Various geochemical studies have yielded conflicting data on whether humic coatings decrease or increase adsorption of heavy metals by soil minerals. The objective of the present study is to determine how humate pre-adsorption affects subsequent retention of Cd and Pb by palygorskite and sepiolite, as special silicate clay minerals of soil in many arid regions. For this purpose, a series of equilibrium batch experiments were conducted on the interactions of Pb and Cd with Ca–palygorskite and Ca–sepiolite before and after humate adsorption. The results showed that the Langmuir (L), Freundlich (F), Langmuir–Freundlich (LF), and Toth (T) equations satisfactorily described metal sorption data on the minerals. In the presence of humate as the pre-adsorbate, the values for sorption capacities of palygorskite and sepiolite for Cd and Pb slightly decreased. This can be attributed to the competition between humates and metal ions for mineral active sites and steric hindrance of the adsorbed humates, which reduces the access of metal ions to the mineral surface and internal channels. Humate coatings decreased the adsorption equilibrium constants of Cd, suggesting that the affinity of the organo-clays for Cd sorption is lower than those of Ca–clays. The values for the heterogeneity factor (β) generally showed an increasing trend with increasing humate coverage on palygorskite and sepiolite, which can be explained by the increased diversity of adsorption centers on humate–clay complexes. It may be concluded that the presence of humate bound on fibrous clay surfaces can influence the sorption, and hence the bioavailability and mobility of heavy metals in fibrous clay-containing arid and semiarid soils.

A novel plastic optical fiber (POF) sensor was investigated to monitor total suspended solids (TSS) concentration continuously, offering insights into wastewater treatment bioreactors without disturbing them. First, off-line experiments with both anaerobic and aerobic sludge (in concentrations ranging between 0.1 and 8.6 g TSS L⁻¹) were used to establish the exponential relationship of the sensor’s transmitted optical power with TSS concentrations. Attenuation coefficients differed clearly with the type of sludge (1.227–1.274 and 0.456–0.679 for anaerobic and aerobic biomass, respectively) and, in the case of the aerobic sludge, with its coloring. The POF sensor was further used for online monitoring of sludge settling profiles inside a sequencing batch reactor (SBR) that was being operated under a “feast-famine” regime. The turbidity profiles agreed very well with the Boltzmann equation. The Boltzmann dx parameter revealed clear differences in the steepness of the settling gradients, which could be explained by the changes in the applied organic loading rates (OLR). OLR in the range of 1.34–1.53 g COD L⁻¹ day⁻¹ resulted in steeper settling gradients than OLR in the range of 2.13–3.12 g COD L⁻¹ day⁻¹ (dx: 0.42–0.50 vs. 0.90–1.36). Thus, the POF sensor not only revealed elevated potential for prediction of biomass concentration but also for becoming an integral part of real-time automation systems in order to diminish repeated sampling and off-line analysis to control the withdrawal phase based on seasonal sludge settling profiles.

The aim of this study is to develop a process that combines electrocoagulation and electroperoxidation (EC-EP) and to evaluate its performance in treating domestic wastewaters (DWW). Electrolysis was performed using a parallelepipedic electrolytic cell (0.5 L) containing one sacrificial anode (mild steel or aluminum) and one cathode (vitreous carbon). The effects of the treatment time, current density, and type of anode electrode on the process performance were examined. The experimental results revealed that a current density of 4.0 mA cm⁻² was beneficial for DWW treatment. There was a decrease in the chemical oxygen demand (COD), suspended solid (SS), turbidity, color, and total phosphorus (Pₜₒₜ) by 67 ± 9, 98 ± 2, 55 ± 10, 61 ± 9, and 97 ± 0 %, respectively, for a treatment time of 60 min in the electrolysis cell in the presence of mild steel (anode) and vitreous carbon (cathode) electrodes. The process was also determined to be effective for removing pathogens (99 ± 1 % removal), such as fecal coliform (the log-inactivation was higher than 2 units).

