Predicting NOM Removal by Fixed-Bed GAC Adsorbers

Natural Organic Matter (NOM) normally exists in raw surface water as a complex mixture of organic compounds, mainly humic acids and fulvic acids. In water treatment plants, free chlorine reacts with NOM and forms a wide range of substances known as Disinfection Byproducts (DBPs). Granular Activated Carbon (GAC) adsorption is one of the best available technologies employed for the removal of NOM. A mathematical model for the adsorption of NOM onto GAC in a fixed bed column and in a batch reactor was built. The mathematical model was solved numerically using finite element and orthogonal collocation methods. Experiments were conducted using Rapid Small Scale Column Test (RSSCT) to evaluate the performance of GAC column to remove or reduce the concentration of NOM in raw water. The predicted values from the mathematical model showed very good agreement with the experimental measurements for a range of empty bed contact time, GAC particle size and raw water pH. Most of the mathematical model parameters were determined experimentally in adsorption equilibrium isotherm and batch reactor experiments

Natural Transport of Volatile Organic Compounds Due to Annual Variation of Soil Temperature

A theoretical investigation of factors affecting gas phase transport of volatile organic compounds in unsaturated zone is presented. Studying annual soil temperature variation with time and depth declares that there is a considerable temperature variation in the upper few meters that may affect the overall natural mass transport of volatile organic compounds. A one-dimensional mathematical model is used to study the effect of soil temperature variation on diffusive mass transport. From the analytical solution, it is clear that there is a significant net mass transport upward direction and a stimulated spatial oscillation of contaminant concentration in soil. The magnitude of these two modes of mass transport is higher as the contaminant is more volatile

Control of saltwater intrusion by aquifer storage and recovery

This is the final version of the article. Available from the publisher via the DOI in this record.Published Online 18th August 2016This paper presents the results obtained from the application of aquifer storage and recovery (ASR) technique to control seawater intrusion (SWI) in coastal aquifers. The study is based on the numerical modelling experiments performed using the SUTRA (Saturated–Unsaturated TRAnsport) finite-element code on the Wadi Ham aquifer in the UAE. A three-dimensional numerical model of this aquifer is developed and calibrated based on the available hydrogeological data in real scale. A significant amount of SWI has been calculated for the year 2015 due to the high rates of pumping from the available local well fields. To study the future responses of the aquifer to different control actions, the transient responses of SWI are simulated over a 10-year planning horizon. The proposed management measure (ASR) is implemented in repeated cycles of artificial recharge, storage and recovery using an additional set of wells defined in the model. The results show that ASR is a reliable method in controlling SWI in coastal aquifer systems besides its conventional role in subsurface water banking.The authors acknowledge their gratitude to the British Council, UK, for providing funding (project code: SH-04509) to support this research

A fast computational algorithm to evaluate large transmit-arrays

Transmit-arrays (TAs) have become popular solutions for point-to-point communications due to their lowprofile and high-efficiency. However, simulation of these large and detailed structures demands a great amount of memory and time. Here, we propose a fast algorithm to estimate the performance of a beam-steering TA to accelerate its design optimization process. The results and the required resources of the algorithm are compared with the ones of Ansys HFSS. It is shown that this algorithm can fairly evaluate the key factors of the performance of a TA within couple of minutes with memory resource of only 1 GB.info:eu-repo/semantics/acceptedVersio

Antenna-filter-antenna-based cell for linear-to-circular polarizer transmit-array

In this paper, we propose a dual-band linear-to-circular polarization converter element based on the antenna-filter-antenna (AFA) structure. The traits of this cell include thin three-layer structure and ability to convert a linear incident wave to two orthogonal circular polarizations at two non-adjacent frequency bands. This combination of physical and electrical specifications makes this cell a novel solution. An example of this cell suitable for satellite communication is designed to operate at 20GHz and 30GHz (satellite Ka-band) with 4% and 8% bandwidth, respectively.info:eu-repo/semantics/acceptedVersio

Beam-steering ka-band phase rotation cells-based transmit-array for circular-polarization

Planar transmit-arrays (TAs) have been an attractive solution as gain-enhancers for various applications, e.g. satellite communications. For the first time, a TA composed of sequentially rotated cells is employed as beam-steering circular polarization Ka-band satellite ground terminal. Moreover, it is shown that the intrinsic filtering effect of phase rotation (PR) cells for this kind of TA enables improvement in the axial ratio bandwidth. The performance of the TA is evaluated through simulation. The TA presents only 2.7dB loss over zenith scan between 15° and 50° while its structure rotation provides 360° azimuth scan. The TA offers 2GHz (28.730.7GHz) combined 3dB axial ratio and 3dB gain bandwidth.info:eu-repo/semantics/acceptedVersio

Phase-delay versus phase-rotation cells for circular polarization transmit arrays - application to Satellite Ka-Band Beam steering

Planar transmit arrays (TAs) have been an attractive solution as gain enhancers for various applications, e.g., satellite communications. The TA performance directly depends on its composing unit-cell characteristics. Planar unit cells can be categorized into two main types: phase-rotation (PR) and phase-delay (PD) cells. There is no hint in the literature about the relative merits of these two types of cells for circular polarization when assessing the final TA performance. This paper offers a systematic comparison between the cells’ working principles and analyzes their impacts on TA performance. Examples of a PR-based TA and a PD-based TA are designed for single-band wide-angle beam steering operating at the satellite Ka-band. They are evaluated by simulation and measurement to quantify performance differences. No previous work employed a PR TA for wide-angle beam steering. This paper shows that PR TA offers a filtering effect toward the cross-polarization component of the source. This leads to better axial ratio and combined 3 dB axial ratio and 3 dB gain bandwidth. However, PD cells are easier to design and insensitive to feed polarization. The analysis in this paper allows a more informed decision when selecting the unit-cell category for any given TA application