Enhanced Bio-P removal: Past, present, and future - A comprehensive review

Distinguished denitrifying phosphorus removal in the high-rate anoxic/microaerobic system for sewage treatment

This study re-evaluated the role of anoxic and anaerobic zones during the enhanced biological phosphorus (P) removal process by investigating the potential effect of introducing an anoxic zone into a high-rate microaerobic activated sludge (MAS) system (1.60-1.70 kg chemical oxygen demand (COD) m-3 d-1), i.e., a high-rate anoxic/microaerobic (A/M) system for sewage treatment. In the absence of a pre-anaerobic zone, introducing an anoxic zone considerably reduced effluent NOx--N concentrations (7.2 vs. 1.5 mg L-1) and remarkably enhanced total nitrogen (75% vs. 89%) and total P (18% vs. 60%) removal and sludge P content (1.48% vs. 1.77% (dry weight)) due to further anoxic denitrifying P removal in the anoxic zone (besides simultaneous nitrification and denitrification in the microaerobic zone). High-throughput pyrosequencing demonstrated the niche differentiation of different polyphosphate accumulating organism (PAO) clades (including denitrifying PAO [DPAO] and non-DPAO) in both systems. Introducing an anoxic zone considerably reduced the total PAO abundance in sludge samples by 42% and modified the PAO community structure, including 17-19 detected genera. The change was solely confined to non-DPAOs, as no obvious change in total abundance or community structure of DPAOs including 7 detected genera was observed. Additionally, introducing an anoxic zone increased the abundance of ammonia-oxidizing bacteria by 39%. The high-rate A/M process provided less aeration, higher treatment capacity, a lower COD requirement, and a 75% decrease in the production of waste sludge than the conventional biological nutrient removal process.

Digitalization of phosphorous removal process in biological wastewater treatment systems: Challenges, and way forward

Phosphorus in wastewater poses a significant environmental threat, leading to water pollution and eutrophication. However, it plays a crucial role in the water-energy-resource recovery-environment (WERE) nexus. Recovering Phosphorus from wastewater can close the phosphorus loop, supporting circular economy principles by reusing it as fertilizer or in industrial applications. Despite the recognized importance of phosphorus recovery, there is a lack of analysis of the cyber-physical framework concerning the WERE nexus. Advanced methods like automatic control, optimal process technologies, artificial intelligence (AI), and life cycle assessment (LCA) have emerged to enhance wastewater treatment plants (WWTPs) operations focusing on improving effluent quality, energy efficiency, resource recovery, and reducing greenhouse gas (GHG) emissions. Providing insights into implementing modeling and simulation platforms, control, and optimization systems for Phosphorus recovery in WERE (P-WERE) in WWTPs is extremely important in WWTPs. This review highlights the valuable applications of AI algorithms, such as machine learning, deep learning, and explainable AI, for predicting phosphorus (P) dynamics in WWTPs. It emphasizes the importance of using AI to analyze microbial communities and optimize WWTPs for different various objectives. Additionally, it discusses the benefits of integrating mechanistic and data-driven models into plant-wide frameworks, which can enhance GHG simulation and enable simultaneous nitrogen (N) and Phosphorus (P) removal. The review underscores the significance of prioritizing recovery actions to redirect Phosphorus from effluent to reusable products for future considerations.

Nitrogen and phosphorus removal performance of sequential batch operation for algal cultivation through suspended-solid phase photobioreactor

Nitrogen (N) and phosphorus (P) absorbed by algae in the suspended-solid phase photobioreactor (ssPBR) have emerged as an efficient pathway to purify the effluent of wastewater treatment plants (WWTPs). However, the key operational parameters of the ssPBR need to be optimized. In this study, the stability of the system after sequential batch operations and the efficiency under various influent P concentrations were evaluated. The results demonstrated that the ssPBR maintained a high N/P removal efficiency of 96 % and 98 %, respectively, after 5 cycles. When N was kept at 15 mg/L and P ranged from 1.5 to 3.0 mg/L, the system yielded plenty of algae products and guaranteed the effluent quality that met the discharge standards. Notably, the carriers were a key contributor to the high metabolism of algae and high performance. This work provided theoretical ideas and technical guidance for effluent quality improvement in WWTPs.

