Membrane and Desalination Technologies - TCE Moodle Website

Potable Water Biotechnology, Membrane Filtration and Biofiltration 497
removal from drinking water showed that the IEMB process allows for the most selective
removal of the target pollutant simultaneously avoiding microbial and secondary contamination
of the treated water stream. Velizarov et al. (99) investigation on the IEMB uses a
mono-anion permselective membrane as a barrier between a water stream, containing a
target polluting anion, and a biocompartment, containing a suitable driving counter-ion for
coupled counter-diffusion of the target pollutant, and a microbial culture capable of its
bioreduction to harmless product(s). Resistances-in-series to trace counter-ion approximation
model based on the Fick formalism and the Donnan equilibrium principle was proposed
for analysis of the transport rate of dilute inorganic anionic pollutants with relevance to
drinking water treatment. Transport of co-ions (cations) is negligible due to their electrostatic
repulsion (Donnan exclusion) from the positively charged membrane. The model was
tested in a system, containing NO 3 as the target pollutant and chlorides as the driving bulk
counter-ions. The effect of the most important process variables on the target pollutant flux
were assessed using the model, making possible the comparison between different IEMB
process options, which can be quantified and used for process design. Donnan dialysis was
also evaluated for the possibility of using various membranes in IEMB by Velizarov et al. in
2004 (96). The anion-exchange membrane, Neosepta ACS, proved to be a good choice for
perchlorate and NO3 , but was not suitable for arsenate, for which the Ionac MA-3475
allowed more than a three-order magnitude increase in flux. The cation-exchange membrane,
Nation-112, showed promising results for the transport of mercuric ions, while the
Neosepta CMX was almost impermeable to this micropollutant. Tap water from the Lisbon
public distribution network was supplemented with 100 mg/L of perchlorate and 60 mg/L of
NO 3 and was continuously treated in the IEMB incorporating a Neosepta ACS membrane
for a period of about 2 months. Highly selective simultaneous removal of both pollutants
was observed, in spite of their very different concentrations in the contaminated water.
There was no secondary pollution of the treated water by microbial cells and residual
organics (96).
The results of the experiments on selected anions removal from water investigated by
Wis´niewski et al. (97) indicated the removal of some ions, especially ‘troublesome’ anions
(sulfates and bicarbonates), and a high degree of water desalination by means of electrodialysis.
Selemion (AMV, DMV) and Neosepta (AFN, AMX) anion-exchange membranes (AEMs)
were used in an ion-exchange study. For each of the four examined membranes, the following
high efficiencies of anions removal were obtained: 87–98% removal of NO3 , 94–100%
removal of sulfates, whereas for bicarbonates the removal efficiency was 77–99%. It was
found out that with higher concentrations of NaCl (300 and 500 mM), the equilibrium
concentration of the exchanged ions in the feed was lower. However, with the higher
ratio of feed and receiver volumes (4:1), the concentration at the point of Donnan equilibrium
was set at an elevated level. The best transport properties for the examined anions were
shown for the Neosepta AFN membrane. The average flux of NO3 and sulfates was up to
two times higher than with other membranes and bicarbonate flux was even three times
higher (97).