Conductive carrier promotes synchronous biofilm formation and granulation of anammox bacteria

The extracellular electron transfer capability of some anaerobic ammonium oxidation (anammox) bacteria was confirmed in recent years. However, the effect of conductive carriers on the synchronous formation of anammox biofilm and granules is rarely reported. Anammox biofilm and granules with compact and stable structures accelerate the initiation and enhance the stability of the anammox process. In this study, we found that the conductive carbon fiber brush (CB) carrier promoted synchronous biofilm formation and granulation of anammox bacteria in the internal circulation immobilized blanket (ICIB) reactor. Compared with polyurethane sponge and zeolite carrier, the ICIB reactor packed with CB carrier can be operated under the highest total nitrogen loading rate of 6.53 kg-N/(m³·d) and maintain the effluents NH₄⁺-N and NO₂^--N at less than 1 mM. The volatile suspended solids concentration in the ICIB reactor packed with conductive carrier increased from 5.17 ± 0.40 g/L of inoculum sludge to 24.24 ± 1.20 g/L of biofilm, and the average particle size of granules increased from 222.09 µm to 879.80 µm in 150 days. Fluorescence in situ hybridization analysis showed that anammox bacteria prevailed in the biofilm and granules. The analysis of extracellular polymeric substances indicated that protein and humic acid-like substances played an important role in the formation of anammox biofilm and granules. Microbiome analysis showed that the relative abundance of Candidatus Jettenia was increased from 0.18% to 38.15% in the biofilm from CB carrier during start-up stage. This study provides a strategy for rapid anammox biofilm and granules enrichment and carrier selection of anammox process.

Bioaugmentation of Anammox Activated Sludge with a Nitrifying Bacterial Community as a Way to Increase the Nitrogen Removal Efficiency

Abstract—

Bioaugmentation, i.e., increasing the abundance of certain microorganisms in the community by adding appropriate cells or establishing the conditions promoting their growth, is widely used in environmental technologies. Its application for launching of the anammox reactors is usually limited to introduction of anammox bacteria. We expected addition of nitrifiers during anammox bioreactor launching to stimulate the anammox process due to rapid production of nitrite, which anammox bacteria use for ammonium oxidation. The present work investigated the effect of introduction of a nitrifying community on the composition and activity of the microbial community in an anammox reactor. At the time of inoculation of a laboratory SBR reactor, an active nitrifying community (5 days old) (ASB) (bioaugmenting activated sludge, ASB) containing group I nitrifiers, primarily Nitrosospira, was added (1 : 100 by biomass) to anammox activated sludge (ASA) stored for 1 month at 4°C and exhibiting low metabolic activity. The use of ASB resulted in increased efficiency of nitrogen removal. While noticeable nitrogen removal in the control (7%) was observed since day 11 of incubation, nitrogen removal in the experimental reactor began on day 4 at the level of 20%. Nitrogen removal after 30 days of incubation was ~60% in the experiment and 20% in the control. The rate of ammonium oxidation in the presence of ASB increased due to activity of nitrifying bacteria (during the first 10 days of operation) and anammox bacteria of the genus Brоcadia, which were already present in ASA (throughout all period of operation). Activity of group II nitrifiers (genera Nitrobacter and Nitrococcus), which were present in ASB, prevented accumulation of nitrite, which in high concentrations is toxic to both nitrifiers and anammox bacteria. High activity of the Nitrosospira nitrifiers introduced with ASB probably provided the anammox bacteria with one of the substrates (nitrite), promoting their rapid growth. During subsequent operation of the reactor, nitrifiers of the genus Nitrosomonas from the initial ASA community were mainly responsible for growth of the anammox bacteria. Thus, ASA bioaugmentation at the loading of the anammox reactor by active nitrifiers resulted in significantly improved efficiency of ammonium removal via the anammox process and accelerated transition of the reactor to the working mode.

New Insight Into the Interspecies Shift of Anammox Bacteria Ca. "Brocadia" and Ca. "Jettenia" in Reactors Fed With Formate and Folate

The sensitivity of anaerobic ammonium-oxidizing (anammox) bacteria to environmental fluctuations is a frequent cause of reactor malfunctions. It was hypothesized that the addition of formate and folate would have a stimulating effect on anammox bacteria, which in turn would lead to the stability of the anammox process under conditions of a sharp increase in ammonium load, i.e., it helps overcome a stress factor. The effect of formate and folate was investigated using a setup consisting of three parallel sequencing batch reactors equipped with a carrier. Two runs of the reactors were performed. The composition of the microbial community was studied by the 16S rRNA gene profiling and metagenomic analysis. Among anammox bacteria, Ca. "Brocadia" spp. dominated during the first run. A stimulatory effect of folate on the daily nitrogen removal rate (dN) was identified. The addition of formate led to progress in dissimilatory nitrate reduction and stimulated the growth of Ca. "Jettenia" spp. The spatial separation of two anammox species was observed in the formate reactor: Ca. "Brocadia" occupied the carrier and Ca. "Jettenia"-the walls of the reactors. Biomass storage at low temperature without feeding led to an interspecies shift in anammox bacteria in favor of Ca. "Jettenia." During the second run, a domination of Ca. "Jettenia" spp. was recorded along with a stimulating effect of formate, and there was no effect of folate on dN. A comparative genome analysis revealed the patterns suggesting different strategies used by Ca. "Brocadia" and Ca. "Jettenia" spp. to cope with environmental changes.

