Enhanced phosphorus recovery and biofilm microbial community changes in an alternating anaerobic/aerobic biofilter

Glycogen-accumulating organisms promote phosphate recovery from wastewater by pilot-scale biofilm sequencing batch reactor: Performance and mechanism

A high phosphate (P) recovery concentration was achieved in pilot-scale biofilm sequencing batch reactor (BSBR) with a low carbon source (C) cost. Especially, a high-abundance glycogen-accumulating organisms (GAOs) (13.93-31.72%) was detected that was accompanied by a high P recovery concentration of BSBR. High-abundance GAOs obtain additional C through various C compensation pathways (split tricarboxylic acid cycle (TCA cycle), glyoxylate shunt and gluconeogenesis), thus reducing the need to compete with polyphosphate-accumulating organisms (PAOs) for C and weakening the adverse effects on P recovery by PAO cells. Under the action of N-acyl homoserine lactones (AHLs)-mediated quorum sensing (QS), GAOs promoted the secretion of a large amount of extracellular polymeric substances (EPS), which helped to realize the P recovery of EPS-dominated biofilms (68.02%-96.89%). This study provides a low-carbon technology for the recovery of high concentration P from municipal wastewater, and improves the ecological theory of P recovery in collaboration with GAOs and PAOs.

Formation mechanism of high biofilm phosphorus storage capacity and its effect on phosphorus uptake-release and carbon source consumption

Phosphorus recovery from wastewater is an effective method to alleviate the shortage of phosphorus resources. The biofilm phosphorus recovery process can realize simultaneous removal and enrichment of phosphorus in wastewater. In this study, a sequencing batch biofilm reactor was constructed to study the rapid phosphorus release and slow phosphorus release stages in the phosphorus recovery cycle. The relationship between high biofilm phosphorus storage capacity (Pbiofilm), phosphorus recovery solution concentration, phosphorus uptake-release behavior and carbon source consumption were explored. The increase in phosphorus recovery solution concentration promotes the elevation of Pbiofilm, which, conversely promotes phosphorus release in the next recovery cycle. In addition, the distinct phosphorus uptake-release characteristics of extracellular polymeric substances and cells were illustrated. This study provides a theoretical foundation to elevate the phosphorus recovery efficiency and reduce carbon source consumption in biofilm phosphorus recovery process.

Phosphate recovery from urban sewage by the biofilm sequencing batch reactor process: Key factors in biofilm formation and related mechanisms

The biofilm sequencing batch reactor (BSBR) technique has been deployed in the laboratory to enrich phosphorus from simulated wastewater, but it is still not clear what its performance will be when real world sewage is used. In this work, the effluent from the multi-stage anoxic-oxic (AO) activated sludge process at a sewage plant was used as the feed water for a BSBR pilot system, which had three reactors operating at different levels of dissolved oxygen (DO). The phosphorus adsorption and release, the biofilm growth, and the extracellular polymeric substances (EPS) components and contents were examined. The microbial communities and the signaling molecules N-acyl-l-homoserine lactones (AHLs) were also analyzed. Gratifyingly, the BSBR process successfully processed the treated sewage, and the biofilm developed phosphorus accumulation capability within 40 days. After entering stable operation, the system concentrated phosphate from 2.59 ± 0.77 mg/L in the influent to as much as 81.64 mg/L in the recovery liquid. Sludge discharge had profound impacts on all aspects of BSBR, and it was carried out successfully when the phosphorus absorption capacity of the biofilm alone was comparable to that of the reactor containing the activated sludge. Shortly after the sludge discharge, the phosphate concentration of the recovery liquid surged from 50 to 140 mg/L, the biofilm thickness grew from 20.56 to 67.32 μm, and the diversity of the microbial population plunged. Sludge discharge stimulated Candidatus competibacter to produce a large amount of AHLs, which was key in culturing the biofilm. Among the AHLs, both C10-HSL and 3OC12-HSL were significantly positively correlated with EPS and the abundance of Candidatus competibacter. The current results demonstrated BSBR as a viable option to enrich phosphorus from real world sewage with low phosphorus content and fluctuating chemistry. The mechanistic explorations also provided theoretical guidance for cultivating phosphorus-accumulating biofilms.

