Nitrite and nitrate inhibition thresholds for a glutamate-fed bio-P sludge.

Enhanced biological phosphorus removal (EBPR) is an efficient and sustainable technology to remove phosphorus from wastewater. A widely known cause of EBPR deterioration in wastewater treatment plants (WWTPs) is the presence of nitrate/nitrite or oxygen in the anaerobic reactor. Moreover, most existing studies on the effect of either permanent aerobic conditions or inhibition of EBPR by nitrate or free nitrous acid (FNA) have been conducted with a "Candidatus Accumulibacter" or Tetrasphaera-enriched sludge, which are the two major reported groups of polyphosphate accumulating organisms (PAO) with key roles in full-scale EBPR WWTPs. This work reports the denitrification capabilities of a bio-P microbial community developed using glutamate as the sole source of carbon and nitrogen. This bio-P sludge exhibited a high denitrifying PAO (DPAO) activity, in fact, 56% of the phosphorus was uptaken under anoxic conditions. Furthermore, this mixed culture was able to use nitrite and nitrate as electron acceptor for P-uptake, being 1.8 µg HNO2-N·L-1 the maximum FNA concentration at which P-uptake can occur. Net P-removal was observed under permanent aerobic conditions. However, this microbial culture was more sensitive to FNA and permanent aerobic conditions compared to "Ca. Accumulibacter"-enriched sludge.

Glutamate as sole carbon source for enhanced biological phosphorus removal.

Enhanced Biological Phosphorus Removal (EBPR) is based on the enrichment of sludge in polyphosphate accumulating organisms (PAO). Candidatus Accumulibacter is the bacterial community member most commonly identified as PAO in EBPR systems when volatile fatty acids (VFA) are the carbon source. However, it is necessary to understand the role of non-Accumulibacter PAO in the case of wastewater with low VFA content. This work shows the first successful long-term operation of an EBPR system with glutamate as sole carbon and nitrogen source, resulting in the enrichment of sludge in the genus Thiothrix (37%), the family Comamonadaceae (15.6%) and Accumulibacter (7.7%). The enrichment was performed in an anaerobic/anoxic/oxic (A2/O) continuous pilot plant, obtaining stable biological N and P removal. This microbial community performed anaerobic P-release with only 18-29% of the observed PHA storage in Accumulibacter-enriched sludge and with slight glycogen storage instead of consumption, indicating the involvement of other carbon storage routes not related to PHA and glycogen. Thiothrix could be clearly involved in P-removal because it is able of accumulating Poly-P, probably without PHA synthesis, but with glutamate involvement. On the other hand, Comamonadaceae could participate in degradation of glutamate and denitrification, but its involvement in P-uptake cannot be reliably concluded.