Nitrate and phosphorus removal from synthetic water and their coupling effect using nanofiltration membrane
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Date
2018-06
Authors
Fatima Zahara Aizadshah
Journal Title
Journal ISSN
Volume Title
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Abstract
Nitrate and phosphate contamination of groundwater is a growing problem both
in developed and developing countries. Such contamination comes mainly from the
intensive use of fertilizers in agriculture, improper discharges of industrial effluents and
effluents from intensive farming. Nanofiltration (NF) is chosen as the treatment for nitrate
and phosphorus removal from contaminated waters. In this work, the removal of nitrates
and phosphate from synthetic water using a commercial NF270 and NF90 membrane is
studied. The efficiency of both membranes is evaluated based on the influence of
transmembrane pressure, stirring speed and initial concentration of each solute on
rejection and flux. NF90 shows higher rejection on nitrate (97.8%) while NF270 shows
higher removal of phosphate (99.1%) which shows that NO3
-
removal is via diffusional
control while PO4
3-
removal is via charge repulsion control. The coupling effect of nitrate
and phosphate was also investigated. It was proven that rejection of nitrate is greatly
influenced by the presence of phosphate ions due to the electro-neutrality principle.
Lastly, effect of stirring speed on flux and the mass transfer coefficient were also
established for each membrane. NF270 shows linear increase in mass transfer coefficient
against stirring speed for both individual nitrate and phosphate removal. This behavior of
the NF270 membrane can be explained by relatively larger pore size of the NF270
membrane allowing more solution to pass through thus less concentration polarisation
which describes the accumulation of the species being retained close to the surface of the
membrane.