Clarification of the phosphorus release mechanism for recovering phosphorus from biofilm sludge in alternating aerobic/anaerobic biofilm system

A novel wastewater treatment plant process was constructed to overcome the challenge of simultaneous nitrate removal and phosphorus (P) recovery. The results revealed that the P and nitrate removal efficiency rose from 39.0 % and 48.4 % to 92.8 % and 93.6 % after 136 days of operation, and the total P content in the biofilm (TPbiofilm) rose from 15.8 mg/g SS to 57.8 mg/g SS. Moreover, the increase of TPbiofilm changed the metabolic mode of denitrifying polyphosphate accumulating organisms (DPAOs), increasing the P concentration of the enriched stream to 172.5 mg/L. Furthermore, the acid/alkaline fermentation led to the rupture of the cell membrane, which released poly-phosphate and ortho-phosphate of cell/EPS in DPAOs and released metal‑phosphorus (CaP and MgP). In addition, high-throughput sequencing analysis demonstrated that the relative abundance of DPAOs involved in P storage increased, wherein the abundance of Acinetobacter and Saprospiraceae rose from 8.0 % and 4.1 % to 16.1 % and 14.0 %. What's more, the highest P recovery efficiency (98.3 ± 1.1 %) could be obtained at optimal conditions for struvite precipitation (pH = 7.56 and P: N: Mg = 1.87:3.66:1) through the response surface method (RSM) simulation, and the precipitates test analysis indicated that P recovery from biofilm sludge was potentially operable. This research was of great essentiality for exploring the recovery of P from biofilm sludge.

Metagenomics, metatranscriptomics, and proteomics reveal the metabolic mechanism of biofilm sequencing batch reactor with higher phosphate enrichment capacity under low phosphorus load

The biofilm sequencing batch reactor (BSBR) process has higher phosphate recovery efficiency and enrichment multiple when the phosphorus load is lower, but the mechanism of phosphate enrichment at low phosphorus load remains unclear. In this study, we operated two BSBR operating under low and high phosphorus load (0.012 and 0.032 kg/(m3·d)) respectively, and used metagenomic, metatranscriptomic, and proteomics methods to analyze the community structure of the phosphorus accumulating organisms (PAOs) in the biofilm, the transcription and protein expression of key functional genes and enzymes, and the metabolism of intracellular polymers. Compared with at high phosphorus load, the BSBR at low phosphorus load have different PAOs and fewer types of PAOs, but in both cases the PAOs must have the PHA, PPX, Pst, and acs genes to become dominant. Some key differences in the metabolism of PAOs from the BSBR with different phosphorus load can be identified as follows. When the phosphorus load is low, the adenosine triphosphoric acid (ATP) and NAD(P)H in the anaerobic stage come from the TCA cycle and the second half of the EMP pathway. The key genes that are upregulated include GAPDH, PGK, ENO, ppdk in the EMP pathway, actP in acetate metabolism, phnB in polyhydroxybutyrate (PHB) synthesis, and aceA, mdh, sdhA, and IDH1 in the TCA cycle. In the meantime, the ccr gene in the PHV pathway is inhibited. As a result, the metabolism of the PAOs features low glycogen with high PHB, Pupt, Prel, and low PHV. That is, more ATP and NAD(P)H flow to phosphorus enrichment metabolism, thus allowing the highly efficient enrichment of phosphorus from low concentration phosphate thanks to the higher abundance of PAOs. The current results provide theoretical support and a new technical option for the enrichment and recovery of low concentrations of phosphate from wastewater by the BSBR process.