The present and past mining activity left several abandoned tailings and dams in the Panasqueira tin–tungsten mining area. Seasonal water samples and stream sediments were collected during two different periods (rainy and dry seasons) and analyzed for a wide range of major and trace elements, in order to define the present hydrochemical situation. Rain waters interact with the altered sulfides stored in the tailings which generate runoff waters with high metal concentrations. The waste material derived from the exploitation enhanced acidification and metal-releasing processes, due to the increase in the specific surface, which favors the oxidation of sulfide minerals. Acid drainage and high metal(loid)s (Cd, Fe, Mn, Zn, Cu, As) concentrations in solution were observed in waters leaching the Panasqueira tailing deposits. In dry season, generally the acidic waters, enriched in metals, evaporate progressively depositing sulfate efflorescences characteristic of acidic environments. The elements distribution in precipitated minerals helps in the interpretation of aqueous geochemical data. Aqueous concentrations may be attenuated by goethite, gibbsite, and/or ferrihydrite precipitation in the oxidation zone through adsorption processes. The use of these waters for human consumption and for irrigation represents a threat to humans as they have a potential carcinogenic risk, especially due to the As concentrations. The acid water precipitation is present on the stream sediments, with concentrations exceeding the toxicity limits. Stream sediments are good receptors of metals and metalloids transported by waters. The enrichment factor values, of heavy metal(loid)s from Casinhas stream and Zêzere river sediments, are extremely high in Ag, As, Cd, and Cu revealing enrichments for these potential toxic elements. Igₑₒvalues shows that samples are strongly to very strongly polluted for Ag, As, Bi, Cd, and Cu. According to the consensus-based SQGs, 80 % of the samples were classified at the level of great concern and adverse biological effects are to be expected frequently in this area.

Aquatic plant biomass has been shown to have a great potential for biogas production. The use of ruminal fluid has been shown to improve the degradation of the lignocellulosic material with its conversion into volatile fatty acids (VFA) during a first phase of hydrolysis–acidogenesis. VFAs are important as the feedstock for methane and hydrogen production in a second phase process within a biorefinery. The objective of this work was to produce a high yield of VFA during a first phase of anaerobic hydrolysis–acidogenesis of Pistia stratiotes biomass assessing the effect of the use of rumen fluid as inoculum and of daily adjustment of pH in batch-operated reactors. One liter anaerobic reactors containing 15 gSV L⁻¹ of P. stratiotes biomass were incubated at 30 ± 2 °C and agitated once a day. The inoculum concentration had no significant effect on the increase in VFA concentration and 20 % (V/V) was used in all treatments. The final average VFA concentration and conversion coefficients from VS to VFA in the inoculated treatment with no pH adjustment (T1) and with pH adjustment (T2) (1817 mgCOD L⁻¹ and 0.1319 mgVFA mgVS⁻¹, respectively) were significantly higher than those found in the treatment with no inoculum (T0). There were no significant differences between T0 and T1 in the VS degradation rate. In contrast, the degradation rate in T2 was significantly higher. Thus, the addition of ruminal fluid promoted the production of VFA, and the pH adjustment had no significant effect on this parameter but did influence the biomass degradation.

Bacterial antibiotic resistance has long been a public health concern worldwide. Although antibiotic abuse highly correlates with occurrence of resistant pathogens in hot spots like animal feedlots, it remains obscure how frequently these resistance genotypes would emerge and/or retain in natural circumstances. In this study, we monitored seven antibiotic resistance genes in various surface waters. All seven resistance genes were detectable in Puzih River samples, including strA (40.6 %), cmlA (29.7 %), blaTEM (9.1 %), tet(B) (8.5 %), sul1 (7.9 %), mecA (3.6 %), and tet(A) (2.4 %). Among these genes, strA was observed in four out of five sampling occasions during the 1.5-year monitoring period and most of the genes were detected at least two times over five samplings. These results imply that surface waters in Taiwan act as potential reservoirs for several resistance genotypes. Moreover, high prevalence of tet(A) (92.0 %) and sul1 (96.0 %) in swine farm wastewater samples suggests routine antibiotic usage and particularly, the fodder supplements could indeed be a risk factor to antibiotic resistance in environments. sul1, tet(A), blaTEM, and strA were detectable in domestic water treatment plants and reservoirs, suggesting that several resistance genotypes against antibiotics as streptomycin, ampicillin, tetracycline, and sulfonamides are likely to persist in natural circumstance and may consequently contaminate the drinking water systems.

The study provided a critical appraisal of the extended aeration process as a single-sludge system for nitrogen removal, emphasizing its inherent deficiencies. For this purpose, the system was designed first using the prescribed procedure in the German practice, ATV A-131. The design used the basic data reported in different studies related to conventional characterization and chemical oxygen demand (COD) fractionation defining the biodegradation characteristics of domestic wastewater. A critical appraisal of the design was made with emphasis on the fate of biodegradable COD and oxidized nitrogen in the anoxic phase by process modeling and evaluation. The results obtained were evaluated using basic stoichiometry and mass balance for major nitrogen fractions. The A-131 design based on a total sludge age of 20 days defined a system with a hydraulic residence time of 1.2 days where half of the volume was operated under anoxic conditions; the effluent nitrate concentration was reduced to 8.3 mg N/L with an internal recycle (nitrate) ratio of 4.9. Model evaluation of the prescribed design indicated that oxidized nitrogen was totally consumed within the first 25–30 % portion of the anoxic volume. The remaining volume was forced to operate under anaerobic conditions, where no appreciable endogenous decay would occur. ATV A-131 procedure, relying on empirical coefficients and expressions, was neither consistent with process stoichiometry nor justifiable by modeling. Evaluations based on modeling and process stoichiometry revealed significant inherent weaknesses of extended aeration for providing a sustainable basis for nitrogen removal.

