Microbial community composition and dynamics of moving bed biofilm reactor systems treating municipal sewage

Identifying potential introduced and natural sources of pollution in Delaware watersheds

Managing water quality with microbial impairment caused by Enterococcus poses unique challenges regarding the determination of fecal host origin. Most water monitoring is performed based on Enterococcus counts that neither detect the location of the introduction of pollution nor identify the type of contaminating Enterococcus. The use of sequenced-based microbial source tracking could allow for identification of fecal origin and potential remediation of pollution. The state of Delaware has numerous waterways with high microbial impairment from unknown sources, so we used sequence-based microbial source tracking to investigate potential microbial pollution in three watersheds with significant variation in land use and population density. In this study, we use a 16S rRNA sequence reference library of microbial communities from relevant fecal sources (wild animal, domestic animal, sediment, and septic/wastewater) to determine the most likely sources of microbial impairment in three Delaware watersheds. This study assigned sources of microbial contamination to mostly human-related sources (septic and wastewater) or unknown sources indicating that waste infrastructure may have a larger influence on microbial community structure in Delaware watersheds than previously considered. Our results suggest that long-term source tracking is valuable for ruling out native or domesticated animals as contributors to water pollution.IMPORTANCETraditional microbial pollution monitoring utilizes specific fecal indicator bacteria that need to grow in the laboratory for detection. Here, we show the use of sequence information from whole microbial communities and an expanded reference library in microbial source tracking. Expanding the host detection range by including the whole microbial community may allow for a wider range of potential fecal origin identification even when specific fecal indicators are absent or in low concentration. We show that many Delaware waterways bear the signature of human influence compared to natural sources. In addition, the robust reference library built in this study can be used to conduct source tracking studies in the mid-Atlantic USA.

Deciphering community assembly and succession in sequencing batch moving bed biofilm reactor: Differentiation between attached and suspended communities

Elucidating community assembly and succession is crucial to understanding the ecosystem functioning. Herein, the ecological processes underpinning community assembly and succession were studied to uncover the respective ecological functions of attached biofilms and suspended biomass in a sequencing batch moving bed biofilm reactor. Compared with suspended biomass, attached biofilms presented higher relative abundances of Nitrospira (2.94 %) and Nitrosomonas (1.25 %), and contributed to 66.89 ± 11.37 % and 68.11 ± 12.72 % of nitrification and denitrification activities, respectively. The microbial source tracking result demonstrated that early formation of suspended biomass was dominated by the seeding effect of detached biofilms in the start-up period (days 0-30), while self-growth of previous suspended biomass was eventually outcompeted the seeding effect when the reactor stabilized (days 31-120). Null model and ecological network analysis further suggested distinctive ecological processes underpinning the differentiation between attached and suspended communities in the same reactor. Specifically, in the start-up period, positive interactions facilitated early formation of attached (73.84 %) and suspended communities (59.41 %), while homogenous selection (88.89 %) and homogenizing dispersal (65.71 %) governed assembly of attached and suspended communities, respectively. When the reactor stabilized, attached and suspended communities showed low composition turnover as reflected by dominant homogenizing dispersal, while they presented distinctive trends of interspecies interactions. This study sheds light on discrepant ecological processes governing community differentiation of attached biofilms and suspended biomass, which would provide ecological insights into the regulation of hybrid ecosystems.

Enhancing anaerobic methane production in integrated floating-film activated sludge system filled with novel MWCNTs-modified carriers

Conductive materials can enhance anaerobic methane production by accelerating interspecies electron transfer between electroactive bacteria and methanogens. However, the daily loss or less specific surface area of small/big size of conductive materials always limits their application in anaerobic digestion. In this study, the conductive multi-walled carbon nanotubes (MWCNTs) (15 wt% and 20 wt%) were mixed with high-density polyethylene (HDPE) and novel conductive suspended carriers were prepared. Results showed the conductivity of the novel conductive suspended carriers increased by 1-2 orders of magnitude comparing with HDPE carriers, as well as the attached biomass improved from 3.93 g/m² (HDPE carriers) to 5.82 g/m² (15 wt% MWCNTs-modified carriers) and 6.67 g/m² (20 wt% MWCNTs-modified carriers). Integrated floating-film activated sludge (IFFAS) filled with MWCNT-modified carriers showed significant advantages in chemical oxygen demand (COD) removal (removal efficiency increased by 3.6-37.2%) and methanogenic performance (cumulative methane increased by 12.28-62.91%) compared with the control reactor filled with conventional HDPE carriers when treating sodium propionate wastewater at the organic loading rates (OLR) of 11.3-26.3 kg COD/(m³∙d). SEM images and high-throughput sequencing results proved potential direct interspecies electron transfer (DIET) had been established successfully on the MWCNTs-modified carriers. The syntrophic electroactive bacteria (Geobacter, Thauera) and Methanotrix were enriched by 2.28-4.58% and 9.41-16.80% respectively owning to the addition of novel conductive carriers. This study proved IFFAS process filled with novel MWCNTs-modified suspended carriers showed great potential in establishing DIET to enhance anaerobic digestion in practical application.

