Attachment of anaerobic ammonium-oxidizing bacteria to augmented carrier material

Rapid start-up strategy and microbial population evolution of anaerobic ammonia oxidation biofilm process for low-strength wastewater treatment

The implementation of the anaerobic ammonium oxidation (anammox) process in treating low-strength wastewater is limited by the difficulty in enriching anammox bacteria (AnAOB). Here, the first enrichment of AnAOB at a high nitrogen (N) loading rate (NLR) as a strategy was proposed to achieve the rapid start-up of the anammox biofilm process treating low-strength wastewater. The long-term stability of the anammox biofilm process after start-up operating at a low NLR of 0.2-0.4 kg N/(m3⋅d) was evaluated. Results showed that the N removal efficiency was up to 75 % under a low NLR of 0.2 kg N/(m3⋅d) condition. Low-strength organic matter promoted the metabolic coupling between partial denitrifying bacteria (PDB) and AnAOB. The genus Candidatus Brocadia as AnAOB (18 %-27 %) can coexist with Limnobacter (PDB, 9 %-12 %) for efficient N removal. This study offers a rapid start-up strategy of anammox biofilm process in treating low-strength wastewater.

Roles and regulation of quorum sensing in anaerobic granular sludge: Research status, challenges, and perspectives

Anaerobic granular sludge (AnGS) has a complex and important internal microbial communication system due to its unique microbial layered structure. As a concentration-dependent communication system between bacterial cells through signal molecules, QS (quorum sensing) is widespread in AnGS and exhibits great potential to regulate microbial behaviors. Therefore, the universal functions of QS in AnGS have been systematically summarized in this paper, including the influence on the metabolic activity, physicochemical properties, and microbial community of AnGS. Subsequently, the common QS-based AnGS regulation approaches are reviewed and analyzed comprehensively. The regulation mechanism of QS in AnGS is analyzed from two systems of single bacterium and mixed bacteria. This review can provide a comprehensive understanding of QS functions in AnGS systems, and promote the practical application of QS-based strategies in optimization of AnGS treatment process.

Fabric Fiber as a Biofilm Carrier for Halomonas sp. H09 Mixed with Lactobacillus rhamnosus GG

Biofilm bacteria have stronger resistance to the adverse external environment compared to planktonic bacteria, and biofilms of non-pathogenic bacteria have strong potential for applications in food. In this experiment, Halomonas sp. H09 and Lactobacillus rhamnosus GG, which have film-forming ability in monoculture and better film-forming ability in mixed culture than the two strains alone, were selected as the target strains for mixed culture. According to SEM observation and bacterial dry weight measurement, the target strain formed a dense biofilm on a 0.1 g/L chitosan-modified cellulose III carrier. Furthermore, the presence of extracellular polymeric substances in biofilms was verified by EDS and FTIR. The results showed that 0.1 g/L chitosan-modified cellulose III was an ideal carrier material for immobilization of Halomonas sp. H09 with Lactobacillus rhamnosus GG biofilm. This research provided a basis for the selection of non-pathogenic mixed-bacteria biofilm carriers.

Nitrogen removal from mature landfill leachate through enhanced Partial Nitrification-Anammox process in an innovative multi-stage fixed biofilm reactor

In the current integrated PN/A method/process for mature landfill leachate treatment, microbial inhibition and low nitrogen removal capacity are the big barriers due to high ammonia concentration and low C/N. This study aimed to evaluate the performance of a high-rate nitrogen removal lab-scale reactor, which combines pre-denitrification and Partial Nitrification-Anammox (PN/A) in a multi-stage fixed biofilm reactor (MFBR), for mature landfill leachate treatment. A nitrogen removal efficiency (NRE) of 90.43 % and an average nitrogen removal rate (NRR) of 0.94 kg/m³·d were observed at an influent NH+ 4-N concentration of 2274.39 mg/L during the last operational phase. The nitrogen mass balance showed that the nitrogen concentration gradually decreases along the course, and nitrogen was mainly removed in the aerobic chambers, in which Anammox contributed to 86.4 % of the removed nitrogen, while the front anoxic chamber is mainly used to remove NO- 3-N from the recirculation. Redundancy analysis showed that the variation in NH+ 4-N concentration along the course was the main factor affecting microbial community succession, which shows that the reactor configuration enables efficient cooperation and distribution of different microorganisms. Moreover, economic analysis of MFBR process showed that the energy consumption and carbon addition were reduced by 58.9 % and 100 %, respectively. Therefore, the MFBR established in this study, with its new configuration, achieves efficient treatment of landfill leachate in a single reactor and is environmentally friendly, and could be considered as a reference for full-scale landfill leachate treatment.

