Spatial and seasonal mobilization trends of metals in surface water were evaluated in the US–Mexico San Pedro River (SPR). Water samples were collected at five sampling stations for the analysis of dissolved oxygen, pH, electric conductivity, sulfates, and metals (Cd, Cu, Fe, Mn, Pb, and Zn). Quality of the water was characterized through Ecological Criteria of Water Quality (ECWQ) established in Mexico and Water Quality Criteria (Environmental Protection Agency (EPA)). High total metal concentrations were detected as follows: Fe > Cu > Mn > Zn > Pb > Cd. Metal concentrations were slightly higher in dry season than in rainy season: Cd (below detection limit (BDL)–0.21 mg L⁻¹), Cu (BDL–13 mg L⁻¹), Fe (0.16–345 mg L⁻¹), Mn (0.12–52 mg L⁻¹), Pb (BDL–0.48 mg L⁻¹), and Zn (0.03–17.8 mg L⁻¹). Low pH and dissolved oxygen values as well as high sulfate content were detected in both seasons. High values of metals (Cd, Cu, Fe, Mn, Pb, Zn) were detected at station E1 representing pollution source, as well as at stations E2 (Cd, Cu, Fe, Mn), E3 (Fe, Mn, Pb), and E4 and E5 (Fe, Mn). Detected concentrations exceeded maximum permissible established in ECWQ and Water Quality Criteria (EPA). Efflorescence salts on sediments in the dry season could increase levels of metals in water column. This study provides valuable information on the potential mobility of metals in surface water of SPR located in an arid environment where transport processes are strongly linked to climate. The information derived from this study should help the regional and national authorities to address present environmental regulations.

The aim of the present study was to evaluate the influence of the recirculation rate on the efficiency of a 1,000-L pilot anaerobic sequencing batch biofilm reactor (ASBBR) treating effluent from a small dairy plant over a long-term period (570 days). Three operational conditions were studied, in which recirculation rates were varied, resulting in upflow velocities of 0.2, 3.8, and 6.4 m h⁻¹and the cycle time of 48 h. The biomass was immobilized on plastic supports containing polyurethane foam. The organic loading rate varied according to the operations occurring in the dairy plant. After system stability had been verified, temporal profiles of the substrate and metabolite concentrations were obtained, allowing kinetic parameter inference. Sludge samples from the inoculum and from the reactor were analyzed through microscopic examination, molecular biology analyses, and specific methanogenic activity assays. The average efficiencies of organic matter removal were 82 ± 11, 84 ± 9, and 87 ± 9 % at velocities of 0.2, 3.8, and 6.4 m h⁻¹, respectively. Microscopic examinations indicated that the fluorescent microorganisms decreased throughout the experiment, and they were not detected in the last condition. Homoacetogenesis was inferred as a possible pathway for H₂removal and for maintenance of the methanogenic process. Specific methanogenic activity increased throughout the monitoring period. It was possible to conclude that the ASBBR was efficient, robust, and reliable in treating dairy effluents under the conditions used.

The degradation of methyl orange (MO) in aqueous solution by microwave irradiation in the presence of granular-active carbon (GAC) was investigated. It was found that a synergistic rather than an additive effect of microwave irradiation and GAC contributes to the high-degradation efficiency. The ultraviolet and visible spectrum (UV–vis), infrared spectroscopy (IR), and scanning electron microscopy (SEM) measurements were conducted to trace the MO degradation process. It was demonstrated that the decrease in performance of GAC after repetitive use is largely attributed to the adsorption of some intermediate products on the surface of GAC. The regeneration of the spent GAC under microwave radiation was also investigated. The results show that the activity of spent GAC can be effectively recovered by microwave radiation and 74.1 % of its initial activity remains after six reaction cycles.

