Water softening in a crossflow membrane reactor

This paper presents an investigation on the removal of hardness by using a crossflow membrane reactor. Lime soda (LS) and caustic soda (CS) were added to hard water as softening chemical agents. The effect of the LS-CS dosage, specific cake resistances (α) and transmembrane pressure drop (ΔP) on steady-state rejection and flux was investigated. Also, flux declines were evaluated with respect to various flux decline models. It was found that hardness rejections decrease for LS and increase for CS with increasing LS and CS dosage, respectively. As ΔP increases, it was observed that while steady-state fluxes rise for both additives, hardness rejections were decreased for CS and remained constant for LS. A maximum of 97.5% hardness removal was achieved for 100% stochiometric dosages of CS. Obtained steady-state flux values varied between 224 to 881 L/m² h, depending on added chemical dosages and applied ΔP. It was determined that the reason for the flux decline at the beginning of the filtration (i.e., in the rapid flux decline period, RPD) was due to an intermediate pore blocking mechanism. As filtration progressed to the slow flux decline period (SDP), it was concluded that cake filtration occurred for all experiments. If solid matter concentration in the feed solution and applied ΔP are relatively low, the experiments showed that flux decline is due to the intermediate pore blocking mechanism. However, it was determined that if solid matter concentration in the feed solution and applied ΔP are relatively high, the flux decline model fits well with the cake filtration model.     

Denial-of-Service attacks and countermeasures in IEEE 802.11 wireless networks

IEEE 802.11 access points deployed in shopping malls, university campuses, crowded streets, airports, and many other locations provide ubiquitous Internet access to millions of stations. However, these hot spots are vulnerable to Denial-of-Service (DoS) attacks due to the broadcast nature of wireless communication. It does not require specialized hardware or particularly high level of experience to render 802.11 networks inoperable through DoS attacks. Standard off-the-shelf equipment is sufficient for a malicious station to disrupt the service between access points and stations. In this paper we present a systematic survey of DoS attacks, which exploits MAC and physical layer vulnerabilities of 802.11 networks. Available countermeasures against DoS attacks are discussed and compared. Future research directions and open issues are also discussed.     

Bioattenuation of Detergent Plant Effluents Enhanced via Single Microbial Augmentations

Due to natural attenuation, anionic detergents in surface waters are not inferred as big environmental issues. However, the effluents from large industrial areas with high detergent concentrations can have significant local impacts. These circumstances can be diminished by using efficient detergent‐degrading bacterial isolates through bioaugmentation. In this study, detergent plant effluents were analysed by using a methylene blue active substance assay to determine detergent content during natural attenuation processes, and after single augmentations of 12 anionic detergent‐degrading bacterial isolates with high detergent tolerating abilities in batch microcosms. Maximum bioattenuation of detergents was determined as 56 % after 66 h incubation under the conditions that mimicked the natural environment. Bioattenuation was enhanced as much as 83 and 91 % in 78 h incubation time through single microbial augmentations of filter‐sterilized and non‐sterilized effluents, respectively. Eight Pseudomonas and one Aeromonas species were found to be highly competitive by showing high biodegradation abilities in pure culture experiments as well as enhancing degradation of detergents in both filter‐sterilized and non‐sterilized effluents through their single augmentations. Although remaining three isolates, namely Pseudomonas fluorescens SDS6, P. resinovorans SDS10‐2, and P. corrugata SDS10‐3 displayed lower degrading abilities in pure culture experiments than the natural attenuation, they later turned out to be actively enhancing the degradation of detergents during their single augmentations.     

A survey on packet size optimization for terrestrial,underwater, underground,and body area sensor networks

Packet size optimization is a critical issue in wireless sensor networks (WSNs) for improving many performance metrics (eg, network lifetime, delay, throughput, and reliability). In WSNs, longer packets may experience higher loss rates due to harsh channel conditions. On the other hand, shorter packets may suffer from greater overhead. Hence, the optimal packet size must be chosen to enhance various performance metrics of WSNs. To this end, many approaches have been proposed to determine the optimum packet size in WSNs. In the literature, packet size optimization studies focus on a specific application or deployment environment. However, there is no comprehensive and recent survey paper that categorizes these different approaches. To address this need, in this paper, recent studies and techniques on data packet size optimization for terrestrial WSNs, underwater WSNs, wireless underground sensor networks, and body area sensor networks are reviewed to motivate the research community to further investigate this promising research area. The main objective of this paper is to provide a better understanding of different packet size optimization approaches used in different types of sensor networks and applications as well as introduce open research issues and challenges in this area.     

