Phosphate-accumulating Organisms Research Articles

Distinct microdiversity of phosphate accumulating organisms (PAOs) between side-stream and conventional enhanced biological phosphorus removal (EBPR) systems with performance implications

Polyphosphate Accumulating Organisms (PAOs) microdiversity is a key factor to elucidate the mechanisms involved in the side-stream enhanced biological phosphorus removal (S2EBPR) systems, which has been shown to improve the process stability over conventional EBPR. However, fast, effective and cost-efficient methods to resolve PAO microdiversity in real-world activate sludge samples is still in absence. In this study, we applied oligotyping analysis following the regular 16S rRNA gene amplicon sequencing standard operation pipeline (SOP) to resolve subgenus-level PAO oligotypes, which cannot be achieved using traditional 16S rRNA sequencing SOP. The identified oligotype profiles of PAO-containing genera Ca. Accumulibacter, Tetrasphaera and Comamonas showed distinguished community-level differences across 12 water resource recovery facilities (WRRFs), which would not be revealed at the genus level. The WRRF-level differences were observed larger than the temporal differences in the same WRRF, indicating intrinsic sub-genus level microdiversity fingerprint between EBPR/S2EBPR systems. The identified oligotypes can be associated with known PAO clades phylogenetically, suggesting that oligotyping can suffice as a fast and cost-efficient approach for PAO microdiversity profiling. In addition, network analysis can be used to identify coexistence patterns between oligotypes with respect to EBPR/S2EBPR configurations and performance, enabling more detailed analysis between EBPR system performance and PAOs microdiversity. Correlation analyses between oligotype profiles and key EBPR performance parameters revealed potential different biological functional traits among these PAO species with P-removal performance implications.

Start-up of glycerol-driven denitrifying phosphorus removal from wastewater: The effects of the microaerobic environment

Glycerol, an abundant by-product of biodiesel production, represented a promising carbon source for enhancing nutrient removal from low C/N ratio wastewater. This study discovered a novel approach to initiate glycerol-driven denitrifying phosphorus removal (DPR) in situ by creating a short-term microaerobic environment within the aerobic zone. This approach facilitated the in-situ conversion of glycerol, which was subsequently utilized by denitrifying phosphate accumulating organisms (DPAOs) for DPR. The feasibility and stability of glycerol-driven DPR were validated in a continuous-flow pilot-scale reactor. Anaerobic phosphorus release increased from 1.0 mg/L/h to 2.5 mg/L/h, with fermentation bacteria and related functional genes showing significant increases. The stable stage exhibited 92.8% phosphorus removal efficiency and 55.5% DPR percentage. The microaerobic environment enhanced fermentation bacteria enrichment, crucial for glycerol-driven DPR stability. The collaborative interaction between fermentation bacteria and phosphate accumulating organisms (PAOs) played a key role in sustaining glycerol-driven DPR stability. These findings provide a robust theoretical foundation for applying glycerol-driven DPR in established wastewater treatment plants.

Combined Effects of Tetracycline and Copper Ion on Microorganisms During the Biological Phosphorus Removal.

Tetracycline and copper ion are common pollutants in wastewater, and the effects of mixed pollutants on microorganisms in wastewater biological treatment have been less studied. In order to reveal the effects of mixed pollutants of tetracycline and copper ion on the microorganisms during the biological phosphorus removal, three ratios of tetracycline and copper ions were designed by the direct equipartition ray method. The relative abundance and diversity of microbial community were investigated, and the microbial interactions were revealed through microbiological methods. The results demonstrated that, for three different ratios, the inhibitory effect of specific phosphorus uptake rate became more significant with the increase of the tetracycline-copper ions concentration and the reaction time. The microbial community decreased with the increase of the proportion of tetracycline in different ratios. The relative abundance of Acinetobacter decreased with the increase of the proportion of tetracycline, while the relative abundance of Ca.Competibacter was higher under the conditions of low mixtures concentrations. Positive interactions and symbiotic relationships among microorganisms were predominant for three different ratios. However, as the proportion of tetracycline increased, the community structure of microorganisms shifted from phosphate-accumulating organisms to glycogen accumulating organisms and denitrifying bacteria. This study can provide a reference for the effect of mixed pollutants on microorganisms and the mechanism of wastewater treatment.

