SURFACE COMPLEXATION OF MONOSUBSTITUTED ORGANOARSENICALS ON HEMATITE: ATR-FTIR INVESTIGATIONS

Little is known about the surface chemistry of organoarsenic compounds with iron-containing materials commonly found in geosorbents and arsenic removal technologies. In this thesis, these organoarsenicals include aliphatic and aromatic arsenicals that historically have been used as herbicides, pesticides and in the poultry feed industry, respectively. Attenuated total internal reflectance Fourier transform infrared spectroscopy has been used to study the surface interactions of organoarsenicals at the molecular level under various environmentally-relevant conditions. Kinetic and thermodynamic parameters extracted from these molecular level experiments provide trends that are not observed in any published bulk experiments. Apparent initial rates of adsorption and desorption for these arsenicals were extracted from experimental data as a function of spectral components. Initial first order pseudo-adsorption rate constants () for arsenate (iAs), monomethylarsonic acid (MMA), p-arsanilic acid (pAsA) and phenylarsonic acid (PhAs) were quantified and show that arsenate and monosubstituted organoarsenicals adsorb with similar rate on Fe-(oxyhydr)oxide. Hydrogen phosphate was used as a desorbing agent due to its ubiquitous presence in arsenic contaminated aquatic environments. The desorption of monosubstituted organoarsenicals from hematite surfaces takes place faster than iAs(ads). The initial desorption of these organoarsenicals with an overall non-unity order suggests the existence of more than one type of surface complex. Adsorption kinetics for aqueous hydrogen phosphate was also investigated on surfaces in the presence and absence of surface arsenic, and the values of follow the order: Fresh hematite \u3e pAsA/hematite ≥ PhAs/hematite \u3e MMA(V)/hematite ≥ iAs(V)/hematite. From this study, it is observed that the amount of weakly bonded pAsA(ads) and PhAs(ads) surface species are larger than those for MMA(ads) and iAs(ads) at neutral pH. Moreover, thermodynamic parameters were obtained for the adsorption of iAs(V), MMA(V) and DMA(V) on iron (oxyhydr)oxide surfaces as a function of concentration (0.001 to 2 mM) and temperature (5 to 50 °C). Values of the free energy of adsorption (∆G°) were extracted from fits using the Langmuir adsorption model and found to be negative within the experimental temperatures range. The entropy (∆S°) and enthalpy (∆H°) of adsorption were also extracted from the linear least-squares regression analysis of van’t Hoff plots constructed from the experimental data. The values of ∆S° are positive for all the arsenicals undertaken in this study. The values of ∆H° suggest that adsorption of iAs(ads) and MMA(ads) are endothermic processes whereas those for DMA(ads) are exothermic. The positive ∆S° along with the positive ∆H° suggest that the ligand exchange reactions are entropy driven. In order to gain further insight into the mechanism of binding, pH(D) edge experiments were carried out for the adsorption of iAs(V) and the monosubstituted organoarsenicals, MMA(V) and PhAs, on hematite nanoparticles at room temperature. The arsenicals show stronger adsorption on iron (oxyhydr)oxide with slight shifting of the spectral features to higher wavenumbers in relatively acidic pH(D). The infrared signatures obtained from the pD edge experiments provide clear spectral information for the surface species. Spectra show that the extent of adsorption increases with decreasing pH(D). Arsenate forms mainly bidentate surface complex. In the case of MMA(ads) and PhAs(ads), surface complexes are most likely to be inner-sphere monodentate in acidic pD with longer adsorption time

Interactions of Phosphate and Silicate with Iron oxides in Freshwater Environments

