T. Y. Yee; M. Omar Fatehah
Abstract
Silicon dioxide (SiO2) in nanoscale had been detected as waste product in river water for the past two decades and it is recently proven to have adverse effects toward human and animal health, the ecosystem and water treatment system. The removal of SiO2 nanoparticles (NPs) from water still remains a ...
Read More
Silicon dioxide (SiO2) in nanoscale had been detected as waste product in river water for the past two decades and it is recently proven to have adverse effects toward human and animal health, the ecosystem and water treatment system. The removal of SiO2 nanoparticles (NPs) from water still remains a challenge due to its small size and unknown interactions within the water body. In this study, dynamic light scattering (DLS) technique was applied to characterize SiO2 in terms of surface charge and particle size as a function of pH within the range of 2 to 11 to analyze the aggregation behavior and significance of the intermolacular interactions in deionized (DI) water and tap water. DLS analysis identified both pH values of the point of zero charge (pHPZC) of SiO2 NPs in DI water and tap water at pH 3.2 and pH 2.8 respectively. The initial pH was discovered at 7.1 in tap water with a mean particle size of 346 nm and an average surface charge value of -27 mV compared to initial pH of DI water which was 5.4 with mean particle size of 295 nm and an average surface charge value of -33 mV. It was found that both in DI water and tap water, SiO2 NPs aggregated and increased in particle size but reduced in surface charge when pH slowly decreased towards their respective pHPZC from the initial pH by adding 0.25M of hydrochloric acid. The mean particle size at pHPZC in DI water is measured at 1750 nm larger compared to the mean particle size in tap water indicating that the presence of other ions in tap water suppressed the aggregation process. In conclusion, results suggests that pH does influence the surface charge of SiO2 NPs and affect the stability behavior and its interaction processes in aqueous suspensions.
S. N. Larimi; B. Ayati
Abstract
The present study used the adsorption process of activated carbon produced from agricultural wastes and the photocatalytic process of nano-ZnO to break down complex compounds available in removing Direct Blue 71 (henceforth, DB71). The two processes were done under three varied circumstances- adsorption/photocatalytic, ...
Read More
The present study used the adsorption process of activated carbon produced from agricultural wastes and the photocatalytic process of nano-ZnO to break down complex compounds available in removing Direct Blue 71 (henceforth, DB71). The two processes were done under three varied circumstances- adsorption/photocatalytic, photocatalytic/ adsorption, and simultaneous use of the processes. First, DB71 was exposed to activated carbon produced from walnut and almond shells and the efficiency achieved at equilibrium time (45 and 60 minutes) was 55 and 60 percent, respectively. Then, DB71 was exposed to different dosages of nano-ZnO to remove the dye completely. The result showed that amount of AC/ZnO in an optimum condition for two walnut and almond shell absorbents were 0.75/0.096 and1/0.096 g/L. Second, (photocatalytic/ adsorption) the complex compound of DB71 with a dosage of 0.024 g/L was broken down as a result of UV radiation. The experiment proceeded with different dosages of walnut and almond shells after achieving the efficiency of 50% in removing DB71 in the second process. The amounts of AC/ZnO were 0.75/0.024 and 1/0.024 for walnut and almond shells respectively under the optimum condition for the second process. In the third process advantages of the simultaneous use of photocatalytic and adsorption processes were taken in which different dosages of AC/ ZnO were used. Given the smaller dosages of nano-ZnO and less dye removal time, amounts of 0.75/ 0.288 g/L and 0.75/0.288 g/L were measured for walnut and almond shells. The findings show that photocatalytic/adsorption process was the more optimal process because of the less dosages of nano-ZnO, efficiency of removing DB71 and shorter dye removing time. Furthermore, the effect of the intensity of UV radiant on the efficiency and time of removing DB71 was also examined. The experiment revealed that removing COD in the optimum conditions were 47.22 and 49.6 and 62.23 and 63.15 percent using walnut and almond shell respectively both in the first experiment and the simulations use of adsorption and photocatalytic processes after 30 hours. While, in the second experiment (photocatalytic/ adsorption) 42.21 and 39.18 percent of COD were removed using walnut and almond shell respectively after 30 hours. The LC-mass test of photocatalytic/adsorption process also showed the degradation of DB 71 complex compounds.
V. S. Jie Wei; C. Han Bing; Agus Saptoro; J. Nandong
Abstract
Composting is a biochemical process in a controlled aerobic environment where thermophilic microorganisms stabilize organic waste substrates into valuable humus-like products. Three parameters which are known to affect the composting process including temperature, aeration rate and composting time. This ...
Read More
Composting is a biochemical process in a controlled aerobic environment where thermophilic microorganisms stabilize organic waste substrates into valuable humus-like products. Three parameters which are known to affect the composting process including temperature, aeration rate and composting time. This research aims at developing a model to describe the relative influence of different temperatures, aeration rates and reaction time on the composting process and how it affects the final quality of EFB compost produced. EFB samples were mixed with urea as a source of nitrogen and fresh compost as inoculum. The composting process was carried out in a composting test bench for a total of 42 days. The moisture content was found to be significantly affected by temperature and reaction time. Carbon loss was significantly affected by all three factors. Nitrogen content was affected by aeration rate, reaction time as well as interaction between temperature and reaction time. Changes in total ions over time showed a positive correlation with the value of conductivity (Pearson correlation coefficient of 0.853) and the largest reduction in C/N ratio (from 30.2:1 to 17.6:1) was obtained at temperature of 40°C and aeration rate of 0.4 L/min kg. The results of this study could form a basis for palm oil mills to improve the quality of EFB composts produced within a short maturation period and with low C/N ratio.
A. A. Nurhanim; I. Norli; N. Morad; H.P.S.A. Khalil
Abstract
Recycling of Construction and Demolition Waste (CDW) aims to minimize the generation of waste and reduce the dependency on natural resources. The aims of the research are to characterize inorganic element and to determine the leaching behavior of CDW (concrete and gypsum) by means of ...
Read More
Recycling of Construction and Demolition Waste (CDW) aims to minimize the generation of waste and reduce the dependency on natural resources. The aims of the research are to characterize inorganic element and to determine the leaching behavior of CDW (concrete and gypsum) by means of the leaching test. The analyzed results were compared with the European Union (EU) Landfill Directive to assess their acceptance criteria. Both wastes were found to have elements of Ca, Mg, Fe, Zn, Mn, Pb, Cu, Cd, As, Cr, Se, Ni, CI and SO42-. The highest concentration and variety of inorganic element found in waste gypsum (WG) were SO42->Ca>CI>Mg>Zn>Cu>Fe. X-ray diffractometric (XRD) analysis proved that the WCo was dominated by quartz, calcite, ettringite, cordierite, diopside and the WG was only dominated by gypsum. The leaching behavior of WG demonstrated pH dependent particularly for the elements of Ca, Mg, Fe, Zn, Cu and Mn but only the elements of Ca and Cr in WCo were shown to be pH dependent in the leaching test. The element of SO42- from the WG indicated a higher reading than WCo without the influence of pH. Noticeably, the concentration of SO42- within the WG strongly require regulation and control before it can be utilized as part of raw materials in the production of environmental friendly recycled building materials.