Improving carbon management through maximizing hydrolysis and fermentation at water resource recovery facilities

Wastewater treatment plants are transitioning from a sole focus on treatment objectives to integrated resource recovery and upcycling. Effective carbon management is critical for upcycling within a water resource recovery facility (WRRF) to produce energy or other usable products, which involves carbon diversion at primary treatment and waste activated sludge (WAS) from biological treatment processes. Many WRRFs are also driven to meet stringent effluent nutrient discharge targets while minimizing energy usage and chemical addition. Nutrient removal systems still rely on biodegradable organic carbon to support denitrification and enhanced biological phosphorus removal (EBPR). Biological nutrient removal not only requires sufficient organic substrate, but also the right type of bioavailable carbon for optimal utilization. The main objective of this pilot fermentation testing was to evaluate the most effective utilization of the range of organic-carbon rich feedstocks within a WRRF. Preliminary results suggest that a 50–50 blend of primary sludge (PS) and return activated sludge (RAS) fermentation leads to highest volatile fatty acid (VFA) yield. PS fermentation resulted in the minimum nutrients release per unit of volatile suspended solids (VSS), which makes it a best suited for biological nutrients removal WRRFs with stringent nitrogen (N) and phosphorus (P) limits. The volatile fatty acids fractions produced from different combinations of RAS and PS can impact the most suitable end use for each sludge type fermentation. PS resulted into higher levels of propionate, which are ideal for selecting phosphate accumulating organisms (PAO) over glycogen-accumulating organisms (GAO). On the other hand, for denitrification, acetate is the preferred substrate, which was most abundant with RAS only fermentation. Our research outcomes will be of value to utilities aiming to integrate the stringent effluent nutrient (N and P) discharge targets with energy and resource recovery.

Synergistic reduction of pollution and carbon mitigation in constructed wetlands-microbial fuel cell using sludge-derived biochar

Integrating microbial fuel cells (MFC) into constructed wetland systems (CW) has been an efficient wastewater treatment to improve the pollutants removal and regenerate power energy. This study fabricated a sludge biochar material (SBM) to sequestrate the carbon of residual sludge. Thereafter used SBM and modified SBM as the substrate materials to construct three groups of CW-MFC for decreasing the greenhouse gas (GHG) emission. The water quality improvement in removal efficiency achieved (2.59 %, 3.10 %, 5.21 % for COD; 3.31 %, 3.60 %, 6.71 % for TN; 1.80 %, 7.38 %, 4.93 % for TP) by the application of MFC, SBM, and modified SBM in wastewater treatment, respectively. Additionally, the reduction in global warming potential (GWP) realized 17.2 %, 42.2 %, and 64.4 % resulting from these applications. The carbon flow and fate diagrams showed MFC shifted the gas phase‑carbon flow from CH4 to CO2, and SBM promoted this shift trends. Microbial diversity indicated enrichment of electrochemically active bacteria (EAB), denitrifying bacteria, and phosphate accumulating organisms (PAOs) by SBM. Metabolic pathways analysis showed that introduction of MFC and SBM exhibited significant increases of key functional genes in metabolic pathway of anaerobic oxidation of methane (AOM). This study highlights the benefit of CW-MFC in and provides a new strategy for removing pollutants and abating GHG emissions in wastewater treatment.

Towards low carbon demand and highly efficient nutrient removal: Establishing denitrifying phosphorus removal in anaerobic/anoxic/oxic + nitrification system

