A preliminary test for nitrogen recovery potential of nitrogen fixing cyanobacteria and its granules treating wastewater containing different nitrogen species

Abstract

Nitrogen compounds in wastewater can be regarded as both troublesome pollutants and nutrients/resources that may be reused and recycled. Currently, nitrogen (N) removal from wastewater in most wastewater treatment plants (WWTPs) is implemented by the destructive methods like nitrification/denitrification processes, and little attention has been paid to recovery and recycle of N resource in WWTPs. In this preliminary study, the granulation of cyanobacteria (i.e., Aphanizomenon flos-aquae Ralfs ex Bornet &Flahault) was achieved, and comparison was made in terms of N recovery/fixation potential when treating wastewater containing different N species. During the granulation process, the settleability indicated by sludge volume index at 5 min (SVI5) and biomass concentration varied from initially > 3000 mL/g and 0.2 g/L to 59 mL/g and 1.2 g/L, respectively. This observation suggests biogranulation may be utilized to effectively and simultaneously cultivate and harvest cyanobacteria, greatly reducing energy consumption and operation costs. Both cyanobacteria and its granules were found to remove 57–100 % of NO3–-N in 5 days under N2 recirculation at an initial NO3–-N of 15.0 mg/L. Compared to the seed cyanobacterial cells, after 3-day batch test the granular biomass contained 83 % higher total N content, about 73.3 mg N in comparison to 40.0 mg N for per gram of biomass under the same N2 recirculation condition, 236 % more proteins, and 115 % times higher N fixation capability. Results from this work can provide a promising solution for N recovery/fixation with reduced N loss/emission from WWTPs and then create nitrogen bioeconomy in wastewater industry.