Major problems encountered in biological treatment of
saline wastewaters were (i) a limited extent of adaptation,
as conventional cultures could not be effectively used to
treat saline wastewaters of values higher than 3–5% (w/v)
salt. (ii) salt adaptations of cultures were easily lost when
subjected to salt-free medium. (iii) changes in ionic
strength cell disruptions due to shifts in salt concentration,
from 0.5 to 2% (w/v), caused significant reductions
in system performance [12]. (Even with acclimatized cultures,
satisfactory performance required a constant ionic
composition). (iv) rapid changes in salt concentrations
created adverse effects more than gradual changes. Normalization
to constant salt concentration is essential
before saline wastewaters were treated. Reduced degradation
kinetics too occurred. Thus available information
indicated that the removal of BOD by biological treatment
processes is reduced at salt concentrations above
8,000 mg l-1. So saline wastewater should be treated at
lower food to micro-organism (F/M) ratios, or higher than
usual bacteria Mixed Liquor Volatile Suspended Solids
(MLVSS) concentrations. Rapid changes in salt concentration
cause adverse effects more than gradual changes. The
treatment process should provide sufficient hydraulic
retention time (HRT) to even out changes in salt concentration.
In recent years there have been a few studies on
biological treatment of tannery soak liquor. Lefebvre et al
[13] made an attempt to treat tannery saline wastewater
biologically. They studied the microbial diversity of
hypersaline tannery wastewater [14] and anaerobic digestion
of tannery soak liquor in an Upflow Anaerobic
Sludge Blanket (UASB) reaching 78% COD removal [15].
Unidentified microbial consortia and halophillic/moderate
halophillic cultures were used.
Major problems encountered in biological treatment ofsaline wastewaters were (i) a limited extent of adaptation,as conventional cultures could not be effectively used totreat saline wastewaters of values higher than 3–5% (w/v)salt. (ii) salt adaptations of cultures were easily lost whensubjected to salt-free medium. (iii) changes in ionicstrength cell disruptions due to shifts in salt concentration,from 0.5 to 2% (w/v), caused significant reductionsin system performance [12]. (Even with acclimatized cultures,satisfactory performance required a constant ioniccomposition). (iv) rapid changes in salt concentrationscreated adverse effects more than gradual changes. Normalizationto constant salt concentration is essentialbefore saline wastewaters were treated. Reduced degradationkinetics too occurred. Thus available informationindicated that the removal of BOD by biological treatmentprocesses is reduced at salt concentrations above8,000 mg l-1. So saline wastewater should be treated atlower food to micro-organism (F/M) ratios, or higher thanusual bacteria Mixed Liquor Volatile Suspended Solids(MLVSS) concentrations. Rapid changes in salt concentrationcause adverse effects more than gradual changes. Thetreatment process should provide sufficient hydraulicretention time (HRT) to even out changes in salt concentration.In recent years there have been a few studies onbiological treatment of tannery soak liquor. Lefebvre et al[13] made an attempt to treat tannery saline wastewaterbiologically. They studied the microbial diversity ofhypersaline tannery wastewater [14] and anaerobic digestionof tannery soak liquor in an Upflow AnaerobicSludge Blanket (UASB) reaching 78% COD removal [15].Unidentified microbial consortia and halophillic/moderatehalophillic cultures were used.
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