Enhanced biological phosphorus removal by high concentration powder carrier bio-fluidized bed (HPB): Phosphorus distribution, cyclone separation, and metagenomics

This study provides a comparative investigation of phosphorus removal between anaerobic-anoxic-oxic (AAO) and high-concentration powder carrier bio-fluidized bed (HPB) in the same full-scale wastewater treatment plant. The results showed that the total phosphorus removal of HPB was 71.45%-96.71%. Compared with AAO, the total phosphorus removal of HPB can be increased by a maximum of 15.73%. The mechanisms of enhanced phosphorus removal by HPB include the followings. Biological phosphorus removal was significant. The anaerobic phosphorus release capacity of HPB was enhanced and polyphosphate (Poly-P) in the excess sludge of HPB was 1.5 times higher than that of AAO. The relative abundance of Candidatus Accumulibacter was 5 times higher than that of AAO, and oxidative phosphorylation and butanoate metabolism were enhanced. The analysis of phosphorus distribution showed that cyclone separation increased the chemical phosphorus precipitation (Chem-P) in the excess sludge by 16.96% to avoid accumulation in the biochemical tank. The phosphorus adsorbed by extracellular polymeric substance (EPS) in the recycled sludge was stripped, and the EPS bound-P in the excess sludge increased by 1.5 times. This study demonstrated the feasibility of HPB to improve the phosphorus removal efficiency for domestic wastewater.

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.

Biomineralization and AHLs-guided quorum sensing enhanced phosphorus recovery in the alternating aerobic/anaerobic biofilm system under metal ion stress

The alternating aerobic/anaerobic biofilm system had been applied for phosphorus (P) enrichment and recovery because of the advantage of low energy consumption and high efficiency. The metal ions and N-acyl-L-homoserine lactones (AHLs) in system were studied to better clarify the mechanism of P uptake/release under metal ion stress. The results indicated that the increase of metal ions stimulated the release of AHLs, and AHLs-guided quorum sensing (QS) enhanced P uptake. Moreover, biomineralization could stimulate the increase of P content in biofilm (P_biofilm). Meanwhile, some ortho-p was converted to short-chain poly-p in extracellular polymer substance (EPS), and others were transferred into cell through EPS to synthesize poly-p. With the P_biofilm increased, more P could be absorbed/released due to the shift in the metabolic model of polyphosphate accumulating organisms (PAOs). The release of AHLs between microorganisms was also inhibited when PAOs reached the state of P saturation (75.6 ± 2.5 mg/g SS), which meant that the effect of signaling function would tend to stabilize, and the 169.2 ± 2.6 mg/L P concentration in the enriched solution was obtained due to the P release was inhibited. Moreover, P was rapidly transferred to the new enriched solution after the P was recovered, and PAOs restored its capability of P uptake/release. In addition, ³¹P-NMR analysis demonstrated that EPS played a major role in PAOs compared to cell, and inorganic phosphorus (IP) played an essential role in the uptake/release of P compared to organic phosphorus (OP). Furthermore, the microbiological analysis showed that Candidatus Accumulibacter was positively correlated with AHLs (P < 0.05). This study provided essential support for clarifying the P metabolism mechanism of PAOs.

Performance evaluation and microbial community structure of a modified trickling filter and conventional activated sludge process in treating urban sewage

This study compares the performance and microbial composition of a conventional activated sludge process (ASP) with a modified trickling filter (MTF) for urban sewage treatment. MTF (2 h HRT with effluent recycling) and ASP (8 h HRT) showed >60 % removal efficiency for COD, NH₃-N and PO₄^3--P. MTF outperformed ASP in denitrification and 5 mg/L of NO₃^--N was detected in the effluent of MTF. The widespread distribution of nitrogen removal functional genes (amoA, nirK, nirS, napA, narG and nosZ) in MTF indicates simultaneous nitrification and denitrification (SND) as a key process controlling nitrogen removal. In addition, Miseq sequencing was used to examine the microbial community composition in MTF and ASP. The sequencing result revealed that Proteobacteria, Planctomycetes, Chloroflexi and Actinobacteriota were the dominant phyla in both MTF and ASP. Moreover, the co-occurrence of various nitrifiers, denitrifiers, aerobic denitrifiers, and ANAMMOX bacteria in MTF suggested their role in nitrogen removal.

