Biochemical conversions and biomass morphology in a long-term operated SBR with aerobic granular sludge

Abstract

The experiment was carried on for about one year (995 cycles) in a constantly aerated, column sequencing batch reactor with granular sludge fed with a mixture of anaerobic sludge digester supernatant and synthetic wastewater. The research proved the usefulness of granular sludge technology for the removal of ammonium from highly concentrated ammonium streams with an unfavorable chemical oxygen demand (COD)/nitrogen (N) ratio. In the period of stable reactor performance, all ammonium in the influent was oxidized and nitrification–denitrification via nitrite occurred with an efficiency of 26%. The calculated carbon (COD) and N balances showed how the substances were distributed in the reactor under the conditions of low organic accessibility and high N load. Despite the low organic availability, intracellular storage occurred and the yield of polyhybroksybutyrate (PHB) was Y_PHB = 0.206 g COD/g COD. Detailed characteristics of the biomass operating under conditions of low COD/N was performed and showed that the wastewater composition and reactor operational parameters promoted the growth of dense, smooth granules with an average fractal dimension of 2.75 ± 0.15, characterized by settling velocity and equivalent diameter of 11.6 ± 7.9 mm/s and 2.13 ± 1.29 mm, respectively. The presented results can be used for the modeling of reactors with granular sludge for treating wastewater with the very low COD/N ratio.

Keywords:

• Granular sludge
• Anaerobic sludge digester supernatant
• Partial nitrification
• Granule morphology
• Mass balance
• Fractal dimension

Acknowledgment

We are grateful for the financial support of the Ministry of Scientific Research and Information Technology of Poland (Project No. N N523 423337).