Removal of fluoride from water using activated carbon fibres modified with zirconium by a drop-coating method

This research article published by Elsevier Ltd., 2020Metal-modified carbon materials have been widely used for fluoride removal, but the traditional impregnation by soaking method suffers from low loading of metals and substantial use of chemicals. This study proposed a new approach to prepare zirconium modified activated carbon fibres (Zr-ACF) by a drop-coating method. Using the same amount of chemicals, the drop-coating method yielded a 5.5 times higher fluoride adsorption capacity than the soaking method due to more effective loading of Zr(IV) onto ACF. The effects of various preparation conditions, including the addition of a complexing agent (oxalic acid) and Zr/ACF mass ratio (0.2-1), were investigated. Zr-ACF prepared by drop-coating was characterised by SEM and BET, and the functional groups involved in the anchoring of Zr(IV) on ACF and the adsorption of fluoride onto Zr-ACF were identified by FTIR and XPS. Adsorption experiments at pH between 3 and 11 revealed that ion exchange and electrostatic attraction were the main adsorption mechanisms at different pH levels. Co-existing anions such as CO, HCO and Cl had an insignificant negative impact (<5%) on fluoride adsorption capacity while SO decreased fluoride adsorption capacity by 11.5%. The adsorption kinetics followed the pseudo-second-order model. The adsorption isotherms followed the Langmuir isotherm model with a maximum fluoride adsorption capacity of 28.50 mg/L at 25 °C, which was higher than other carbon-based materials in the literature. The remarkable improvement of adsorption capacity and reduced chemical consumption demonstrate that Zr-ACF prepared by drop-coating is a promising adsorbent for fluoride removal

Lazer sinterleme hızlı prototipleme yöntemi kullanılarak derecelendirilmiş homojen ve gözenekli pölimerik malzeme üretimi ve karakterizasyonu.

Selective laser sintering is a rapid prototyping method (RP), which was originally developed, along with other RP methods, to speed up the prototyping stage of product design. The sole needed input for production being the solid model of the part, the mold/tool-free production characteristics and the geometric part complexity that can be achieved due to layer-by-layer production have extended the applicability/research areas of these methods beyond prototyping towards new applications and material development. Local pore formation in a part that occurs as a result of the discrete manufacturing nature of selective laser sintering is normally considered a defect. In the current research, this is viewed as an opportunity for material development: Exploitation of rapid prototyping methods to produce composites/functionally graded materials with controlled porous structures. That the material interior structure (porous structure) and exterior shape are formed during the same course renders selective laser sintering process as an attractive manufacturing alternative for producing complex-geometry composite/porous materials, which may be difficult or impossible to manufacture with other techniques. In this thesis, the use of selective laser sintering (a rapid prototyping method) in producing uniformly porous and graded polymeric graded porous structures is studied. The material used was polyamide powder (PA 2200) and the selective laser sintering machine used was the EOSINT P 380 system. In this research, three process parameters of the SLS system, the hatching distance, the laser power and the laser scanning speed were varied to produce parts that have different porosities. Porous parts with a homogenous porous microstructure (uniformly porous parts) could be produced, as well as graded porous parts. The results of uniformly porous structure production were utilized to build graded porous structures by imparting different porosities along a certain direction within a single part. Both, uniformly porous and graded structures were characterized physically and mechanically. The porous parts (both uniformly porous and graded porous) were infiltrated with epoxy resin to produce epoxy-PA composites and graded materials. The physical and mechanical properties of these parts were compared with those of the uninfiltrated (porous PA) structuresM.S. - Master of Scienc

Effects of raw and different calcined bentonite on durability and mechanical properties of cement composite material

Bentonite is a natural pozzolanic material mostly composed of SiO2 and employed in cementing materials for the reduction of cement consumption and CO2 emission besides improving performance of cement composite material by consuming portlandite to form extra C-S-H gel. So, many researchers studied on partial replacement of bentonite to improve concrete performance. However, bentonite mostly exists as a consolidated form that needs treatment for activation of pozzolanic reactivity to improve performance of cement composite materials. However, it is not well known how different replacement of raw and calcined bentonite affects performance of cementing materials in different hazardous environment. Hence, the present study identified the most influential replacement of bentonite, evaluating different calcined and raw bentonite in environments of acids, salt, and elevated temperature in addition to assessing the mechanical and physical properties of cement composite material. So, the results indicate that the employment of raw and calcined bentonite reduces the fresh bulk density, improves compressive strength, and Vicker hardness at 28 days, reduces the mass loss due to 56 days immersion in 5% HCl, 10% NaCl, and 5% HNO3 compared to the control mixture. Moreover, the employment of calcined bentonite at 800 °C significantly improved the durability and mechanical properties of cement composite materials compared to the control mixture. Specifically, replacing bentonite calcined at 800 °C for 3hs by 20% has the highest compressive strength than all samples after 28 and 56 days. Besides these, the study reveals that the corrosion potential of steel bars embedded in the mortar is reduced as the proportion of raw and different calcined bentonite increases. Generally, the employment of calcined bentonite is very beneficial to get improved performance on mechanical and durability properties of cement composite materials

