The reduction of nitrous oxide (N₂O) emission during nitrogen removal process in municipal wastewater treatment is of great urgency. Sequencing batch biofilm reactor (SBBR) system could be a promising and efficient way to solve the problem. In order to get the high chemical oxygen demand (COD) and nitrogen removal efficiency and low nitrous oxide emission, the influence of biofilm density on SBBR was investigated. When the biofilm density changed from 15 to 30 %, the effluent COD, total nitrogen (TN) and ammonia nitrogen decreased, but the effluent TN concentration did not meet the class I-B standard of the Discharge Standard of Pollutants for Municipal Wastewater Treatment Plant in China. COD, TN, and ammonia nitrogen concentration was 42.34, 19.14 and 2.97 mg/L at 50 % biofilm density. When the density turned from 50 to 70 %, although the effluent COD, TN, and ammonia nitrogen were still decreased, N₂O emission increased from 0.45 to 0.77 %. Considering the effluent quality and N₂O emission, the optimal biofilm density in SBBR was 50 %.

A biogeochemical investigation was carried out on Origanum majorana grown on limestone substrate in Greece. Possible health risks from consumption of dried herbs and infusions were assessed. Macronutrients and essential and toxic metals were determined in the leaves of O. majorana plants and in their soil substrates. Toxic metals were measured in the herbal infusions. Macroelements were found generally in low concentrations for normally developing plants, except for Ca. The ratios N/P and N/K were found lower than the optimum range for normal growth, while the values of K/(Ca + Mg) ratio prevent the development of grass tetany. Manganese and arsenic were enriched in distinct samples. O. majorana plants can be used as indicators for soil environmental assessment. They can also be applied in phytoremediation methods in metal-polluted soils. Hazard indices were far below 1. Carcinogenic risks were found to be within the acceptable range. No health risk is anticipated by the consumption of the specific plants investigated in the present study.

Phosphogypsum (PG) is an industrial waste composed mainly by sulfate, turning it a suitable sulfate source for sulfate-reducing bacteria (SRB). In the present work, the capability of two SRB communities, one enriched from Portuguese PG (culture PG) and the other from sludge from a wastewater treatment plant (culture WWT-1), to use sulfate from PG was compared. In addition, the impact of this sulfate-rich waste in the microbial community was assessed. The highest efficiency in terms of sulfate reduction was observed with culture WWT-1. The bacterial composition of this culture was not significantly affected when sodium sulfate from the nutrient medium was replaced by PG as a sulfate source. Next generation sequencing (NGS) showed that this community was phylogenetically diverse, composed by bacteria affiliated to Clostridium, Arcobacter, and Sulfurospirillum genera and by SRB belonging to Desulfovibrio, Desulfomicrobium, and Desulfobulbus genera. In contrast, the bacterial structure of the community enriched from PG was modified when sodium sulfate was replaced by PG as the sulfate source. This culture, which showed the poorest performance in the use of sulfate from PG, was mainly composed by SRB related to Desulfosporosinus genus. The present work provides new information regarding the phylogenetic characterization of anaerobic bacterial communities with the ability to use PG as sulfate donor, thus, contributing to improve the knowledge of microorganisms suitable to be used in PG bioremediation. Additionally, this paper demonstrates that an alternative to lactate and low-cost carbon source (wine wastes) can be used efficiently for that purpose.

Polyether trisiloxane surfactants are widespread used as agricultural adjuvants because they increase the activity and the rainfastness of pesticides. On the contrary to pesticides, the environmental fate of agricultural adjuvants has not been much investigated, yet. Especially for trisiloxane surfactants, the knowledge on their environmental fate is scarce. To fill this gap, the mobility of a polyether trisiloxane surfactant on soil was studied. With a sorption batch equilibrium method, distribution coefficients between water and soil (K d, K ₒc, and K cₗₐy) were estimated for two standard soils (loam and sandy loam) and for every homologue of the trisiloxane surfactant. The obtained values for K d were between 15 and 135 cm³ g⁻¹, indicating that the trisiloxane surfactant is only slightly mobile in soil. The leaching in soil column was studied in a worst case scenario where the application of the trisiloxane surfactant was done on quartz sand and was immediately followed by a heavy rainfall. Less than 0.01 % of the initially applied trisiloxane surfactant had leached through 20 cm of quartz sand. Based on the K d values and the leaching in a soil column, the studied trisiloxane surfactant seems to be unlikely to leach through soil after application as agricultural adjuvant.