The effects of magnetite on anammox performance: Phenomena to mechanisms

Low temperature is adverse to anaerobic ammonium oxidation (anammox) reaction while proper Fe addition can enhance anammox performance. Therefore, batch assays were conducted to investigate the potential effects of magnetite (100 μm, 20 μm and 200 nm) on anammox performance which were achieved from the reactor operated at 10-25 °C. After 3 runs, the results indicated that nano-scale magnetite improved the nitrogen elimination significantly. The specific anammox activity (SAA) of the group with nano-magnetite amendments was greater than the other groups after 3 runs (13.5, 12.9, 14.3, 15.4 and 15.7 mgTN/(gVSS·h)), reaching 18.0 mgTN/(gVSS·h). The distribution of magnetite in the granules were then analyzed using X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDS). The results indicated that nano-magnetite was more feasible to attached to the surface of the granules which might accelerate the release of Fe(II) or Fe(III) to enhance anammox performance.

Holistic insights into extracellular polymeric substance (EPS) in anammosx bacterial matrix and the potential sustainable biopolymer recovery: A review

Anaerobic ammonia oxidation (anammox) process has been proven to be a favorable and innovative process, for treatment of nitrogen-rich wastewater due to decreased oxygen and carbon requirements at very high nitrogen loading rates. Anammox process is mainly operated through biofilm or granular sludge structures, as for such slow-growing microorganisms, elevated settling velocity of granules allows for adequate biomass retention and lowered potential risk of washouts. Stability of granular sludge biomass is extremely critical, yet the formation mechanism is poorly understood. There are number of important functions linked to Extracellular Polymeric Substance (EPS) in anammox bacterial matrix, such as; structural stability, aggregation promotion, maintenance of physical structure in the granules, water preserving and protective cell barrier. There is an increasing demand to introduce accurate methods for proper EPS extraction and characterization, to expand the perception of anammox granule stability and potential resource recovery. Analyzing EPS with a focus on various (mechanical and physical) properties can lead to biopolymer production from granular sludge. Biopolymers such as EPS are attractive alternatives substituting the conventional chemical polymers furthermore their recovery from the waste sludge and the potential applications in industrial sectors, leads to a radical enhancement of both environmental and economical sustainability, accelerating the circular economy advancements. Here, this study aims to overview the newest understanding on the structure of anammox sludge EPS, obtained recently and to assess the potential challenges and prospects to identify the knowledge gaps towards constructing an inclusive anammox EPS recovery and characterization procedure.

Towards mainstream deammonification: Comprehensive review on potential mainstream applications and developed sidestream technologies

Deammonification (partial nitritation-anammox) process is a favorable and innovative process, for treatment of nitrogen-rich wastewater due to decreased oxygen and carbon requirements at very high nitrogen loadings. The bacterial groups responsible for this process are anaerobic ammonium oxidation (anammox) bacteria in symbiosis with ammonium oxidizing bacteria (AOB) which have an active role in development of nitrogen removal biotechnology in wastewater. Development and operation of sidestream deammonification processes has augmented since the initial full-scale systems, yet there are several aspects which mandate additional investigation and deliberation by the practitioners, to reach the operating perspective, set for the facility. Process technologies for treatment of streams with high ammonia concentrations continue to emerge, correspondingly, further investigation towards feasibility of applying the deammonification concept, in the mainstream treatment process is required. Mainstream deammonification can potentially improve the process of achieving more sustainable and energy-neutral municipal wastewater treatment, however feasible applications are not accessible yet. This critical review focuses on a comprehensive assessment of the worldwide lab-scale, pilot-scale and full-scale sidestream applications as well as identifying the major issues obstructing the implementation of mainstream processes, in addition to the designs, operational factors and technology advancements at both novel and/or conventional levels. This review aims to provide a novel and broad overview of the status and challenges of both sidestream and mainstream deammonification technologies and installations worldwide to assess the global perspectives on deammonification research in the recent years. The different configurations, crucial factors and overall trends in the development of deammonification research are discussed and conclusively, the future needs for feasible applications are critically reviewed.