Startup strategies for mainstream anammox polishing in moving bed biofilm reactors

This study evaluated startup strategies for mainstream polishing anammox moving bed biofilm reactors (MBBRs) without anammox bacterial (AMX) biomass inoculation. Two types of startups were tested: anammox only (no external carbon addition) and partial denitrification/anammox (PdNA) with glycerol addition. Reactors were started with either virgin carriers or carriers with a preliminary biofilm from a mainstream aerobic integrated fixed-film activated sludge (IFAS) process. Three pilot-scale startups were completed under the following conditions: anammox-only with preliminary biofilm carriers, PdNA with preliminary biofilm carriers, and PdNA with virgin carriers. AMX presence was confirmed via quantitative polymerase chain reaction (qPCR) after 57, 57, and 77 days, respectively. Prior to AMX detection, average influent concentrations of ammonia and nitrite ranged from 1.7-2.7 mg/L and 0.98-1.8 mg/L, respectively. This study demonstrated that AMX can be grown on carriers without AMX seeding under mainstream conditions (temperature 17-29°C, low ammonia and nitrite), regardless of whether nitrite came from upstream or partial denitrification within the reactor. This study also showed that using preliminary biofilm carriers can decrease startup time by approximately 1 month. These results address critical questions for moving mainstream anammox processes to full-scale implementation, and suggest that PdNA MBBRs are feasible and sustainable for full-scale ammonia, nitrate, and nitrite polishing to meet stringent total nitrogen requirements. PRACTITIONER POINTS: This research will help utilities develop methods for starting up mainstream anammox MBBRs without the barrier of anammox biomass seeding. Preliminary biofilm carriers accelerated startup time in a PdNA MBBR, but a virgin carrier reactor started up in a similar timeframe, contrary to expectations. Also, contrary to expectations, high concentrations of ammonia and nitrite are not necessary for startup of an anammox or PdNA MBBR.

Biofilm carriers for anaerobic ammonium oxidation: Mechanisms, applications, and roles in mainstream systems

The anaerobic ammonium oxidation (ANAMMOX) process was proposed as the most promising nitrogen removal process. Biofilm carriers were demonstrated to effectively enhance the anaerobic ammonium oxidating bacteria (AnAOB) retention. This paper reviews the effect of carrier properties on the AnAOB biofilm development according to the biofilm development process and the application state-of-art of three major kinds of conventional carriers, organic-based, inorganic-based carriers, and gel carriers, from the view of system performance and functional microorganisms. The carrier modification methods and purpose are thoroughly summarized and classified into three categories corresponding to various carrier defects. Four important aspects of the desirable carrier for the mainstream ANAMMOX process were proposed, including providing spatial configuration, enhancing the biomass retention, reinforcing the activity, and improving the growth environment, which needs to combine the advantages of organic and inorganic materials. Eventually, the future application directions of novel carriers for the ANAMMOX-based process were also highlighted.

A review of biomass immobilization in anammox and partial nitrification/anammox systems: Advances, issues, and future perspectives

Two biomass immobilization techniques; entrapment and carrier-based, attract increasing attention in anammox and partial nitrification/anammox (PN/A) systems. This paper provides a comprehensive review of the advances, outstanding issues, and future research directions in this field. The application of both entrapment and carrier-based biofilm immobilization for reactor start up, improving the nitrogen removal performance, and protecting autotrophic bacteria from environmental fluctuations in anammox and partial nitrification/anammox systems are summarized and discussed. The key characteristics of carriers for biomass immobilization are biocompatibility for supporting microbial growth, permeability for effective mass transfer, and physical/chemical stability for long-term use. Carriers without these characteristics must be improved and re-evaluated for their feasibility in applications. Lab-scale, pilot, and full-scale studies are needed to overcome the potential obstacles of preliminary studies, and to investigate the long-term performance of biomass immobilization techniques, especially using real wastewater as influent, which may introduce more complexity and threaten the carrier's immobilization. In addition, calculating the 'nitrogen removal rate normalized by the packing ratio of carriers (NRR-C)' in the immobilization system is strongly suggested to obtain a direct comparison of immobilization performance/limitations from different studies. This review will improve understanding of the major challenges of immobilization technology in anammox and PN/A systems and provide insights into the next-stage of research and full-scale applications.

