Granulation of Nitrifying Bacteria in a Sequencing Batch Reactor for Biological Stabilisation of Source-Separated Urine

Abstract

Biological stabilisation of human urine highly depends on the abundance and activities of nitrifying bacteria. However, it is quite difficult to enrich nitrifiers as bio-aggregation by self-immobilized biomass. In this study, granulation of nitrifying bacteria involving inoculation strategy was developed. Two sequencing batch reactors, the one inoculated with nitrifying bacteria and the other inoculated with aerobic granules, were operated in laboratory side by side with a feeding of urine solution. Aerobic nitrifying granules (ANG), with compact morphological structure and good nitrifying activity, were achieved in the reactor inoculated with aerobic granules. Enrichment of nitrifying bacteria favors the nutrient uptake, and hence, to obtain a high ammonia oxidation efficiency. Nonetheless, nitrite accumulation gradually dominated in reactor, partly attributes to a high concentration of free nitrous acid and free ammonia in bulk. The matured ANG had a rather stable microbial profile, as that a number of activated bacteria occupied the surface of granule. It was also found that ANG were much more impermeable than aerobic granules and activated sludge, which was demonstrated as smaller porosities, and therewith an excellent settleability. The results herein reveal that granulation of nitrifying bacteria could enrich the biomass to implement stabilisation of urine in biological way.