Thifluzamide fungicide is widely used to protect rice (Oryza sativa) against the sheath blight fungus (Rhizoctonia solani). The continuous application of thifluzamide may lead to accumulation in soil and contaminate rice crop. To sustain the environment, it is necessary to assess its accumulation and degradation in field. The method limit of detection (LOD) was 0.022 ng. The limits of quantitation detection (LOQ) were 5.0 μg L⁻¹in water and 4.0 μg kg⁻¹in paddy soil and rice crop. In this study, a 2-year (2011–2012) field study was performed to monitor thifluzamide degradation in the rice production areas of Nanjing, Xiaoxian, and Changsha. The degradation dynamics of thifluzamide in paddy water, paddy soil, and rice crop were well described by the first-order kinetics equation. The 2-year average half-lives of thifluzamide in paddy water, paddy soil, and rice crop were 26.19, 17.92, 14.61 days (Nanjing), 15.63, 20.71, 9.10 days (Xiaoxian), and 9.47, 13.92, 10.08 days (Changsha), respectively. Thifluzamide degraded more rapidly in rice crop than in soil and paddy water. The variation in thifluzamide degradation was attributed to the difference in rainfall during the period of rice cultivation. The maximum residue of thifluzamide in brown rice was 0.0303 mg kg⁻¹in Nanjing and the residue of thifluzamide in brown rice was not detected in other two sites before thifluzamide was applied at pre-harvest. The experimental data demonstrated that thifluzamide recommended dosage of 72 g a.i.ha⁻¹can be used in rice fields with less than three times within a 30-day time interval.

Salinization is a global problem, including in California, USA, where over two million hectares of irrigated lands have deteriorated due to salt loading. Because of freshwater shortage, some farmlands are also irrigated with agricultural drainage water, which further exacerbates the salinization process. With the objectives of rapidly quantifying spatial and temporal progression of salinization and identifying yield potential for a high-value crop, we conducted 2-year salinity surveys in a salt-affected farm in California by utilizing a dual dipole electromagnetic induction technology (EM38). The EM-predicted conductivity (ECₑ) was consistent with the ground-truth soil data ECₛ and increased with depth. About 50 and 25 % of the ECₑ data in moderately (A) and severely (B) affected salinity zones surpassed 500 and 1000 mS m⁻¹ levels, respectively. In the northern part of B, up to 70 % samples remained within 500–1000 mS m⁻¹ range. There was eastbound salt loading in the northern and southern parts of A. Rhizosphere salinity showed spatial dependence up to 500 m lateral distance. The shifts in salinity could be due to dispersion and leaching of solutes. High crop yield reduction was estimated in the southwestern and northeastern parts of the field that had typically elevated ECₑ. Around 43 % surveyed area was conducive to attaining 80 % of full yield potential, and the central part of the field was determined to be most suitable for crop growth. Coupling of EM results with production values indicated that under elevated saline condition, it would be feasible to grow a high-value tomato crop.

Bioindicators are useful in monitoring air pollution. This study assessed the efficacy of various tree leaf morphological, physiological and biochemical biomarkers in reflecting different intensities of air pollution. Leaves from Brachylaena discolor trees growing 0, 2.5, 6 and 11 km from an industrial hub (pollution source) in eThekwini, South Africa, were analysed for leaf area, chlorophyll (Chl) content, superoxide and hydrogen peroxide (H₂O₂) production, electrolyte leakage, total antioxidant activity and concentration of selected minerals. B. discolor saplings grown under greenhouse conditions served as an ex situ control. Surface SO₂ and NOₓ levels which were measured at the in situ and control sites declined significantly with increasing distance from the source but were below detectable limits at the control site. At the site closest to the source, leaf area was significantly lower and Chl, electrolyte leakage, and copper (Cu) and phosphorous (P) levels were significantly higher than the control. Leaf area was significantly positively, and Chl content significantly negatively, correlated with distance from the source, while H₂O₂ production, electrolyte leakage and Cu and P concentrations were all significantly negatively correlated with distance from the source. The aforementioned parameters represent potential biomarkers of air pollution in B. discolor and in some cases (e.g., H₂O₂ and electrolyte leakage; leaf area and leaf Chl content) should be measured in conjunction with each other to accommodate for interactive effects. Using B. discolor leaves as bioindicators of air pollution may represent a more viable option for monitoring air pollution than monitoring stations.