New concepts of microbial treatment processes for the nitrogen removal in wastewater

Accelerated start-up, long-term performance and microbial community shifts within a novel upflow porous-plated anaerobic reactor treating nitrogen-rich wastewater via ANAMMOX process

The anaerobic ammonium oxidation (anammox) process has gained much popularity in recent years following its success in nitrogen removal. However, not much has been reported on techniques to promote anammox bacteria immobilization and associated microbial community evolution. In this study, a novel upflow porous-plate anaerobic reactor (UPPAR) was developed and explored to promote biomass (anammox) retention and growth. To comprehend the performance of the UPPAR, its nitrogen removal efficiencies, as well as the microbial community dynamics involved in the nitrogen removal process, was evaluated and reported. When NLR ranging 0.98-1.08 kg m-3 d-1 was introduced at various stages of the UPPAR operation, a rapid start-up was achieved in 63 d, and the overall nitrogen removal rate could reach 90-95%. By the end of the start-up period, it was revealed that Proteobacteria abundance had reduced by 43.92% as opposed Planctomycetes which increased from 2.95% to 43.52%. Conversely, after the UPPAR had been operated for 124 d, thus at steady-state, the most pronounced phylum observed was Planctomycetes (43.52%) followed by Proteobacteria (26.63%), Chloroflexi (5.87%), Ignavibacteriae (5.55%), and Bacteroidetes (4.9%). Predominant genera observed included Candidatus Kuenenia - (25.46%) and Candidatus Brocadia - (3.15%), an indication that nitrogen removal mechanism within the UPPAR was mainly conducted via autotrophic anammox process. Scanning electron microscopy (SEM) revealed that sludge samples obtained at steady-state were predominantly in granular form with sizes ranging between 2 mm to 5 mm. Granules surfaces were dominated with normal to coccoid-shaped cells as revealed by the SEM.

A novel approach for fouling mitigation in anaerobic-anoxic-oxic membrane bioreactor (A2O-MBR) by integrating worm predation

Membrane fouling is one of the biggest challenges in the widespread application of membrane bioreactors. In this study, a combined system of anaerobic-anoxic-oxic membrane bioreactor (A²O-MBR) and worm reactor (WR) was established for fouling control. In A²O-MBR-WR, the membrane filtration cycle was prolonged by 66.7% due to the confluence of microaerobic treatment and worm predation in WR with the interaction between WR and A²O-MBR. Compared with conventional A²O-MBR, membrane rejection of soluble and colloidal foulants (SCF) in the combined system was decreased by 26.0%, which could be attributed to the higher biodegradability of SCF and the higher bacterial activity in A²O-MBR. Although floc size in A²O-MBR was reduced due to sludge disintegration and worm predation in WR, changes of floc surface properties could counteract this negative effect on fouling. Complex effects of sludge flocs on membrane fouling were further analyzed by the interaction energy between sludge flocs and the clean/fouled membrane based on extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory. The energy barriers indicated that flocs in A²O-MBR-WR were difficult to adhere to the membrane and were more likely to detach. Moreover, high-throughput sequencing analysis revealed that the microbial community of the cake layer in the combined system was more even and had a higher proportion of foulants degradation related bacteria, which was beneficial for fouling mitigation. The combination of A²O-MBR and WR has shown significant advantages in membrane fouling mitigation.

Complete genome sequence of Paracoccus denitrificans ATCC 19367 and its denitrification characteristics

Studies show that Paracoccus denitrificans can denitrify nitrogen sources under aerobic conditions. However, the lack of data on its genome sequence has restricted molecular studies and practical applications. In this study, the complete genome of P. denitrificans ATCC 19367 was sequenced and its nitrogen metabolism properties were characterized. The size of the whole genome is 5 242 327 bp, with two chromosomes and one plasmid. The average G + C content is 66.8%, and it contains 5308 protein-coding genes, 54 tRNA genes, and nine rRNA operons. Among the protein-coding genes, 71.35% could be assigned to the Gene Ontology (GO) pathway, 86.66% to the Clusters of Orthologous Groups (COG) pathway, and 50.57% to the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway. Comparative genome analysis between P. denitrificans ATCC 19367 and P. denitrificans PD1222 revealed that there are 428 genes specific to ATCC 19367 and 4738 core genes. Furthermore, the expression of genes related to denitrification, biofilm formation, and nitrogen metabolism (nar, nir, and nor) by P. denitrificans ATCC 19367 under aerobic conditions was affected by incubation time and shaking speed. This study elucidates the genomic background of P. denitrificans ATCC 19367 and suggests the possibility of controlling nitrogen pollution in the environment by using this bacterium.

Achieving energy-efficient nitrogen removal and excess sludge reutilization by partial nitritation and simultaneous anammox denitrification and sludge fermentation process

Energy savings via achieving the reduction of aeration and excess sludge is required to realize energy self-sufficiency in wastewater treatment plants. A novel partial nitritation + simultaneous anammox denitrification and sludge fermentation (PN + SADF) process was operated for nearly two years, during which simultaneous energy-efficient nitrogen removal and waste activated sludge (WAS) reduction was achieved, with a stable nitrogen removal efficiency of 80% and external WAS reduction of 40%-50%. In the PN reactor, presence of ammonia oxidizing bacteria and absence of nitrite oxidizing bacteria ensured the stable nitritation. In the SADF reactor, nitrogen was removed via denitrification and anammox by using nutrients and organics released from WAS solubilization. Comparable performance of the SADF reactor at ambient temperature (12-32 °C) to that at 30 °C indicated a practical application potential for the PN + SADF process. An initial estimation of a full-scale PN + SADF process serving a population of 100000 showed that it could save economy and energy in comparison with conventional nitrification-denitrification process. Despite some challenges in implementation, this paper highlights the potential implication for sustaining mainstream nitritation-anammox towards energy-efficient operation with excess sludge reutilization.