Insight into enrichment of anammox bacteria by a polyurethane sponge carrier coupled with iron-carbon micro-electrolysis under no strict anaerobic condition

A novel composite carrier (ICME-PS) was formed by coupling polyurethane sponge carriers (PS) with different pore sizes (15, 25, 40 ppi) and iron-carbon micro-electrolysis (ICME), which was used for enrichment of anammox bacteria and stable operation under no strict anaerobic condition. An increase of 5.67%-38.55% in specific anammox activity (SAA), an significant enhancement of biofilm stability and an improvement of 14.61%-42.38% in Ca.Brocadia were observed in ICME-PS, compared to PS carriers. ICME played a dual role: 1) contributed to the formation of an anaerobic microenvironment; 2) used for nitrogen cycle reactions. Additionally, small-pore carriers with highest biofilm stability can be used in high shear environments, while medium-pore carriers achieved the highest SAA in stable environments. Extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) analysis indicated that ICME application reduced the energy barrier and improved aggregation performance. This study designed a novel composite carrier to broaden the application of anammox under no strict anaerobic condition.

Using anammox biofilms for rapid start-up of partial nitritation-anammox in integrated fixed-film activated sludge for autotrophic nitrogen removal

Integrated fixed-film activated sludge (IFAS) reactors are suitable for partial nitritation-anammox (PNA) for autotrophic nitrogen removal; however, its start-up and biofilm formation are slow and difficult. In this study, a new sludge seeding strategy was developed for the start-up of PNA-IFAS by using the pre-cultivated anammox biofilms. Two bioreactors were used in the experimental study, including a reactor that was started conventionally with the pre-acclimated suspended PNA sludge and bare biocarriers (PA-S) and a reactor that used the new seeding method with anammox biofilms pre-acclimated on biocarriers and ammonia-oxidizing bacteria (AOB) sludge in the suspension (PA-B). The use of anammox biofilms as the seed biomass greatly shortened the start-up period of the PNA-IFAS reactor to 1 month or so. Moreover, reactor PA-B achieved a higher nitrogen removal rate (707.3 mg N/(L·d)), better nitrogen removal efficiency (86.8 ± 2.8%), and lower nitrate yield (9.4%) than reactor PA-S. The biofilm development in PA-B was accelerated and its biofilm content was nearly 10 times higher than that of PA-S. The initial segregation of anammox in the biofilm and AOB in the suspended sludge provided an environment that not only accelerated the start-up of PNA-IFAS but also helped suppress the enrichment of unwanted nitrite-oxidizing bacteria (NOB) in the bioreactor, as evidenced by the lower NOB abundance in PA-B (<0.5%) than in PA-S (>2.2%) according to microbial community analysis.

Ecological Linkages between a Biofilm Ecosystem and Reactor Performance: The Specificity of Biofilm Development Phases

In biofilm-based engineered ecosystems, the reactor performance was closely linked to interspecies interactions within a biofilm ecosystem, whereas the ecological processes underpinning such linkage were still unenlightened. Herein, the principles of community succession and assembly were integrated to capture the ecological laws of biofilm development by molecular ecological networks and assembly model analysis based on the 16S rRNA sequencing analysis and metagenomics in a well-controlled moving bed biofilm reactor. At the initial colonization phase (days 0-2, driven by initial colonizers), interspecific cooperation (74.18%) facilitated initial biofilm formation, whereas some pioneers, and keystone species disappeared at later phases. At the accumulation phase (days 3-30, rapid biofilm development), interspecific cooperation (81.41 ± 5.07%) contributed to rapid biofilm development and keystone species were mainly involved in quorum sensing or positively correlated with extracellular polymeric substance production. At the maturation phase (days 31-106, a well-adapted quasi-equilibrium state), increased interspecific competition (32.74 ± 4.77%) and higher small-world property facilitated the rapid information transportation and pollutant treatment, and keystone species were positively correlated with the removal of COD and NH₄⁺-N. Homogenizing dispersal diminished the contemporary community dissimilarities, while turnover but rather nestedness governed the temporal variations in the biofilm succession period. This study highlighted the specificity of ecological processes at distinct biofilm development phases, which would advance our understanding on the development-to-function linkages in biofilm-based treatment processes.