Simultaneous biological removal of nitrogen and phosphorus from secondary effluent of wastewater treatment plants by advanced treatment: A review

With the advancement of water ecological protection and water control standard, it is the general trend to upgrade the wastewater treatment plants (WWTPs). The simultaneous removal of nitrogen and phosphorus is the key to improve the water quality of secondary effluent of WWTPs to prevent the eutrophication. Therefore, it is urgent to develop the applicable technologies for simultaneous biological removal of nitrogen and phosphorus from secondary effluent. In this review, the composition of secondary effluent from municipal WWTPs were briefly introduced firstly, then the three main treatment processes for simultaneous nitrogen and phosphorus removal, i.e., the enhanced denitrifying phosphorus removal filter, the pyrite-based autotrophic denitrification and the microalgae biological treatment system were summarized, their performances and mechanisms were analyzed. The influencing factors and microbial community structure were discussed. The advanced removal of nitrogen and phosphorus by different technologies were also compared and summarized in terms of performance, operational characteristics, disadvantage and cost. Finally, the challenges and future prospects of simultaneous removal of nitrogen and phosphorus technologies for secondary effluent were proposed. This review will deepen to understand the principles and applications of the advanced removal of nitrogen and phosphorus and provide some valuable information for upgrading the treatment process of WWTPs.

Enhancing anoxic denitrification of low C/N ratio wastewater with novel ZVI composite carriers

External organic carbon sources are needed to provide electron donors for the denitrification of wastewater with a low COD/NO₃^--N (C/N) ratio, increasing the treatment cost. The economic strategy is to enhance the bioactivity and/or biodiversity of denitrifiers to efficiently utilize organic substances in wastewater. In this study, novel zero-valent iron (ZVI) composite carriers were prepared and implemented in a suspended carrier biofilm reactor to enhance the bioactivity and/or biodiversity of denitrifiers. At the influent C/N ratio of 4 (COD was 179.5 ± 5.0 mg/L and TN was 44.2 ± 0.8 mg/L), COD and TN removal efficiencies were 85.1% and 66.4%, respectively, in the reactors filled with 3 wt% ZVI composite carriers. In contrast, COD and TN removal efficiencies were 70.4% and 55.3%, respectively, in the reactor filled with conventional high-density polyethylene (HDPE) biofilm carriers. The biofilm formation on the 3 wt% ZVI composite carriers was optimized due to its higher roughness (surface square roughness increased from 76.0 nm to 93.8 nm) and favorable hydrophilicity (water contact angle dropped to 72.5° ± 1.4° from 94.3° ± 3.2°) compared with the HDPE biofilm carriers. In addition, heterotrophic denitrifiers, Thauera and Dechloromonas, were enriched, whereas autotrophic denitrifiers, Raoultella and Thiobacillus, exhibited high relative abundance in the biofilm of ZVI composite carriers. The coexistence of heterotrophic denitrifiers and autotrophic denitrifiers on the surface of ZVI composite carriers provided mixotrophic metabolism of denitrification (including heterotrophic and iron-based autotrophic), thereby ensuring effective denitrification for wastewater with a low C/N ratio without external organic carbon source addition.

Simultaneous nitrification and denitrification in continuous flow MBBR with novel surface-modified carriers

ABSTRACTMoving-Bed Biofilm Reactor (MBBR) process is an ideal preference for simultaneous nitrification and denitrification (SND) attributing to the longer sludge age and aerobic/anoxic microenvironment along biofilm. However, conventional carriers generally exhibit negative charge and surface hydrophobicity, which are unbeneficial for biofilm formation. In this study, novel surface-modified carriers with favourable hydrophilicity (surface contact angle dropped to 60.2 ± 2.3°) and positive surface charge (+11.7 ± 1.1 mV, pH 7.0) were prepared via polymer blending and implemented for SND in continuous flow MBBR system. Results indicated SND started up quickly with more biomass in MBBR filled with surface-modified carriers. At the operation condition of low dissolved oxygen level (0.75 ± 0.25 mg/L), pH of 7.5 ± 0.5, 23 ± 2°C and C/N ratio of 7, COD, NH₄⁺-N and TN removal efficiencies were 90.5%, 88.6% and 76.6% respectively in MBBR filled with surface-modified carriers, which ensured the effluent met the first grade A of the Discharge Standard of China. On the contrary, COD, NH₄⁺-N and TN removal efficiencies were 89.7%, 82.3% and 60.4% respectively in the control reactors filled with conventional polyethylene carriers. The worse performance of the control reactor was mainly attributed to the less biomass and lower functional bacteria abundance developed on conventional carriers. Moreover, novel carriers provided a favourable niche for more types of functional bacteria, of which autotrophic nitrification, anoxic denitrification, heterotrophic nitrification and aerobic denitrification co-existed and participated in nitrogen removal.