Overcoming challenges in mainstream Anammox applications: Utilization of nanoscale zero valent iron (nZVI)

Although Anammox process is a proven technology for sidestream nitrogen removal, the process faces challenges for mainstream applications in sewage treatment plants (STPs). The aim of this study was to investigate the effect of zero valent iron nanoparticles (nZVI) on process performance to eliminate confronts for mainstream applications. An SBR (sequencing batch reactor) system was fed with various nZVI concentrations (0.04-5000 ppb) within 310 days of operation. Ammonium (NH₄⁺-N) and nitrite (NO₂^--N) removal rates showed 58% increase in daily measurements and 73% increase in instant measurements. Specific Anammox Activity (SAA) was noticeably higher on the days the system was exposed to nZVI compared to the unexposed days. EPS secretion, which enhances granulation of Anammox bacteria was favored by nZVI. Despite lower sludge retention time (SRT) values, the fraction of Anammox bacteria in total bacteria reached to 91-92% implying a boosting effect of nZVI on growth rate of Anammox bacteria. High Resolution Melting (HRM) analyses showed that four distinct clades were present in the reactor.

Impacts of different morphologies of anammox bacteria on nitrogen removal performance of a hybrid bioreactor: Suspended sludge, biofilm and gel beads

The difficulties in the anaerobic ammonium oxidation (anammox) process mainly consist of low microbial growth rates and long start-up times of bioreactors. The morphologies of anammox bacteria might affect nitrogen removal performance and microbial community. In this study, three morphologies of anammox bacteria, namely, suspended sludge, biofilm and suspended sludge embedded in gel beads, were compared in a hybrid bioreactor under anoxic conditions (DO concentration < 0.1 mg L^-1). The results show that the average total inorganic nitrogen removal efficiency of a hybrid bioreactor reached 67 ± 15% with a maximum value of 80% for continuous synthetic wastewater feeding, and that the specific total inorganic nitrogen removal rate reached 15.75 mg·(gVSS·h)^-1 regardless of the organic matter stress. Batch tests indicate that mainly suspended sludge (67%) and biofilm (26%) contributed to the anammox process, with the specific total inorganic nitrogen removal rate reaching 10.55 and 4.05 mg·(gVSS·h)^-1, respectively. However, the embedding of sludge in gel resulted in nitrification instead of anammox with a nitrification rate of 0.20 ± 0.01 mg·(L·h)^-1 due to the expansion of gel beads floating on the water surface. Therefore, a pore-forming technique was developed to produce more channels for gas dispersion inside the gel beads. In terms of microbial community, Candidatus Kuenenia involved in the anammox group was the most abundant genus in biofilm (43.4%) and suspended sludge (15.7%), while Nitrospira occupied the largest proportion in gel beads (25.6%). This study offers useful information for the selection of anammox bacteria morphology.

Novel design and optimisation of a nitritation/anammox set-up for ammonium removal from filtrate of digested sludge

Although the anammox process is extensively applied for the treatment of NH4-rich wastewater, new technical solutions overcoming the operational difficulties remain an important task. An innovative design of anammox-based set-up was employed to improve sludge settling under high ammonium load. The set-up included a completely mixed bioreactor with suspended and immobilised activated sludge. To prevent sludge flotation, recycled suspended sludge was additionally treated in an aerated tank at dissolved oxygen (DO) concentration of 1.5 ± 0.2 mg/l followed by processing in a flow-homogeniser. Introduction of these elements resulted in a 3.5-fold increase in total nitrogen removal efficiency (TNRE). The bioreactor achieved maximal TNRE of 86% corresponding to total nitrogen removal rate of 0.77 kg N/m3/d under defined optimal conditions: temperature of 35 ± 2°C, DO of 0.6 ± 0.2 mg/l, hydraulic retention time of 12 h, and dose of suspended sludge of 1.5 ± 0.1 g total suspended solids (TSS)/l. A weakly attached sludge was first described as a technologically important factor. Suspended, weakly and firmly attached sludge exhibited the highest heterotrophic, nitrifying, and anammox activities, respectively. New probes were constructed to detect anammox bacteria by fluorescence in situ hybridisation. Probe for Candidatus 'Jettenia' could be recommended for widespread use.

Startup and operating characteristics of an external air-lift reflux partial nitritation-ANAMMOX integrative reactor

The differences in the physiological characteristics between AOB and ANAMMOX bacteria lead to suboptimal performance when used in a single reactor. In this study, aerobic and anaerobic zones with different survival environments were constructed in a single reactor to realize partitioned culture of AOB and ANAMMOX bacteria. An external air-lift reflux system was formed which used the exhaust from the aeration zone as power to return the effluent to the aeration zone. The reflux system effectively alleviated the large pH fluctuations and promoted NO₂^--N to rapidly use by ANAMMOX bacteria, effectively inhibiting the activity of NOB. After 95d of running, the nitrogen removal rate increased from the initial 0.21kg/(m³·d) to 3.1kg/(m³·d). FISH analyses further demonstrated that AOB and ANAMMOX bacteria acquired efficient enrichment in the corresponding zone. Thus, this type of integrative reactor may create the environments needed for the partial nitritation-ANAMMOX processing.