Water defluoridation, water denitrification and water desalination in rural areas in South Africa

Many borehole waters in rural areas in South Africa are unfit for human consumption because the fluoride (>1,5 mg/ℓ), nitrate-nitrogen (>6 mg/ℓ) and salinity (>1 500 mg/ℓ) concentrations are too high. Ion exchange (IX) and reverse osmosis (RO) technology are available that can be used for defluoridation, denitrification and desalination of water. However, methodology, guidelines and the economics for the use of these technologies in rural areas are not readily available. Therefore, the objectives of this investigation were to develop methodology, guidelines and the economics for the defluoridation, denitrification and desalination of water in rural areas. The capital costs of ion-exchange household defluoridation and denitrification units are estimated at R5 000 each. Operational costs vary from R0,43 to R3,99/kℓ depending on the feed water concentration. The capital cost of a small RO unit to produce approximately 50 ℓ/d defluoridated water is estimated at approximately R3 000. (Operational cost R3,00/kℓ). The capital cost of an RO unit to produce approximately 5 kℓ/d desalinated water is estimated at approximately R20 000. (Operational cost R1,69/kℓ). The capital cost of an RO unit to produce approximately 50 kℓ/d denitrified water is estimated at approximately R150 000. (Operational cost R2,17/kℓ).Paper presented at the the Third IASTED African Conference Power and Energy Systems (AfricaPES 2010), September 6-8, Gaborone, Botswana

An analytic model employing an elliptical surface area to determine the gaseous thermal conductance of uncooled VOx microbolometers

This work presents a detailed overview ofthe analytic methods for calculating the beam and gaseous thermal conductance components associated with uncooled VOx microbolometers. The conventional method to calculate the gaseous component relies on the assumption that the entire plate is maintained at a uniform temperature,thus the surface area ofthe plate is used for the calculation. We have observed using an industry leading multiphysics simulator thatthis assumption is not strictly true for VOx microbolometers as the conduction pattern exhibits an elliptical shape. Based on this, we have developed and propose an analyticmethod that employs anelliptical surface area scaledappropriately withthedevice dimensions to obtain an estimate ofthe average temperature conduction pattern. Prototype devices were manufactured and experimentally characterised. The devices exhibit thermal conduction characteristics comparable to those in literature and industry, and we could achieve 0.5 W/K under vacuum conditions and 15 W/K at atmospheric pressure with a TCR of −1%/K. However, both simulated and experimental result sets of the gaseous thermal conductance exhibit large deviations from the conventional analytic method, on average approximately 40%. The proposed method reduces this average error significantly to less than 10% when compared to the simulated results.The authors thank the Advanced Manufacturing Technology Strategy (AMTS) of the Department of Science and Technology, South Africa, for the financial support of the research, as well as the National Research Foundation (NRF) for Sabbatical Grants to Complete Doctoral Degrees Funding Instrument (UID Number 86451).http//: www.elsevier.com/locate/sna2017-10-30hb2017Electrical, Electronic and Computer Engineerin

Characterisation of the electrical response of a novel dual element thermistor for low frequency applications

This work is aimed at characterising the DC electrical response of a temperature sensitive microbolometer device. The contribution lies with the choice and the structure of the device, a novel bolometer infrared sensing structure consisting of dual sensing elements that are thermally very closely coupled on a single membrane supporting structure. A mathematical model is presented to characterise the behaviour of the device resistance and conductance for a given biasing current. A modified experiment of a well published non-optical method exploiting the normally unwanted Joule heating of a device when biased with a large direct current is employed for the experimental verification and validation of the theoretical model. The measured results indicate that the proposed model approximates the measured results well. Although some deviation occurs, this is to be expected and discussed.The authors thank the Advanced Manufacturing Technology Strategy (AMTS) of the Department of Science and Technology, South Africa for the financial support of the research.http://www.saiee.org.za//content.php?pageID=200#am2013ai201

Investigation into a treatment strategy for the Berg River water at the Voëlvlei water treatment plant

The main aim of this study was to determine a treatment strategy for the Berg River water at the Voëlvlei water treatment plant (WTP). Jar tests were conducted using ferric and aluminium sulphate as coagulants to determine the optimum treatment parameters of the Berg River water and the Voëlvlei WTP raw water. The results for the Voëlvlei WTP raw water and the Berg River water with ferric sulphate as the coagulant showed an optimum Fe3+ dosage of 3.0 to 4.0 mg/L and 4.0 to 6.0 mg/L, respectively, with and optimum coagulation pH range of 6.6 to 9.5 and 5.0 to 10.0, respectively. The results with aluminium sulphate as the coagulant showed and optimum AI3+ dosage of 2.5 to 3.0 mg/L and 4.0 to 5.0 mg/L, respectively, with an optimum coagulation pH of 6.0 to 7.0 and 6.0, respectively. This study concluded that the Berg River water cannot be effectively treated at the Voëlvlei WTP using the plants treatment parameters, even if it is blended with the Voëlvlei WTP raw water. The best treatment strategy for the Berg River water would be pre-treatment using either ferric sulphate or the MIEX ® resin on its own, or in conjunction with one another.http://www.iwaponline.com/ws

Optimisation of CMOS compatible microbolometer device performance

Uncooled IR (infrared) microbolometer performance is greatly affected by the thermal properties associated with the structural layout of each design. Equations are derived in this article which make use of basic structural dimensions to predict the expected thermal conductance and thermal capacitance of a microbolometer device. These equations enable a microbolometer designer to determine the estimated thermal time constant of a design without performing complicated analytical calculations for each layer in the design. Calculation results shown indicate the effect structural changes have on the thermal time constant of microbolometer devices. These changes aid microbolometer designers in adjusting the layout of the device to change the thermal time constant to the desired value. Structural deviations that occur during manufacturing of microbolometers are calculated and the possible causes are discussed.The Advanced Manufacturing Technology Strategy (AMTS) of the Department of Science and Technology, South Africahttp://www.saiee.org.za//content.php?pageID=200#am2013ai201

