Nitrous oxide (N₂O) is emitted from a modified Ludzak–Ettinger (MLE) process, as a primary activated sludge system, which requires mitigation. The effects of aeration rates and internal recycle flow (IRF) ratios on N₂O emission were investigated in an MLE process fed with glycerol. Reducing the aeration rate from 1.5 to 0.5 L/min increased gaseous the N₂O concentration from the aerobic tank and the dissolved N₂O concentration in the anoxic tank by 54.4 and 53.4 %, respectively. During the period of higher aeration, the N₂O–N conversion ratio was 0.9 % and the potential N₂O reducers were predominantly Rhodobacter, which accounted for 21.8 % of the total population. Increasing the IRF ratio from 3.6 to 7.2 decreased the N₂O emission rate from the aerobic tank and the dissolved N₂O concentration in the anoxic tank by 56 and 48 %, respectively. This study suggests effective N₂O mitigation strategies for MLE systems.

This study investigated the microbial diversity established in a combined system composed of a continuous stirred tank reactor (CSTR), expanded granular sludge bed (EGSB) reactor, and sequencing batch reactor (SBR) for treatment of cellulosic ethanol production wastewater. Excellent wastewater treatment performance was obtained in the combined system, which showed a high chemical oxygen demand removal efficiency of 95.8 % and completely eliminated most complex organics revealed by gas chromatography–mass spectrometry (GC–MS). Denaturing gradient gel electrophoresis (DGGE) analysis revealed differences in the microbial community structures of the three reactors. Further identification of the microbial populations suggested that the presence of Lactobacillus and Prevotella in CSTR played an active role in the production of volatile fatty acids (VFAs). The most diverse microorganisms with analogous distribution patterns of different layers were observed in the EGSB reactor, and bacteria affiliated with Firmicutes, Synergistetes, and Thermotogae were associated with production of acetate and carbon dioxide/hydrogen, while all acetoclastic methanogens identified belonged to Methanosaetaceae. Overall, microorganisms associated with the ability to degrade cellulose, hemicellulose, and other biomass-derived organic carbons were observed in the combined system. The results presented herein will facilitate the development of an improved cellulosic ethanol production wastewater treatment system.

Carwashes are highly water-consuming processes that require wastewater treatment before discharge into a sewer system due to the complex composition of leachate. Anionic surfactants (AS) are the main constituents of this wastewater because of their cleaning and solubilization properties; they can be potentially dangerous for the environment if not adequately treated. Constructed wetlands (CWs) are low-cost systems increasingly used to treat different types of wastewater; however, there are few studies on their use for the treatment of carwash wastewater. In this study, an innovative constructed wetland arranged in a “cascade” to simulate a wall system (WCCW) was experimented in 2010 and 2011 to treat AS. Three plant species were tested at different AS inlet concentrations (10, 50, and 100 mg L⁻¹) with two hydraulic retention times (HRTs; 3 and 6 days): ribbon grass (Typhoides arundinacea (L.) Moench (syn. Phalaris arundinacea L.) var. picta; Ta), water mint (Mentha aquatica L.; Ma), and divided sedge (Carex divisa Hudson; Cd). All plant species grew constantly over the experimental period, showing a capacity to tolerate even the highest AS concentration. Using the HRT of 6 days, raising the inlet concentration increased the AS outlet concentration, with similar values for the treatments (median values of 0.13–0.15, 0.47–0.78, and 1.19–1.46 mg L⁻¹ at inlet concentrations in the order 10, 50, and 100 mg L⁻¹). The shorter HRT led to significant differences among treatments in the reduction of outlet concentration, the best result being given by the tanks vegetated with Ma (A = 97.7 % with outlet concentration 0.35 mg L⁻¹). After treatments of the WCCW, the AS content was reduced almost completely, with removal in the ranges 0.07–10.2 g m⁻² day⁻¹ for tanks planted with Ta, 0.10–9.1 g m⁻² day⁻¹ for Ma tanks, and 0.11–9.5 g m⁻² day⁻¹ for Cd tanks depending on the inlet concentration.