Electro-sorption of ammonium by a modified membrane capacitive deionization unit

A modified membrane capacitive deionization (MCDI) unit with additional flow channels in the anode and cathode chambers was used to study the performance of ammonium ion removal. The influences of operating parameters including initial ammonium concentration, flow rate and applied potential and the effect of flow in the anode and cathode chambers were investigated. Flow through the anode and cathode chambers significantly enhanced the electro-sorption efficiency. The electro-sorption of ammonium at 5 mL/min was about 65% greater than without flow.     

Water Quality Assessment Using Multivariate Statistical Methods—A Case Study: Melen River System (Turkey)

This study is focused on water quality of Melen River (Turkey) and evaluation of 26 physical and chemical pollution data obtained five monitoring stations during the period 1995–2006. It presents the application of multivariate statistical methods to the data set, namely, principal component and factor analysis (PCA/FA), multiple regression analysis (MRA) and discriminant analysis (DA). The PCA/FA was employed to evaluate the high–low flow periods correlations of water quality parameters, while the principal factor analysis technique was used to extract the parameters that are most important in assessing high–low flow periods variations of river water quality. Latent factors were identified as responsible for data structure explaining 72–97% of the total variance of the each data sets. PCA/FA was supported with multiple regression analysis to determine the most important parameter in each factor. It examines the relation between a single dependent variable and a set of independent variables to best represent the relation in the each factor. Obtained important parameters provided us to determine the major pollution sources in Melen River Basin. So factors are conditionally named soil structure and erosion, domestic, municipal and industrial effluents, agricultural activities (fertilizer, irrigation water and livestock wastes), atmospheric deposition and seasonal effects factors. DA applied the data set to obtain the parameters responsible for temporal and spatial variations. Assessment of high–low flow period changes in surface water quality is an important aspect for evaluating temporal and spatial variations of river pollution. The aim of this study is illustration the usefulness of multivariate statistical analysis for evaluation of complex data sets, in Melen River water quality assessment identification of factors and pollution sources, for effective water quality management determination the spatial and temporal variations in water quality.     

Variations in cross-link density with deposition pressure in ultrathin plasma polymerized benzene and octafluorocyclobutane films

Neutron reflectometry (NR) measurements of ultrathin films from octafluorocyclobutane (OFCB) and benzene (B) precursors deposited using Plasma Enhanced Chemical Vapor Deposition (PECVD) at two pressures (0.6 and 0.05 torr) reveal that under both deposition conditions there are a 7 nm-thick surface layer and an approximately 1 nm-thick transition layer next to the substrate which have structures different than those in the middle of the film. NR measurements of films swollen with solvent reveal that the density of cross-linking next to the substrate is lower than that in the middle of the film or the region adjacent to the surface of the film for both precursors. Variations in the cross-link density with processing pressure are much stronger for PP-B films than for PP-OFCB films.     

Effects of ultrasonication on glycerin separation during transesterification of soybean oil

The aim of this study was to determine the effects of high-intensity ultrasound irradiation and temperature on glycerin separation start time and separation rate during the transesterification of soybean oil. Response surfaces methodology was used to design the experiments. Reaction temperature, ultrasonication level and duration of ultrasonication at three levels were assigned as the control variables. The progressing transesterification reactions were monitored using a low-intensity ultrasound measurement system, which measures the ultrasound time of flight in glycerin as glycerin separates during the reaction. The effects of ultrasonication level, duration of ultrasonication and temperature on glycerin separation start time and separation rate were statistically significant at p < 0.01 level. The effect of the interaction between temperature and duration of ultrasonication on glycerin separation start time was also statistically significant at p < 0.05 level. The process conditions that provided the lowest starting times for glycerin separation were determined to be the reaction temperature of 50 °C, ultrasonication of 5 min and ultrasonication rate of 90%. Low-intensity ultrasound measurement techniques and response surfaces experimental design are useful tools in determining the effects of various variables on the transesterification of vegetable oils.     

The effect of the wrapped carbon fiber reinforced polymer material on fir and pine woods

The aim of this study is to observe the strength changes of the wood material. The compression and bending strength of the specially wrapped wood materials were investigated. Carbon fiber reinforced polymer (CFRP) material was wrapped onto the wood surface by using a polymer-based glue. The strength ratio of the wrapped and non-wrapped materials was investigated. The specimens were prepared from fir and pine woods that are used widely in buildings. At the same time, two types of woods were compared in terms of strength ratios. As a result of this study, the increase of the compression and three-point bending strength was determined for wrapped CFRP wood materials.