Microbial nitrate removal efficiency in groundwater polluted from agricultural activities with hybrid cork treatment wetlands

Agricultural practices have raised the level of nutrients reaching aquifers. In Europe, nitrate pollution is considered as one of the main threats for the quality of groundwater in agricultural areas. Treatment wetlands (TWs), also known as Constructed Wetlands, are used for groundwater treatment in areas with an important concentration of nitrogen compounds; total nitrogen removal depends on the type and operation scheme. Cork by-product from the industry has shown clear adsorbent properties to remove organic pollutants. The work is focused on the characterization of microbial communities involved in the nitrate‑nitrogen removal process in groundwater polluted from agricultural activities. The experimental design allowed the comparison of nitrate removal efficiency depending on the filter media material, cork by-product or gravel, used in two hybrid TWs (a vertical flow cell followed by a horizontal subsurface flow cell), installed in areas close to two irrigated agricultural plots at the Lleida plain area (Spain). Both physicochemical and microbial results were consistent and confirm the nitrate removal efficiency using cork as a filter media. A significant (p = 0.0025) higher removal in Bellvís TW using cork compared with the Vilanova de la Barca gravel system was observed, achieving a removal rate from 80 to 99% compared to the 5-46%, respectively. Regarding the community composition of the two different TWs, microorganisms were mainly related to the phylum Proteobacteria, and included members found to be key players in the nitrogen cycle, such as ammonia and nitrite oxidizers, as well as denitrifiers. Also, the group Bacteroidetes turns to be another abundant phylum from our bacterial dataset, whose members are suggested to be strongly involved in denitrification processes. Some groups showed to prevail depending on the type of media (cork or gravel); Firmicutes and Delta and Epsilonproteobacteria had a significant higher abundance in the TW with cork, while Acidobacteria and Planctomyces were prevalent in gravel. Therefore, cork could be an alternative material used by treatment wetlands to minimize the impact in the environment caused by nitrogen pollution in groundwater bodies.

The Performance and Microbial Community Identification in Mesophilic and Atmospheric Anaerobic Membrane Bioreactor for Municipal Wastewater Treatment Associated with Different Hydraulic Retention Times

The anaerobic membrane bioreactors (AnMBR) with ring membrane module were operated under mesophilic temperature (M-AnMBR) and atmospheric temperature (A-AnMBR). Compared to the M-AnMBR, the removal efficiency of the A-AnMBR was found to be lower and the faster membrane fouling occurred in the A-AnMBR under corresponding hydraulic retention time (HRT). The MiSeq high-throughput sequencing was applied to analyze the microbial community structure. The HRT change had different effects on the community richness and diversity of the cake and bulk sludge. The abundance of phylum Proteobacteria in the M-AnMBR was higher than that in the A-AnMBR, which should account for the higher removal of nutrients in the M-AnMBR. The faster membrane fouling would occur in the A-AnMBR due to the relatively high abundance of Bacteroidetes in the bulk sludge and cake sludge. Moreover, specific comparison down to the genus level showed that the dominant abundant bacterial genera were Candidate division OP8 norank and Anaerolineaceae uncultured in the cake sludge for M-AnMBR, and were VadinHA17 norank, WCHB1-69 norank, VadinBC27 wastewater-sludge group, and Synergistaceae uncultured in the cake sludge for A-AnMBR The different representative genera with the variation of the HRTs for the two bioreactors might indicate the different performance between the two AnMBRs.

Nitrogen cycling during wastewater treatment

Many wastewater treatment plants in the world do not remove reactive nitrogen from wastewater prior to release into the environment. Excess reactive nitrogen not only has a negative impact on human health, it also contributes to air and water pollution, and can cause complex ecosystems to collapse. In order to avoid the deleterious effects of excess reactive nitrogen in the environment, tertiary wastewater treatment practices that ensure the removal of reactive nitrogen species need to be implemented. Many wastewater treatment facilities rely on chemicals for tertiary treatment, however, biological nitrogen removal practices are much more environmentally friendly and cost effective. Therefore, interest in biological treatment is increasing. Biological approaches take advantage of specific groups of microorganisms involved in nitrogen cycling to remove reactive nitrogen from reactor systems by converting ammonia to nitrogen gas. Organisms known to be involved in this process include autotrophic ammonia-oxidizing bacteria, heterotrophic ammonia-oxidizing bacteria, ammonia-oxidizing archaea, anaerobic ammonia oxidizing bacteria (anammox), nitrite-oxidizing bacteria, complete ammonia oxidizers, and dissimilatory nitrate reducing microorganisms. For example, in nitrifying-denitrifying reactors, ammonia- and nitrite-oxidizing bacteria convert ammonia to nitrate and then denitrifying microorganisms reduce nitrate to nonreactive dinitrogen gas. Other nitrogen removal systems (anammox reactors) take advantage of anammox bacteria to convert ammonia to nitrogen gas using NO as an oxidant. A number of promising new biological treatment technologies are emerging and it is hoped that as the cost of these practices goes down more wastewater treatment plants will start to include a tertiary treatment step.