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.

Full dynamic control of dairy wastewater treatment by aerobic granular sludge using electric conductivity and oxygen uptake rate

The objective of the current study was to determine the applicability of a sensor-based dynamic control strategy for the treatment of real variable dairy wastewater by aerobic granular sludge (AGS) performing enhanced biological phosphorus removal (EBPR). Two parallel sequencing batch reactors (SBRs) were set up that used only an anaerobic feast/aerobic famine microbial selection strategy to successfully obtain sludge granulation. SBR-STA used a fixed cycle length, while the duration of the reaction steps in SBR-DYN was variable. The control strategy was based solely on (derived) signals from low-cost and common sensors. The profile of the electric conductivity during the anaerobic reaction step was related to the microbial release of phosphate (PO4-P) and the associated uptake of dissolved organic carbon (DOC) by polyphosphate-accumulating organisms (PAOs). Control of the aerobic reaction step was based on the oxygen uptake rate (OUR). This resulted in a dynamic reactor operation with significant efficiency gains, such as 32% shorter cycle times and 42% higher sludge loading rates without impairing the effluent quality. These results extend the existing potential of indirect control strategies to full biological nutrient removal processes, which may be of great assistance to the operators and designers of industrial installations.

Effect of biofilm thickness on the activity and community composition of phosphorus accumulating bacteria in a moving bed biofilm reactor

Can biofilms enhance the rates of phosphorus removal in wastewater treatment? In order to narrow the scientific gap on the effect of biofilm thickness on the activity and microbial community of phosphorus-accumulating bacteria, this study investigated biofilms of 30 to 1000 µm thickness in a moving bed biofilm reactor. Measurements on 5 different biofilm carriers showed that biomass-specific phosphorus release and uptake rates increased as a function of biofilm thickness for biofilms thinner than about 110 µm but were lower for thicker biofilms of about 550-1000 µm. The reduced phosphorus uptake and release rates in the thickest biofilms can result from substrate mass transfer limitations whereas the low activity in the thinnest biofilms can be related to a too high turnover rate in the biofilm due to heterotrophic growth. Additionally, the microbial ecology of the different biofilms confirms the observed phosphorus uptake and release rates. The results from the full-length 16S rRNA gene sequencing of the bacterial community showed that the thicker biofilms were characterized by higher relative abundance (40-58%) of potential phosphorus accumulating genera Zoogloea, Acinetobacter, Dechloromonas and Ca. Accumulibacter. In contrast, the thinner biofilms were dominated by the genus Ferribacterium (34-60%), which might be competing with phosphorus-accumulating bacteria as indicated by the relatively high acetate uptake rates in the thinner biofilms. It is concluded that there is an optimal biofilm thickness of 100-500 µm, at which the phosphorus accumulating bacteria have the highest activity.

Distinguished denitrifying phosphorus removal in the high-rate anoxic/microaerobic system for sewage treatment

This study re-evaluated the role of anoxic and anaerobic zones during the enhanced biological phosphorus (P) removal process by investigating the potential effect of introducing an anoxic zone into a high-rate microaerobic activated sludge (MAS) system (1.60-1.70 kg chemical oxygen demand (COD) m-3 d-1), i.e., a high-rate anoxic/microaerobic (A/M) system for sewage treatment. In the absence of a pre-anaerobic zone, introducing an anoxic zone considerably reduced effluent NOx--N concentrations (7.2 vs. 1.5 mg L-1) and remarkably enhanced total nitrogen (75% vs. 89%) and total P (18% vs. 60%) removal and sludge P content (1.48% vs. 1.77% (dry weight)) due to further anoxic denitrifying P removal denitrification in the anoxic zone (besides simultaneous nitrification and denitrification in the microaerobic zone). High-throughput pyrosequencing demonstrated the niche differentiation of different polyphosphate accumulating organism (PAO) clades (including denitrifying PAO [DPAO] and non-DPAO) in both systems. Introducing an anoxic zone considerably reduced the total PAO abundance in sludge samples by 42% and modified the PAO community structure, including 17-19 detected genera. The change was solely confined to non-DPAOs, as no significant change in total abundance or community structure of DPAOs including seven detected genera was observed. Additionally, introducing an anoxic zone increased the abundance of ammonia-oxidizing bacteria by 39%. The high-rate A/M process provided less aeration, higher treatment capacity, a lower COD requirement, and a 75% decrease in the production of waste sludge than the conventional biological nutrient removal process.

