Modeling the Cd(II) adsorption onto goethite

The surface complexation of Cd(II) to goethite (α‐FeOOH) at varying concentrations of solid, background electrolyte and Cd(II) has been investigated. The data was quantified according to the generalized version of triple layer (TLM) surface complexation model. In the presence of atmospheric CO₂, it was found that the experimental data of Cd(I) α‐FeOOH system could be explained satisfactorily by incorporating both the > FeOHCd⁺ and > FeOCdHCO₃ in the calculations. However, at excessive concentrations of Cd(II), typically over 13% surface coverages, the TLM predictions significantly underestimated the experimentally observed data obtained for Cd(II)/α‐FeOOH systems.     

Optimized pre-treatment of high strength food waste digestate by high content aluminum-nanocluster based magnetic coagulation

Coagulation-based pre-treatment efficiency of high strength digestate of food waste (HSDFW) anaerobic digestion is negated by organic ligand-catalyzed decomposition of coagulants. In this study, an efficient HSDFW pre-treatment method, magnetic seeds (MS) coagulation, was employed by using highly stable Keggin Al₃₀ nanocluster (PAC₃₀), MS and polyacrylamide (PAM), and its operation was optimized by evaluating the performance of removing turbidity, total suspended solids (TSS), chemical oxygen demand (COD), and total phosphorous (TP) phosphate. Results showed that at the optimum dosage of 4.82 g/L, PAC₃₀ demonstrated excellent removals as high as 98.93% ± 0.1% of turbidity, 98.04% ± 0.1% of TSS, 58.28% ± 0.3% of total COD, 99.98% ± 0.01% of TP and 99.50% ± 0.01% of dissolved phosphate, respectively. Apparent molecular weight (AMW) and three-dimensional excitation-emission matrix (3D-EEM) fluorescence spectroscopy analyses demonstrated more efficient removal of dissolved organic matter (DOM), particularly non-biodegradable and hydrophobic components by PAC₃₀ than commercial coagulant. The sedimentation was much improved from 40 min by coagulation/flocculation to about 5 min settling by MS coagulation. The PAC₃₀ based magnetic coagulation (MC) presents theoretical guidance on a cost-effective and much less footprint pre-treatment alternative for high strength wastewater.     

Synthesis of 4,4′-dichloro-3,5,3′,5′-tetramethylbiphenyl by the sandmeyer reaction

4,4′-Dichloro-3,5,3′,5′-tetramethylbiphenyl was prepared by -diazotization of 3,5,3′,5′-tetramethylbenzidine followed by the Sandmeyer reaction. The starting material is a noncarcinogenic analogue of benzidine, and the product may be of interest as a model compound for studying the metabolism of chlorinated biphenyls.     

Modeling interactions at the tributyltin-kaolinite interface

Tributyltin (TBT) is a common pollutant in natural environments and the interaction with mineral surfaces largely determine its solubility, speciation, bioavailability, and transport in aqueous systems. The present work aimed at quantifying the TBT adsorption using kaolinite and a kaolinite-rich sediment as sorbent materials. Experiments were conducted under conditions that are important from an environmental perspective. Proton adsorption data were determined for kaolinite as a function of pH and electrolyte concentrations to ascertain intrinsic acidity constants and site density values. The pH(zpc) of kaolinite sample KGa was determined at 4.9 by surface titration. The generalized diffused double layer model (DLM) was used to quantify both, proton and TBT adsorption. Following intrinsic acidity and TBT binding constants resulting from the TBT/kaolinite system were used: >SOH ==> >SO- + H+, logK = -5.4; >SOH + H+ ==> SOH2+, logK = 4.6; >XNa + H ==> XH + Na+, logK(X/H+) = -1.1; >SO- + TBT+ ==> >SOTBT, logK = 3.5; >XNa + TBT+ ==> Na+, logK(X/TBT) = 1.0. All surface-active variable charge sites on kaolinite, namely >AlOH and >SiOH are grouped and collectively refer to as >SOH in this paper. >XNa refers to ion exchange sites. Modeling of TBT adsorption onto kaolinite was conducted distinguishing selective (high affinity) sites (>S(S)OH) in addition to non-selective sites (>SOH). The inclusion of >S(S)OH was essential in order to quantify TBT adsorption successfully, while the inclusion of >XNa was optional. The reduction of surface coverage values by a 10-fold TBT adsorption modeling is in agreement with the results of molecular model calculations of the system. Parameters calculated for the monophase kaolinite were subsequently used to quantify the TBT adsorption onto kaolinite-rich sediment.     