A two-sludge anaerobic/anoxic/oxic + nitrification system with simultaneous nitrogen and phosphorus removal was studied for enhanced low-strength wastewater treatment. After 158 days of operation, excellent NH4+-N, chemical oxygen demand (COD) and PO43−-P removal (99.0 %, 90.0 % and 92.0 %, respectively) were attained under a low carbon/nitrogen ratio of 5, resulting in effluent NH4+-N, COD and PO43−-P concentrations of 0.3, 30.0 and 0.5 mg/L, respectively. The results demonstrate that the anaerobic/anoxic/oxic sequencing batch reactor (A2-SBR) and nitrification sequencing batch reactor (N-SBR) had favorable denitrifying phosphorus removal and nitrification performance, respectively. High-throughput sequencing results indicate that the phosphate-accumulating organisms Dechloromonas (1.1 %) and Tetrasphaera (1.2 %) were enriched in the A2-SBR, while the ammonia-oxidizing bacteria Nitrosomonas (7.8 %) and the nitrite-oxidizing bacteria Nitrospira (18.1 %) showed excellent accumulation in the N-SBR. Further analysis via functional prediction revealed that denitrification is the primary pathway of nitrogen metabolism throughout the system. Overall, the system achieved low carbon and high efficiency nutrient removal.

Bacterial community and filamentous population of industrial wastewater treatment plants in Belgium.

The discharge of industrial water requires the removal of its pollutants, where biological wastewater treatment plants (WWTPs) are the most used systems. Biological WWTPs make use of activated sludge (AS), where bacteria are responsible for the removal of pollutants. However, our knowledge of the microbial communities of industrial plants is limited. Understanding the microbial population is essential to provide solutions to industrial problems such as bulking. The aim of this study was to identify at a high taxonomic resolution the bacterial population of 29 industrial WWTPs using 16S rRNA amplicon sequencing. Our results revealed that the main functional groups were dominated by Thauera and Zoogloea within denitrifiers, Dechloromonas in phosphate-accumulating organisms, and Defluviicoccus in glycogen-accumulating organisms. The activated sludge characterization indicated that 59% of the industrial plants suffered from bulking sludge, with DSVI values of up to 448 mL g-1. From the bulking cases, 72% corresponded to filamentous bulking with Thiothrix as the most abundant filament; meanwhile, the other 28% corresponded to viscous bulking sludge in which Zoogloea was the most abundant genus. Furthermore, the bacterial population did not share a core of taxa across all industrial plants. However, 20 genera were present in at least 50% of the plants comprising the general core, including Thauera, Ca. Competibacter, and several undescribed microorganisms. Moreover, statistical analysis revealed that wastewater salinity strongly affected the microbial richness of the industrial plants. The bacterial population across industrial plants differed considerably from each other, resulting in unique microbial communities that are attributed to the specificity of their wastewaters. KEY POINTS: • The general core taxa of industrial plants were mostly made up of undescribed bacterial genera. • Filamentous bacteria constituted on average 4.1% read abundance of the industrial WWTPs. • Viscous bulking remains a significant type of bulking within industrial WWTPs.

Study on culture of stable aerobic granular sludge

In this study, three reactors were established with anaerobic plug-flow times of 1.5 hours, 1 hour, and 0.5 hours. The results indicated that the anaerobic plug-flow time of 1 hour constructed favorable "feast- famine" period ratio, promoting the enrichment of microorganisms that stored and utilized the internal carbon source, such as Phosphate and Glycogen Accumulating Organisms (PAO and GAO). This resulted in the formation of granular sludge with both short granulation time and structural stability. In contrast, shortening the anaerobic feed time to 0.5 hours was detrimental to the growth of GAO, leading to slow granularization of aerobic sludge. The anaerobic influent time of 1.5 h leads to the shortening of starvation period and poor stability of particle structure.

New insight into the granule formation in the reactor for enhanced biological phosphorus removal.

While granulated activated sludge exhibits high productivity, the processes of granule formation are incompletely studied. The processes of granule formation and succession of communities were investigated in a laboratory sequencing batch reactor (SBR) under conditions for enhanced biological phosphorus removal (EBPR) using microbiological and molecular techniques. Active consumption of acetate, primarily by the phosphate-accumulating organisms (PAO), commenced at day 150 of cultivation. This was indicated by the high ratio of molar P-released/acetate uptake (0.73-0.77 P-mol/C-mol), characteristic of PAO. During this period, two types of granule-like aggregates formed spontaneously out of the activated sludge flocs. The aggregates differed in morphology and microbial taxonomic composition. While both aggregate types contained phosphorus-enriched bacterial cells, PAO prevailed in those of morphotype I, and glycogen-accumulating organisms (GAOs) were predominant in the aggregates of morphotype II. After 250 days, the elimination of the morphotype II aggregates from the reactor was observed. The subsequent selection of the community was associated with the development of the morphotype I aggregates, in which the relative abundance of PAO increased significantly, resulting in higher efficiency of phosphorus removal. Metagenomic analysis revealed a predominance of the organisms closely related to Candidatus Accumulibacter IС and IIС and of Ca. Accumulibacter IIB among the PAO. Based on the content of the genes of the key metabolic pathways, the genomes of potential PAO belonging to the genera Amaricoccus, Azonexus, Thauera, Zoogloea, Pinisolibacter, and Siculibacillus were selected. The patterns of physicochemical processes and the microbiome structure associated with granule formation and succession of the microbial communities were revealed.

