Achieving nitrogen and phosphorus removal at low C/N ratios without aeration through a novel phototrophic process

Fe(II)-driven spatiotemporal assembly of heterotrophic and anammox bacteria enhances simultaneous nitrogen and phosphorus removal for low-strength municipal wastewater

The mainstream anaerobic ammonium oxidation (anammox) faces considerable challenges with low-strength municipal wastewater. A Fe(Ⅱ)-amended partial denitrification coupled anammox (PD/A) process was conducted and achieved a long-term and efficient nitrogen and phosphorus removal, yielding effluent total nitrogen and phosphorus concentrations of 1.97 ± 1.03 mg/L and 0.23 ± 0.13 mg/L, respectively, which could well meet more stringent effluent discharge standard of some wastewater treatment plants in specific geographical locations, e.g., estuaries. Fe(Ⅱ)-driven vivianite formation provided key nucleuses for the optimization of the spatial distribution of heterotrophic and anammox bacteria with enhanced extracellular polymeric substances as key driving forces. Metagenomics analysis further revealed the increase of key genes, enhancing anammox bacteria homeostasis, which also bolstered the resistance to environmental perturbations. This study provided a comprehensive sight into the function of Fe(Ⅱ) in mainstream PD/A process, and explored a promising alternative for synergetic nitrogen and phosphorus removal for low-strength municipal wastewater treatment.

A review of emerging membrane-based microalgal-bacterial processes for wastewater treatment: Process configurations, biological and membrane performance, and perspectives

Microalgal-bacterial (MB) consortia create an excellent eco-system for simultaneous COD/BOD and nutrients (N and P) removals in a single step with significant reduction in or complete elimination of aeration and carbonation in the biological wastewater treatment processes. The integration of membrane separation technology with the MB processes has created a new paradigm for research and development. This paper focuses on a comprehensive and critical literature review of recent advances in these emerging processes. Novel membrane process configurations and process conditions affecting the biological performance of these novel systems have been systematically reviewed and discussed. Membrane fouling issues and control of MB biofilm formation and thickness associated with these emerging suspended growth or immobilized biofilm processes are addressed and discussed. The research gaps, challenges, outlooks of these emerging processes are identified and discussed in-depth. The findings from the literature suggest that the membrane-based MB processes are advanced biotechnologies with a significant reduction in energy consumption and process simplification and high process efficiency that are not achievable with current technologies in wastewater treatment. There are endless opportunities for research and development of these novel and emerging membrane-based MB processes.

Review of the mechanisms involved in dissimilatory nitrate reduction to ammonium and the efficacies of these mechanisms in the environment

Dissimilatory nitrate reduction to ammonium (DNRA) is currently of great interest because it is an important method for recovering nitrogen from wastewater and offers many advantages, over other methods. A full understanding of DNRA requires the mechanisms, pathways, and functional microorganisms involved to be identified. The roles these pathways play and the effectiveness of DNRA in the environment are not well understood. The objectives of this review are to describe our current understanding of the molecular mechanisms and pathways involved in DNRA from the substrate transfer perspective and to summarize the effects of DNRA in the environment. First, the mechanisms and pathways involved in DNRA are described in detail. Second, our understanding of DNRA by actinomycetes is reviewed and gaps in our understanding are identified. Finally, the effects of DNRA in the environment are assessed. This review will help in the development of future research into DNRA to promote the use of DNRA to treat wastewater and recover nitrogen.

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.

Oxygen affinity and light intensity induced robust phosphorus removal and fragile ammonia removal in a non-aerated bacteria-algae system

Non-aerated bacteria-algae system gaining O2 through photosynthesis presents an alternative for costly mechanical aeration. This study investigated oxygen supply and performance of nutrients removal at low and high light intensity (LL and HL). The results showed that P removal was high and robust (LL 97 ± 1.8 %, HL 95 % ± 2.9 %), while NH4+-N removal fluctuated dramatically (LL 66 ± 14.7 %, HL 84 ± 8.6 %). Oxygen generated at illumination of 200 μmol m-2 s-1, 6 h was sufficient to sustain aerobic phase for 2.25 g/L MLSS. However, O2 produced by algae was preferentially captured in the order of heterotrophic bacteria (HB), ammonia oxidizing bacteria (AOB), nitrite oxidizing bacteria (NOB). Oxygen affinity coupled with light intensity led to NOB suppression with stable nitrite accumulation ratio of 57 %. Free nitrous acid (FNA) and light stimulated the abundance of denitrifying polyphosphate accumulating organism (DPAO) of Flavobacterium, but with declined P-accumulating metabolism (PAM) of P release, P/C, K/P and Mg/P ratios. Flavobacterium and cyanobacteria Leptolyngbya, along with biologically induced CaP in extracellular polymeric substances was the key to robust P removal. AOB of Ellin6067 and DPAO of Flavobacteria offer a promising scenario for partial nitrification-denitrifying phosphorus removal.