Effect of Natural Pozzolana on Physical and Mechanical Properties of Concrete

Construction industries are rapidly growing, sacking high amounts of concrete which has a highly dense microstructure with excellent mechanical properties, more durable, and highly eco-friendly materials. Hence, many of the researchers are interested in solving this problem with replacing concrete by natural pozzolana (NP) which is a supplementary cementitious material mostly from volcanic sources having much active silica content that can improve the durability and mechanical properties of concrete. However, it is not well-known which common optimum replacement range can give the most desirable concrete properties. So, the present study sought to review the effects of replacing NP from volcanic sources on the durability, physical, mechanical, and microstructural properties of concrete, also, to identify the most common dose of a positive effect as a replacement in concrete. The review shows that many of NP used by different literature from different places satisfy ASTM replacement standard in concrete, especially, based on its chemical compositions. Also, the review observed that employing NP in concrete significantly improves concrete workability, lengthens setting time, and reduces bulk density, porosity, water absorption, and chloride ion migration by making denser concrete microstructure. In general, adding 5%–20% of NP in concrete significantly improves compressive strength, split tensile strength, and flexural strength. Specifically, most of the studies found 15% replacement of NP having volcanic sources can give optimum strength. Besides these, most of the studies indicated that the improvement of the strength was more visible at the concrete age of 7–28 days

Fast Rate Production of Biodiesel from Neem Seed Oil Using a Catalyst Made from Banana Peel Ash Loaded with Metal Oxide (Li-CaO/Fe2 (SO4)3)

Biodiesel is a possible remedy to the present toxic, finite sources and ever-diminishing crude fuels. Nonedible and locally available (Azadirachta indica) neem seed oil (NSO) as a second-generation feedstock was transformed into biodiesel using calcined banana ash (CBA) derived from banana peels blended with lithium calcium oxide iron (III) sulphate Li-CaO/Fe2 (SO4)3 catalyzed transesterification. Transesterification process was employed to minimize the free fatty acid (FFA) content of NSO to afford 99.8% yield under the condition of the reaction oil/methanol ratio 8 : 1, followed by addition of 1.7%wt calcined banana peels ash and 1.3%wt Li-CaO/Fe2(SO4)3 catalysts in 53 min, a notable time. It is important to note that the physicochemical properties of biodiesel in this study such as initial boiling points, flash point, pour point, cloud point, density, kinematic viscosity, final boiling points, and cetane index met ASTM D-6751 and EN 14214 standards. Decomposition profile of CBA was displayed by thermal gravimetric analysis (TGA), whereas in-depth analysis by scanning electron microscope (SEM), X-ray diffraction (XRD), X-ray fluorescence (X-RF), and Fourier-transform infrared spectroscopy (FT-IR) revealed that the high efficiency displayed by a catalyst from banana ash calcined at 650°C was due to the presence of potassium carbonate (K2CO3), a calcium magnesium silicate (CaMgSiO4), and potassium sodium sulphate (KNaSO4) contents that accounted for the high basicity of up to 11.09. Additionally, the nitrogen adsorption/desorption studies revealed that CBA interestingly exhibits a high BET surface area of 411.2 m2/g and promising mesopores (3.014 nm). The catalyst also displayed better recyclability evidenced by the fact that it was able to be reused after five successive runs with better recyclability of 75%. Based on the aforementioned properties, this work, therefore, opens an avenue for developing a supreme heterogeneous catalyst from available banana peels ash

Clustering and Fuzzy Logic-Based Demand-Side Management for Solar Microgrid Operation: Case Study of Ngurudoto Microgrid, Arusha, Tanzania

