'Thermophilic aerobic treatment of a synthetic wastewater in a membrane-coupled bioreactor

Synthetic wastewater containing alpha -lactose and gelatin was treated in a thermophilic membrane-coupled bioreactor (MBR), Thermophilic( >45 degreesC ) treatment represents a potentially advantageous process for high-temperat ure as well els high-strength industrial wastewaters susceptible to reactor autoheating, Thermophilic systems, however, generally support a nonfloccul ating biomass that resists conventional methods of cell separation from the treated wastewater. MBRs were applied to thermophilic treatment systems be cause bacterial cells can be retained regardless of cell aggregation. Therm ophilic aerobic MBRs were successfully operated at high levels of biocataly st and produced at better effluent quality than analogous thermophilic bior eactors without cell recycle, At a hydraulic residence time (HRT) of 13.1 h , the chemical oxygen demand (COD) of the membrane eluate improved from 760 mg l(-1) (without cell recycle) to 160 mg l(-1) (with cell recycle), Bacte rial community shifts were detected by denaturing gradient gel electrophore sis (DGGE) of polymerase chain reaction (PCR)-amplified 16S rRNA gene fragm ents - 6 of 13 bands dlisappeared within 2 days of MBR operation. A concomi tant 40-50% reduction in physiological indicators of cell reactivity (RNA:p rotein; ATP:protein) was also observed. The specific activity of beta -gala ctosidase and aminopeptidase, however, increased by 10-25%, indicating that there is a definite advantage to MBR operation at the highest biomass leve l possible. Nucleotide sequence analysis of 16S rDNA clones identified phyl otypes from the low-G+C Gram-positive division and the beta- and gamma -sub divisions of Proteobacteria.