Anionic surfactant modification of activated carbon for enhancing adsorption of ammonium ion from aqueous solution

This study investigates the effect of anionic surfactant modification on activated carbon (AC) to enhance the adsorption of ammonium ion in aqueous solution. Sodium dodecyl sulfate (SDS), sodium dodecyl benzene sulfonate (SDBS) or sodium octanoate (SO) was used for the modification. At the initial aqueous concentration of 55 mg NH₄-N/L and the adsorbent dose of 50 g/L, the SDS-modified AC showed the highest ammonium removal efficiency of 82% among the modified ACs studied. The hydrophobic group of SDS was strongly attached to AC showing almost negligible desorption after the modification. At the same time, the sulfate functional group of SDS provided ion exchange sites favorable for the ammonium ion adsorption. By maximizing SDS loading to the AC, ammonium removal efficiency can further be improved (5% increase). When Na⁺, K⁺ or Ca²⁺ coexisted in the ammonium solution at the concentration of 55 mg/L, the inhibition effect of these cations on ammonium removal efficiency was negligible (<5%). This study shows the potential of anionic surfactant-modified ACs as the excellent adsorbents for ammonium removal from water.

Contrasting microbial community composition and function perspective of the biofilms in shrimps (Macrobrachium nipponense) cultured systems

Biofilm microbial communities and the water quality environment were studied in either carrier biofilm in isolation, or in combination with shrimp (Macrobrachium nipponense) from Baiyangdian Lake. Use of biofilm treatment effectively improved the water quality environment, however, the content of NH₄-N, TN, and TP increased by 2.49, 1.93, and 0.94 folds, with the addition of high shrimp populations into the aquatic environment over a long-term period (75 d). The relative abundance of dominant phyla in carrier biofilms was Proteobacteria (50.20%), Cyanobacteria (23.31%) and Planctomycetes (8.14%) in control group (no shrimps). The relative abundance of Cyanobacteria decreased by 60.6%, whereas Planctomycetes increased by 1 folds with the high shrimp population addition. In addition, the inclusion of low density shrimp populations decreased by 21.1%, and 31.6% in NH₄-N and TP concentrations compared to controls over a short-term period (15 d), respectively. The abundance of Planctomycetes increased by 92.9% with the addition of low shrimp populations on 15 d. Our results showed that the addition of low shrimp population (286 animals/m²) could improve the water quality environment containing carrier biofilm according to the regulation of the bacterial diversity in the biofilm system in short-term period (15 d).

Autotrophic and heterotrophic nitrification-anoxic denitrification dominated the anoxic/oxic sewage treatment process during optimization for higher loading rate and energy savings

This study clarified the dominant nitrogen (N)-transformation pathway and the key ammonia-oxidizing microbial species at three loading levels during optimization of the anoxic/oxic (A/O) process for sewage treatment. Comprehensive N-transformation activity analysis showed that ammonia oxidization was performed predominantly by aerobic chemolithotrophic and heterotrophic ammonia oxidization, whereas N₂ production was performed primarily by anoxic denitrification in the anoxic unit. The abundances of ammonia-oxidizing bacteria (AOB), nitrite-oxidizing bacteria, and anaerobic AOB in activated sludge reflected their activities on the basis of high-throughput sequencing data. AOB amoA gene clone libraries revealed that the predominant AOB species in sludge samples shifted from Nitrosomonas europaea (61% at the normal loading level) to Nitrosomonas oligotropha (58% and 81% at the two higher loading levels). Following isolation and sequencing, the predominant culturable heterotrophic AOB in sludge shifted from Agrobacterium tumefaciens (42% at the normal loading level) to Acinetobacter johnsonii (52% at the highest loading level).

Long-term operation of oxygen-limiting membrane bioreactor (MBR) for the development of simultaneous partial nitrification, anammox and denitrification (SNAD) process

In this study, an oxygen-limiting membrane bioreactor (MBR) with recirculation of biogas for relieving membrane fouling was successfully operated to realize the simultaneous partial nitrification, anammox and denitrification (SNAD) process. The MBR operation was considered effective in the long-term test with total nitrogen (TN) and chemical oxygen demand (COD) removal efficiencies of 94.86% and 98.91%, respectively. Membrane fouling was significantly alleviated due to the recirculation of biogas and the membrane had been cleaned four times with a normal filtration period of 52 days. The co-existence of ammonia-oxidizing bacteria (AOB), anammox and denitrifying bacteria in MBR was confirmed by scanning electron microscopy (SEM) and fluorescence in situ hybridizations (FISH) analysis. Furthermore, AOB were found close to the granule surface, while denitrifying bacteria and anammox were in the deeper layer of granules. Potential in excellent TN and COD removal, operational stability and sustainability, as well as in alleviating membrane fouling is expected by using this oxygen-limiting MBR.

Stable isotopes demonstrate the effectiveness of a tidally-staged sewage release system

Nutrient loading from sewage wastewater discharge contributes to the eutrophication of coastal waters. Wastewater from the Gold Coast, Australia is discharged into the Gold Coast Seaway (GCS) for 13.5 h d^-1 primarily on the ebbing tide to disperse wastewater seawards. Nitrogen stable isotopes were used to assess how effectively the tidally staged release system dispersed wastewater out of the GCS and identified pathways by which sewage-N was incorporated into food webs. Turf algae, limpets and barnacles were sampled at the GCS, at two coastal sites and at the mouth of a control estuary that lacked point-source discharge. In the GCS δ¹⁵N values of algae and limpets returned to coastal baseline levels within 250 m of the diffusers. In contrast, δ¹⁵N of filter-feeding barnacles did not significantly vary indicating wastewater-N does not dominate the pelagic food web. Nitrogen stable isotopes clearly demonstrated that the tidally-staged wastewater release system effectively disperses wastewater offshore.

Evolving wastewater infrastructure paradigm to enhance harmony with nature

Restoring and improving harmony between human activities and nature are essential to human well-being and survival. The role of wastewater infrastructure is evolving toward resource recovery to address this challenge. Yet, existing design approaches for wastewater systems focus merely on technological aspects of these systems. If system design could take advantage of natural ecological processes, it could ensure infrastructure development within ecological constraints and maximize other benefits. To test this hypothesis, we illustrate a data-driven, systems-level approach that couples natural ecosystems and the services they deliver to explore how sustainability principles could be embedded into the life phases of wastewater systems. We show that our design could produce outcomes vastly superior to those of conventional paradigms that focus on technologies alone, by enabling high-level recovery of both energy and materials and providing substantial benefits to offset a host of unintended environmental effects. This integrative study advances our understanding and suggests approaches for regaining a balance between satisfying human demands and maintaining ecosystems.