Combined Phototrophic Simultaneous Nitrification-Endogenous Denitrification with Phosphorus Removal (P-SNDPR) System Treating Low Carbon to Nitrogen Ratio Wastewater for Potential Carbon Neutrality

Conventional biological nutrient removal processes rely on external aeration and produce significant carbon dioxide (CO2) emissions. This study constructed a phototrophic simultaneous nitrification-denitrification phosphorus removal (P-SNDPR) system to treat low carbon to nitrogen (C/N) ratios wastewater and investigated the impact of sludge retention time (SRT) on nutrient removal performance, nitrogen conversion pathway, and microbial structure. Results showed that the P-SNDPR system at SRT of 15 days had the highest nutrient removal capacity, achieving over 85% and 98% removal of nitrogen and phosphorus, respectively, meanwhile maintaining minimal CO2 emissions. Nitrogen removal was mainly through assimilation at SRTs of 5 and 10 days, and nitrification-denitrification at SRTs of 15 and 20 days. Stable partial nitrification was facilitated by photoinhibition and low DO levels. Flow cytometry sorting technique results revealed SRT drove community structural changes in translational activity (BONCAT+) microbes, where BONCAT+ microbes were mainly simultaneous nitrogen and phosphorus removal bacteria (Candidatus Accumulibacter), denitrifying bacteria (Candidatus Competibacter and Plasticicumulans), ammonia-oxidizing bacteria (Nitrosomonas), and microalgae (Chlorella and Dictyosphaerium). The P-SNDPR system represents a novel, carbon-neutral process for efficient nutrient removal from low C/N ratio wastewater without aeration and external carbon source additions.

Critical analysis on the transformation and upgrading strategy of Chinese municipal wastewater treatment plants: Towards sustainable water remediation and zero carbon emissions

In the light of circular economy aspects, processing of large-scale municipal wastewater treatment plants (WWTPs) needs reconsideration to limit the overuse of energy, implement of non-green technologies and emit abundant greenhouse gas. Along with the huge increase in the worldwide population and agro-industrial activities, global environmental organizations have issued several recent roles to boost scientific and industrial communities towards sustainable development. Over recent years, China has imposed national and regional standards to control and manage the discharged liquid and solid waste, as well as to achieve carbon peaking and carbon neutrality. The aim of this report is to analyze the current state of Chinese WWTPs routing and related issues such as climate change and air pollution. The used strategies in Chinese WWTPs and upgrading trends were critically discussed. Several points were addressed including the performance, environmental impact, and energy demand of bio-enhanced technologies, including hydrolytic acidification pretreatment, efficient (toxic) strain treatment, and anaerobic ammonia oxidation denitrification technology, as well as advanced treatment technologies composed of physical and chemical treatment technologies, biological treatment technology and combined treatment technology. Discussion and critical analysis based on the current data and national policies were provided and employed to develop the future development trend of municipal WWTPs in China from the construction of sustainable and "Zero carbon" WWTPs.

Insights on biological phosphorus removal with partial nitrification in single sludge system via sidestream free ammonia and free nitrous acid dosing

The sidestream sludge treatment by free ammonium (FA)/free nitrous acid (FNA) dosing was frequently demonstrated to maintain the nitrite pathway for the partial nitrification (PN) process. Nevertheless, the inhibitory effect of FA and FNA would severely influence polyphosphate accumulating organisms (PAOs), destroying the microbe-based phosphorus (P) removal. Therefore, a strategic evaluation was proposed to successfully achieve biological P removal with a partial nitrification process in a single sludge system by sidestream FA and FNA dosing. Through the long-term operation of 500 days, excellent phosphorus, ammonium and total nitrogen removal performance were achieved at 97.5 ± 2.6 %, 99.1 ± 1.0 % and 75.5 ± 0.4 %, respectively. Stable partial nitrification with a nitrite accumulation ratio (NAR) of 94.1 ± 3.4 was attained. The batch tests also reported the robust aerobic phosphorus uptake based on FA and FNA adapted sludge after exposure of FA and FNA, respectively, suggesting the FA and FNA treatment strategy could potentially offer the opportunity for the selection of PAOs, which synchronously have the tolerance to FA and FNA. Microbial community analysis suggested that Accumulibacter, Tetrasphaera, and Comamonadaceae collectively contributed to the phosphorus removal in this system. Summarily, the proposed work presents a novel and feasible strategy to integrate enhanced biological phosphorus removal (EBPR) and short-cut nitrogen cycling and bring the combined mainstream phosphorus removal and partial nitrification process closer to practical application.

