Electrochemically selective ammonium recovery from wastewater via coupling hydrogen bonding and charge storage.

Electrochemical ammonium (NH4+) storage (EAS) has been established as an efficient technology for NH4+ recovery from wastewater. However, there are scientific difficulties unsolved regarding low storage capacity and selectivity, restricting its extensive engineering applications. In this work, electrochemically selective NH4+ recovery from wastewater was achieved by coupling hydrogen bonding and charge storage with self-assembled bi-layer composite electrode (GO/V2O5). The NH4+ storage was as high as 234.7 mg N g-1 (> 102 times higher than conventional activated carbon). Three chains of proof were furnished to elucidate the intrinsic mechanisms for such superior performance. Density functional theory (DFT) showed that an excellent electron-donating ability for NH4+ (0.08) and decrease of diffusion barrier (22.3 %) facilitated NH4+ diffusion onto electrode interface. Physio- and electro-chemical results indicated that an increase of interlamellar spacing (14.3 %) and electrochemical active surface area (ECSA, 388.9 %) after the introduction of GO were responsible for providing greater channels and sites toward NH4+ insertion. Both non-ionic chemical-bonding (V5+=O‧‧‧H, hydrogen-bonding) and charge storage were contributed to the higher capacity and selectivity for NH4+. This work offers underlying guideline for exploitation a storage manner for NH4+ recovery from wastewater.

Dosing with pyrite significantly increases anammox performance: Its role in the electron transfer enhancement and the functions of the Fe-N-S cycle.

Anaerobic ammonium oxidation (anammox) represents an energy-efficient process for biological nitrogen removal from ammonium-rich wastewater. However, there are mechanistic issues unsolved regarding the low microbial electron transfer and undesired accumulation of nitrate in treated water, limiting its widespread engineering applications. We found that the addition of pyrite (1 g L-1 reactor), an earth-abundant iron-bearing sulfide mineral, to the anammox system significantly improved the nitrogen removal rate by 52% in long-term operation at a high substrate shock loading (3.86 kg N m-3 d-1). Two lines of evidence were presented to unravel the underlying mechanisms of the pyrite-induced enhancement. Physiochemical evidence indicated that an increase of cytochromes c and Fe-S protein was responsible for the accelerated electron transfer among metabolic enzymes. Multi-omics evidence showed that the depletion of nitrate was attributed to the Fe-N-S cycle driven by nitrate-dependent Fe(II) oxidation and S-based denitrification. This study deepens our understanding of the roles of electron transfer and the Fe-N-S cycle in anammox systems, providing a fundamental basis for the development of mediators in the anammox process for practical implications.

Understanding the slight inhibition of high As(III) stress on nitritation process: Insights from arsenic speciation and microbial community analyses.

Nitritation process with ammonia-oxidizing bacteria frequently suffers inhibition from heavy metals in industrial wastewater treatment. However, As(III), one of the most toxic metalloids, showed slight inhibition though the arsenic accumulation content in the sludge reached 91.8 mg L-1 in this study. Here, we combined long-term reactor operation with microbiological analyses to explore the slight inhibition mechanisms of As(III) on nitritation consortia. The results showed that no obvious changes induced by As(III) occurred in apparent characteristics and morphology of the nitritation consortia, whereas dosing As(III) induced shifts in the arsenic speciation and microbial community. 84.1% of As(III) was oxidized to As(V) in the acclimated sludge, decreasing the toxicity of As(III) to nitritation consortia. Insight to the microbial community, the relative abundances of Thermaceae and Phycisphaeraceae responsible for As(III) oxidation were increased to 7.4% and 6.6% under the stress of high-concentration As(III), respectively. Further, these increased arsenite-oxidizing bacteria probably accepted electron acceptor NO2- from ammonia-oxidizing bacteria to oxidize As(III). Our results indicated that microbial As(III) oxidation was the dominant detoxification pathway, providing new insights into nitritation characteristics under long-term As(III) stress.

Distinct membrane fouling characteristics of anammox MBR with low NO2--N/NH4+-N ratio.