The mechanism of enhanced wastewater nitrogen removal by photo-sequencing batch reactors based on comprehensive analysis of system dynamics within a cycle

To understand the mechanism of enhanced nitrogen removal by photo-sequencing batch reactors (photo-SBRs), which incorporated microalgal photosynthetic oxygenation into the aerobic phases of a conventional cycle, this study performed comprehensive analysis of one-cycle dynamics. Under a low aeration intensity (about 0.02 vvm), a photo-SBR, illuminated with light at 92.27 μ·mol·m^-2·s^-1, could remove 99.45% COD, 99.93% NH₄⁺-N, 90.39% TN, and 95.17% TP, while the control SBR could only remove 98.36% COD, 83.51% NH₄⁺-N, 78.96% TN, and 97.75% TP, for a synthetic domestic sewage. The specific oxygen production rate (SOPR) of microalgae in the photo-SBR could reach 6.63 fmol O₂·cell^-1·h^-1. One-cycle dynamics shows that the enhanced nitrogen removal by photo-SBRs is related to photosynthetic oxygenation, resulting in strengthened nitrification, instead of direct nutrient uptake by microalgae. A too high light or aeration intensity could deteriorate anoxic conditions and thus adversely affect the removal of TN and TP in photo-SBRs.

An integrated membrane bioreactor system with iron-dosing and side-stream co-fermentation for enhanced nutrient removal and recovery: System performance and microbial community analysis

An integrated membrane bioreactor (MBR) system was developed for enhanced nutrient (N and P) removal and effective P recovery in wastewater treatment. The system consisted of an iron-dosing MBR and side-stream fermentation for P removal and recovery and side-stream denitrification for N removal. Around 98.1% of the total phosphorus (TP) in wastewater was removed by ferric iron-induced precipitation and membrane filtration in the aerobic MBR, and nearly 53.4% of the TP could be recovered via anaerobic fermentation from the MBR sludge. In addition, the fermenter that allowed acidogenic co-fermentation with food waste provided sufficient soluble organics for biological denitrification, and an overall 91.8% total N removal was achieved through the side-stream denitrification. High-throughput sequencing was applied to analyse the microbial communities in the integrated system, and important functional bacteria were identified for nitrification, denitrification, acidogenic fermentation and dissimilatory iron reduction through the different components of the system.

The increase of process stability in removing ammonia nitrogen from wastewater

This work focuses on the removal of ammonia nitrogen pollution from wastewaters in a two-stage laboratory model based on a combination of the nitritation and anammox processes with the biomass immobilized in a polyvinyl alcohol (PVA) matrix. Owing to the immobilization approach inside the PVA pellets, the bacterial activity remained nearly unchanged on an abrupt change in the environmental conditions. The nitritation kinetics were significantly dependent on the dissolved oxygen concentration. The critical dissolved oxygen concentration at which the nitritation process using the immobilized bacterial culture stops is 0.6 mg/L. The volumetric rate of nitrogen removal by the anammox bacteria was 158 mg/(L·d). The technology presented is well-suited for removing high ammonia nitrogen concentrations (≥300 mg/L).

Complete ammonia oxidation: an important control on nitrification in engineered ecosystems?

Nitrification has long been considered to be mediated by two distinct microbial guilds, the ammonia-oxidizing bacteria and archaea, and the nitrite-oxidizing bacteria. The process has been widely applied as an environmental biotechnology for ammonium removal during water and wastewater treatment. Recently, bacteria capable of complete nitrification of ammonia to nitrate (a process termed complete ammonia oxidation, or comammox) have been discovered. These novel nitrifiers have been identified in a range of engineered, natural freshwater and terrestrial ecosystems, challenging previously held knowledge on the key microorganisms and biochemical pathways controlling nitrification. This paper discusses the distribution of comammox bacteria with a focus on engineered ecosystems, as well as emerging insights from recent genomic and experimental studies on their ecophysiology.

Study on the effect of total dissolved solids (TDS) on the performance of an SBR for COD and nutrients removal

In this study, the effect of total dissolved solids (TDS) on the performance of a sequencing batch reactor (SBR) system to treat synthetic wastewater with microbial inoculum was evaluated. The SBR was operated continuously for eight days on a 6-h cycle with anaerobic/anoxic/aerobic phases in each cycle after entering the steady state, and the influent TDS was tested at five levels, i.e., 750, 1500, 3000, 4500, and 6000 mg L^-1. The results showed that only two TDS levels (750 and 1500 mg L^-1) could achieve good COD removal efficiencies (94.8 and 92.2%, respectively). For TDS levels equal to, or greater than, 3000 mg L^-1, a 20% reduction in COD removal efficiency resulted. Different from COD, removal of NH₄⁺-N appeared not to be affected by the TDS content, and a removal efficiency of higher than 97% was obtained, regardless of the TDS content. However, only the lowest two TDS levels achieved high phosphate removals (>99%), and the removal efficiency dropped to 57.8 and 45.9%, respectively, for TDS levels of 3000 and 4500 mg L^-1. More interestingly, a phosphate release, instead of uptake, was observed at the TDS level of 6000 mg L^-1. It may be concluded that for effective phosphate removal, the TDS level in the liquid should be controlled under 1500 mg L^-1, and higher liquid TDS levels were detrimental to the aerobes and could disrupt the aerobic metabolism, leading to the failure of the SBR treatment system. A tendency that raising TDS content would adversely affect the aerobic oxygen uptake rate was observed, which could also result in SBR upset. A power regression with an R of 0.9844 was established between the influent TDS concentration and the TDS removal efficiency, which may be used to estimate the SBR performance in TDS removal based on the influent TDS content.

