistry is WWTP effluent. Water samples were collected from 28 locations on the Enoree River, 13 of its tributaries, and the effluent of four WWTPs. Effluent from the WWTP furthest upstream increased the salinity of the river and temporal variation and concentrations of most ions, especially nitrate, phosphate, sulfate, sodium, and chloride. The upstream WWTP set the downstream chemical composition of the river, with increasing proportions of chloride, sodium, and sulfate and decreasing proportions of dissolved silicon and bicarbonate. Downstream WWTPs had little or no impact on the chemical composition of the river. Mixing model results show that dilution was the dominant process of the downstream decrease in solute concentrations, but in-channel uptake mechanisms also contributed to declines in concentrations of nitrate, phosphate, and carbon dioxide. Despite dilution and uptake, the chemical signature of WWTP effluent was still evident 135 km downstream. These results lead to a better understanding of the effects of WWTP effluent on the biogeochemistry of rivers.

Precipitate adsorbent was produced from aluminum tanning wastewater by alkali precipitation and characterized by XPF, XRD, and FTIR. The results showed that the main components of the precipitate were Al, Ti, and Zr. The adsorption equilibrium for Cr³⁺ on the precipitate was reached within 60 min. The precipitate had better removal for Cr³⁺ from wastewater at pH 7.0. The kinetic process of adsorption can be described by the pseudo-second-order kinetic equation, and the adsorption isotherm fitted to the Langmuir model very well. Co-existed cations (Na⁺, Ca²⁺) in aqueous solution restrained Cr³⁺ adsorption on the precipitate. The adsorption of Cr³⁺ on the precipitate was mainly through the complexation and ion-exchange mechanisms, and oxide may play a major role in Cr³⁺ adsorption process.

Titanate whiskers were prepared by hydrothermal method starting from hydrous metatitanic acid and potassium hydroxide. The titanate whiskers were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, inductively coupled plasma, and N₂ adsorption/desorption techniques. When the concentrations of potassium hydroxide ranged from 6 to 12 mol L⁻¹, titanate whiskers were formed by bundling layer-structured nanoribbons. The titanate whiskers were certified with the formula of H₂ ₋ ₓKₓTi₃O₇ · nH₂O (x = 0.6, n = 3.8–4.0). After hydrochloric acid treatment, the potassium content and the layer distance decreased due to the replacement of potassium ions by protons. The maximum adsorption capacities of titanate whiskers for Cu(II), Pb(II), and Cr(III) ions were 142.0, 395.7, and 97.0 mg g⁻¹ when their initial concentrations were 150, 300, and 80 mg L⁻¹, respectively. The adsorption equilibriums were almost established in 30 min. The adsorption of Cu(II), Pb(II), and Cr(III) ions on titanate whiskers followed the pseudo-second-order adsorption kinetics. The Langmuir adsorption isotherms well fitted the adsorption equilibriums of Cu(II) and Pb(II) ions while the Freundlich adsorption isotherm well fitted the adsorption equilibrium of Cr(III) ions.

The aim of the present study is to investigate the effects of operating conditions and establish the mechanism of xanthene dye removal from aqueous solutions by electrocoagulation (EC) using a batch-stirred cell operated under galvanostatic regime. The influence of the operating parameters such as: initial pH and dye concentration, electrolysis time, current density, electrode configuration, and electrical current type on the EC performances was investigated. EC tests were performed at current density values ranging from 45 to 109 A/m, initial dye concentrations ranged between 0.1 and 1 g/L, and initial pH values adjusted in the range from 3 to 9. The effects of several electrode configurations (aluminum–aluminum, mild steel–mild steel, and aluminum–mild steel) and current regimes (direct current and alternating pulsed current) on the removal efficiency and energy and material consumption are also discussed. Total organic carbon (TOC) analysis, UV–vis spectroscopy, Fourier transform infrared spectroscopy (FTIR), and cyclic voltammetry (CV) were employed in order to elucidate the decolorization mechanism of Rhodamine 6G (R6G) dye by EC in aqueous solutions. With this aim in view, chemical coagulation tests were also carried out. The best performance was obtained when the EC process was conducted with iron-based electrode configuration in alternative pulse current (APC) mode. It was found that the removal of R6G is due to the co-precipitation of polymeric iron flocs with the phenyl-xanthene radicals remained in the bulk solution after the demethylation and deamination processes. Furthermore, the flocs are separated by flotation with the support of the molecular hydrogen generated at the cathode (in particular at relatively high values of current density) or by sedimentation.

The purpose of this study is to examine the development and effectiveness of a persistent dissolved-phase treatment zone, created by injecting potassium permanganate solution, for mitigating discharge of contaminant from a source zone located in a relatively deep, low-permeability formation. A localized 1,1-dichloroethene (DCE) source zone comprising dissolved- and sorbed-phase mass is present in lower-permeability strata adjacent to sand/gravel units in a section of the Tucson International Airport Area (TIAA) Superfund Site. The results of bench-scale studies conducted using core material collected from boreholes drilled at the site indicated that natural oxidant demand was low, which would promote permanganate persistence. The reactive zone was created by injecting a permanganate solution into multiple wells screened across the interface between the lower-permeability and higher-permeability units. The site has been monitored for 9 years to characterize the spatial distribution of DCE and permanganate. Permanganate continues to persist at the site, and a substantial and sustained decrease in DCE concentrations in groundwater has occurred after the permanganate injection. These results demonstrate successful creation of a long-term, dissolved-phase reactive treatment zone that reduced mass discharge from the source. This project illustrates the application of in situ chemical oxidation as a persistent dissolved-phase reactive treatment system for lower-permeability source zones, which appears to effectively mitigate persistent mass discharge into groundwater.