Comparison of Myriophyllum Spicatum and artificial plants on nutrients removal and microbial community in constructed wetlands receiving WWTPs effluents

The impacts of WWTPs effluents on nutrients removal and epiphytic microbial community in constructed wetlands dominated by submersed macrophytes remain to be fully illustrated. In this study, compared to M. Spicatum, artificial submersed macrophytes (control) generally had higher NH₄⁺-N (78.35% vs 80.52%) and TN (73.35% vs 90.25%) removal rates and similar COD (70.64% vs 70.80%) and TP (59.86% vs 60.82%) removal rates in wetlands receiving simulated effluents of WWTPs (GB18918-2002). Microbial population richness was higher in epiphytic biofilms on M. Spicatum than artificial ones, and substrates played the most decisive role in determining the microbial diversities. Network analysis revealed that there were more complex interactions among environmental parameters, bacteria and eukaryotes in M. Spicatum systems than in artificial ones. Nutrients in effluents could cause damage to M. Spicatum. The results highlight that artificial plants have better performance on effluents deep treatments than submerged plants.

Applications of Chemically Modified Clay Minerals and Clays to Water Purification and Slow Release Formulations of Herbicides

This review deals with modification of montmorillonite and other clay-minerals and clays by interacting them with organic cations, for producing slow release formulations of herbicides, and efficient removal of pollutants from water by filtration. Elaboration is on incorporating initially the organic cations in micelles and liposomes, then producing complexes denoted micelle- or liposome-clay nano-particles. The material characteristics (XRD, Freeze-fracture electron microscopy, adsorption) of the micelle– or liposome–clay complexes are different from those of a complex of the same composition (organo-clay), which is formed by interaction of monomers of the surfactant with the clay-mineral, or clay. The resulting complexes have a large surface area per weight; they include large hydrophobic parts and (in many cases) have excess of a positive charge. The organo-clays formed by preadsorbing organic cations with long alkyl chains were also addressed for adsorption and slow release of herbicides. Another examined approach includes “adsorptive” clays modified by small quaternary cations, in which the adsorbed organic cation may open the clay layers, and consequently yield a high exposure of the siloxane surface for adsorption of organic compounds. Small scale and field experiments demonstrated that slow release formulations of herbicides prepared by the new complexes enabled reduced contamination of ground water due to leaching, and exhibited enhanced herbicidal activity. Pollutants removed efficiently from water by the new complexes include (i) hydrophobic and anionic organic molecules, such as herbicides, dissolved organic matter; pharmaceuticals, such as antibiotics and non-steroidal drugs; (ii) inorganic anions, e.g., perchlorate and (iii) microorganisms, such as bacteria, including cyanobacteria (and their toxins). Model calculations of adsorption and kinetics of filtration, and estimation of capacities accompany the survey of results and their discussion.

Microbial Communities and Sulfate-Reducing Microorganisms Abundance and Diversity in Municipal Anaerobic Sewage Sludge Digesters from a Wastewater Treatment Plant (Marrakech, Morocco)

Both molecular analyses and culture-dependent isolation were combined to investigate the diversity of sulfate-reducing prokaryotes and explore their role in sulfides production in full-scale anaerobic digesters (Marrakech, Morocco). At global scale, using 16S rRNA gene sequencing, Proteobacteria, Bacteroidetes, Firmicutes, Actinobacteria, Synergistetes, and Euryarchaeota were the most dominant phyla. The abundance of Archaea (3.1–5.7%) was linked with temperature. The mcrA gene ranged from 2.18 × 105 to 1.47 × 107 gene copies.g−1 of sludge. The sulfate-reducing prokaryotes, representing 5% of total sequences, involved in sulfides production were Peptococcaceae, Syntrophaceae, Desulfobulbaceae, Desulfovibrionaceae, Syntrophobacteraceae, Desulfurellaceae, and Desulfobacteraceae. Furthermore, dsrB gene ranged from 2.18 × 105 to 1.92 × 107 gene copies.g−1 of sludge. The results revealed that exploration of diversity and function of sulfate-reducing bacteria may play a key role in decreasing sulfide production, an undesirable by-product, during anaerobic digestion.