Internal phosphorus loads, from bottom sediments to surface waters, are often comparable in magnitude to external phosphorus loads, particularly in water bodies with a history of high external phosphorus inputs from point and non-point sources. The benthic release of phosphorus can be influenced by several factors including pH, redox potential, temperature, microbial activity and the concentration of competitive anions at or near the sediment-water interface. Dissolved silicate occurs ubiquitously in natural waters and may act as a competitive ion to phosphate. Nonetheless, prior to the work in this thesis, the effect of silicate on internal phosphorus loading remained poorly understood. This thesis addresses several of the mechanisms through which silicate may influence the mobilization of aqueous phosphate from sediments in aquatic environments. The thesis starts with a thorough literature review of phosphorus biogeochemical cycling in relation to eutrophication, sediment-surface water interactions, mineralogy, competitive anions and microbial activity (Chapter 1). Next, adsorption/desorption of phosphate on/from goethite, a model ferric (hydr)oxide mineral, is investigated in the absence and presence of dissolved silicate. The influence of dissolved silicate on phosphate adsorption is evaluated through laboratory experiments and application of the CD-MUSIC model (Chapter 2). The results show that increasing concentrations of silicate decrease phosphate adsorption, leaving more phosphate in the aqueous phase. The competitive effect of dissolved silicate is more pronounced under alkaline conditions. Subsequently, phosphate desorption experiments were conducted under dynamic pH conditions in the presence and absence of silicate (Chapter 3). The experimental results show that the gradual transition from acidic to alkaline conditions induces the desorption of phosphate adsorbed to goethite under acidic conditions. The presence of silicate in the phosphate/goethite system does not affect phosphate desorption, because of the stronger surface complexation of phosphate to goethite. In addition to adsorption and desorption processes, the co-precipitation of phosphate with iron and the potential subsequent dissolution of these co-precipitates as a result of changing physico-chemical conditions may also control the mobility of phosphate in aquatic environments. The effects of dissolved silicate on the co-precipitation of phosphate with iron and the reactivity of the resulting solids are examined (Chapter 4). Ferric (co)-precipitates (i.e., Fe-P-Si) with variable Si:Fe ratios, were synthesized either via oxidation of Fe2+(aq) or by increasing the pH of Fe3+(aq) solution. The solids were characterized by a combination of chemical and spectroscopic techniques including attenuated total internal reflectance Fourier transform infrared spectroscopy (ATR-FTIR) and X-ray powder diffraction spectroscopy (XRD). Similar solid phase P:Fe ratios were found in co-precipitates formed from solutions with different dissolved silicate concentrations, regardless of the method of preparation. This suggests that the interactions between phosphate and iron during co-precipitation were not affected by dissolved silicate. The ferric (co)-precipitates were subsequently reductively dissolved abiotically in buffered ascorbate-citrate solution to determine their reactivity under reducing conditions. The kinetic data show that the co-precipitates with higher Si:Fe ratios were more recalcitrant to dissolution. For co-precipitates synthesized via oxidation of Fe2+(aq), reductive dissolution experiments were also conducted in the presence of the facultative anaerobic iron reducing bacteria Shewanella putrefaciens. XRD analyses of the residual solids imply that solids with the higher Si:Fe ratios may be more resistant to microbially mediated reductive dissolution. The relative reactivities of the co-precipitates obtained by the two synthesis methods are also addressed in Chapter 4. In Chapter 5, the effect of silicate on the mobility of phosphate in a natural sediment was evaluated via flow-through experiments. The results show that dissolved silicate enhances the mobility of phosphate at the sediment-water interface. Ferric (co)-precipitates were formed at the oxic surface of sediment columns via the oxidation of ferrous iron supplied with upflowing solutions containing variable silicate concentrations. The subsequent dissolution of these co-precipitates under imposed anoxic conditions at the sediment-water interface indicates that the co-precipitates formed at higher dissolved silicate concentrations were more reactive towards reductive dissolution. These results are therefore in apparent contradiction to those observed in Chapter 4. The ferric (co)-precipitates (i.e., Fe-P-Si) evaluated in Chapter 4 were prepared from solutions containing high concentrations of iron, phosphate and silicate, by imposing either rapid aeration or pH increase. These conditions were selected to maximize the yield from the syntheses. The synthesis methods in Chapter 4 are therefore most representative of aquatic environments where co-precipitation occurs rapidly (e.g., groundwater springs) and the concentrations of these dissolved constituents are fairly high. However, in many other aquatic environments, the diffusion-controlled release of Fe2+(aq) from the deeper sediments results in the gradual oxidation of Fe2+ at the sediment-water interface under oxic conditions. This process is typical in lake sediments with minimal advective exchange between surface water and groundwater. This gradual oxidation (at relatively low concentrations of Fe2+) results in the slow formation of ferric (co)-precipitates which may be dissimilar to those synthesized herein and discussed in Chapter 4. The ferric (co)-precipitates synthesized with the flow-through column system in Chapter 5 may be better analogues of slow forming co-precipitates in diffusion dominated or moderately advection influenced aquatic sediments than those synthesized in Chapter 4. Finally, to elucidate the likely importance of the various influences of dissolved silicate on phosphate mobility investigated in this thesis, concentrations of dissolved phosphate and silicate as well as pH data are extracted from the US National Water Information System (NWIS) network (data shown in Chapter 1 and Chapter 2). The NWIS data along with combined experimental and modeling results suggest that silicate-mediated phosphate mobilization is likely a commonly occurring process at the sediment-water interface of lakes and reservoirs. This thesis also demonstrates the multiple roles of silicate on the mobilization of phosphate in aquatic environments, and improves our fundamental knowledge of iron, phosphorus and silicon cycling in freshwater environments

Impact of Using Internet during Covid-19 Lockdown on University Students: A Study of Bangladesh Perspectives