Study on community structure and metabolic mechanism of dominant polyphosphate-accumulating organisms (PAOs) and glycogen-accumulating organisms (GAOs) in suspended biofilm based on phosphate recovery

Biofilm sequencing batch reactor (BSBR) can achieve efficient phosphate (P) removal and enrichment, but its process performance and metabolic mechanisms for P removal and enrichment of municipal wastewater remain largely unclear. In the present study, we assessed the P removal and enrichment of municipal wastewater at influent P concentrations of 2.5 mg/L and 10 mg/L. The efficiency of P removal and enzyme activity in polyphosphate-accumulating organisms (PAOs) and glycogen-accumulating organisms (GAOs) were compared, and the growth and metabolic characteristics of dominant PAOs and GAOs at different influent P concentrations were studied with the macro-sequencing technology. The results showed that the P recovery efficiencies were 70.03% and 76.19% when the influent P concentration was 2.5 mg/L and 10 mg/L in BSBR, respectively, and the maximum P concentration of recovery liquid was 81.29 mg/L and 173.12 mg/L, respectively. There were no phosphate kinase (PPK) and phosphate hydrolase (PPX) in extracellular polymeric substances (EPS). The dominant PAOs were Candidatus_Contendobacter, Dechloromonas, and Flavobacterium, and the dominant GAO was Candidatus_Competibacter. The abundance of Candidatus_Contendobacter was the highest with the most potential contribution to P removal. PAOs had competitive advantages in carbon (C) source uptake, glycogen metabolism, P metabolism, and adenosine triphosphate (ATP) metabolism. HMP was unique to PAOs, EMP had the highest abundance in glycogen metabolism, and ED was contained in PAOs of BSBR. These results indicated that BSBR provided sufficient reducing power and ATP for PAOs through different glycogen decomposition pathways to promote P uptake and obtained competitive advantages in P metabolism, C source uptake, and ATP utilization to achieve efficient P removal and enrichment. Collectively, our current findings provided valuable insights into the P removal and enrichment mechanism of BSBR in municipal sewage.

Phosphorus recovery in the alternating aerobic/anaerobic biofilm system: Performance and mechanism

To balance the high phosphorus concentration in recirculated solution and the stability of biofilm system, this study explored the performance and mechanism of phosphorus uptake/release for recovering phosphorus from sewage when the phosphorus content in biofilm (P_biofilm) changed. The results showed that the maximum phosphorus concentration in the concentrated solution reached 171.2 ± 2.5 mg·L^-1 in harvest 1st-5th stages. Polyphosphate accumulating organisms (PAOs) performed a metabolic shift from glycogen accumulation metabolism (GAM) to polyphosphate accumulation metabolism (PAM) when P_biofilm increased at each phosphorus enrichment stage, and more phosphorus was absorbed/released by PAOs. Nevertheless, the release of poly-phosphate from PAOs was inhibited after phosphorus concentration stabilized, and PAOs were unable to absorb phosphorus from wastewater as it reached the phosphorus saturation stage. To maintain the stability of the system, phosphorus had to be harvested so that the saturated phosphorus in PAOs was easily released in a new recirculated solution, resulting in adequate storage space for PAOs to absorb phosphorus. Meanwhile, the ³¹P NMR analysis demonstrated that phosphorus was stored in EPS and cell of PAOs, whereas EPS played a significant role than cell at the anaerobic phase. Particularly, ortho-phosphate was the major component of phosphorus release by EPS and poly-phosphate was the major part of phosphorus release by cell. Furthermore, the change of P_biofilm had no impact on biofilm characteristics and microbial communities, whereas some PAOs would be enriched, and others that were not suitable for this process would be inhibited with repeated cycles of alternating aerobic/anaerobic operation.

