Semi-starvation fluctuation driving rapid partial denitrification granular sludge cultivation in situ by microorganism exudate metabolites feedbacks

In this study, semi-starvation fluctuation driving PD granules cultivation in situ by microorganism exudate metabolites feedbacks was firstly investigated. The PD granules of high nitrite production were cultivated with an excellent mean nitrate-to-nitrite transformation rate (NTR) of 56.39% in just 30 days. The granules size was improved from the initial size of 0.09 ? 0.01 mm in diameter to a size above 2 mm when the extracellular polymeric substance (EPS) content increased from 80.21 ? 10.20 mg/g MLVSS to 777.00 ? 22.13 mg/g MLVSS. Acyl-homoserine lactone signals (AHLs) ultimately increased ten-fold more than the initially through 30 days of cultivation. Meanwhile, Thauera had been identified as the main function bacteria of PD, which enriched from 0.47% to 10.67%. Results demonstrated that AHLs, EPS, PD bacteria and the PD granules cultivation were closely associated. Semi-starvation fluctuation produced oligotrophic stress on bacterial community, a part of bacteria would be eliminated on starvation for oligotrophic stress and AHLs of bacteria regarded as distress signals resulted in the rapid formation of PD granules. A mechanism for PD granular cultivation with semi-starvation fluctuation was proposed from the aspect of oligotrophic stress. A better strategy for rapid PD granules cultivation was obtained and it could be useful for the mainstream granule-based PD combined with the anammox process application in the future.

Automated summary

This study investigated the cultivation of PD granules in situ by microorganism exudate metabolites feedback, resulting in high nitrite production with an excellent nitrate-to-nitrite transformation rate. It was found that increased EPS content led to improved granule size, while Thauera was identified as the main bacteria involved in PD. The study also revealed a close association between AHLs, EPS, PD bacteria, and the cultivation of PD granules.