Achieving Discharge Limits in Single-Stage Domestic Wastewater Treatment by Combining Urban Waste Sources and Phototrophic Mixed Cultures

This work shows the potential of a new way of co-treatment of domestic wastewater (DWW) and a liquid stream coming from the thermal hydrolysis of the organic fraction of municipal solid waste (OFMSW) mediated by a mixed culture of purple phototrophic bacteria (PPB) capable of assimilating carbon and nutrients from the medium. The biological system is an open single-step process operated under microaerophilic conditions at an oxidative reduction potential (ORP) < 0 mV with a photoperiod of 12/24 h and fed during the light stage only so the results can be extrapolated to outdoor open pond operations by monitoring the ORP. The effluent mostly complies with the discharge values of the Spanish legislation in COD and p-values (<125 mg/L; <2 mg/L), respectively, and punctually on values in N (<15 mg/L). Applying an HRT of 3 d and a ratio of 100:7 (COD:N), the presence of PPB in the mixed culture surpassed 50% of 16S rRNA gene copies, removing 78% of COD, 53% of N, and 66% of P. Furthermore, by increasing the HRT to 5 d, removal efficiencies of 83% of COD, 65% of N, and 91% of P were achieved. In addition, the reactors were further operated in a membrane bioreactor, thus separating the HRT from the SRT to increase the specific loading rate. Very satisfactory removal efficiencies were achieved by applying an HRT and SRT of 2.3 and 3 d, respectively: 84% of COD, 49% of N, and 93% of P despite the low presence of PPB due to more oxidative conditions, which step-by-step re-colonized the mixed culture until reaching >20% of 16S rRNA gene copies after 49 d of operation. These results open the door to scaling up the process in open photobioreactors capable of treating urban wastewater and municipal solid waste in a single stage and under microaerophilic conditions by controlling the ORP of the system.

Long term operation of a phototrophic biological nutrient removal system: Impact of CO2 concentration and light exposure on process performance

The utilization of non-aerated microalgae-bacterial consortia for phototrophic biological nutrient removal (photo-BNR) has emerged as an alternative to conventional wastewater treatment. Photo-BNR systems are operated under transient illumination, with alternating dark-anaerobic, light-aerobic and dark-anoxic conditions. A deep understanding of the impact of operational parameters on the microbial consortium and respective nutrient removal efficiency in photo-BNR systems is required. The present study evaluates, for the first time, the long-term operation (260 days) of a photo-BNR system, fed with a COD:N:P mass ratio of 7.5:1:1, to understand its operational limitations. In particular, different CO₂ concentrations in the feed (between 22 and 60 mg C/L of Na₂CO₃) and variations of light exposure (from 2.75 h to 5.25 h per 8 h cycle) were studied to determine their impact on key parameters, like oxygen production and availability of polyhydroxyalkanoates (PHA), on the performance of anoxic denitrification by polyphosphate accumulating organisms. Results indicate that oxygen production was more dependent on the light availability than on the CO₂ concentration. Also, under operational conditions with a COD:Na₂CO₃ ratio of 8.3 mg COD/mg C and an average light availability of 5.4 ± 1.3 W h/g TSS, no internal PHA limitation was observed, and 95 ± 7%, 92 ± 5% and 86 ± 5% of removal efficiency could be achieved for phosphorus, ammonia and total nitrogen, respectively. 81 ± 1.7% of the ammonia was assimilated into the microbial biomass and 19 ± 1.7% was nitrified, showing that biomass assimilation was the main N removal mechanism taking place in the bioreactor. Overall, the photo-BNR system presented a good settling capacity (SVI ∼60 mL/g TSS) and was able to remove 38 ± 3.3 mg P/L and 33 ± 1.7 mg N/L, highlighting its potential for achieving wastewater treatment without the need of aeration.