Permanent electricity availability should not be taken for granted since grid sustainability and reliability are at stake when there is no balance between supply and demand. This paper employs a load balancing demand-side management (DSM) approach based on fuzzy logic, considering the low energy users who have insignificant influence on system peaks. Through the K-means clustering algorithm, suitable candidates for DSM are identified, and the control mechanism is based on energy utilization and load priority. The results reveal that about 3.7 kW in power saving was achieved per month. This result indicates that, with a proper energy management strategy for an individual customer, almost a flatter load profile and power saving can be achieved

Establishing the optimal condition for nutrient recovery from domestic wastewater using the freeze concentration method

The freezing concentration method is one of the potential techniques for recovering nutrients from wastewater. In this study, the method of freeze concentration was studied to establish its optimal conditions in recovering nitrate-nitrogen and phosphate nutrients from domestic wastewater. Water in the form of an ice crystal block is produced and leaves behind a solution with a higher concentration. The effects of coolant temperature from −10 to −80 °C, freezing time from 1 to 8 h, and energy consumption on nutrient recovery were investigated. The optimal conditions were found at a coolant temperature of −20 °C, freezing time of 7 h, and energy consumption of 0.197 kWh/L that resulted in the highest nitrate-nitrogen and phosphate nutrient recovery values of 1.114 and 4.667, respectively, at the inlet of anaerobic digester 1; 1.325 and 4.975, respectively, at the outlet of anaerobic digester 1; 1.099 and 4.859, respectively, at the inlet of anaerobic digester 2; 1.132 and 4.755, respectively, at the outlet of anaerobic digester 2; and for gravel filter at the outlet the values were 1.111 and 4.861, respectively. The recovered nutrients can be used as biofertilizers. HIGHLIGHTS Effects of coolant temperature at −10, −20, −30, −40, −50, −60, −70, and −80 °C on the operation of the freezing concentration technique.; Effects of freezing time at 1,2,3,4,5,6,7 and 8 h on the operation of the freezing concentration method.; Low energy consumption on the operation of the freezing concentration technique.; High amount of nitrate-nitrogen and phosphate nutrients recovered from domestic wastewater.

Numerical Analysis of Heat Exchanger for Spray-Assisted Low-Temperature Desalination System

A numerical study for heat exchanger for spray-assisted low-temperature desalination system is presented for an existing low-temperature desalination unit at Arusha Technical College. This is aimed at recognizing the effect of mass flow and physical parameters like tube layout (diameter and length) on the overall heat transferred and the pressure drop in the shell-and-tube heat exchanger (STHX), as well as the impact of these parameters on the heat transfer coefficient and the overdesign of the STHX. Also, the study provides a suitable mathematical model for the replacement of the current condensation unit which tends to reduce energy consumption by reducing some of the electrical components in the system. A Math CAD model was developed using the Delaware method to obtain the mentioned parameters. The results show that at 0.8 kg/s flow rate a maximum heat transfer coefficient of 23212 W/m2K is achieved in a minimum diameter of 10 mm within a maximum tube length of 1000 mm heat exchanger and the pressure drop seems to be very low in a range of 0.328-0.957 Pa from all configurations. The configuration with 1000 mm tube length and 10 mm diameter performed well on the mass flow of 0.3 kg/s-0.8 kg/s by providing a suitable overall heat transfer coefficient of 2306-2539 W/m2K, while 12.8 is a maximum overdesign coefficient achieved on 0.8 kg/s mass flow. The study results show the possibility of using STHX instead of the current condensation unit in implementing a proposed system layout with the minimum effect of energy consumption

Strength and Durability Properties of Concrete Containing Pumice and Scoria as Supplementary Cementitious Material

Concrete structures suffer serious deterioration under a corrosive environment. Consequently, the service life of these concrete structures is decreased and deteriorates under combined attack of sulphate and chlorides. Most studies confined on single deteriorating factor such as sulphate attack only or chloride attack only but the current study focused on the influence of natural pumice (NP) and natural scoria (NS) on the strength performance of concrete exposed to the combined attack of sulphate and chloride. Portland cement (PLC) was replaced with NP or NS at a substitution level of 10%. Concrete samples were cured in water for the curing period of 28 days. Afterwards, the specimens were immersed in 5% sodium sulphate (Na2SO4), 5% sodium chloride (NaCl), and combined sodium sulphate and chloride solutions for additional curing of 28, 56, and 90 days. The results were compared between concrete mixes with NP or NS and control mix (CT) with PLC. The effects of sulphate, chloride, and combined sulphate and chloride were evaluated in terms of change in weight, variation in compressive strength, and degree of damage. Conclusively, the application of NP and NS has extraordinary potential to be utilized as a cementitious material in concrete to increase the resistance against aggressive salts