The bacterial growth and death, and extracellular polymeric substances (EPS) and soluble microbial products (SMP) in aerobic membrane bioreactor (MBR) cause severe membrane fouling. Anammox bacteria grow slowly but produce much EPS and SMP. Therefore, the membrane fouling characteristic of anammox MBR is still indistinct. A NO2--N/NH4+-N < 1.0 into in the influent of an anammox MBR applies to investigate: 1) the slowest growing anammox bacteria (Candidatus Jettenia) could be enriched or not; 2) its membrane fouling characteristic. Results showed that Candidatus Jettenia successfully accumulated from 0.01% to 26.19%. The fouling characteristic of anammox MBR was entirely different from other MBRs. Firstly, obvious low transmembrane pressure (<4 KPa, 125 days) and low amount of foulants (0.22 gVSS/m2) might result from N2 production and the slow-growing Candidatus Jettenia. Secondly, the analysis of the components of membrane foulants indicated that polysaccharides of SMP in the gel layer and pore foulants were the key factors affecting membrane fouling. Finally, the large particle size of foulants (200 µm) might be caused by anammox bacteria living inside the foulants under anaerobic conditions. This study provides systematic insights into membrane characteristics of anammox MBR and a basis for the enrichment of anammox bacteria by MBR.

Hydroxylamine addition enhances fast recovery of anammox activity suffering Cr(VI) inhibition.

Hydroxylamine (NH2OH), one of the most important intermediates of anammox was employed to test the recovery performance because of its stimulation to anammox bacteria. Batch test indicated simultaneous addition of 1.83 ~ 9.17 mg N /L NH2OH relieved Cr(VI) inhibition because of extracellular reduction to Cr(III). The recovery efficiency (RE) was over 166%, with the effluent Cr(VI) and Cr(III) below 0.25 and 0.12 mg/L, respectively. Anammox activity after Cr(VI) inhibition was effectively recovered by 8 mg N/L NH2OH with RE at 218%. The long-term operation showed 1 ~ 2 mg N/L NH2OH accelerated the recover speed of nitrogen removal rate with 2.84 folds, as well as improving NH4+ conversion ratio and reducing NO3- production. After 55 days recovery, extracellular polymeric substance concentration, anammox activity and heme content recovered better with NH2OH addition. This study will provide the theoretical basis for rapid recovery of anammox activity by NH2OH when suffering Cr(VI) inhibition.

Development and simulation of a struvite crystallization fluidized bed reactor with enhanced external recirculation for phosphorous and ammonium recovery.

Recovering nitrogen and phosphorus from waste water in the form of struvite is an effective way to recycle resources. The insufficient purity of the resulting struvite and the large loss of nitrogen and phosphorus are the challenges at present. Therefore, it is urgent to develop innovative method in struvite crystallization process for efficient nitrogen and phosphorus recovery. This study proposed a crystallization method to reduce the loss of nitrogen and phosphorus by a struvite fluidized bed reactor (FBR) with optimized structure and operation conditions. The properties of struvite obtained under various conditions in the reactor were studied, and the internal operating conditions of the reactor were simulated with COMSOL Multiphysics to verify the effectiveness of the reactor optimization. This reactor achieved stable operation under the conditions of N/P = 1:1 and pH = 9.0. The purity of struvite obtained reached 98.5%, the conversion rate of ammonia nitrogen reached 97.2%, and struvite crystals could grow to 84 µm within 24 h. The simulation results showed that the Venturi tubes installed at multiple locations increased the turbulent energy to 4 × 10-4 m2/s2, which greatly improved the mass transfer efficiency. The trajectory of the crystal particles was consistent with the fluid flow field, which promoted the purification and growth of the crystal. In general, the new FBR with enhanced external recirculation would be a very feasible way to improve crystal growth and crystal purification of struvite, and it could enhance the recovery efficiency of nitrogen and phosphorus with reduced cost.

The application of aged refuse in nitrification biofilter: Process performance and characterization.

High adsorption capacity, good biocompatibility and low cost are highly demanded for biofilter used in ammonium-rich wastewater treatment. In this study, we used SEM, BET, XRD and 16S rRNA to document the evidence for good performance in adsorption and biodegradation in aged refuse. Parallel experiment between raw and inert refuse showed ammonium adsorption occurred at the initial week, with the highest ammonium removal efficiency of 90.36%, but saturated during the subsequent long-term operation. Meanwhile, over 6months' operation of an aged refuse biofilter was conducted to confirm that nitrification was the main pathway of ammonium conversion. The maximum nitrogen loading rate could reach up to as high as 1.28kg/m3/d, with ammonium removal efficiency at 99%. Further, high nitrifier biodiversity were detected with 'Nitrosomonas' and 'Nitrospira' in domination in the refuse. However, Nitrospira would outcompete Nitrosomonas under the oxygen limiting condition and resulted in the failure of partial nitrification. The physicochemical and biological analysis show that biodegradation is the main ammonium conversion pathway, which is the critical finding of this work. This investigation would help to accelerate the application of the aged refuse process in ammonium-rich wastewater treatment.