Microbial removal of nutrients from anaerobic digestate: assessing product-coupled and non-product-coupled approaches.

Although anaerobic digestate contains >90% water, the high nutrient content of digestate makes it economically and technically intractable to treatment by existing wastewater treatment technologies. This study separately assessed the feasibility of nutrient removal from digestate by Rhizopus delemar DSM 905 and a culture of phosphate-accumulating organisms (PAOs). With Rhizopus delemar DSM 905, we investigated concomitant nutrient removal from digestate-supplemented medium and fumaric acid production, as a potentially economical strategy for digestate treatment. Following the cultivation of R. delemar DSM 905 in a fermentation medium containing 25% (v/v) digestate, the concentrations of Al, Cr, Cu, Fe, K, Mg, Mn, Pb, and Zn reduced 40, 12, 74, 96, 12, 26, 23%, ~18, and 28%, respectively. Similarly, the concentrations of total phosphorus, total nitrogen, phosphate (PO4-P), ammonium (NH4-N), nitrate (NO3-N), and sulfur decreased 93, 88, 97, 98, 69, and 13%, respectively. Concomitantly, cultures supplemented with 25 and 15% (v/v) digestate produced comparable titers of fumarate (~11 and ~ 17 g/L, respectively) to the digestate un-supplemented control cultures. With PAOs, we assessed the removal of total phosphorus, total nitrogen, PO4-P, and NH4-N, of which the concentrations reduced 86, 90%, ~99, and 100%, respectively in 60% (v/v) digestate. This study provides additional bases for microbial removal of excess nutrients from anaerobic digestate, with the potential to engender future water recovery from this waste stream that is currently largely recalcitrant to treatment.

Oxygen Uptake Rate as an Indicator of the Substrates Utilized by Candidatus Accumulibacter

Candidatus Accumulibacter belongs to phosphate-accumulating organisms (PAOs) which exhibit a cyclic metabolism and are capable of intracellular polyphosphate accumulation and their hydrolysis under feast-famine anaerobic-aerobic cycling. In consortia of activated sludge microorganisms, these bacteria are responsible for enhanced biological phosphorus removal (EBPR). The spectrum of the substrates used by Ca. Accumulibacter remains insufficiently studied. It was investigated by measuring the oxygen uptake rates (OUR) of Ca. Accumulibacter-enriched culture supplemented with 17 different organic substrates. The highest oxygen uptake rate values were observed in the presence of tryptone, volatile fatty acids (acetate, propionate, and butyrate), succinate, pyruvate, and amino acids (aspartate and glutamate). Phosphate dynamics in the medium under shifts from anaerobic to aerobic cultivation in batch experiments were studied for these compounds (except for tryptone). All tested substrates were shown to cause phosphate cycling (release in the anaerobic phase and uptake in the aerobic one), with OURs for the substrates correlating with the number of phosphates consumed during the aerobic phase. It was concluded that OUR may be used as an indicator of the monosubstrates used by Ca. Accumulibacter in the anaerobic/aerobic cycle. The possible pathways for substrate transport and metabolism by Ca. Accumulibacter are discussed using stoichiometric data and the results of metagenomic analysis.