This paper employs the autoregressive distributed lag (ARDL) bounds methodological approach to investigate the relationship between economic growth, combustible renewables and waste consumption, carbon dioxide (CO₂) emissions, and international tourism for the case of Tunisia spanning the period 1990–2010. The results from the Fisher statistic of both the Wald test and the Johansen test confirm the presence of a long-run relationship among the variables under investigation. The stability of estimated parameters has been tested, while Granger causality tests recommend a short-run unidirectional causality running from economic growth and combustible renewables and waste consumption to CO₂ emissions, a bidirectional causality between economic growth and combustible renewables and waste consumption and unidirectional causality running from economic growth and combustible renewables and waste consumption to international tourism. In the long-run, the error correction terms confirm the presence of bidirectional causality relationships between economic growth, CO₂ emissions, combustible renewables and waste consumption, and international tourism. Our long-run estimates show that combustible renewables and waste consumption increases international tourism, and both renewables and waste consumption and international tourism increase CO₂ emissions and output. We recommend that (i) Tunisia should use more combustible renewables and waste energy as this eliminates wastes from touristic zones and increases the number of tourist arrivals, leading to economic growth, and (ii) a fraction of this economic growth generated by the increase in combustible renewables and waste consumption should be invested in clean renewable energy production (i.e., solar, wind, geothermal) and energy efficiency projects.

The nature of most environmental contaminants comes from chemical mixtures rather than from individual chemicals. Most of the existed mixture models are only valid for non-interactive mixture toxicity. Therefore, we built two simple linear regression-based concentration addition (LCA) and independent action (LIA) models that aim to predict the combined toxicities of the interactive mixture. The LCA model was built between the negative log-transformation of experimental and expected effect concentrations of concentration addition (CA), while the LIA model was developed between the negative log-transformation of experimental and expected effect concentrations of independent action (IA). Twenty-four mixtures of pesticide and ionic liquid were used to evaluate the predictive abilities of LCA and LIA models. The models correlated well with the observed responses of the 24 binary mixtures. The values of the coefficient of determination (R ²) and leave-one-out (LOO) cross-validated correlation coefficient (Q ²) for LCA and LIA models are larger than 0.99, which indicates high predictive powers of the models. The results showed that the developed LCA and LIA models allow for accurately predicting the mixture toxicities of synergism, additive effect, and antagonism. The proposed LCA and LIA models may serve as a useful tool in ecotoxicological assessment.

Laboratorial scale experiments were performed to investigate and evaluate the performance and removal characteristics of organics, color, and genotoxicity by an integrated process including ozonation, activated carbon (AC), and biological aerated filter (BAF) for recycling biotreated dyeing wastewater (BTDW) collected from a cotton textile factory. Influent chemical oxygen demand (COD) in the range of 156 − 252 mg/L, 5-day biochemical oxygen demand (BOD₅) of 13.5 − 21.7 mg/L, and color of 58 − 76° were observed during the 20-day continuous operation. Outflows with average COD of 43 mg/L, BOD₅ of 6.6 mg/L, and color of 5.6° were obtained after being decontaminated by the hybrid system with ozone dosage of 0.25 mg O₃ₐₚₚₗᵢₑd/mg COD₀, 40 min ozonation contact time, 30 min hydraulic retention time (HRT) for AC treatment, and 2.5 h HRT for BAF treatment. More than 82 % of the genotoxicity of BTDW was eliminated in the ozonation unit. The genotoxicity of the BAF effluent was less than 1.33 μg 4-nitroquinoline-N-oxide/L. Ozonation could change the organics molecular structures, destroy chromophores, increase the biodegradability, and obviously reduce the genotoxicity of BTDW. Results showed that the combined process could guarantee water reuse with high quality.

Chromium (Cr) toxicity is widespread in crops grown on Cr-contaminated soils and has become a serious environmental issue which requires affordable strategies for the remediation of such soils. This study was performed to assess the performance of citric acid (CA) through growing Brassica napus in the phytoextraction of Cr from contaminated soil. Different Cr (0, 100, and 500 μM) and citric acid (0, 2.5, and 5.0 mM) treatments were applied alone and in combinations to 4-week-old seedlings of B. napus plants in soil under wire house condition. Plants were harvested after 12 weeks of sowing, and the data was recorded regarding growth characteristics, biomass, photosynthetic pigments, malondialdehyde (MDA), electrolytic leakage (EL), antioxidant enzymes, and Cr uptake and accumulation. The results showed that the plant growth, biomass, chlorophyll contents, and carotenoid as well as soluble protein concentrations significantly decreased under Cr stress alone while these adverse effects were alleviated by application of CA. Cr concentration in roots, stem, and leaves of CA-supplied plant was significantly reduced while total uptake of Cr increased in all plant parts with CA application. Furthermore, in comparison with Cr treatments alone, CA supply reduced the MDA and EL values in both shoots and roots. Moreover, the activity of superoxide dismutase (SOD), guaiacol peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX) in shoots and roots markedly increased by 100 μM Cr exposure, while decreased at 500 μM Cr stress. CA application enhanced the activities of antioxidant enzymes compared to the same Cr treatment alone. Thus, the data indicate that exogenous CA application can increase Cr uptake and can minimize Cr stress in plants and may be beneficial in accelerating the phytoextraction of Cr through hyper-accumulating plants such as B. napus.