Electro-thermal properties of integrated circuit microbolometers

The use of uncooled infrared sensors in thermal imaging is a fast growing market in the fields of security and health. The integration of uncooled or room temperature infrared sensors onto a silicon CMOS chip will facilitate the manufacture of large imaging arrays. At the University of Pretoria we are researching the integration of microbolometer infrared sensors onto CMOS readout electronic circuits using post processing techniques. The microbolometer utilises the change in resistance of a temperature sensitive resistive material, e.g. vanadium oxide or a thin metal film, to measure the amount of infrared radiation falling onto the device and heating the device. The microbolometer structure should be thermally isolated from the bulk silicon to achieve the required sensitivity. In this paper we will describe the device structures, as well as the techniques we used to determine experimentally the electrical, thermal and electro-thermal properties of the devices. Of interest to us are the following parameters: 1) temperature coefficient of the bolometer resistive layer, 2) thermal conductivity of the device, 3) thermal capacitance of the total sensor structure and 4) the thermal time constant. The microbolometer thermal characteristics can also be modelled and simulated using CoventorWare software.The AMTS (Advanced Manufacturing Technology Strategy)http://www.saiee.org.za//content.php?pageID=200#ai201

Nitrate-nitrogen removal with small-scale reverse osmosis, electrodialysis and ion-exchange units in rural areas

The nitrate-nitrogen concentration in water supplied to clinics in Limpopo Province is too high to be fit for human consumption (35 to 75 mg/ℓ NO3-N). Therefore, small-scale technologies (reverse osmosis, ion-exchange and electrodialysis) were evaluated for nitrate-nitrogen removal to make the water potable (< 10 mg/ℓ NO3-N). It was found that the reverse osmosis process should function well for nitrate-nitrogen removal. Nitrate-nitrogen could be reduced from a concentration of 35 to 43 mg/ℓ in 1 case to a concentration of between 1.4 and 5.5 mg/ℓ in the treated water. In another case it could be reduced from 54 to 72 mg/ℓ to 12 to 17 mg/ℓ in the treated water. The water was also effectively desalinated. The ion-exchange process could also reduce the nitrate-nitrogen concentration to less than 10 mg/ℓ in the treated water. However, the water could not be efficiently desalinated and the process should function better when the level of total dissolved solids in the feed is not very high. The electrodialysis process should also function well for nitrate-nitrogen and salinity removal. However, the electrodialysis process is more complicated to operate. The reverse osmosis and ion-exchange processes are therefore suggested for nitrate-nitrogen removal at clinics. Capital costs for small-scale reverse osmosis and ion-exchange units are estimated at ZAR7 000 and ZAR10 000, respectively. Operational costs for reverse osmosis and ion-exchange are estimated at ZAR3.16/m3 and ZAR3.60/m3 of treated water, respectively.nf201

Performance of a water defluoridation plant in a rural area in South Africa

The fluoride concentration of a borehole water supply in a rural area (Madibeng Local Municipality, North West Province, South Africa) varies between 5 and 6 mg/ℓ. This water is therefore not suitable for potable purposes because the high fluoride concentration may cause mottling of tooth enamel in children and fluorosis in adults. Therefore, the fluoride concentration should be reduced to less than 1.5 mg/ℓ to make the water suitable for potable purposes. The activated alumina and reverse osmosis processes are both processes that can be very effectively applied for water defluoridation. The activated alumina process, however, is considered to be a more simple and robust process for water defluoridation, especially in a rural area. Therefore, the activated alumina process was selected for water defluoridation. An activated alumina plant was designed, constructed and commissioned in the rural area. Fluoride in the feed water is removed from 6 to 8 mg/ℓ to less than 1.5 mg/ℓ. No reduction in plant output was experienced over 6 service cycles. Therefore, it appears that fouling of the activated alumina should not be a problem. Plant output varied between 940 and 1 296 m3 to a fluoride breakthrough of approximately 2.0 mg/ℓ. No significant operational problems were experienced during commissioning and the plant is performing satisfactorily. Spent regenerant is disposed of into evaporation ponds. It was demonstrated that a 1st world technology could be effectively applied in a rural area with proper training and supervision of the operators. The capital and operational costs of the 200 m3/d defluoridation plant are estimated at approximately R1.2m. and R0.7/m3 treated water

Evaluation of microfiltration for the treatment of spent cutting-oil

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Performance of tubular reverse osmosis for the desalination/concentration of a municipal solid waste leachate

Municipal solid waste leachate (MSWL) has the potential to pollute the water environment and to affect biological treatment processes adversely if not properly handled. Reverse osmosis (RO) has the ability to remove both organics and inorganics effectively from effluents. Therefore, RO was evaluated for the treatment of MSWL. It was found that both cellulose acetate and polyamide RO membranes should function effectively for the treatment of the leachate and that it should be possible to control membrane fouling with chemical cleaning. The polyamide membranes, however, performed somewhat better than the cellulose acetate membranes for the treatment of the leachate. The quality of the treated leachate with the exception of ammonia-nitrogen and COD should comply with the quality requirements for discharge into the water environment. Biological treatment processes are effective in complete removal (to only traceable levels) of ammonia-nitrogen and biodegradable COD. The quality of the treated effluent further complies with the quality requirements (chloride and heavy metals) for discharge into the municipal biological treatment system. The capital and operational cost of a 250 m3/d tubular reverse osmosis (TRO) plant is estimated at R1.95 m. and R11.45/m3, respectively