Vanadium (V) is an essential trace element for certain biological enzymatic reactions but becomes toxic at higher concentrations. The impact of V at concentrations of 0 − 500 mg/kg V(V) spiked in soils on soil enzymatic activities, and microbial diversity was investigated in soybean pot experiments. The results from sequential extraction of soil V indicated increasing V mobilizable fractions with increase of soil V concentrations. The soil sulfatase activity decreased drastically from 2.35 − 5.55 to 0.30 − 0.88 μmol methylumbelliferon (MUB)/[h g soil] with increasing soil V loading at different vegetative stages. Surprisingly, the activity of soil phenol oxidase increased from 0 − 0.73 to 3.74 − 7.61 μmol L-3,4-dihydroxyphenylalanine (DOPA)/[h g soil] with increasing soil V concentrations at different vegetative stages probably due to oxidation stress caused by V in soils. These observations were not affected by the presence of soybean plants. In comparison, soil phosphatase, protease, and ß-glucosidase showed no significant reaction to V concentrations in soil. Both fungal and bacterial communities changed significantly at different levels of V treatments. Accordingly, V may pose a threat to some biologically mediated functions in soils even at low bioavailable amounts.

Management strategies that prevent the onset of nuisance and noxious cyanobacteria blooms are needed to preserve the integrity and safety of freshwater resource uses. Scientifically defensible data are needed regarding efficacy of proactive approaches in order to assist water resource managers in making informed decisions. As phosphorus availability has been indicated as a crucial aspect of cyanobacteria presence/dominance in freshwater systems, the integration of novel technologies to inactivate phosphorus is a critical component to achieve improved water quality. Phoslock (Phoslock Water Solutions, Ltd.) phosphorus locking technology is composed of the element lanthanum in a bentonite clay matrix that has a high specificity to bind and inactivate soluble reactive phosphorus. This research evaluated the phosphorus binding efficiency of Phoslock in aqueous and sediment matrices and the consequent impact on algae assemblage composition and water quality parameters. Laguna Niguel Lake in California afforded an opportunity to evaluate the operational effectiveness of Phoslock in a system historically plagued by high phosphorus concentrations, potentially toxic cyanobacteria (Aphanizomenonflos-aquae dominant), and lake closures. Phoslock was able to rapidly (<2 weeks) and significantly (p < 0.0005) decrease total (>80 %) and free reactive (>95 %) phosphorus in the water column and shift potentially releasable sediment phosphorus fractions to residual forms after treatment. Despite documented cyanobacteria blooms and high pretreatment cell densities, cyanobacteria levels remained below or near detection limits and only comprised a small fraction of the algae assemblage following Phoslock application. This study provides water resource managers an information on operational implementation and efficacy of a phosphorus binding technology.

Natural clinoptilolite from Zlatokop deposit, Serbia, was activated by microwave irradiations (10 min, 550 W) and its adsorptive efficiency for removal of crystal violet (CV) dye from aqueous solution was investigated. The process variables were specified by response surface method and the central composite design (CCD). Percentage of dye removal as a function of two numeric factors (the amount of zeolite and the concentration of crystal violet) with five values (rotatibility factor α = 0. 41) and one numeric factor (contact or agitation time) with three values (rotatibility factor α = 1. 00) at dynamic ambient conditions and pH = 6 was tested. The optimal conditions for 91.99 % decolorization were predicted to be 2 g of the zeolite in 100 ml of CV aqueous solution with concentration of 250 mg/l, and contact time of 678 s. The model was validated experimentally. Two isotherm models—Langmuir type 2 and Freundlich could describe the adsorption process with high correlation to experimental data. The calculated adsorbent capacity from the CCD (12.625 mg/g) showed a good agreement with the adsorption capacity obtained by Langmuir-2 isotherm (13.477 mg/g) and with pseudo-second-order kinetic model (12.404 mg/g).

The incineration fly ash (IFA), molten fly ash (MFA), thermal power plant fly ash (TPP-FA), and nonferrous metal processing plant ash (MMA) have been screened in terms of the following rare-termed metal contents: B, Ce, Co, Dy, Eu, Ga, Gd, Hf, In, Li, Lu, Mn, Nb, Nd, Ni, Pr, Rb, Sb, Se, Sm, Sr, Ta, Tb, Te, Ti, Tm, V, W, Y, and Yb. The pseudo-potential for recycling of the waste ashes, as compared to the cumulative concentration in the crust (mg kg⁻¹), was determined as follows: MMA > IFA > MFA > TPP-FA. The comparison with the crude ore contents indicates that the MMA is the best resource for reprocessing. The recovery of the target metals using aminopolycarboxylate chelants (APCs) has been attempted at varying experimental conditions and ultrasound-induced environment. A better APC-induced extraction yield can be achieved at 0.10 mol L⁻¹ concentration of chelant, or if the system temperature was maintained between 60 to 80 °C. Nevertheless, the mechanochemical reaction induced by the ultrasound irradiation has been, so far, the better option for rare metal dissolution with chelants as it can be conducted at a minimum chelant concentration (0.01 mol L⁻¹) and at room temperature (25 ± 0.5 °C).