Enhancing phosphorus removal of photogranules by incorporating polyphosphate accumulating organisms

Photogranules are a novel wastewater treatment technology that can utilize the sun's energy to treat water with lower energy input and have great potential for nutrient recovery applications. They have been proven to efficiently remove nitrogen and carbon but show lower conversion rates for phosphorus compared to established treatment systems, such as aerobic granular sludge. In this study, we successfully introduced polyphosphate accumulating organisms (PAOs) to an established photogranular culture. We operated photobioreactors in sequencing batch mode with six cycles per day and alternating anaerobic (dark) and aerobic (light) phases. We were able to increase phosphorus removal/recovery by 6 times from 5.4 to 30 mg/L/d while maintaining similar nitrogen and carbon removal compared to photogranules without PAOs. To maintain PAOs activity, alternating anaerobic feast and aerobic famine conditions were required. In future applications, where aerobic conditions are dependent on in-situ oxygenation via photosynthesis, the process will rely on sunlight availability. Therefore, we investigated the feasibility of the process under diurnal cycles with a 12-h anaerobic phase during nighttime and six short cycles during the 12 h daytime. The 12-h anaerobic phase had no adverse effect on the PAOs and phototrophs. Due to the extension of one anaerobic phase to 12 h the six aerobic phases were shortened by 47% and consequently decreased the light hours per day. This resulted in a decrease of phototrophs, which reduced nitrogen removal and biomass productivity up to 30%. Finally, we discuss and suggest strategies to apply PAO-enriched photogranules at large-scale.

The impact of pH on the anaerobic and aerobic metabolism of Tetrasphaera-enriched polyphosphate accumulating organisms

Members of the genus Tetrasphaera are putative polyphosphate accumulating organisms (PAOs) that have been found in greater abundance than Accumulibacter in many full-scale enhanced biological phosphorus removal (EBPR) wastewater treatment plants worldwide. Nevertheless, previous studies on the effect of environmental conditions, such as pH, on the performance of EBPR have focused mainly on the response of Accumulibacter to pH changes. This study examines the impact of pH on a Tetrasphaera PAO enriched culture, over a pH range from 6.0 to 8.0 under both anaerobic and aerobic conditions, to assess its impact on the stoichiometry and kinetics of Tetrasphaera metabolism. It was discovered that the rates of phosphorus (P) uptake and P release increased with an increase of pH within the tested range, while PHA production, glycogen consumption and substrate uptake rate were less sensitive to pH changes. The results suggest that Tetrasphaera PAOs display kinetic advantages at high pH levels, which is consistent with what has been observed previously for Accumulibacter PAOs. The results of this study show that pH has a substantial impact on the P release and uptake kinetics of PAOs, where the P release rate was >3 times higher and the P uptake rate was >2 times higher at pH 8.0 vs pH 6.0, respectively. Process operational strategies promoting both Tetrasphaera and Accumulibacter activity at high pH do not conflict with each other, but lead to a potentially synergistic impact that can benefit EBPR performance.

Simultaneous removal of nitrate, lead, and tetracycline by a fixed-biofilm reactor assembled with kapok fiber and sponge iron: Comparative analysis of operating conditions and biotic community

In recent years, under the condition of lack of carbon source, the presence of composite micro-pollutants make the removal of nitrate seriously damaged, and to find a suitable way to solve this problem is imminent. A fixed-biofilm carrier modified by mixing sponge iron (SI) and kapok fiber (KF) combined with strain Zoogloea sp. FY6 was constructed in this study to get a fixed-biofilm reactor with merit denitrification performance. By adjusting the operation parameters, it can be concluded that when the carbon to nitrogen (C/N) ratio was 1.5, the hydraulic retention time (HRT) was 6.0 h, and the pH was 6.0, the nitrate removal efficiency (NRE) of the fixed-biofilm reactor was up to 95.4% (2.95 mg L^-1 h^-1). In addition, the fixed-biofilm reactor constructed in this study can remove lead (Pb²⁺) and tetracycline (TC) excellently in the presence of SI and Zoogloea sp. FY6, and the denitrification performance can still maintain a high level under the influence of different concentrations of Pb²⁺ and TC. Furthermore, the addition of SI not only removes the compound pollutants, but also protects the toxicity of the pollutant inflow in the bioreactor, and the metabolic process of microorganisms in the bioreactor also removes some of the compound pollutants. The high-throughput data showed the abundance of strain Zoogloea sp. FY6 was still the highest value under the influence of various pollutants, and the metagenomic prediction showed that the fixed-biofilm reactor had perfect denitrification process and iron redox cycle benefits. This study provides a valuable reference for sustainable utilization of natural biological resources and reduction of material costs in wastewater treatment plants (WWTPs).