Engineering biological nitrogen removal in wastewater treatment via the control of nitrite oxidising bacteria using free nitrous acid

Nitrogen compounds need to be removed or captured from wastewater streams before disposal to protect our aquatic environments from eutrophication. Particular bacteria facilitating the biological removal of nitrogen during wastewater treatment include ammonia oxidising bacteria (AOB), nitrite oxidising bacteria (NOB), denitrifiers, as well as anaerobic ammonium oxidising (Anammox) bacteria. Manipulating these microbial communities can improve efficiency in nitrogen removal. Bypassing nitrate production by selectively inhibiting NOB reduces the need for oxygen and the addition of external carbon for the nitrogen removal. Various approaches to selectively inhibit NOB in the nitrification process are available. Here we present an approach using the biocide, free nitrous acid (FNA) to selectively suppress NOB growth thereby improving the efficiency of the nitrogen removal process.

Purification and reuse of non-point source wastewater via Myriophyllum-based integrative biotechnology: A review

In this review, the applications of Myriophyllum-based integrative biotechnology to remove common non-point source (NPS) pollutants, such as nitrogen, phosphorus, heavy metals, and organic pollutants (e.g., pesticides and antibiotics) are summarized. The removal of these pollutants via various mechanisms, including uptake by plant and microbial communities in macrophyte-based treatment systems are discussed. This review highlights the potential use of Myriophyllum biomass to produce animal feed, fertilizer, and other valuable by-products, which can yield cost-effective returns and attract more attention to the regulation and recycling of NPS pollutants. In addition, it demonstrates that utilization of Myriophyllum species is a promising and reliable strategy for wastewater treatment. The future development of sustainable Myriophyllum-based treatment systems is discussed from various perspectives.

High rate nitrogen removal by ANAMMOX internal circulation reactor (IC) for old landfill leachate treatment

This study aimed to evaluate the performance of a high rate nitrogen removal lab-scale ANAMMOX reactor, namely Internal Circulation (IC) reactor, for old landfill leachate treatment. The reactor was operated with pre-treated leachate from a pilot Partial Nitritation Reactor (PNR) using a high nitrogen loading rate ranging from 2 to 10kgNm^-3d^-1. High rate removal of nitrogen (9.52±1.11kgNm^-3d^-1) was observed at an influent nitrogen concentration of 1500mgNL^-1. The specific ANAMMOX activity was found to be 0.598±0.026gN₂-NgVSS^-1d^-1. Analysis of ANAMMOX granules suggested that 0.5-1.0mm size granular sludge was the dominant group. The results of DNA analysis revealed that Candidatus Kueneniastuttgartiensis was the dominant species (37.45%) in the IC reactor, whereas other species like uncultured Bacteroidetes bacterium only constituted 5.37% in the system, but they were still responsible for removing recalcitrant organic matter.

Elucidation of microbial nitrogen-transformation mechanisms in activated sludge by comprehensive evaluation of nitrogen-transformation activity

Using prepared nitrifying sludge, anaerobic ammonia oxidization (anammox) sludge and two heterotrophic ammonia oxidization bacterial (AOB) species as inocula, this study elucidated the effect of oxygen conditions, assay media, and selective metabolic inhibitors on various microbial nitrogen (N)-transformation activities including aerobic chemolithotrophic ammonia and nitrite oxidization, aerobic heterotrophic ammonia oxidization, anammox, and aerobic and anoxic denitrification. The oxygen conditions and assay media effectively differentiated among almost all ammonia removal pathways except for separating aerobic chemolithotrophic ammonia oxidization from aerobic heterotrophic ammonia oxidization. A final allylthiourea concentration of 10mg·L^-1 was optimal for accurate determination of aerobic heterotrophic ammonia oxidization activity in the presence of aerobic chemolithotrophic AOB. Finally, this study developed a simple and reliable method to individually determine and compare the comprehensive N-transformation activity characteristics of several activated sludge samples from different origins, and to elucidate the major microbial N-transformation mechanisms for ammonia removal and N₂ production.

Quantitative dynamics of ammonia-oxidizers during biological stabilization of municipal landfill leachate pretreated by Fenton's reagent at neutral pH

The application of multi-stage systems including biological step, for the treatment of leachate from municipal landfills, is economically and technologically justified. When microbial activity is utilized as 2nd stage of treatment, the task of 1st stage is to increase the bioavailability of organic matter. In this work, the effect of advanced oxidation process by Fenton's reagent for treatment efficiency of landfill leachate in the sequencing batch reactor was assessed. The quantitative dynamics of bacteria taking a part in ammonia removal process was evaluated by determination of number of DNA copies of 16S rRNA and amoA. Products of neutral pH chemical oxidation, had a definite positive impact on the quantity of β-proteobacteria 16S rRNA, whereas the same gene specified for Nitrospira sp. as well as amoA did not show a significant increase during the process of biological treatment, regardless of whether the reactor was fed with raw leachate or chemically pre-treated.