Hydrodynamic effect on biofouling of milli-labyrinth channel and bacterial communities in drip irrigation systems fed with reclaimed wastewater

The clogging of drippers due to the development of biofilms reduces the benefits and is an obstacle to the implementation of drip irrigation technology in a reclaimed water context. The narrow section and labyrinth geometry of the dripper channel results the development of a heterogeneous flow behaviours with the vortex zones which it enhance the fouling mechanisms. The objective of this study was to analyse the influence of the three dripper types, defined by their geometric and hydraulic parameters, fed with reclaimed wastewater, on the biofouling kinetics and the bacterial communities. Using optical coherence tomography, we demonstrated that the inlet of the drippers (mainly the first baffle) and vortex zones are the most sensitive area for biofouling. Drippers with the lowest Reynolds number and average cross-section velocity v (1 l·h^-1) were the most sensible to biofouling, even if detachment events seemed more frequent in this dripper type. Therefore, dripper flow path with larger v should be consider to improve the anti-clogging performance. In addition, the dripper type and the geometry of the flow path influenced the structure of the bacterial communities from dripper biofilms. Relative abundancy of filamentous bacteria belonging to Chloroflexi phylum was higher in 1 l·h^-1 drippers, which presented a higher level of biofouling. However, further research on the role of this phylum in dripper biofouling is required.

Performance and bacterial community structure of a novel inverse fluidized bed bioreactor (IFBBR) treating synthetic municipal wastewater

The performance of a lab-scale integrated anoxic and aerobic inverse fluidized bed bioreactors (IFBBR) for biological nutrient removal from synthetic municipal wastewater was studied at chemical oxygen demand (COD) loading rates of 0.34-2.10 kg COD/(m³-d) and nitrogen loading rates of 0.035-0.213 kg N/(m³-d). Total COD removal efficiencies of >84% were achieved, concomitantly with complete nitrification. The overall nitrogen removal efficiencies were >75%. Low biomass yields of 0.030-0.101 g VSS/g COD were achieved. Compared with other FBBR systems, the energy consumption for this IFBBR system was an average 59% less at organic loading rates (OLRs) of 1.02 and 2.10 kg COD/(m³-d). Bacterial community structures of attached and suspended biomass revealed that the dominant phyla were Proteobacteria, Bacteroidetes, and Epsilonbacteraeota, etc. The relative abundance of ammonia-oxidizing bacteria (AOBs) and nitrite-oxidizing bacteria (NOBs) in the aerobic attached biomass were 0.451% and 0.110%, respectively. COD mass balance in the anoxic zone was closed by consideration of sulfate reduction, which was confirmed by the presence of genus Chlorobium (sulfate-reducing bacteria) in the anoxic attached biofilm with a relative abundance of 0.32%.

Simultaneous nitrification and denitrification process using novel surface-modified suspended carriers for the treatment of real domestic wastewater

Moving-bed biofilm reactor (MBBR) is a well-established technology for simultaneous nitrification and denitrification (SND). In MBBR, biofilm development and pollutant removal performance are strictly governed by the physico-chemical properties of the carriers. In this study, novel surface-modified carriers with enhanced hydrophilicity (surface contact angle of 60.2 ± 2.3°) and positively-charged surfaces (+11.7 ± 1.1 mV, pH 7.0) had been prepared successfully via polymer blending, and they had also been implemented in SND system for the treatment of real domestic wastewater. Results showed that accelerated startup of SND with more biomass on the carriers was observed in MBBR system filled with surface-modified carriers. At low DO level (0.6-0.8 mg L^-1) and low C/N ratio (≤5), highly efficient organics removal and SND performance could be achieved with COD removal, TN removal and SND efficiencies of 79.3-85.7%, 62.0-75.9% and 58.5-71.8%, respectively. The efficient performance of SND in MBBR system filled with surface-modified carriers was mainly attributed to the coexistence of enriched mixtrophic nitrifiers and denitrifiers like autotrophic nitrifers (Nitrosomonas, Nitrospira, Nitrobacter), heterotrophic nitrifers (Rudaea), aerobicdenitrifiers (Dokdonella, Terrimonas), anoxic denitrifiers (Gemmobacter, Ottowia, Methyloversatilis, Thermomonas) and N₂O producer (Mesorhizobium).