Introduction: Government of Bangladesh declared lock down several times in the educational institutions for the purpose of retains the rapid speed of COVID-19. During the lockdown period students stayed in home and totally depended on internet for spending times, contract friends, attained in online classes etc. The purpose of the study is to measure the impact of long- time internet usage that brought various complications among the students in their physical and mental health during COVID-19 lockdown period. Methods: A structured online based questionnaire link was sent using Google forms and distributed to students via what’s app and Facebook Messenger and 360 respondents were filled up the questionnaire in the period of June 2021-August 2021 COVID-19. The distribution of respondent demographic variables was investigated using descriptive statistical methods; Pearson’s chi-square tests have been applied. Result: About 40.8% of students’ perception was that COVID-19 lockdown had changed their internet usage habits a little more than the normal time. The measures of the duration of time of internet usages there was a significant change. The respondents usage increased rapidly on 5-6 hours (42.05%) and 10 hours + (32.8%) whereas it was 30.3 % and only 6.9% respectively in before the lock down. The usages of internet hampered the students in their studies, night’s sleep, food habits, loneliness, frustration and depression during the lock down situation. Conclusion: The concern authority should take necessary steps to reduce the habit of internet usage the COVID-19 situation and motivate the students for concentrating on their studies and minimize the excessive use of the internet

MEASUREMENT OF TRENDS OF SOME INFLUENTIAL VARIABLES: A COMPARISON BETWEEN BRAC BANK LTD. AND ISLAMI BANK BANGLADESH LTD.

Banking sector is a fundamental element of a financial system of a country. Bangladesh is a developing country and its financial system is good and upward trend oriented. Islami Bank Bangladesh Limited (IBBL) and BRAC Bank Limited (BBL) are the two prospective banks in Bangladesh. The paper attempts to measure trends of some influential variables. Through Kaiser-Meyer-Olkin (KMO) and Bartlett’s test of Sphericity five influential variables are identified like net profit, investment/loans and advances, fixed assets, other assets and cash. All the variables show better position in IBBL than BBL. The researchers also have identified some problems in IBBL and BBL and recommended some suggestions for overcoming the problems

Total Quality Management as a Tool for Decision Making

TQM means keeping the organization running smoothly with continuous input from our owners/customers. The major components of TQM are quality information, rewards for results, cooperation, secured jobs, fairness, equitable compensation, employees ownership stake etc the guiding principles are customer satisfaction safety, elimination of errors and defects, continuous improvement, employee empowerment etc The major constraints are lack of top management support, commitment, over dependence on computerized quality control, no market research, management by fear etc

Effect of Micro-EDM Parameters on Material Removal Rate of Nonconductive ZrO2 Ceramic

Micro-electro discharge machining (micro-EDM) technique, an advanced noncontact machining process, is used for structuring of nonconductive ZrO2 ceramic. In this study copper foil as a conductive layer is adhered on the workpiece surface to initiate the sparks and kerosene is used as dielectric for creation of continuous conductive pyrolytic carbon layer on the machined surface.Voltage (V) and capacitance (C) are considered as the parameters to investigate the process capability of machining parameters in continuous micro-EDM of ZrO2. Different voltage pulses are studied to examine the causes of lower material removal rate (MRR) in micro-EDM of nonconductive ceramics. The results showed that in micro-EDM of ZrO2 MRR increases with the increase of voltage and capacitance initially, but decreases at higher values and no significant materials are removed at capacitances higher than 1nF

Prevalence and Therapeutic Efficacy of Anthelmintic against Neoascaris vitulorum in Buffalo Populations from Sylhet District of Bangladesh

Background and Objectives: The epidemiological features of Neoascaris vitulorum infection in buffaloes are important to know their transmission and risk factors assessment as well treatment regimens. This study was conducted with the objectives of determining the prevalence of Neoascaris vitulorum infection in buffaloes in Sylhet district of Bangladesh and to evaluate the efficacy of anthelmintics against the parasite. Materials and Method: A total of 211 fecal samples were collected from buffaloes and examined for the detection of parasitic eggs during the period from July 2017 to June 2018. For the determination of therapeutic efficacy, animals were randomly divided into 6 groups (T0, Ti, T1, T2, T3, T4) where each group consisting of 3 buffaloes. The group T0 (negative control-non infected) and Ti (positive control-infected) were treated only with phosphate buffer saline (PBS). The other four infected groups were treated as T1 with albendazole, T2 with piperazine citrate, T3 with ivermectin and T4 with combination of tetramisole HCL and oxyclosanide. Before trials day 0 and after treatment of 7th, 14th, 21st and 28th days fecal samples examined using McMaster technique. Results: The overall prevalence was estimated 17.06% (36/211). The prevalence was higher among buffalo calves of below six months (39.28%) followed by 6 months to 1 year, 1 to 2 years and above 2 years as 25%, 22.5% and 7.20% respectively. The infection rate was high in females (20.0%) than males (13.18%). The parasite was more prevalent in rainy (21.42%) than summer (16.67%) and winter (14.29%) seasons. The EPG results revealed piperazine citrate was the most effective (100%) against Neoascaris vitulorum. The percent efficacies of other anthelmintic used in this study were albendazole, ivermectin and combination of tetramisole HCL and oxyclozanide as 95.49%, 86.20% and 95.58% respectively. Conclusion: The prevalence of Neoascaris vitulorum infection in buffalo at Sylhet district of Bangladesh was relatively high. The results revealed that piperazine citrate, tetramisole HCL and oxyclozanide combination are highly effective for the reduction of egg per gram (EPG) of Neoascaris vitulorum infection in buffalo. On the other hand ivermectin and albendazole were also around ninety percent effective respectively