Photo-Fenton self-cleaning carbon fibers membrane supported with Zr-MOF@Fe2O3 for effective phosphate removal from algae-rich water

Adsorbents featuring abundant binding sites and high affinity to phosphate have been used to resolve water eutrophication. However, most of the developed adsorbents were focused on improving the adsorption ability of phosphate but ignored the effect of biofouling on the adsorption process especially used in the eutrophic water body. Herein, a novel MOF-supported carbon fibers (CFs) membrane with high regeneration and antifouling capability, was prepared by in-situ synthesis of well-dispersed MOF on CFs membrane, to remove phosphate from algae-rich water. The hybrid UiO-66-(OH)₂@Fe₂O₃@CFs membrane exhibits a maximum adsorption capacity of 333.3 mg g^-1 (pH 7.0) and excellent selectivity for phosphate sorption over coexisting ions. Moreover, the Fe₂O₃ nanoparticles anchored on the surface of UiO-66-(OH)₂ through 'phenol-Fe(III)' reaction can endow the membrane with the robust photo-Fenton catalytic activity, which improves long-term reusability even under algae-rich condition. After 4 times photo-Fenton regenerations, the regeneration efficiency of the membrane could remain 92.2%, higher than that of hydraulic cleaning (52.6%). Moreover, the growth of C. pyrenoidosa was significantly reduced by 45.8% within 20 days via metabolism inhibition due to membrane-induced P-deficient conditions. Hence, the developed UiO-66-(OH)₂@Fe₂O₃@CFs membrane holds significant prospects for large-scale application in phosphate sequestration of eutrophic water bodies.

Advanced nitrogen and phosphorus removal by the symbiosis of PAOs, DPAOs and DGAOs in a pilot-scale A2O/A+MBR process with a low C/N ratio of influent

Cooperating in harmony to avoid competition with dominant functional microbial symbiosis is an efficient way in advanced nitrogen and phosphorus removal in wastewater treatment processes. In this study, a niche-based coordinating strategy was implemented to cooperate in harmony with phosphorus-accumulating organisms (PAOs), denitrifying phosphorus-accumulating organisms (DPAOs) and denitrifying glycogen-accumulating organisms (DGAOs) to advance nitrogen and phosphorus removal based on an anaerobic-anoxic-oxic-anoxic-membrane bioreactor (A²O/A+MBR) under low C/N in municipal wastewater influent. The niche-based strategy was conducted based on the ORP change during the process as an indicator combined with the adjustment of recirculation and anoxic zone shifting. The results indicated that the strategy of the post-anoxic unit could enable significant enhancement of biological nitrogen and phosphorus removal (BNPR) by 9.9% and 16.3%, respectively, with low effluent concentrations of 7.0 ± 2.2 mg N/L and 0.36±0.32 mg P/L. The satisfactory performance was dominated along with the shift in the microbial community: the relative abundance of Tetrasphaera (PAO genus) increased from 0.14±0.08% to 0.32±0.12%, while the relative abundance of Decchloromonas (DGAO genus) and Candidatus Competibacter (DGAO genus) also increased. The advanced combination of anaerobic phosphorus release, anoxic denitrification, denitrifying phosphorus removal and endogenous denitrification was qualified by the modeling simulation of the biochemical kinetics mechanism of activated sludge in the A²O+MBR and A²O/A+MBR processes, which means that cooperation in the harmony of PAOs, DPAOs and DGAOs could be efficiently realized by a promising control strategy to enhance BNPR in an A²O+MBR with a post-anoxic unit. This study provides an efficient and simple novel control strategy to overcome the limitation of traditional nitrogen and phosphorus removal under an insufficient carbon source.