Simultaneous nitrogen and carbon removal in a packed A/O reactor: effect of C/N ratio on microbial community structure

In this research, a novel packed anoxic/oxic moving bed biofilm reactor (MBBR) was established to achieve high-organic matter removal rates, despite the carbon/nitrogen (C/N) ratio of 2.7-5.1 in the influent. Simultaneous nitrification-denitrification (SND) was investigated under a long sludge retention time of 104 days. The system exhibited excellent performance in pollutant removal, with chemical oxygen demand and total nitrogen (TN) enhanced to 93.6-97.4% and 34.4-60%, respectively. Under low C/N conditions, the nitrogen removal process of A/O MBBR system was mainly achieved by anaerobic denitrification. The increase of C/N ratio enhanced SND rate of the aerobic section, where dissolved oxygen was maintained at the range of 4-6 mg/L, and resulted in higher TN removal efficiency. The microbial composition and structures were analyzed utilizing the MiSeq Illumina sequencing technique. High-throughput pyrosequencing results indicated that the dominant microorganisms were Proteobacteria and Bacteroidetes at the phylum level, which contributes to the removal of organics matters. In the aerobic section, abundances of Nitrospirae (1.12-29.33%), Burkholderiales (2.15-21.38%), and Sphingobacteriales (2.92-11.67%) rose with increasing C/N ratio in the influent, this proved that SND did occur in the aerobic zone. As the C/N ratio of influent increased, the SND phenomenon in the aerobic zone of the system is the main mechanism for greatly improving the removal rate of TN in the aerobic section. The C/N ratio in the aerobic zone is not required to be high to exhibit good TN removal performance. When C/NH₄⁺ and C/TN in the aerobic zone were higher than 2.29 and 1.77, respectively, TN removal efficiency was higher than 60%, which means that carbon sources added to the reactor could be saved. This study would be vital for a better understanding of microbial structures within a packed A/O MBBR and the development of cost-efficient strategies for the treatment of low C/N wastewater.

Large-sized planktonic bioaggregates possess high biofilm formation potentials: Bacterial succession and assembly in the biofilm metacommunity

Wanted and unwanted surface-attached growth of bacteria is ubiquitous in natural and engineered settings. Normally, attachment of planktonic cells to media surfaces initiates biofilm formation and fundamentally regulates biofilm assembly processes. Here, culturing biofilm with planktonic sludge as source community, we found distinct succession profiles of biofilm communities sourced from the size-fractionated sludge flocs (<25; 25-120; >120 μm). Null model analyses revealed that deterministic process dominated in biofilm community assemblies but decreased with decreasing floc size. Additionally, the relative importance of environmental selection increased with increasing floc size of the source sludge, whereas homogenizing dispersal and ecological drift followed opposite trends. Phylogenetic molecular ecological networks (pMENs) indicated that species interactions were intensive in biofilm microbiota developed from large-sized flocs (>120 μm), as evidenced by the low modularity and harmonic geodesic distance and the high average degree. Intriguingly, the keystone taxa in these biofilm ecological networks were controlled by distinct interaction patterns but all showed strong habitat characteristics (e.g., facultative anaerobic, motile, hydrophobic and involved in extracellular polymeric substance metabolism), corroborating the crucial roles of environmental filtering in structuring biofilm community. Taken together, our findings highlight the role of planktonic floc properties in biofilm community assembly and advance our understanding of microbial ecology in biofilm-based systems.

Assessment and characterization of the bacterial community structure in advanced activated sludge systems

The present study is aimed to assess and characterize the structure of bacterial community in advanced activated sludge systems. In particular, activated sludge samples were collected from an Integrated Fixed-film Activated Sludge - Membrane Bioreactor pilot plant under a University of Cape Town configuration with in-series anaerobic (Noair)/anoxic (Anox)/aerobic (Oxy) reactors - and further analyzed. The achieved results - based on Next Generation Sequencing (NGS) of 16S rDNA amplicons - revealed that the bacterial biofilm (bf) communities on plastic carriers of Oxy and Anox reactors had a greater diversity compared to suspended (sp) bacterial flocs of Oxy, Anox and Noair. Indeed, the Shannon diversity indices of both biofilm communities were higher than those of suspended growth samples (Oxy-bf = 4.1 and Anox-bf = 4.2 vs. Oxy-sp = 3.4, Anox-sp = 3.5 and Noair-sp = 3.4). The most striking differences have been reported in Rhodobacteraceae being more abundant in biofilm specimens than in suspended biomass samples. The vast majority of the identified bacteria differs from those obtained by culture dependent method, thus suggesting that NGS-based method is really suitable to analyze the bacterial community composition, even in advanced systems for wastewater treatment.

Drip irrigation biofouling with treated wastewater: bacterial selection revealed by high-throughput sequencing

Clogging of drippers due to the development of biofilms weakens the advantages and impedes the implementation of drip irrigation technology. The objective of this study was to characterise the bacterial community of biofilms that develop in a drip irrigation system supplied with treated wastewater. High-throughput sequencing of 16S rRNA gene amplicons indicated that the bacterial community composition differed between drippers and pipes, mainly due to changes in the abundance of the genus Aquabacterium. Cyanobacteria were found to be involved in the biological fouling of drippers. Moreover, bacterial genera including opportunistic pathogenic bacteria such as Legionella and Pseudomonas were more abundant in dripper and pipe biofilms than in the incoming water. Some genera such as Pseudomonas were mostly recovered from drippers, while others (ie Bacillus, Brevundimonas) mainly occurred in pipes. Variations in the hydraulic conditions and properties of the materials likely explain the shift in bacterial communities observed between pipes and drippers.