A new strategy for obtaining highly concentrated phosphorus recovery solution in biofilm phosphorus recovery process

Recovery of phosphorus (P) from wastewater is of great significance for alleviating the shortage of P resources. At present, the P recovery process is faced with the problem of excessive organic carbon consumption when obtaining a P-concentrated recovery solution. This study proposed a new strategy to obtain a more highly concentrated P recovery solution with minimal carbon consumption by strengthening the P storage capacity of the biofilm. A biofilm sequencing batch reactor (BSBR) process was modified to treat synthetic wastewater. The effect of the dissolved oxygen (DO) concentration on the P storage capacity of the biofilm was investigated at DO concentrations of DO 3.5 mg/L (P_L) and DO 6.5 mg/L (P_H). The results showed a maximum P storage of 101.2 and 149.6 mg-P/g-mixed liquid suspended solids under the two conditions. Strengthening the P storage capacity of the biofilm resulted in a net increase in the P recovery rate, which was as high as 66.96% in a harvesting cycle, and total soluble P>220 mg/L in the P recovery solution was successfully achieved. Meanwhile, the carbon cost of P recovery in the BSBR was reduced to 41.57 g-chemical oxygen demand/g-P, and the carbon utilization efficiency was enhanced. To highlight the new strategy, the P recovery performance of the BSBR was given and the relationship between P content and anaerobic P release was discussed. In addition, the changes in the microbial communities under P_L and P_H conditions were analyzed.

Chicken manure-based bioponics: Effects of acetic acid supplementation on nitrogen and phosphorus recoveries and microbial communities

Bioponics has the potential to recover nutrients from organic waste streams, such as chicken manure and digestate with high volatile fatty acid (VFA) contents through crop production. Acetic acid, a dominant VFA, was supplemented weekly (0, 500, 1000, and 1500 mg/L) in a chicken manure-based bioponic system, and its effect on the performance of bioponics (e.g., plant yield and nitrogen and phosphorus availabilities) was examined. Microbial communities were analyzed using 16S rRNA gene sequencing, and the functional gene abundances were predicted using PICRUSt. Although acetic acid negatively affected plant yield, no significant difference (p > 0.05) was noted in the average nitrogen or phosphorus concentration. In terms of nutrient recovery, the bioponic systems still functioned well, although higher concentrations of acetic acid decreased plant yield and altered the bacterial communities in plant roots and chicken manure sediments. These data suggest that an acetic acid concentration of < 500 mg/L or a longer loading interval is recommended for the effective operation of chicken manure and digestate-based bioponics.

Enhanced phosphorus storage in suspended biofilm by increasing dissolved oxygen

The phosphorus recovery efficiency in PAOs-biofilm system is so far limited to stimulating phosphorus release by adding concentrated organic carbon solution during the anaerobic stage. In present study, a PAOs-biofilm sequence batch reactor (BSBR) were operated to investigate whether increase of the phosphorus storage content via DO control can stimulate the release in the biofilm. During the operation of BSBR for 160 days, the phosphorus content in biofilm (P_biofilm) was doubled via increasing dissolved oxygen (DO) from 4 to 6 mg/L. With the COD of 200 mg/L in the anaerobic phase, the phosphorus release was enhaced, resulting in an significant increase of phosphorus concentration from 94.85 to 179.5 mg/L in recirculated solution. Batch tests further clarified explicitly the increase of P_biofilm stimulated a phosphorus release rate but this must be balanced since high P_biofilm reduced the phosphorus removal capacity of the biofilm. With analysis of P³¹-NMR, Ortho-P and Poly-P were the main phosphorus species stored in biofilm. The microbial cell played a more important role than EPS in phosphorus storage. The dominant phylum in the master reactor was Proteobacteria with an abundance of 64.4%, in which the Rhodocyclaceae was the dominant PAOs with an abundance of 10.1%. The outcome of this study elucidated that increase of phosphorus storage via DO control which facilitated more efficient phosphorus release with much lower organic carbon source consumption during the enrichment of phosphorus. Meanwhile, we provided a new perspective for the recovery of phosphorus in future wastewater treatment plants.