Quantitative insights into phosphorus loadings and speciation in urban catchments

Phosphorus (P) loadings in stormwater runoff drained from urban landscapes causes eutrophication in aquatic ecosystems downstream of urban areas. Many recent research have addressed urban P dynamics to improve understanding about magnitudes and speciation of P in urban watersheds. We quantified P export and forms in four research sites including three urban sewersheds and a stormwater pond, all located within the drainage basin of Lake Ontario. P speciation laboratory analyses were conducted on water and sediment samples taken from our sites to measure a suite of P species, including total P (TP), total dissolved P (TDP), dissolved reactive P (DRP), dissolved unreactive P (DUP), particulate P (PP), and particulate reactive P (PRP). Using multiple linear regression (MLR) models, we quantified annual loadings of these P species, which appeared to be close to the lower limit of ranges reported in the literature. Average loadings among urban catchments were 0.54 kg ha-1 yr-1 for TP, 0.064 kg ha-1 yr-1 for TDP, 0.007 and 0.045 kg ha-1 yr-1 for DRP and DUP, 0.46 kg ha-1 yr-1 for PP, and 0.16 kg ha-1 yr-1 for PRP. Results indicated that larger catchment-scale loadings of reactive P species (DRP and PRP) were exported as residential development increased. We also found that the pond retained all P species significantly (77-94%), which, according to mass balance and sequential P extraction analyses, was attributed to both sedimentation and chemical precipitation of P with calcium mineral phases. Findings in our study imply that, due to loadings’ variability imposed by land-use characteristics, urban P management options need to vary from a catchment to another. Furthermore, enhancing the formation of calcium phosphate and other redox-stable mineral phases could be explored as a best management practice in existing and new ponds for improving P retention.This research was undertaken thanks, in part, with support from the Global Water Futures Program funded by the Canada First Research Excellence Fund (CFREF)

URBAN PHOSPHORUS SPECIATION AND EXPORT LOADS: A PAIRED SEWERSHED FIELD AND MODELING STUDY

In this study, annual and seasonal loads of phosphorus (P) exported from two neighbouring urban sewersheds (AJE and AJW) discharging into Lake Ontario were estimated. The following different chemical pools of P were considered: total P (TP), particulate P (PP), and dissolved P (DP), that in turn were divided in their respective reactive (R) and unreactive (U) fractions. The AJW sewershed is more residential while AJE is dominated by commercial and industrial land cover. A load-flow regression model coupled to the Stormwater Management Model (PCSWMM) was calibrated against measured flow and P speciation data and used to derive seasonal export concentrations (ECs) for the two sewersheds. The annual P loads from the sewersheds were significantly different (AJE: 0.61±0.05 kg/ha/year; AJW: 0.39±0.07 kg/ha/year). Relative to AJE, the TP loads from the more vegetated AJW were enriched in both total DP (TDP) and reactive DP (DRP). Overall, the TP loads were dominated by PP (83-91% of TP), with slightly higher PP contributions for AJE. Our chemical extraction results further simplied that close to half (38-47%) of the PP loads were comprised of reactive P forms. The large contribution of PRP to the TP loads indicates that DRP alone may not provide a reliable measure of the potentially bioavailable P exported from urban areas to downstream aquatic environments.This research was undertaken thanks, in part, with support from the Global Water Futures Program funded by the Canada First Research Excellence Fund (CFREF)

Total Quality Management as a Tool for Decision Making

TQM means keeping the organization running smoothly with continuous input from our owners/customers. The major components of TQM are quality information, rewards for results, cooperation, secured jobs, fairness, equitable compensation, employees ownership stake etc the guiding principles are customer satisfaction safety, elimination of errors and defects, continuous improvement, employee empowerment etc The major constraints are lack of top management support, commitment, over dependence on computerized quality control, no market research, management by fear etc