Abstract:
The objective of this study was to determine whether inoculating a hybrid fixed-film bioreactor with exogenous bacterial
and diatoma species would increase the removal of chemical oxygen demand, nitrogenous compounds and suspended solids
from a real-time coal gasification wastewater to meet environmental discharge requirements specified for petrochemical
refineries. The COD removal increased by 25% (45% to 70%) at a relatively high inoculum dosage (370 g∙m−3) and unit
treatment cost (12.21 €∙m−3). The molar ratio of monovalent cations to divalent cations (M/D >2) affected nitrification,
settling of solids and dewatering of the sludge. The use of a low-charge cationic flocculant decreased the suspended solids
in the effluent by 70% (180 mg∙L−1 to 54 mg∙L−1) and increased the sludge dewatering rate by 88% (61 s∙L∙g−1 to 154 s∙L∙g−1)
at a unit treatment cost of 2.5 €∙t−1 dry solids. Organic compounds not removed by the indigenous and exogenous microbial
species included benzoic acids (aromatic carboxylic acids), 2-butenoic acid (short-chain unsaturated carboxylic acid),
I(2H)-isoquinolinone (heterocyclic amine), hydantoins (highly polar heterocyclic compounds), long-chain hydrocarbon
length (carbon length > C15) and squalene. These organic compounds can thus be classified as poorly degradable or nonbiodegradable
which contributed to the 30% COD not removed by the H-FFBR. The use of exogenous microbial species
improved the quality of CGWW; however, not sufficiently to meet discharge requirements. The cost of such treatment
to meet discharge requirements would be unsustainable. Alternative technologies need to be investigated for reusing or
recycling the CGWW rather than discharging.