Positive Interactions Between Irrawaddy Dolphins and Artisanal Fishers in the Chilika Lagoon of Eastern India are Driven by Ecology,Socioeconomics, and Culture

In human-dominated landscapes, interactions and perceptions towards wildlife are influenced by multidimensional drivers. Understanding these drivers could prove useful for wildlife conservation. We surveyed the attitudes and perceptions of fishers towards threatened Irrawaddy dolphins (Orcaella brevirostris) at Chilika Lagoon India. To validate the drivers of fisher perceptions, we : (1) observed dolphin foraging behavior at stake nets, and (2) compared catch per unit effort (CPUE) and catch income of fishers from stake nets in the presence and absence of foraging dolphins. We found that fishers were mostly positive towards dolphins, believing that dolphins augmented their fish catch and using culture to express their perceptions. Foraging dolphins were observed spending half their time at stake nets and were associated with significantly higher catch income and CPUE of mullet (Liza sp.), a locally preferred food fish species. Wildlife conservation efforts should use the multidimensional drivers of human–wildlife interactions to involve local stakeholders in management.     

The dynamics of shifting cultivation captured in an extended Constrained Cellular Automata land use model

This paper presents an extension to the Constrained Cellular Automata (CCA) land use model of White et al. [White, R., Engelen, G., Uljee, I., 1997. The use of constrained cellular automata for high-resolution modelling of urban land-use dynamics. Environment and Planning B: Planning and Design 24(3), 323–343] to make it better suited for modelling the dynamics of shifting cultivation. In the extended model the time passed since the last land use transition of a location is a factor of its land use potential. The model can now account for the gradual decrease in soil fertility after an area of forest has been cleared for cultivation and also capture the process of regeneration once the plot is fallowed. The model is applied for the Ruhunupura area of Sri Lanka where chena, a particular practice of shifting cultivation, is a common land use that dominates the landscape dynamics. The model is calibrated for the period 1985–2001 and the results are assessed in terms of location to location overlap as well as structural similarity at multiple scales. These results give confidence in the representation of land use dynamics for the main land use classes. On the basis of a long term scenario run for the period 2001–2030, it is verified that the model captures stylized facts related to chena dynamics, in particular shortening fallow periods and increasingly long cultivation periods of chena, as a result of increasing land use pressure.     

Conserving the abundance of nonthreatened species

Human modification of the environment is driving declines in population size and distributional extent of much of the world's biota. These declines extend to many of the most abundant and widespread species, for which proportionally small declines can result in the loss of vast numbers of individuals, biomass, and interactions. These losses could have major localized effects on ecological and cultural processes and services without elevating a species’ global extinction risk. Although most conservation effort is directed at species threatened with extinction in the very near term, the value of retaining abundance regardless of global extinction risk is justifiable based on many biodiversity or ecosystem service metrics, including cultural services, at scales from local to global. The challenges of identifying conservation priorities for widespread and abundant species include quantifying the effects of species’ abundance on services and understanding how these effects are realized as populations decline. Negative effects of population declines may be disconnected from the threat processes driving declines because of species movements and environment flows (e.g., hydrology). Conservation prioritization for these species shares greater similarity with invasive species risk assessments than extinction risk assessments because of the importance of local context and per capita effects of abundance on other species. Because conservation priorities usually focus on preventing the extinction of threatened species, the rationale and objectives for incorporating declines of nonthreatened species must be clearly articulated, going beyond extinction risk to encompass the range of likely harmful effects (e.g., secondary extinctions, loss of ecosystem services) if declines persist or are not reversed. Research should focus on characterizing the effects of local declines in species that are not threatened globally across a range of ecosystem services and quantifying the spatial distribution of these effects through the distribution of abundance. The case for conserving abundance in nonthreatened species can be made most powerfully when the costs of losing this abundance are better understood.     

On the mechanistic modeling of As(III) adsorption on gibbsite

Arsenite adsorption on gibbsite was examined as a function of pH, ionic strength (I) and contact time (t(C)). As(III) showed a weak affinity for gibbsite surface. The trends of pH=f(Gamma(ads)) curves have showed a marked deviation from a typical anion adsorption edge showing a maximum Gamma(ads) around pH approximately 8.2. The experimentally derived proton exchange ratio has always converged to zero when 0.26< summation operator [As(III)]<7 microM and 6.2相似文献   

The environmental pollution of Kandy Lake: A case study from Sri Lanka

The water pollution levels of Kandy Lake in Sri Lanka were monitored to probe the impacts and influences of urban environment in a developing country. Although Kandy Lake is a source of drinking water for the town, it was observed that a large number of effluent channels drained in to it, carrying a continuous flow of contaminated water. The hydrogeochemistry, pH, and bacterial levels were studied using lake and drain water samples. A high coliform count and a high degree of faecal contamination was observed in all water samples obtained from the lake and drains. The Cu²⁺ and F^? concentrations were relatively low and did not reach harmful levels, but were higher than that in the background. The pH of water remained almost neutral and provided ideal conditions for bacterial growth. All laboratory and field experiments indicated eutrophic conditions in the lake and the unsuitability of water in the unpurified state for drinking purposes. The purified water had a zero coliform count, but the chlorine content added was relatively high and may also prove to be a health hazard. On the whole, the polluted water in Kandy Lake indicated the adversities of human involvements with nature and provided a good case study for human influence on water pollution in a developing country.