Natural volcanic tuff was used for the synthesis of geopolymer and then for the removal of Zn⁺². The characteristics of the natural volcanic tuff and the synthesized geopolymer were determined by X-ray diffraction (XRD), X-ray fluorescence (XRF), Fourier transform infrared (FTIR), and scanning electron microscopy (SEM). Results referred that the synthesized geopolymer had a higher efficiency uptake of 97.7 % as against 78.5 % for the natural volcanic tuff. The uptake capacity of geopolymer for Zn⁺² adsorption increased with increasing temperature in the studied range of 25–45 °C, contact time up to 30 min, pH up to 7, and initial concentration up to 160 ppm, while it decreased with an increase in geopolymer dosage. The isotherm study showed best fit on Langmuir and Radlich-Peterson models. The maximum uptake capacity obtained from Langmuir model increased from 14.7 to 17.63 mg/g as the temperature increased from 25 to 45 °C. The pseudo-second-order model showed the best fitness for the experimental data followed by intraparticle diffusion model. The adsorption process can be characterized as endothermic, homogeneous, spontaneous, irreversible, physical, and a high adhesion of the ions to the geopolymer surface. The results obtained buttressed the feasibility and applicability of producing geopolymer from natural volcanic tuff for the removal of heavy metals.

This paper first time reports the geochemical processes that are controlling fluoride enrichment in the groundwater of western Kumamoto area, Japan. Fifty (50) groundwater samples were collected and analyzed for the study where fluoride (F⁻) concentration ranges from 0.1 to 1.57 mg/L. About 58 % of the shallow groundwater and 26 % of the deep groundwater samples contain fluoride concentration beyond the Japanese drinking water permissible limit (0.8 mg/L). High F⁻ is largely accumulated in the stagnant zone of the Kumamoto Plain area and associated with Na-HCO₃-type groundwater. High pH, high HCO₃, low Ca²⁺, and high Na⁺ are the major characteristics of high-F⁻ groundwater. Hydrolysis of F⁻-bearing minerals and desorption of F⁻ from hydrous metal oxides are considered to be the primary sources of fluoride in groundwater. A positive correlation between F⁻ and Na⁺/Ca²⁺ ratio (r ² = 0.53) indicates that major ion chemistry plays a significant role in fluoride mobilization. Weakly alkaline nature of groundwater with high pH (7.05–9.45) expedites the leaching process of exchangeable F⁻ from F⁻-bearing minerals as well as favors desorption of F⁻ from metal oxide surfaces. High HCO₃ ⁻ and high PO₄ ³⁻ in the groundwater facilitate desorption process as competing anions, while high Na⁺/Ca²⁺ ratio largely control this process by decreasing positive-charge density of the metal-oxide surfaces. High Na⁺/Ca²⁺ ratio is attributed due to the cation-exchange process, while high pH and HCO₃ ⁻ are the result of both silicate hydrolysis and microbial reduction processes. In addition, calcite and fluorite seem to have a control on groundwater fluoride geochemistry.

Biochar (BC) as a soil amendment has found considerable interest in global agriculture and food production. However, BC application to agricultural soils requires knowledge about side-effects on leachate composition potentially affecting deeper soil layers and groundwater. We investigated the effects of BC application on leachate water characteristics in a greenhouse pot experiment with two crops cultivated in series, mustard (Sinapis alba L., cv. Serval) and barley (Hordeum vulgare L., cv. Xanadu). The experiment was set up with three agricultural soils (Planosol, Cambisol, Chernozem), four different BC types, derived from three different feedstocks (wheat straw, woodchips, and vineyard pruning), added at two application rates of 1 % (w/w) and 3 % (w/w). Leachate sampling was performed five times from November 2010 to May 2011 by excess watering. The leachates were analyzed for their pH, electrical conductivity (EC), as well as their nitrate (NO₃ ⁻), dissolved phosphorus (PDISS), potassium (K⁺), and dissolved organic carbon (DOC) concentrations. The application of all BCs caused a significant pH increase in the leachates; EC increased most noticeably in the straw biochar treatment. All BC types significantly decreased leachate NO₃ ⁻ loads (by up to 80 % for woodchip-derived BC) compared to the control, while PDᵢₛₛ and K⁺ loads most significantly increased in the straw-derived BC treatment. The results show that BC may be suitable as soil amendment in soils prone to NO₃ ⁻ leaching; moreover, whereas straw-derived BC in particular may support soil nutrient status by introducing P and K.

