Vertical flow constructed wetlands for the treatment of inorganic ...

Saline effluents are conventionally treated by physico-chemical processes as
biological treatment can be strongly inhibited by NaCl (Lefebvre and Moletta, 2006).
Physico-chemical treatments, however, are costly so alternative biological treatments
have been the focus of recent research. Salt is known to reduce microbial activity and
therefore constitutes a microbiological agent of stability (Lozach, 2001). High
percentages of salt are known to compromise the correct operation of conventional
aerobic WWTP. Ludzack and Norman (1965) found that Cl - concentrations above 5-8ppt
affected performance of aerobic processes. Biological treatment to remove carbon,
nitrogen and phosphorus are feasible at high salt concentrations but adaptation of the
biomass or use of halophilic (salt tolerant) organisms will dictate treatment
performance (Lefebvre and Moletta, 2006).
Acclimation means the exposure of organisms to increasing concentrations of
salt in order to obtain satisfactory effluent treatment. Salt tolerant organisms have to
be present in the original conditions or introduced to the treatment system via
inoculation, then slow increases in salinity permit such tolerant organisms to reproduce
while non salt tolerant organism are eliminated. Abrupt increases in salinity usually
cause performance disruptions which can be either permanent, if halophilic organisms
are absent in the initial microbial biomass, or temporary, when halophilic organisms are
initially present and the reduced performance represents the lag time their populations
take to increase and consume substrate (Ludzack and Norman, 1965; Lefebvre and
Moletta, 2006). It is usual to see a reduced pollutant removal rate in saline systems,
the theory postulated here is that this is probably due to reduced richness and diversity
of organisms capable of withstanding high salt concentrations and therefore niches
that were previously occupied by some organisms remain vacant.
Panswad and Anan (1999) used salt “adapted” organisms in the
anaerobic/anoxic/aerobic treatment system resulting in improved removal percentages
of organic matter and nitrogen. They initially verified a 55% inhibition of nitrification at
30g/L NaCL, but after a few days normal activity was recovered. Campos et al. (2002)
achieved efficient nitrification in an activated sludge unit treating saline wastewater
with influent NH4 + -N up to 3.3g/L. Once NH4 + -N increased over 3.3g/L nitrification
efficiency decreased and ammonium accumulated in the system. At the time of
ammonium accumulation, total salt concentrations were 13.7g NaCl/L, 19.9g NaNO3/L
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