Unraveling microbial characteristics of simultaneous nitrification, denitrification and phosphorus removal in a membrane-aerated biofilm reactor

This study describes the simultaneous removal of carbon, ammonium, and phosphate from domestic wastewater by a membrane-aerated biofilm reactor (MABR) which was operated for 360 days. During the operation, the maximum removal efficiencies of chemical oxygen demand (COD), total nitrogen (TN) and total phosphorus (TP) reached 93.1%, 83.98%, and 96.41%, respectively. Statistical analysis showed that the MABR could potentially treat wastewater with a high ammonium concentration and a relatively low C/N ratio. Dissolved oxygen and multiple pollutants, including ammonium, carbon, phosphate, and sulfate, shaped the structure of the microbial community in the MABR. High throughput sequencing uncovered the crucial microbiome in ammonium transformation in MABR. Phylogenetic analysis of the ammonia monooxygenase (amoA) genes revealed an important role for comammox Nitrospira in the nitrification process. Diverse novel phosphate-accumulating organisms (Thauera, Bacillus, and Pseudomonas) and sulfur-oxidizing bacteria (Thiobacillus, Thiothrix and Sulfurimonas) were potentially involved in denitrification in MABR. The results from this study suggested that MABR could be a feasible system for the simultaneous removal of nitrogen, carbon, phosphorus, and sulfur from sewage water.

Effect of different enrichment methods on the independent biological phosphorus removal performance after nitrogen removal using immobilized fillers

In order to find a biological phosphorus removal enrichment method with high performance and low energy consumption, two enrichment methods were used in this study, namely gradient carbon source addition (S1) and fixed carbon source addition (S2). The two enrichment methods were applied to the enrichment of phosphorus removing bacteria in an independent biological phosphorus removal system based on nitrogen removal by immobilized fillers. The phosphorus removal performance, stoichiometry and microbial structure were compared for the two enrichment methods. It was found that PO43--P remained 0.15–0.2 mg/L at the end of enrichment in S1, while PO43--P increased from 0.27 to 0.38 mg/L at the end of enrichment in S2. Stoichiometric analysis showed that S1 used more PHAs (1.47 molC/L) for phosphorus absorption, while S2 used nearly half of the PHAs (0.87 molC/L) for glycogen synthesis. Moreover, the absorbed phosphorus content in S2 was significantly less than S1 (5.67 < 8.65 mg/L). As a result, denitrifying phosphorus-removing bacteria predominated S1, while phosphate-accumulating organisms (PAOs) and glycogen-accumulating organisms (GAOs) both played a role in S2. Dechloromonas, the dominant denitrifying PAO in both S1 and S2 increased from 0.26 % to 3.34 % and 1.04 %, respectively, while Defluviicoccus, a typical GAO, changed from 0.24 % to 0.2 % and 2.01 %, respectively. As a result, gradient carbon source enrichment demonstrated a better phosphorus removal effect and dominant bacteria, whereas the fixed carbon source enrichment increased the abundance of GAOs while negatively impacting the phosphorus removal effect.

Effect of influent ammonia nitrogen concentration on the phosphorus removal process in the aerobic granular sludge reactor

The effects of different influent ammonia nitrogen (NH3-N) concentrations (stage I to IV: 20, 40, 60 and 80 mg/L) on the phosphorus (P) removal process were studied in an aerobic granular sludge (AGS) reactor under anaerobic/aerobic operating conditions. The phosphorous removal performance kept stable at first (stage I and II) and then significantly deteriorated at further increase of influent NH3-N concentration (stage III and IV). On the process of microbial metabolism, further increase of NH3-N aggravated the competition between phosphate accumulating organisms (PAOs) and glycogen accumulating organisms (GAOs) for carbon sources in the anaerobic phase, and weakened the P absorption capacity of PAOs in the aerobic phase. Denitrifying phosphate accumulating organisms (DPAOs) showed higher resistance to the increase of NH3-N concentration than traditional PAOs. On the functional structure of the system, microorganisms related to phosphorus removal in the system were mainly enriched in the granules, while microorganisms with heterotrophic denitrifying function dominated the sludge flocs to obtain higher growth advantage at high ammonia nitrogen concentration. The results of this study provide more insight into the biological stability of AGS systems.