Novel advanced porous concrete in constructed wetlands: preparation, characterization and application in urban storm runoff treatment

Common porous concrete templates (CPCT) and advanced porous concrete templates (APCT) were employed in this study to construct wetlands for their applications in pollutant removal from storm runoff. The planting ability of the concrete was investigated by growing Festuca elata plants in them. Strength of the porous concrete (7.21 ± 0.19 Mpa) decreased by 1.8 and 4.9% over a period of six and 12 months, respectively, due to its immersion in lake water. The height and weight of Festuca elata grass growth on the porous concrete were observed to be 12.6-16.9 mm and 63.4-95.4 mg, respectively, after a duration of one month. Advanced porous concrete template based constructed wetland (APCT-CW) showed better removal of chemical oxygen demand (COD) (49.6%), total suspended solids (TSS) (58.9), NH₃-N (52.4%), total nitrogen (TN) (47.7%) and total phosphorus (TP) (45.5%) in storm water, when compared with the common porous concrete template based constructed wetland (CPCT-CW) with 20.6, 29.8, 30.1, 35.4 and 26.9%, respectively. The removal of Pb, Ni, Zn by the CPCT-CW unit were 28.9, 33.3 and 42.3%, respectively, whereas these were 51.1, 62.5 and 53.8%, respectively, with the APCT-CW unit. These results demonstrate that the advanced porous concrete template in constructed wetland could be employed successfully for the removal of pollutants from urban storm water runoff.

Phosphorus (P) recovery coupled with increasing influent ammonium facilitated intracellular carbon source storage and simultaneous aerobic phosphorus & nitrogen removal

Under decreasing C/N (from 8.8 to 3.5) conditions, an alternating anaerobic/aerobic biofilter (AABF) was used to remove nitrogen and accumulate/recover phosphorus (P) from synthetic wastewater. The AABF was periodically (every 10 days) fed with an additional carbon source (10 L, chemical oxygen demand (COD) = 900 mg L^-1 sodium acetate (NaAC) solution) in the anaerobic phase to induce the release of P sequestered in the biofilm. An increase in PHA storage in the biofilm was observed and characterized with TEM and a GC-MS method. The accumulation of P and removal of total nitrogen occurred primarily in the aerobic phase. As the NH₄⁺-N loading rate increased from 0.095 to 0.238 kg m^-3 d^-1 at a total empty bed retention time (EBRT) of 4.6 h, the TN removal in AABF was reduced from 91.2% to 43.4%, while the P removal or recovery rate remained unaffected. The high-throughput community sequencing analysis indicated that the relative abundance of Candidatus Competibacter, Nitrospira and Arcobacter increased while the Accumulibacter phosphatis decreased with an increase of ammonium loading rate within a short operational period (30 days). A putative N and P removal pattern via simultaneous nitrification and PHA-based denitrification, as well as P accumulation in the biofilm was proposed. The research demonstrated that an efficient N removal and P recovery process, i.e., simultaneous nitrification and denitrification, P accumulation and carbon source-regulated P recovery can be achieved by the symbiotic functional groups in a single biofilm reactor.

An efficient approach for phosphorus recovery from wastewater using series-coupled air-agitated crystallization reactors

Homogeneous nucleation of hydroxyapatite (HAP) crystallization in high levels of supersaturation solution has a negative effect on phosphorus recovery efficiency because of the poor settleability of the generated HAP microcrystalline. In this study, a new high-performance approach for phosphorus recovery from anaerobic supernatant using three series-coupled air-agitated crystallization reactors was developed and characterized. During 30-day operation, the proposed process showed a high recovery efficiency (∼95.82%) and low microcrystalline ratio (∼3.11%). Particle size analysis showed that the microcrystalline size was successively increased (from 5.81 to 26.32 μm) with the sequence of series-coupled reactors, confirming the conjectural mechanism that a multistage-induced crystallization system provided an appropriate condition for the growth, aggregation, and precipitation of crystallized products. Furthermore, the new process showed a broad spectrum of handling ability for different concentrations of phosphorus-containing solution in the range of 5-350 mg L^-1, and the obtained results of phosphorus conversion ratio and recovery efficiency were more than 92% and 80%, respectively. Overall, these results showed that the new process exhibited an excellent ability of efficient phosphorus recovery as well as wide application scope, and might be used as an effective approach for phosphorus removal and recovery from wastewater.