Foundry sands from the iron foundry industry were employed as a support source for photocatalysts. TiCl₄ was used as the titanium precursor in the preparation of the supported photocatalysts. The solids were characterized by scanning electron microscopy with energy-dispersive X-ray spectroscopy, X-ray diffraction, diffuse reflectance spectroscopy in the ultraviolet range, small-angle X-ray scattering, nitrogen porosimetry, and zeta potential measurements. The prepared catalyst systems contained Ti, Al, Fe, K, Na, or Cu. All systems were also found to contain carbon. The systems were evaluated in the photodegradation of rhodamine B. For comparative reasons, P25 (Degussa) was also employed as a catalyst. Among the tested systems, the greatest percent dye degradation occurred with ultraviolet (65 %) and visible (38 %) radiation, whereas under the same conditions, the commercial P25 catalyst achieved 93 and 14 % degradation, respectively, for the ultraviolet and visible radiation.

The higher areal productivity and lipid content of microalgae and aquatic weed makes them the best alternative feedstocks for biodiesel production. Hence, an efficient and economic method of extracting lipid or oil from aquatic weed, Salvinia molesta is an important step towards biodiesel production. Since Salvinia molesta is an unexplored feedstock, its total lipid content was first measured as 16 % using Bligh and Dyer’s method which was quite sufficient for further investigation. For extracting more amount of lipid from Salvinia molesta, methanol: chloroform in the ratio 2:1 v/v was identified as the most suitable solvent system using Soxhlet apparatus. Based on the literature and the preliminary experimentations, parameters such as solvent to biomass ratio, temperature, and time were identified as significant for lipid extraction. These parameters were then optimized using response surface methodology with central composite design, where experiments were performed using twenty combinations of these extraction parameters with Minitab-17 software. A lipid yield of 92.4 % from Salvinia molesta was obtained with Soxhlet apparatus using methanol and chloroform (2:1 v/v) as solvent system, at the optimized conditions of temperature (85 °C), solvent to biomass ratio (20:1), and time (137 min), whereas a predicted lipid yield of 93.5 % with regression model. Fatty acid methyl ester (FAME) analysis of S. molesta lipid using gas chromatograph mass spectroscopy (GCMS) with flame ionization detector showed that fatty acids such as C16:0, C16:1, C18:1, and C18:2 contributed more than 9 % weight of total fatty acids. FAME consisted of 56.32, 28.08, and 15.59 % weight of monounsaturated, saturated, and polyunsaturated fatty acids, respectively. Higher cetane number and superior oxidation stability of S. molesta FAME could be attributed to its higher monounsaturated content and lower polyunsaturated content as compared to biodiesels produced from C. vulgaris, Sunflower, and Jatropha.

Indoor air pollution significantly influences personal exposure to air pollution and increases health risks. Nitrogen dioxide (NO₂) is one of the major air pollutants, and therefore it is important to properly determine indoor concentration of this pollutant considering the fact that people spend most of their time inside. The aim of this study was to assess indoor and outdoor concentration of NO₂ during each season; for this purpose, passive sampling was applied. We analyzed homes with gas and electric stoves to determine and compare the concentrations of NO₂ in kitchen, living room, and bedroom microenvironments (MEs). The accuracy of passive sampling was evaluated by comparing the sampling results with the data from air quality monitoring stations. The highest indoor concentration of NO₂ was observed in kitchen ME during the winter period, the median concentration being 28.4 μg m⁻³. Indoor NO₂ levels in homes with gas stoves were higher than outdoor levels during all seasons. The concentration of NO₂ was by 2.5 times higher in kitchen MEs with gas stoves than with electric stoves. This study showed that the concentration of NO₂ in indoor MEs mainly depended on the stove type used in the kitchen. Homes with gas stoves had significantly higher levels of NO₂ in all indoor MEs compared with homes where electric stoves were used.