Effect of Diclofenac Concentration on Activated Sludge Conditions in a Biological Wastewater Treatment Plant

Significant quantities of pharmaceutical substances enter biological wastewater treatment plants, where they interact with activated sludge microorganisms. An example of a pharmaceutical commonly used is the non-steroidal anti-inflammatory drug diclofenac (DCF). The presence of high concentrations of DCF in wastewater can disrupt nutrient removal processes, which are highly sensitive to external environmental factors. This paper discusses the effect of high DCF concentrations (1.04 mg/dm3–12.5 mg/dm3; 0.25 mg/gTS–3.0 mg/gTS) on the efficiency of nitrifying, denitrifying and phosphate-accumulating organisms in the wastewater treatment cycle. The condition of the activated sludge was assessed on the basis of the oxygen and nitrogen uptake rates values and the ability to biologically remove phosphorus compounds from the wastewater. The effect of DCF on the ability of methane-forming bacteria to produce biogas in the anaerobic digester was also investigated. None of the biochemical reactions of activated sludge were inhibited at applied DCF concentrations. A 33% reduction in biogas production was observed at a DCF dose of 0.0391 mg/gTS. Slight deviations from the typical course of biochemical transformation of ammonium compounds were recorded at a DCF concentration of 3 mg/gTS of sludge. However, in the concentration range studied, no negative effect of DCF, on the operation of the activated sludge, was found.

A new insight in enhancing phosphate enrichment in biofilm process: Comparison of the key metabolic pathways in highly-efficient and dominant PAOs based on metagenomics

The formation of dominant phosphate-accumulating organisms (PAOs) is essential for the high enrichment of phosphate in biofilm sequencing batch reactors (BSBR) for phosphorus recovery. The dominant PAOs in the biofilm process have not been isolated and purified, and the key metabolic pathways that promote the formation of dominant PAOs are still unclear. In this study, four strains of highly-efficient PAOs were obtained by an innovative isolation procedure. The relationship between the abundance of highly-efficient and dominant PAOs and the phosphate removal ability was compared. We found that the abundance of PAOs was positively correlated with the phosphate removal efficiency in vitro pure culture and complex biofilm process. Metagenomics analysis revealed that compared with highly-efficient PAOs cultured in vitro, dominant PAOs in biofilms had unique key metabolic pathways, F-ATPases and N-Acyl homoserine lactones (AHLs). F-ATPases are important for maintaining the proton motive force (PMF) required for the uptake of carbon sources by PAOs, and AHLs are participating in phosphate metabolism through quorum sensing (QS) mediated secretion of extracellular polymeric substance (EPS). The formation of dominant PAOs was promoted by optimizing carbon source uptake and phosphate metabolism. This study revealed that the difficult isolation of dominant PAOs was due to the AHLs-mediated QS, and we identified the key pathways regulating the formation of dominant PAOs in biofilms through genomics analysis. Our findings provide insights in enhancing phosphate enrichment in BSBR by modulating the components of microbial community under the low concentration of carbon source consumption.

Effects of adding different ratios of residual sludge and food waste co-anaerobic fermentation liquid to AAO wastewater treatment process

Carbon sources are the main bottleneck which limit the biological treatment of wastewater. In this study, the effects of temperature on the preparation of RFCF and focused on exploring the removal of pollutants in wastewater treatments by the addition of different ratios of CFRF were investigated using residual sludge and food waste co-anaerobic fermentation liquid (RFCF) as external carbon sources. The results showed that anaerobic fermentation at 40 °C had elevated the concentrations of NH4+-N, TN, and volatile fatty acids (VFAs) in the RFCF. It was found that under anaerobic fermentation at 20 °C, increases in RFCF additions significantly increased the average removal rates of NH4+-N, TN and TP by 30.44 %, 66.51 % and 60.90 %. The increase in nitrogen and phosphorus removal efficiency was mainly attributed to the increase of RFCF addition promoting the relative abundance of denitrifiers, denitrification functional genes and phosphate accumulating organisms (PAOs), and phosphorus metabolism functional genes. The control guidelines for the RFCF addition amounts were dependent on the pollutant removal indexes. Therefore, this study is an important guide to the practical engineering application of RFCF.