Micropollutants removal in tertiary moving bed biofilm reactors (MBBRs): Contribution of the biofilm and suspended biomass

The performance of tertiary moving bed biofilm reactors (MBBRs) was evaluated in terms of micropollutants (MPs) removal from secondary-treated municipal wastewater. After stepwise establishment of a mature biofilm, monitored by scanning electron and confocal microscopies, abiotic and biotic removals of MPs were deeply studied. Since no MPs reduction was observed by the both photodegradation and volatilization, abiotic removal of MPs was ascribed to the sorption onto the biomass. Target MPs i.e. Naproxen, Diclofenac, 17β-Estradiol and 4n-Nonylphenol, arranged in the ascending order of hydrophobicity, abiotically declined up to 2.8%, 4%, 9.5% and 15%, respectively. MPs sorption onto the suspended biomass was found around two times more than the biofilm, in line with MPs' higher sorption kinetic constants (k_sor) found for the suspended biomass. When comparing abiotic and biotic aspects, we found that biotic removal outperformed its counterpart for all compounds as Diclofenac, Naproxen, 17β-Estradiol and 4n-Nonylphenol were biodegraded by 72.8, 80.6, 84.7 and 84.4%, respectively. The effect of the changes in organic loading rates (OLRs) was investigated on the pseudo-first order degradation constants (k_biol), revealing the dominant biodegradation mechanism of co-metabolism for the removal of Diclofenac, Naproxen, and 4n-Nonylphenol, while 17β-Estradiol obeyed the biodegradation mechanism of competitive inhibition. Biotic removals and k_biol values of all MPs were also seen higher in the biofilm as compared to the suspended biomass. To draw a conclusion, a quite high removal of recalcitrant MPs is achievable in tertiary MBBRs, making them a promising technology that supports both pathways of co-metabolism and competitive inhibition, next to the abiotic attenuation of MPs.

Shifts in microbial community structure and diversity in a novel waterfall biofilm reactor combined with MBBR under light and dark conditions

In this study, a novel, low-cost, easy-maintenance and effective waterfall aeration biofilm reactor (WFBR) was designed to treat wastewater with MBBR. The chemical oxygen demand (COD), nitrogen removal efficiency, and the microbial community structure in this novel system were evaluated for 70 days under light and dark conditions. The COD and ammonium nitrogen (NH3-N) removal efficiency remained at approximately 90% and 100% respectively after 25 days, even if the influent substrate concentration and illumination condition changes. High-throughput sequencing was used to investigate the composition and function of the microbial community in different fillers in the treatment system. Dark padding, illuminate carrier and fabric play the good performance in nitrogen nitrification, denitrification and fixation respectively. The major classes present were Betaproteobacteria (30.2% on average), Cytophagia (19.8%), Gammaproteobacteria (11.7%), Alphaproteobacteria (11.2%), Sphingobacteriia (5.1%), Flavobacteriia (2.6%), Deltaproteobacteria (2.4%), Verrucomicrobiae (0.7%), Chloroplast (0.6%) and Clostridia (0.5%). These results could provide important guidance for the improvement of MBBR or other tradition wastewater treatment process, and could also enrich our theoretical understanding of microbial ecology.

Sewage Sludge Microbial Structures and Relations to Their Sources, Treatments, and Chemical Attributes

Sewage sludges generation and their disposal have become one of the greatest challenges of the 21st century. They have great microbial diversity that may impact wastewater treatment plant (WWTP) efficiency and soil quality whether used as fertilizers. Therefore, this research aimed to characterize microbial community diversity and structure of 19 sewage sludges from São Paulo, Brazil, as well as to draw their relations to sludge sources [domestic and mixed (domestic+industrial)], biological treatments (redox conditions and liming), and chemical attributes, using molecular biology as a tool. All sludges revealed high bacterial diversity, but their sources and redox operating conditions as well as liming did not consistently affect bacterial community structures. Proteobacteria was the dominant phylum followed by Bacteroidetes and Firmicutes; whereas Clostridium was the dominant genus followed by Treponema, Propionibacterium, Syntrophus, and Desulfobulbus. The sludge samples could be clustered into six groups (C1 to C6) according their microbial structure similarities. Very high pH (≥11.9) was the main sludge attribute segregating C6, that presented very distinct microbial structure from the others. Its most dominant genera were Propionibacterium > > Comamonas > Brevundimonas > Methylobacterium ∼Stenotrophomonas ∼Cloacibacterium. The other clusters' dominant genera were Clostridium > > Treponema > Desulfobulbus ∼Syntrophus. Moreover, high Fe and S were important modulators of microbial structure in certain sludges undertaking anaerobic treatment and having relatively low N-Kj, B, and P contents (C5). However, high N-Kj, B, P, and low Fe and Al contents were typical of domestic, unlimed, and aerobically treated sludges (C1). In general, heavy metals had little impact on microbial community structure of the sludges. However, our sludges shared a common core of 77 bacteria, mostly Clostridium, Treponema, Syntrophus, and Comamonas. They should dictate microbial functioning within WWTPs, except by SS12 and SS13.

