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Industrial brine minimization: determining the physical chemical parameters that affect evaporation rates on multi-component hyper-saline effluents
Expanded Title:This report has summarised the issues relating to industrial brine generation and disposal in South Africa and has reviewed the literature on brines with particular emphasis on the water treatment processes that produce brines as a waste, the chemistry of brines and the factors which influence evaporation and determine brine evolution. The present study focused on the brine produced at the eMalahleni water treatment plant. Analysis of the stage 3 reject brine collected from the plant revealed that it is a Na-SO4 type water although it does contain significant concentrations of other major ions, namely Ca, Mg, K and Cl. Seventy-one percent of the cation mole charge is accounted for by Na+, and the remainder by Ca2+ (15%) K+ (9%) and Mg2+ (4%). In the case of anion charge, SO42- accounts for 88% and Cl- (10%) and HCO3- (1%) for the remainder. The brine has a near-neutral pH. It was this analysis that prompted the choice of salts for the small scale evaporation study designed to find out whether the type of salt has any effect on evaporation rate. The small scale evaporation experiments confirmed that an effect of salt type (single, binary and ternary solutions of Na2SO4, NaCl, KCl, CaSO4, and MgSO4 were studied) was sometimes discernible but not statistically significant, probably in part because while the effect of salt is generally to reduce evaporation the presence of salt also gives rise to greater heating of the solution by absorbing radiant energy. There also seemed to be a solution heating effect leading to a higher evaporation rate (again not significant) in the case of those solutions dominated by divalent as opposed to monovalent cations. Despite these uncertainties the overall effect of salts on evaporation rate was confirmed in both the small scale study as well as the subsequent pilot scale study to be essentially one of concentration, inhibiting evaporation as expected. Comparison of the actual measurements of the Emalahleni brine and the modelled brine evaporation for the same period showed that the daily average of the Emalahleni brine under natural convection was 5.33 mm/day. The Oroud (1999; 2000) model suggests a very similar figure over the same period. Under the forced convection, the model was a bit lower than the actual recorded evaporation. The model also projects 11% increase with wind being applied at 2 m/s every 12 hour cycle. Based on the salinity experiments, all the synthetic salts exposed to various conditions had shown different volume loss. The results indicated that the greatest volume loss was obtained for the least soluble salt amongst the synthetic salts while the more highly soluble salts had the lowest volume loss. The novel high surface area materials developed, namely composite nanofibres comprised of PAN loaded with Zeolite Y nanoparticulates were shown to significantly remove divalent cations from model brine solutions, allowing for brine simplification. The PAN TiO2 nanofibres showed a high Na cation adsorption. This study has been concluded successfully in terms of construction and testing to demonstrate a sensitive response of evaporation to parameters such as salt concentration, wind and irradiance. It also points to the greater potential of generating products of value from the brine.
Date Published:01/08/2015
Document Type:Research Report
Document Subjects:Wastewater Management - Industrial, Wastewater Management - Sewers
Document Format:Report
Document File Type:pdf
Research Report Type:Standard
WRC Report No:2100/1/15
ISBN No:978-1-4312-0649-0
Authors:Petrik LF; Fatoba OO; Fey MV; Ndlela R; Ndlovu NZN; Omoniyi EO; Bent D; Nell P
Project No:K5/2100
Organizations:University of the Western Cape
Document Size:4 347 KB
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