Nitrifying Kinetics and the Persistence of Nitrite in the Seine River, France

Although a higher oxidation rate for nitrite than for ammonia generally prevents nitrite accumulation in oxic waters, nitrite concentrations in the Seine River (1-31 μM) exceed European norms. We investigated the kinetics of in situ ammonia- and nitrite-oxidizing communities in river water and wastewater treatment plant (WWTP) effluents to determine the role of pelagic nitrification in the origin and persistence of nitrite downstream of Paris. The main source of nitrite is the major Parisian WWTP, and its persistence, up to tens of kilometers downstream of the plant, is explained by low ammonia and nitrite oxidation rates and high river flow. Furthermore, similar nitrite and ammonia oxidation rates preclude a rapid consumption of both preexisting nitrite and nitrite produced by ammonia oxidation. Maximum ammonia oxidation rates are two to three times higher downstream than upstream of the WWTP, indicating the input of ammonia oxidizers and ammonia from the WWTP. In both river water and WWTP effluents, nitrite oxidizers were unable to oxidize all available nitrite. In the human-impacted Seine River, this phenomenon might be due to mixotrophy. This study highlights the low resilience of the river to nitrite contamination as well as the importance of managing nitrite, nitrifiers, and organic matter concentrations in WWTP effluents to avoid nitrite persistence in rivers.

Whole-Community Metagenomics in Two Different Anammox Configurations: Process Performance and Community Structure

Anaerobic ammonia oxidation (anammox) combined with partial nitritation (PN) is an innovative treatment process for energy-efficient nitrogen removal from wastewater. In this study, we used genome-based metagenomics to investigate the overall community structure and anammox species enriched in suspended growth (SGR) and attached growth packed-bed (AGR) anammox reactors after 220 days of operation. Both reactors removed more than 85% of the total inorganic nitrogen. Metagenomic binning and phylogenetic analysis revealed that two anammox population genomes, affiliated with the genus Candidatus Brocadia, were differentially abundant between the SGR and AGR. Both of the genomes shared an average nucleotide identify of 83%, suggesting the presence of two different species enriched in both of the reactors. Metabolic reconstruction of both population genomes revealed key aspects of their metabolism in comparison to known anammox species. The community composition of both the reactors was also investigated to identify the presence of flanking community members. Metagenomics and 16S rRNA gene amplicon sequencing revealed the dominant flanking community members in both reactors were affiliated with the phyla Anaerolinea, Ignavibacteria, and Proteobacteria. Findings from this research adds two new species, Ca. Brocadia sp. 1 and Ca. Brocadia sp. 2, to the genus Ca. Brocadia and sheds light on their metabolism in engineered ecosystems.

Constructed Wetlands Revisited: Microbial Diversity in the -omics Era

Constructed wetlands (CWs) constitute an interesting alternative option to conventional systems for wastewater treatment. This technology is based on the utilization of the concerted activity of microorganisms for the removal of contaminants. Consequently, knowledge on the microbial assemblages dwelling CWs and the different environmental factors which can alter their activities is crucial for understanding their performance. In the last decades, the use of molecular techniques to characterize these communities and more recently, application of -omics tools, have broaden our view of microbial diversity and function in wastewater microbiology. In this manuscript, a review of the current knowledge on microbial diversity in CWs is offered, placing particular emphasis on the different molecular studies carried out in this field. The effect of environmental conditions, such as plant species, hydraulic design, water depth, organic carbon, temperature and substrate type on prokaryotic communities has been carefully revised, and the different studies highlight the importance of these factors in carbon, nitrogen and sulfur cycles. Overall, the novel -omics open a new horizon to study the diversity and ecophysiology of microbial assemblages and their interactions in CWs, particularly for those microorganisms belonging to the rare biosphere not detectable with conventional molecular techniques.

Use of horizontal subsurface flow constructed wetlands to treat reverse osmosis concentrate of rolling wastewater

According to the characteristics of the reverse osmosis concentrate (ROC) generated from iron and steel company, we used three sets of parallel horizontal subsurface flow (HSF) constructed wetlands (CWs) with different plants and substrate layouts to treat the high-salinity wastewater. The plant growth and removal efficiencies under saline condition were evaluated. The evaluation was based entirely on routinely collected water quality data and the physical and chemical characteristics of the plants (Phragmites australis, Typha latifolia, Iris wilsonii, and Scirpus planiculmis). The principal parameters of concern in the effluent were chemical oxygen demand (COD), total nitrogen (TN), and total phosphorus (TP). The results showed that the CWs were able to remove COD, TN, and TP from ROC. S. planiculmis was not suitable for the treatment of high-saline wastewater. The sequence of metals accumulated in CW plants was K>Ca>Na>Mg>Zn>Cu. More than 70% of metals were accumulated in the aboveground of P. australis. The CW filled with gravel and manganese ore and planted with P. australis and T. latifolia had the best performance of pollutant removal, with average removal of 49.96%, 39.45%, and 72.01% for COD, TN, and TP, respectively. The effluent water quality met the regulation in China. These results suggested that HSF CW planted with P. australis and T. latifolia can be applied for ROC pollutants removal.

Effect of the chemical composition of filter media on the microbial community in wastewater biofilms at different temperatures

This study investigates the microbial community composition in the biofilms grown on two different support media in fixed biofilm reactors for aerobic wastewater treatment, using next generation sequencing (NGS) technology. The chemical composition of the new type of support medium (TDR) was found to be quite different from the conventionally used support medium (stone). The analysis of 16S rRNA gene fragments recovered from the laboratory scale biofilm system show that biofilm support media and temperature conditions influence bacterial community structure and composition. Greater bacterial diversity was observed under each condition, primarily due to the large number of sequences available and sustenance of rare species. There were 6 phyla found, with the highest relative abundance shown by the phylum Proteobacteria (52.71%) followed by Bacteroidetes (33.33%), Actinobacteria (4.65%), Firmicutes, Verrucomicrobia (3.1%) and Chloroflex (>1%). The dataset showed 17 genera of bacterial populations to be commonly shared under all conditions, suggesting the presence of a core microbial community in the biofilms for wastewater treatment. However, some genera in the biofilms on TDR were observed in high proportions, which may be attributed to its chemical composition, explaining the improved level of wastewater treatment. The findings show that the structure of microbial communities in biofilm systems for wastewater treatment is affected by the properties of support matrix.