Comparative evaluation of piggery wastewater treatment in algal-bacterial photobioreactors under indoor and outdoor conditions

This work evaluated the performance of four open algal-bacterial photobioreactors operated at ≈26days of hydraulic retention time during the treatment of 10 (×10) and 20 (×20) times diluted piggery wastewater (PWW) under indoor (I) and outdoor (O) conditions for four months. The removal efficiencies (REs) of organic matter, nutrients and zinc from PWW, along with the dynamics of biomass concentration and structure of algal-bacterial population were assessed. The highest TOC-RE, TP-RE and Zn-RE (94±1%, 100% and 83±2%, respectively) were achieved indoors in ×10 PWW, while the highest TN-RE (72±8%) was recorded outdoors in ×10 PWW. Chlorella vulgaris was the dominant species regardless of the ambient conditions and PWW dilution. Finally, DGGE-sequencing of the bacterial community revealed the occurrence of four phyla, Proteobacteria being the dominant phylum with 15 out of the 23 most intense bands.

Impact of external carbon dose on the removal of micropollutants using methanol and ethanol in post-denitrifying Moving Bed Biofilm Reactors

Addition of external carbon sources to post-denitrification systems is frequently used in wastewater treatment plants to enhance nitrate removal. However, little is known about the fate of micropollutants in post-denitrification systems and the influence of external carbon dosing on their removal. In this study, we assessed the effects of two different types and availability of commonly used carbon sources -methanol and ethanol- on the removal of micropollutants in biofilm systems. Two laboratory-scale moving bed biofilm reactors (MBBRs), containing AnoxKaldnes K1 carriers with acclimated biofilm from full-scale systems, were operated in continuous-flow using wastewater dosed with methanol and ethanol, respectively. Batch experiments with 22 spiked pharmaceuticals were performed to assess removal kinetics. Acetyl-sulfadiazine, atenolol, citalopram, propranolol and trimethoprim were easily biotransformed in both MBBRs (biotransformations rate constants k_bio between 1.2 and 12.9 L g_biomass^-1 d^-1), 13 compounds were moderately biotransformed (rate constants between 0.2 and 2 L g_biomass^-1 d^-1) and 4 compounds were recalcitrant. The methanol-dosed MBBR showed higher k_bio (e.g., 1.5-2.5-fold) than in the ethanol-dosed MBBR for 9 out of the 22 studied compounds, equal k_bio for 10 compounds, while 3 compounds (i.e., targeted sulfonamides) were biotransformed faster in the ethanol-dosed MBBR. While biotransformation of most of the targeted compounds followed first-order kinetics, removal of venlafaxine, carbamazepine, sulfamethoxazole and sulfamethizole could be described with a cometabolic model. Analyses of the microbial composition in the biofilms using 16S rRNA amplicon sequencing revealed that the methanol-dosed MBBR contained higher microbial richness than the one dosed with ethanol, suggesting that improved biotransformation of targeted compounds could be associated with higher microbial richness. During continuous-flow operation, at conditions representative of full-scale denitrification systems (hydraulic residence time = 2 h), the removal efficiencies of micropollutants were below 35% in both MBBRs, with the exception of atenolol and trimethoprim (>80%). Overall, this study demonstrated that MBBRs used for post-denitrification could be optimized to enhance the biotransformation of a number of micropollutants by accounting for optimal carbon sources and extended residence time.

Novel nitrifiers and comammox in a full-scale hybrid biofilm and activated sludge reactor revealed by metagenomic approach

Biofilms are widely used in wastewater treatment for their particular enhancement of nitrogen removal and other significant advantages. In this study, the diversity and potential functions of nitrogen removal bacteria in suspended activated sludge (AS) and biofilm of a full-scale hybrid reactor were uncovered by metagenomes (∼34 Gb), coupled with PCR-based 454 reads (>33 K reads). The results indicated that the diversity and abundance of nitrifiers and denitrifiers in biofilm did not surpass that in AS, while more nitrification and denitrification genes were indeed found in biofilm than AS, suggesting that the increased nitrogen removal ability by applying biofilm might be attributed to the enhancement of removal efficiency, rather than the biomass accumulation of nitrogen removal bacteria. The gene annotation and phylogenetic analysis results revealed that AS and biofilm samples consisted of 6.0 % and 9.4 % of novel functional genes for nitrogen removal and 18 % and 30 % of new Nitrospira species for nitrite-oxidizing bacteria, respectively. Moreover, the identification of Nitrospira-like amoA genes provided metagenomic evidence for the presence of complete ammonia oxidizer (comammox) with the functional potential to perform the complete oxidation of ammonia to nitrate. These findings have significant implications in expanding our knowledge of the biological nitrogen transformations in wastewater treatment.