Microbial biofilms in biorefinery - Towards a sustainable production of low-value bulk chemicals and fuels

Harnessing the potential of biocatalytic conversion of renewable biomass into value-added products is still hampered by unfavorable process economics. This has promoted the use of biofilms as an alternative to overcome the limitations of traditional planktonic systems. In this paper, the benefits and challenges of biofilm fermentations are reviewed with a focus on the production of low-value bulk chemicals and fuels from waste biomass. Our study demonstrates that biofilm fermentations can potentially improve productivities and product yields by increasing biomass retention and allowing for continuous operation at high dilution rates. Furthermore, we show that biofilms can tolerate hazardous environments, which improve the conversion of crude biomass under substrate and product inhibitory conditions. Additionally, we present examples for the improved conversion of pure and crude substrates into bulk chemicals by mixed microbial biofilms, which can benefit from microenvironments in biofilms for synergistic multi-species reactions, and improved resistance to contaminants. Finally, we suggest the use of mathematical models as useful tools to supplement experimental insights related to the effects of physico-chemical and biological phenomena on the process. Major challenges for biofilm fermentations arise from inconsistent fermentation performance, slow reactor start-up, biofilm carrier costs and carrier clogging, insufficient biofilm monitoring and process control, challenges in reactor sterilization and scale-up, and issues in recovering dilute products. The key to a successful commercialization of the technology is likely going to be an interdisciplinary approach. Crucial research areas might include genetic engineering combined with the development of specialized biofilm reactors, biofilm carrier development, in-situ biofilm monitoring, model-based process control, mixed microbial biofilm technology, development of suitable biofilm reactor scale-up criteria, and in-situ product recovery.

Insight: High intensity and activity carrier granular sludge cultured using polyvinyl alcohol/chitosan and polyvinyl alcohol/chitosan/iron gel beads

The newly developed carrier granular sludge (CGS) with polyvinyl alcohol/chitosan (PVA/CS) and PVA/CS/Fe gel beads assistance showed higher intensity and anammox activity than the natural granular sludge (NGS). Through comprehensive investigation, it was found: (1) the gel beads provided a stable framework of cells entangle with extracellular polymeric substances (EPS) to enhance the sludge intensity. In this framework, β-polysaccharides are distributed at the edge of CGS as a protection layer, α-polysaccharides and proteins are spread in the whole cross-section as backbones, and Fe²⁺/Fe³⁺ in CGS-PVA/CS/Fe act as bridges to link with the negatively charged groups on bacterial surfaces and proteins. (2) The porous gel beads satisfied a relatively unimpeded mass transfer. Thus, the sludge activity, microbe's metabolism, membrane transportation and environmental adaption in CGS were apparently improved. The results improved the understanding about the advantages of the CGS and indicated their possible application in full-scale anammox processes.

Anammox attachment and biofilm development on surface-modified carriers with planktonic- and biofilm-based inoculation

This study investigates the kinetics, attachment, biofilm development and anammox bacteria enrichment of a novel detached anammox biofilm inoculation method on non-modified virgin MBBR carriers and pre-seeded denitrifying carriers. The study compares these results to the more common use of attached anammox carriers for anammox MBBR inoculation. The anammox bacteria specific attachment-growth rates for virgin carriers inoculated with detached anammox biofilm mass were 38.1% greater for the first 25 days, leading to approximately 30% less time required to achieve complete biofilm coverage than those measured in attached biofilm carrier inoculated systems during the attachment and early biofilm growth stages. The biofilm thickness increase rate was also 52.3% higher for virgin carriers with detached biofilm inoculum. Further, inoculation using pre-seeded denitrifying carriers compared to virgin carriers demonstrated a 13.8% preferential increase in anammox bacteria specific attachment-growth rate and a corresponding 47.2% higher NH₄⁺-N removal rate at the time of biofilm maturation.