Promotion of nitrifiers through side-stream bioaugmentation: a full-scale study

Bioaugmentation of nitrifiers from a side-stream treatment is an efficient method for boosting the mainstream process at a wastewater treatment plant (WWTP). Although this technology has been known for several years, the number of full-scale applications for it is limited. For a WWTP approaching its critical nitrogen load capacity, the benefits are doubled if the introduced side-stream treatment for digester supernatant is combined with bioaugmentation. Not only is the nitrogen load to the mainstream process decreased by 10-25%, but the mainstream process is also boosted with nitrifiers, increasing the nitrifying capacity. In this full-scale study, the increment of the nitrification rate is examined in the mainstream process at different temperatures and at different flow rates of returned activated sludge to the side-stream treatment. Our results show that the nitrification rate in the mainstream process was increased by 41% during the coldest period of the study, implying that the examined WWTP could treat considerably higher nitrogen loads if bioaugmentation were permanently installed.

Ammonia Nitrogen Transformations in a Reactor with Aggregate made of Sewage Sludge Combustion Fly Ash

The influence of light weight aggregate made of fly ash from sewage sludge thermal treatment (FASSTT LWA) on ammonia nitrogen metabolism, and on quantitative and qualitative changes of microorganisms colonizing the filling, was investigated. Two reactors were used in the experiment. The first was filled with gravel, the other with FASSTT LWA. The reactors were operated with a wastewater hydraulic loading rate of 5 mm(3) mm(-2) d(-1). During the eleven-week experiment, high efficiency of ammonia removal was observed. The lower concentrations of nitrites and nitrates in the effluent indicate that ammonia nitrogen removal resulted not just from nitrification. Nitrate concentration increase was reflected in a decrease in nitrogen removal efficiency. One possible explanation for this phenomenon is that in the period when ammonia nitrogen and nitrites were present in the reactor's FASSTT LWA filling, facilitating conditions occurred for the deammonification process.

Vertically aligned multi walled carbon nanotubes prevent biofilm formation of medically relevant bacteria

A significant part of human infections is frequently associated with the establishment of biofilms by (opportunistic) pathogens. Due to the increasing number of untreatable biofilms, there is a rising need to develop novel and effective strategies to prevent biofilm formation on surfaces in medical as well as in technical areas. Bacterial initial attachment and adhesion to surfaces followed by biofilm formation is highly influenced by the physical properties of the surfaces. Consequently, changing these properties or applying different nanostructures is an attractive approach to prevent biofilm formation. Here we report on the effect(s) of surface grown and anchored vertically aligned multi walled carbon nanotubes (MWCNT), which have been made wettable by immersion through a graded ethanol series, on biofilm formation of Klebsiella oxytoca, Pseudomonas aeruginosa, and Staphylococcus epidermidis. We evaluated the biofilm formation under continuous flow conditions by confocal laser scanning microscopy and scanning electron microscopy, and demonstrated significant inhibition of biofilm formation of all the different pathogens by MWCNT of different lengths. Furthermore, the anti-adhesive effects of the MWCNT increased with their overall length. The application potential of our findings on surface grown and anchored vertically aligned MWCNT may represent a suitable contact mechanics based approach to prevent biofilm formation on medical devices or technical sensors operating in fluid environments.

Suspended sludge and biofilm shaped different anammox communities in two pilot-scale one-stage anammox reactors

The abundance and diversity of anammox bacteria was investigated in two pilot-scale integrated fixed-film activated sludge (IFAS) reactors treating high ammonium wastewater. Reactor A was inoculated with nitrifying sludge, while Reactor B was inoculated with suspended anammox sludge with the dominant anammox bacteria of Candidatus 'Kuenenia'. After 180days' operation, the predominate anammox bacteria was Candidatus 'Brocadia' (65%) in the biofilm, while Candidatus 'Kuenenia' (86%) outcompeted with other anammox bacteria in suspended sludge in Reactor A. Candidatus 'Kuenenia' were dominated in suspended sludge through the entire experiment in Reactor B. In contrast, the predominated species shifted from Candidatus 'Kuenenia' (89%) into Candidatus 'Brocadia' (66%) in the biofilm of Reactor B. This study indicated that Candidatus 'Brocadia' preferred to grow in the biofilm, while Candidatus 'Kuenenia' would dominant over other anammox bacteria in the suspended sludge. Further studies are required to identify the internal factors affecting the distribution of anammox bacteria.

Treatment of oil sands process-affected water (OSPW) using a membrane bioreactor with a submerged flat-sheet ceramic microfiltration membrane

The release of oil sands process-affected water (OSPW) into the environment is a concern because it contains persistent organic pollutants that are toxic to aquatic life. A modified Ludzack-Ettinger membrane bioreactor (MLE-MBR) with a submerged ceramic membrane was continuously operated for 425 days to evaluate its feasibility on OSPW treatment. A stabilized biomass concentration of 3730 mg mixed liquor volatile suspended solids per litre and a naphthenic acid (NA) removal of 24.7% were observed in the reactor after 361 days of operation. Ultra Performance Liquid Chromatography/High Resolution Mass Spectrometry analysis revealed that the removal of individual NA species declined with increased ring numbers. Pyrosequencing analysis revealed that Betaproteobacteria were dominant in sludge samples from the MLE-MBR, with microorganisms such as Rhodocyclales and Sphingobacteriales capable of degrading hydrocarbon and aromatic compounds. During 425 days of continuous operation, no severe membrane fouling was observed as the transmembrane pressure (TMP) of the MLE-MBR never exceeded -20 kPa given that the manufacturer's suggested critical TMP for chemical cleaning is -35 kPa. Our results indicated that the proposed MLE-MBR has a good potential for removing recalcitrant organics in OSPW.

