A predictive model for N2O production in anammox-granular sludge reactors: Combined effects of nitrite/ammonium ratio and organic matter concentration

Minimizing byproduct formation in bioelectrochemical denitrification with anammox bacteria

Autotrophic bioelectrochemical denitrification (BED) holds promise for nitrate remediation. However, the accumulation of byproducts such as NO2-, N2O, and NH4+, poses a significant challenge to effluent quality and climate adaptation. This study hypothesized that introducing anaerobic ammonium oxidation bacteria (anammox) to BED could alleviate this issue through synergy: a) anammox can utilize NH4+ and NO2- from BED without producing N2O, as seen in canonical denitrification, and b) BED can recycle NO3- from the anammox anabolic pathway. Results showed that Anammox_BED reduced NO2- accumulation by two-thirds, lowered the relative abundance of N2O by 80 %, and eliminated NO. Metagenomic analysis revealed that the anammox species Ca. Brocadia sapporoensis tripled in abundance in the bulk sludge. Meanwhile, Pseudomonas stutzeri and Bosea robiniae, species capable of reducing nitrate via extracellular electron transfer (EET) and supplying NO2- to anammox, halved in relative abundance, while the abundance of Stenotrophomonas acidaminiphila, a non-EET, ammonia assimilation species, doubled following anammox introduction. Metatranscriptomic analysis found upregulation of denitrification-related functional genes in Anammox_BED biofilm and survival- and motility- related genes in bulk sludge, possibly due to insufficient substrate. Overall, BED-Anammox successfully diverted the rate-limiting EET nitrite reduction towards anammox-driven nitrite utilization thereby mitigating the generation of unwanted intermediates.

Achieving stable nitrogen removal through mainstream partial nitrification, anammox and denitrification (SNAD) with a hybrid biofilm-granular reactor

Simultaneous partial nitrification, anammox, and denitrification (SNAD) process offers a promising method for the effective removal of carbon and nitrogen from wastewater. However, ensuring stability is a challenge. This study investigated operational parameters such as hydraulic retention time (HRT) and biomass retention to stabilize SNAD operation, transitioning from synthetic to anaerobically pre-treated municipal wastewater (APMW) in an upflow hybrid biofilm-granular reactor (UHR). The incorporation of hybrid biomass in the form of biofilms and granules resulted in a significant improvement in ammonium oxidation, increasing the efficiency from 45% to 60%. This outcome underscores the significance of biomass retention as a crucial parameter in achieving optimal performance. Furthermore, extending the HRT resulted in a significant improved nitrogen removal, increasing it from 40% (8h) to 70% (12h), which was attributed to the enhanced specific activities of ammonium-oxidizing bacteria (AOB) and anammox bacteria (AnAOB). Microbial characterization unveiled the emergence of partial denitrifiers (Thauera genus) and the suppression of nitrite-oxidizing bacteria (NOB) (Nitrospira genus) at low aeration rates (0.35 L min-1.L-1reactor; estimated 0.5 mgDO.L-1). Notably, stable operation persisted throughout the experimental period, primarily due to the consistent nitrite supply from partial nitrification/denitrification. Our findings highlight the potential of innovative hybrid reactor configuration, for achieving stable and efficient SNAD performance in mainstream wastewater treatment.

Recent advances in swine wastewater treatment technologies for resource recovery: A comprehensive review

Swine wastewater (SW), characterized by highly complex organic and nutrient substances, poses serious impacts on aquatic environment and public health. Furthermore, SW harbors valuable resources that possess substantial economic potential. As such, SW treatment technologies place increased emphasis on resource recycling, while progressively advancing towards energy saving, sustainability, and circular economy principles. This review comprehensively encapsulates the state-of-the-art knowledge for treating SW, including conventional (i.e., constructed wetlands, air stripping and aerobic system) and resource-utilization-based (i.e., anaerobic digestion, membrane separation, anaerobic ammonium oxidation, microbial fuel cells, and microalgal-based system) technologies. Furthermore, this research also elaborates the key factors influencing the SW treatment performance, such as pH, temperature, dissolved oxygen, hydraulic retention time and organic loading rate. The potentials for reutilizing energy, biomass and digestate produced during the SW treatment processes are also summarized. Moreover, the obstacles associated with full-scale implementation, long-term treatment, energy-efficient design, and nutrient recovery of various resource-utilization-based SW treatment technologies are emphasized. In addition, future research prospective, such as prioritization of process optimization, in-depth exploration of microbial mechanisms, enhancement of energy conversion efficiency, and integration of diverse technologies, are highlighted to expand engineering applications and establish a sustainable SW treatment system.

Efficient reactivation of anammox sludge after prolonged storage using a combination of batch and continuous reactors

Due to the slow growth rate of anammox bacteria, enriched sludge is required for the rapid start-up of anammox-based reactors. However, it is still unclear if long-term stored anammox sludge (SAS) is an effective source of inoculum to accelerate reactor start-up. This study explored the reactivation of long-term SAS and developed an efficient protocol to reduce the start-up period of an anammox reactor. Although stored for 13 months, a low level of the specific anammox activity of 28 mg N/g VSS/d was still detected. Experimental Phase 1 involved the direct application of SAS to an upflow sludge bed reactor (USB) operated for 90 d under varying conditions of hydraulic retention time and nitrogen concentrations. In Phase 2, batch runs were executed prior to the continuous operation of the USB reactor. The biomass reactivation in the continuous flow reactor was unsuccessful. However, the SAS was effectively reactivated through a combination of batch runs and continuous flow feed. Within 75 days, the anammox process achieved a stable rate of nitrogen removal of 1.3 g N/L/day and a high nitrogen removal efficiency of 84.1 ± 0.2%. Anammox bacteria (Ca. Brocadia) abundance was 37.8% after reactivation. These overall results indicate that SAS is a feasible seed sludge for faster start-up of high-rate mainstream anammox reactors.

Low-concentration methanol effect on the microorganisms, nitrogen removal, and recovery of the completely autotrophic nitrogen removal over nitrite

Methanol has a significant effect on the performance of the completely autotrophic nitrogen removal over the nitrite (CANON) process. In this research, the effect of low-concentration methanol on the functional microorganisms and nitrogen removal and recovery in the CANON system is investigated. The result shows that the anaerobic ammonium-oxidizing bacteria (AnAOB) was suppressed with low-concentration methanol addition, and the phylum Planctomycetes was hidden. The genus Candidatus Brocadia was restrained, and the relative abundances reduced from 25.5 to 15.0% in the upper biofilm and from 20.3 to 14.3% in the bottom biofilm, respectively. However, low-concentration methanol promoted the nitrifying oxidizing bacteria (NOB) activity. This phenomenon reduced the average ammonium nitrogen removal rate from 95.0 to 70.7%, and the average total nitrogen removal rate decreased from 81.3 to 43.6%, respectively. The results demonstrated that the low-concentration methanol as an organic carbon matter harmed the CANON process. Fortunately, the CANON system had an excellent self-healing ability when the methanol was stopped, with the average ammonium nitrogen removal rate and total nitrogen removal rate returning to 95.5 and 80.9%, respectively. This research supplies a reference for practical engineering design and application by improving the understanding of the effects of low-concentration methanol on CANON process performance.