Tracking the dynamics of heterotrophs and nitrifiers in moving-bed biofilm reactors operated at different COD/N ratios

In this study, the impact of COD/N ratio and feeding regime on the dynamics of heterotrophs and nitrifiers in moving-bed biofilm reactors was addressed. Based on DGGE analysis of 16S rRNA genes, the influent COD was found to be the main factor determining the overall bacterial diversity. The amoA-gene-based analysis suggested that the dynamic behavior of the substrate in continuous and pulse-feeding reactors influenced the selection of specific ammonium-oxidizing bacteria (AOB) strains. Furthermore, AOB diversity was directly related to the applied COD/N ratio and ammonium-nitrogen load. Maximum specific ammonium oxidation rates observed under non-substrate-limiting conditions were observed to be proportional to the fraction of nitrifiers within the bacterial community. FISH analysis revealed that Nitrosomonas genus dominated the AOB community in all reactors. Moreover, Nitrospira was found to be the only nitrite-oxidizing bacteria (NOB) in the fully autotrophic system, whereas Nitrobacter represented the dominant NOB genus in the organic carbon-fed reactors.

A Post-Genomic View of the Ecophysiology, Catabolism and Biotechnological Relevance of Sulphate-Reducing Prokaryotes

Dissimilatory sulphate reduction is the unifying and defining trait of sulphate-reducing prokaryotes (SRP). In their predominant habitats, sulphate-rich marine sediments, SRP have long been recognized to be major players in the carbon and sulphur cycles. Other, more recently appreciated, ecophysiological roles include activity in the deep biosphere, symbiotic relations, syntrophic associations, human microbiome/health and long-distance electron transfer. SRP include a high diversity of organisms, with large nutritional versatility and broad metabolic capacities, including anaerobic degradation of aromatic compounds and hydrocarbons. Elucidation of novel catabolic capacities as well as progress in the understanding of metabolic and regulatory networks, energy metabolism, evolutionary processes and adaptation to changing environmental conditions has greatly benefited from genomics, functional OMICS approaches and advances in genetic accessibility and biochemical studies. Important biotechnological roles of SRP range from (i) wastewater and off gas treatment, (ii) bioremediation of metals and hydrocarbons and (iii) bioelectrochemistry, to undesired impacts such as (iv) souring in oil reservoirs and other environments, and (v) corrosion of iron and concrete. Here we review recent advances in our understanding of SRPs focusing mainly on works published after 2000. The wealth of publications in this period, covering many diverse areas, is a testimony to the large environmental, biogeochemical and technological relevance of these organisms and how much the field has progressed in these years, although many important questions and applications remain to be explored.

dsrAB-based analysis of sulphate-reducing bacteria in moving bed biofilm reactor (MBBR) wastewater treatment plants

Sulphate-reducing bacteria (SRB) are important members of the sulphur cycle in wastewater treatment plants (WWTPs). In this study, we investigate the diversity and activity of SRB within the developing and established biofilm of two moving bed biofilm reactor (MBBR) systems treating municipal wastewater in New Zealand. The larger of the two WWTPs (Moa Point) generates high levels of sulphide relative to the smaller Karori plant. Clone libraries of the dissimilatory (bi)sulphite reductase (dsrAB) genes and quantitative real-time PCR targeting dsrA transcripts were used to compare SRB communities between the two WWTPs. Desulfobulbus (35-53 % of total SRB sequences) and genera belonging to the family Desulfobacteraceae (27-41 %) dominated the SRB fraction of the developing biofilm on deployed plastic carriers at both sites, whereas Desulfovibrio and Desulfomicrobium were exclusively found at Moa Point. In contrast, the established biofilms from resident MBBR carriers were largely dominated by Desulfomonile tiedjei-like organisms (58-100 % of SRB sequences). The relative transcript abundance of dsrA genes (signifying active SRBs) increased with biofilm weight yet remained low overall, even in the mature biofilm stage. Our results indicate that although SRB are both present and active in the microbial community at both MBBR study sites, differences in the availability of sulphate may be contributing to the observed differences in sulphide production at these two plants.