Review of characteristics of anammox bacteria and strategies for anammox start-up for sustainable wastewater resource management

Wastewater management has experienced different stages, including pollutant removal, resource recovery, and water nexus. Within these stages, anaerobic ammonia oxidation-based biotechnology can be incorporated for nitrogen removal, which can help achieve sustainable wastewater management, such as reclamation and ecologization of wastewater. Here, the physiology, metabolism, reaction kinetics and microbial interactions of anammox bacteria are discussed, and strategies to start-up the anammox system are presented. Anammox bacteria are slow growers with a high doubling time and a low reaction rate. Although most anammox bacteria grow autotrophically, some types can grow mixotrophically. The reaction stoichiometric coefficients can be affected by loading rates and other biological reactions. Microbial interactions also contribute to enhanced biological nitrogen removal and promote activities of anammox bacteria. The start-up of the anammox process is the key aspect for its practical application, which can be realized through seed selection, system stimulation, and biomass concentration enhancement.

In situ elimination of nitrite inhibition on AnAOB by acetate dosing in an up-flow granular anammox reactor

The inhibition of over-accumulated nitrite on anaerobic ammonium oxidation (anammox) activity has been widely reported and intensively studied. Surprisingly, there are limited researches on the strategy to deal with nitrite inhibition. In this work, to eliminate nitrite inhibition in an up-flow granular anammox reactor, acetate dosing (600 mg COD L^-1) and simultaneous acetate and denitrifying sludge dosing (600 mg COD L^-1 and 1.4 g dry weight L^-1) were implemented to temporarily activate microbial denitrification to reduce nitrite, respectively. In two strategies, reactor nitrogen removal and extracellular ATP were resumed to initial levels, while the recovery ratios of intracellular ATP and nitrite removal rate (67.1% and 15.6 mg N h^-1) of the former were higher than those (52.5% and 11.2 mg N h^-1) of the latter, indicating acetate dosing was more qualified to nitrite removal. Meanwhile, although a decrease of the dominated Ca. Brocadia from 30.7 to 25.8% was not reversed through high-throughput sequencing, acetate dosing did not cause denitrifiers proliferation. As easily implemented acetate dosing was as effective as direct discharge of inhibitory nitrite as the control strategy, it was recommended when nitrite inhibition happened. Additionally, an irregular behavior of nitrate overproduction via nitrite oxidation and the drastic increase of extracellular ATP were detected and proposed as the response of AnAOB to nitrite inhibition.

Gel immobilization: A strategy to improve the performance of anaerobic ammonium oxidation (anammox) bacteria for nitrogen-rich wastewater treatment

Anaerobic ammonium oxidation (anammox) process appears a suitable substitute to nitrification-denitrification at a lower C/N ratios. Anammox is a chemolithoautotrophic process, belong to phylum Planctomycetes, and they are slow growing bacteria. Different strategies, e.g., biofilm formation, granulation and gel immobilization, have been applied to maintain a critical mass of bacterial cells in the system by avoiding washout from the bioreactor. Gel immobilization of anammox appears the best alternative to the natural process of biofilm formation and granulation. Polyvinyl alcohol-sodium alginate, polyethylene glycol, and waterborne polyurethane are the most reported materials used for the entrapment of anammox bacteria. However, dissolution of the gel beads refrains its application for long term bioprocess. Magnetic powder could coat on the surface of the beads which may increase the mechanical strength and durability of pellets. Application and problem of immobilization technology for the commercialization of this technology also addressed.

Effective nitrogen removal in a two-stage partial nitritation-anammox reactor treating municipal wastewater - Piloting PN-MBBR/AMX-IFAS configuration

A novel partial nitritation-anammox (PNA) reactor configuration was piloted for 250 days. Primary effluent from full-scale municipal wastewater treatment plant was treated in a two-stage biofilm system incorporating innovative process control for cold partial nitritation. Partial nitritation was combined with carbon removal in a moving bed biofilm reactor (MBBR) to achieve high-rate treatment and nitritation was obtained with dissolved oxygen to total ammonium nitrogen (DO/TAN) ratio control and free ammonia (FA) for inhibition of nitratation. Effluent from MBBR was directed to an integrated fixed-film activated sludge (IFAS) reactor where nitrogen was removed via anammox. MBBR achieved partial nitritation at 2.0 ± 0.3 g-N m^-2 d^-1 and nitrogen removal in the IFAS reactor reached 0.45 ± 0.1 g-N m^-2 d^-1 (55 g-N m^-3 d^-1). The process performed well at 19 ± 3 °C with an average effluent total inorganic nitrogen (TIN) concentration of 11 ± 4 mg L^-1.