Nitrogen Removal and Simultaneous Phosphorus Recovery from Agro-Industrial Wastewater Through Partial Nitritation/Anammox Process

Sustainable phosphorus management is crucial for safeguarding global food security and preventing soil and water quality deterioration. This work firstly assessed the feasibility of phosphorus recovery by treating agro-industrial wastewater (743 mgNH4+-N L−1, 29 mgPO43−-P L−1, and Ca/P 1.64) using a single-stage Partial Nitritation/Anammox (PN/A) process. The experimental set-up involved a 3L sequencing batch reactor which was inoculated with ANAMMOX© granulated biocatalyst and ran with a 6-h working cycle. An operating strategy based on a progressive increase in nitrogen loading rate (NLR, from 0.11 to 0.33 kgN (m3⋅d)−1) was adopted to promote biomass cultivation. Moreover, a set of experiments was performed to investigate a novel non-damaging sludge separation protocol to recover active biomass and mineral phosphorus. Granules were exposed to ultrasonication at 37 kHz, and the specific anammox activity (SAA) before and after treatment was measured through the manometric method. As a result of the NLR strategy, biomass and SAA significantly increased over seven months, reaching 6.77 g L−1 and 0.39 gN2 (gMLVSS⋅d)−1, respectively. In the absence of an external calcium source, simultaneous nutrient removal consisting of ammonium conversion rate up to 0.28 kgNH4+-N (m3⋅d)−1 and phosphorus removal efficiency of ca. 34% were achieved. Ultrasonication tests showed that anammox was negatively affected when extending the exposition time, yet a 15-min sonication showed limited activity loss compared to untreated granules. These results suggest the promising application of ultrasonic treatment for non-damaging separation, but further studies are needed to evaluate the effectiveness of phosphorus recovery and biomass bioreactor re-inoculation.