Cyanobacterial toxins have caused worldwide concern because of their lethal effects, which has led to intensive search of cost-effective removal techniques. With the application of a Box–Behnken experimental design combined with response surface methodology, the adsorption process of the potent and commonly occurring microcystin-LR (MC-LR) onto nano-sized montmorillonite (NMMT) K10 was investigated through the HPLC-UV system. The quadratic statistical model was established to predict the interactive effects of pH (1–12), NMMT K10 dose (1–10 mg mL⁻¹), and MC-LR initial concentration (100–1,000 μg L⁻¹) on MC-LR adsorption and to optimize the controlling parameters. The MC-LR adsorption by NMMT K10 was pH dependent and was found to reach a maximum at pH 2.96 with a removal peak of 186.37 μg g⁻¹. The range of optimal pH for MC-LR adsorption was 2.96–3.48, and higher adsorption capacities were achieved with increasing adsorbent dose and MC-LR initial concentration. Sorption kinetics revealed that the sorption process of MC-LR on NMMT K10 was rapid (short equilibrium time) and involved several kinetic stages. The Langmuir isotherm model predicted that the theoretical maximum adsorption capacity at pH 3 was 285.20 μg g⁻¹. Alkali eluting media (0.1 M NaOH) showed the highest desorption percentage (75.3 %) during regeneration studies. The high Brunauer–Emmett–Teller (BET) specific surface area (204.65 m² g⁻¹) of NMMT K10 was also characterized. NMMT K10 was determined to be an effective and economic adsorbent for MC-LR removal on a large scale.

TiO₂-mediated photodegradation is widely reported to degrade recalcitrant pollutants such as nitrophenolics. This paper investigated the TiO₂-mediated photodegradation of trinitrophenol (TNP) in aqueous solution irradiated by an artificial light source. About 28.4 % TNP degradation was attained over 450 min from an initial TNP concentration of 1,000 mg L⁻¹. Ionic chromatographic analysis further revealed the evolution of nitrite and nitrate anions and an unknown intermediate X during the photodegradation process. The trends of nitrite and nitrate anions indicate that the photodegradation process produced nitrite at first, which subsequently turned to nitrate in the presence of oxygen. The removal rate of COD was far slower than that of TNP, inferring the photodegradation reaction gradually mineralized the parent pollutants. The photodegradation of TNP could not proceed under anaerobic condition, presumably a result of oxygen deficiency that disabled the denitration process. Because of the volumetric loss of the test solution, follow-up irradiations were performed after addition of supplementary water. This follow-up irradiation period revealed that direct photolysis, i.e., irradiation in the absence of TiO₂photocatalysts, could not photodegrade TNP but gradually diminish the component X.

Optimization of sludge conditioning and dewatering is a continuing challenge for wastewater treatment plants. This study investigated the use of an in-line UV–vis spectrophotometer to optimize the polymer dose during sludge dewatering. The study established a relationship between the optimum polymer dose and residual polymer concentration in filtrate using UV–vis absorbance measurements at 191.5 nm. Experiments were carried out with four different polymers (FloPolymer CA 475, CAB 4500, FloPolymer CB 4350, and FloPolymer CA 4600), and similar results were obtained from all polymers. Detection limits of the polymers ranged from 0.35 to 0.95 mg/L in centrate. The optimum polymer dose was determined based on capillary suction time (CST) and filtration tests, and a relationship between the filtrate absorbance at 191.5 nm and optimum polymer dose was established. In the under-dose range, increasing the polymer dose resulted in a decrease in filtrate absorbance due to improvement in filtrate quality. The optimum polymer dose corresponded to the minimum filtrate absorbance at 191.5 nm. When the optimum dose was exceeded, absorbance values started to increase corresponding to the increase in the residual polymer concentration in filtrate in the over-dose range. These results indicate that real-time optimization of polymer dose can potentially be achieved at wastewater treatment plants using an in-line UV–vis spectrophotometer based on the absorbance of centrate or filtrate samples at 191.5 nm.