Anammox-based technologies for nitrogen removal: Advances in process start-up and remaining issues

Nitrogen removal from wastewater via anaerobic ammonium oxidation (anammox)-based process has been recognized as efficient, cost-effective and low energy alternative to the conventional nitrification and denitrification processes. To date, more than one hundred full-scale anammox plants have been installed and operated for treatment of NH4(+)-rich wastewater streams around the world, and the number is increasing rapidly. Since the discovery of anammox process, extensive researches have been done to develop various anammox-based technologies. However, there are still some challenges in practical application of anammox-based treatment process at full-scale, e.g., longer start-up period, limited application to mainstream municipal wastewater and poor effluent water quality. This paper aimed to summarize recent status of application of anammox process and researches on technological development for solving these remaining problems. In addition, an integrated system of anammox-based process and microbial fuel cell is proposed for sustainable and energy-positive wastewater treatment.

Characterization of a joint recirculation of concentrated leachate and leachate to landfills with a microaerobic bioreactor for leachate treatment

With comparison of a traditional landfill, a joint recirculation of concentrated leachate and leachate to landfills with or without a microaerobic reactor for leachate treatment was investigated in this study. The results showed that the joint recirculation of concentrated leachate and leachate with a microaerobic reactor for leachate treatment could not only utilize the microaerobic reactor to buffer the fluctuation of quality and quantity of leachate during landfill stabilization, but also reduce the inhibitory effect of acidic pH and high concentrations of ammonium in recycled liquid on microorganisms and accelerate the degradation of landfilled waste. After 390 days of operation, the discharge of COD and total nitrogen (TN) from the landfill with leachate pretreatment by a microaerobic reactor was 7.4 and 0.9 g, respectively, which accounted for 0.7% and 2.6% of COD, 1.9% and 7.5% of the TN discharge from the landfills without recirculation and directly recirculated with leachate and concentrated leachate, respectively. The degradation of the organic matter and biodegradable matter (BDM) in the landfill reactors could fit well with the first-order kinetics. The highest degradation of the organic matter and BDM was observed in the joint recirculation system with a microaerobic reactor for leachate treatment with the degradation constant of the first-order kinetics of 0.001 and 0.002.

Detection of nitrifiers and evaluation of partial nitrification for wastewater treatment: A review

Partial nitrification has gained broad interests in the biological nitrogen removal (BNR) from wastewater, since it alleviates carbon limitation issues and acts as a shortcut nitrogen removal system combined with anaerobic ammonium oxidation (Anammox) process. The occurrence and maintenance of partial nitrification relies on various conditions, which favor ammonium oxidizing bacteria (AOB) but inhibit or limit nitrite oxidizing bacteria (NOB). The studies of the AOB and NOB activities have been conducted by state-of-the-art molecular techniques, such as Polymerase Chain Reaction (PCR), Quantitative PCR, denaturing gradient gel electrophoresis (DGGE), Fluorescence in situ hybridization (FISH) technique, Terminal Restriction Fragment Length Polymorphism (T-RFLP), Live/Dead BacLight, and quinone profile. Furthermore, control strategies for obtaining partial nitrification are mainly focused on the pH, temperature, dissolved oxygen concentration, real-time aeration control, sludge retention time, substrate concentration, alternating anoxic and aerobic operation, inhibitor and ultrasonic treatment. Existing problems and further perspectives for the scale-up of partial nitrification are also proposed and suggested.

Modelling the fate of nitrite in an urbanized river using experimentally obtained nitrifier growth parameters

Maintaining low nitrite concentrations in aquatic systems is a major issue for stakeholders due to nitrite's high toxicity for living species. This study reports on a cost-effective and realistic approach to study nitrite dynamics and improve its modelling in human-impacted river systems. The implementation of different nitrifying biomasses to model riverine communities and waste water treatment plant (WWTP)-related communities enabled us to assess the impact of a major WWTP effluent on in-river nitrification dynamics. The optimal kinetic parameters and biomasses of the different nitrifying communities were determined and validated by coupling laboratory experiments and modelling. This approach was carried out in the Seine River, as an example of a large human-impacted river with high nitrite concentrations. The simulation of nitrite fate was performed at a high spatial and temporal resolution (Δt = 10 min, dx¯ = 500 m) including water and sediment layers along a 220 km stretch of the Seine River for a 6-year period (2007-2012). The model outputs were in good agreement with the peak of nitrite downstream the WWTP as well as its slow decrease towards the estuary. Nitrite persistence between the WWTP and the estuary was mostly explained by similar production and consumption rates of nitrite in both water and sediment layers. The sediment layer constituted a significant source of nitrite, especially during high river discharges (0.1-0.4 mgN h(-1) m(-2)). This points out how essential it is to represent the benthic layer in river water quality models, since it can constitute a source of nitrite to the water-column. As a consequence of anthropogenic emissions and in-river processes, nitrite fluxes to the estuary were significant and varied from 4.1 to 5.5 TN d(-1) in low and high water discharge conditions, respectively, over the 2007-2012 period. This study provides a methodology that can be applied to any anthropized river to realistically parametrize autochthonous and WWTP-related nitrifier communities and simulate nitrite dynamics. Based on simulation analysis, it is shown that high spatio-temporal resolution hydro-ecological models are efficient to 1) estimate water quality criteria and 2) forecast the effect of future management strategies. Process-based simulations constitute essential tools to complete our understanding of nutrient cycling, and to decrease monitoring costs in the context of water quality and eutrophication management in river ecosystems.