The objective of the study is to examine the relationship between environmental indicators and health expenditures in the panel of five selected Asian countries, over the period of 2000–2013. The study used panel cointegration technique for evaluating the nexus between environment and health in the region. The results show that energy demand, forest area, and GDP per unit use of energy have a significant and positive impact on increasing health expenditures in the region. These results have been confirmed by single equation panel cointegration estimators, i.e., fully modified ordinary least squares (FMOLS), dynamic OLS (DOLS), and canonical cointegrating regression (CCR) estimators. In addition, the study used robust least squares regression to confirm the generalizability of the results in Asian context. All these estimators indicate that environmental indicators escalate the health expenditures per capita in a region; therefore, Asian countries should have to upsurge health expenditures for safeguard from environmental evils in a region.

This research aimed at developing comprehensive assessments of physicochemical quality of groundwater for drinking and irrigation purposes at Dalcheon in Ulsan City, Korea. The mean concentration of major ions represented as follows: Ca (94.3 mg/L) > Mg (41.7 mg/L) > Na (19.2 mg/L) > K (3.2 mg/L) for cations and SO₄ (351 mg/L) > HCO₃ (169 mg/L) > Cl (19 mg/L) for anions. Thematic maps for physicochemical parameters of groundwater were prepared, classified, weighted, and integrated in GIS method with fuzzy logic. The maps exhibited that suitable zone of drinking and irrigation purpose occupied in SE, NE, and NW sectors. The undesirable zone of drinking purpose was observed in SW and central parts and that of irrigation was in the western part of the study area. This was influenced by improperly treated effluents from an abandoned iron ore mine, irrigation, and domestic fields. By grouping analysis, groundwater types were classified into Ca(HCO₃)₂, (Ca,Mg)Cl₂, and CaCl₂, and CaHCO₃ was the most predominant type. Grouping analysis also showed three types of irrigation water such as C1S1, C1S2, and C1S3. C1S3 type of high salinity to low sodium hazard was the most dominant in the study area. Equilibrium processes elucidated the groundwater samples were in the saturated to undersaturated condition with respect to aragonite, calcite, dolomite, and gypsum due to precipitation and deposition processes. Cluster analysis suggested that high contents of SO₄ and HCO₃ with low Cl was related with water-rock interactions and along with mining impact. This study showed that the effluents discharged from mining waste was the main sources of groundwater quality deterioration.

The extended aeration activated sludge (EAAS) process is one of the most applied biological processes in small towns. Here, we study the abundance and viability of total bacterial cells in two wastewater treatment plants (WWTPs) operating with an EAAS process. We use flow cytometry (FCM) combined with SYTO13 and propidium iodide (PI) dyes as a rapid, easy, reliable and accurate microbial monitoring tool. A disaggregation procedure with an ultrasonic bath was designed to detach total bacterial cells from activated sludge flocs for subsequent FCM analysis. This procedure permitted the recovery of total bacterial cells from sludge flocs without affecting bacterial viability, as indicated by bacterial strain controls. Since FCM is a multi-parameter technique, it was possible to determine total bacterial abundance and their viability in the activated sludge. As a comparative method, epifluorescence microscopy was also used to quantify total bacterial cells; both methods produced similar results. The FCM analysis revealed relative microbial stability in both the WWTPs. The total bacterial abundance quantified by FCM in the two plants studied was 1.02–6.23 × 10¹¹ cells L⁻¹ with 70–72 % viability, one logarithm less than that reported in the literature for WWTPs using the conventional activated sludge process. This can be explained by the difference in the operational parameters between the conventional plant and EAAS, mainly the organic loading rate.