Towards low carbon demand and highly efficient nutrient removal: Establishing denitrifying phosphorus removal in a biofilm-based system

The combined denitrifying phosphorus removal (DPR) and Anammox process is expected to achieve advanced nutrient removal with low carbon consumption. However, exchanging ammonia/nitrate between them is one limitation. This study investigated the feasibility of conducting DPR in a biofilm reactor to solve that problem. After 46-day anaerobic/aerobic operation, high phosphorus removal efficiency (PRE, 83.15 %) was obtained in the activated sludge (AS) and biofilm co-existed system, in which the AS performed better. Phosphate-accumulating organisms might quickly adapt to the anoxic introduced nitrate, but the following aerobic stage ensured a low effluent orthophosphate (<1.03 mg/L). Because of waste sludge discharging and AS transforming to biofilm, the suspended solids dropped below 60 mg/L on Day 100, resulting in PRE decline (17.17 %) and effluent orthophosphate rise (4.23 mg/L). Metagenomes analysis revealed that Pseudomonas and Thiothrix had genes for denitrification and encoding Pit phosphate transporter, and Candidatus_Competibacter was necessary for biofilm formation.

Application Potential of Constructed Wetlands on Different Operation Mode for Biologically Pre-Treatment of Rural Domestic Wastewater

In order to satisfy the requirements of rural domestic sewage, a bio-ecological combination system was proposed, including a biological treatment section (anaerobic hydrolysis tank and aerobic tank) and an ecological post-treatment section. This study observed the application potential of constructed wetlands (CW) on different operation modes for biologically pre-treated rural domestic wastewater. The organics and nutrient removal efficiency of the tidal flow constructed wetland (TFCW) and the horizontal subsurface flow constructed wetland (HFCW) were compared at a temperature range of 20–40 °C. During the stable phase, the higher chemical oxygen demand (COD), ammonia nitrogen (NH4+-N), and total phosphorus (TP) removal efficiencies existed in TFCW than HFCW, corresponding to the efficiency of COD 69.46%, NH4+-N 96.47%, and TP 57.38%, but lower performance on COD (61.43%), NH4+-N (84.99%), and TP (46.75%) removal in HFCW, which should be attributed to the increasement of aerobic heterotrophic bacteria (Arthrobact and Sphingomonas), nitrifiers (Nitrospira), and phosphate accumulating organisms (PAOs) (Pseudomonas). The microbial biomass was also increased from 2.13 ± 0.14 mg/g (HFCW) to 4.64 ± 0.18 mg/g (TFCW), which proved to strengthen the formation and growth of biofilm under a better oxygen supplement. Based on the relative abundance of functional genera in the microbial community, it showed that TFCW was more favorable for promoting the growth of heterotrophic bacteria, nitrifiers, and phosphate-accumulating organisms (PAOs). When temperature changed from −4 °C to 15 °C, the two-stage constructed wetlands (TFCW-HFCW and HFCW-TFCW) were used for improving the performance of pollutants removal. The results demonstrated that the effluent concentrations of TFCW-HFCW and HFCW-TFCW met the Class 1A discharge standard of DB32/3462-2020 in JiangSu Province, China. Therefore, this study will provide a useful and easy-to-implement technology for the operation as an ecological post-treatment section.

Influence of salt addition to stimulating biopolymers production in aerobic granular sludge systems

The influence of salt addition to stimulating biopolymers production in aerobic granular sludge (AGS) systems was evaluated. The control systems (R1: acetate and R2: propionate) initially obtained less accumulation of mixed liquor volatile suspended solids (MLVSS), indicating that the osmotic pressure in the salt-supplemented systems (R3: acetate and R4: propionate) contributed to biomass growth. However, the salt-supplemented systems collapsed between days 110 and 130 of operation. R3 and R4 showed better performance regarding nutrients removal due to the greater abundance of nitrifying and denitrifying bacteria and phosphate-accumulating organisms. Salt also contributed to the higher production of biopolymers such as alginate-like exopolymers (ALE) per gram of volatile suspended solids (VSS) (R1: 397 mgALE∙gVSS−1, R2: 140 mgALE∙gVSS−1, R3: 483 mgALE∙gVSS−1, R4: 311 mgALE∙gVSS−1). Amino acids like tyrosine and tryptophan were better identified in extracellular polymeric substances extract from salt-operated reactors. This study brings important results in the context of resource recovery by treating saline effluents.