The nitrogen removal performance and mechanisms for urea wastewater by simultaneous urea hydrolysis, partial nitritation and anammox in one reactor

The efficient and economical disposal of urea wastewater for promoting wastewater reuse, are still tough obstacles for the sustainable development of urea industry. In order to explore newly efficient and economical alternative for urea wastewater treatment, a novel one-stage autotrophic nitrogen removal reactor (submerged aerated biological filter, SABF) simultaneously combining with urea hydrolysis, partial nitritation (PN) and anammox was carried out and stably operated for 126 days. The SABF reactor not only presented excellent urea removal efficiency (˃ 99.5%) with average effluent urea concentration of 0.83 mg/L to meet reuse standard, but also achieved high nitrogen removal loading, ammonium removal efficiency and total nitrogen removal efficiency as 1.5 kg N/(m³·d), 89.46% and 77.09%, respectively. The urea removal mechanism was proven as the intracellular urea hydrolysis, which was conducive to accomplish the persistent free ammonia (FA) inhibition on nitrite-oxidizing bacteria for stable PN and guaranteed total nitrogen removal by anammox. High-throughput sequencing analysis results revealed that Nitrosomonas accounting for 15.92% should be responsible for excellent urea hydrolysis and PN performance and Candidatus_Brocadia with relative abundance of 1.63% was the main anammox bacteria for further nitrogen removal in the SABF reactor. The proposed process showed significant advantages of extremely low operational cost and high removal efficiency with recyclable effluent for urea wastewater treatment. This study provided a novel and superior alternative for the cleaner production of urea manufacturing enterprises, which can well alleviate the stress of urea wastewater treatment and further benefit the sustainable development of urea industry in the future.