Natural lighting enhancing the algae proliferation and nitrogen removal in membrane-aerated bacterial-algal biofilm reactor

Membrane-aerated bacterial-algal biofilm reactor (MABAR) is an emerging and novel technology in recent years, which has been attracting increasing attention due to its cost-effectiveness and superior removal performance of pollutants by versatile removal pathways in symbiotic bacterial-algal biofilm. However, the wider application of MABAR is hindered by the dilemma of insufficient algae biomass. In this study, an MABAR under natural sunlight was developed and operated for 160 d to access the feasibility of enhancing algae proliferation by natural lighting. Results showed that the MABAR with natural sunlight (nMABAR) demonstrated better performance of pollutants removal. High removal efficiencies of organic matter and NH₄-N in nMABAR were 90 % and 92 %, respectively. In particular, the removal efficiency of TN in nMABAR, under less aeration, was up to 80 %, which was 15 % higher than the control reactor. The Chlorophyll-a content indicated that natural sunlight facilitated to algae growth in MABAR, and algae assimilation might be the dominant contributor to NH₄-N removal. Moreover, there were microbial shifts in bacterial-algal biofilm in a response to the natural lighting, the nMABAR uniquely possessed a bacterial phylotype termed Thiocapsa, which could play an important role in bacterial nitrification. Algal phylotype Chlorophyceae significantly contributed to pollutants removal and synergistic relationship with bacteria. In addition, the superb performance of nMABAR under less aeration condition suggested that abundant algae were capable of supplying enough O₂ for the system. These results provided insight into the natural lighting on algae-bacteria synergistic growth and cost-effective operation strategy for MABAR.

Microalgae-Enabled Wastewater Remediation and Nutrient Recovery through Membrane Photobioreactors: Recent Achievements and Future Perspective

The use of microalgae for wastewater remediation and nutrient recovery answers the call for a circular bioeconomy, which involves waste resource utilization and ecosystem protection. The integration of microalgae cultivation and wastewater treatment has been proposed as a promising strategy to tackle the issues of water and energy source depletions. Specifically, microalgae-enabled wastewater treatment offers an opportunity to simultaneously implement wastewater remediation and valuable biomass production. As a versatile technology, membrane-based processes have been increasingly explored for the integration of microalgae-based wastewater remediation. This review provides a literature survey and discussion of recent progressions and achievements made in the development of membrane photobioreactors (MPBRs) for wastewater treatment and nutrient recovery. The opportunities of using microalgae-based wastewater treatment as an interesting option to manage effluents that contain high levels of nutrients are explored. The innovations made in the design of membrane photobioreactors and their performances are evaluated. The achievements pave a way for the effective and practical implementation of membrane technology in large-scale microalgae-enabled wastewater remediation and nutrient recovery processes.

Nitrogen recovery from wastewater by microbial assimilation - A review

The increased nitrogen (N) input with low utilization rate in artificial N management has led to massive reactive N (Nr) flows, putting the Earth in a high-risk state. It is essential to recover and recycle Nr during or after Nr removal from wastewater to reduce N input while simultaneously mitigate Nr pollution in addressing the N stress. However, mechanisms for efficient Nr recovery during or after Nr removal remain unclear. Here, the occurrence of N risk and progress in wastewater treatment in recent years as well as challenges of the current technologies for N recovery from wastewater were reviewed. Through analyzing N conversion fluxes in biogeochemical N-cycling networks, microbial N assimilation through photosynthetic and heterotrophic microorganisms was highlighted as promising alternative for synergistic N removal and recovery in wastewater treatment. In addition, the prospects and gaps of Nr recovery from wastewater through microbial assimilation are discussed.

Performance of hydrogel immobilized bioreactors combined with different iron ore wastes for denitrification and removal of copper and lead: Optimization and possible mechanism

Reasonable and efficient removal of mixed pollutants (nitrate and heavy metals) in industrial wastewater under heavy metal pollution has attracted more attention in recent years. The target strain Aquabacterium sp. XL4 was immobilized with different iron ore wastes (IOW) using polyvinyl alcohol (PVA) to construct four immobilized bioreactors. The results showed that when the ratio of C/N was 1.5 and the hydraulic retention time (HRT) was 8.0h, the denitrification performance of the bioreactor was the best, and the maximum denitrification efficiency of the bioreactor with sponge iron (SI) as the iron source was 97.19% (2.42mg L^-1 h^-1). Furthermore, by adjusting the concentration of Cu²⁺ and Pb²⁺, the stress behavior of the bioreactor to heavy metals under the influence of each IOW was investigated. The bioreactor has stronger tolerance and removal efficiency to Pb²⁺ and Cu²⁺ in the presence of pellets ore (PO) and refined iron ore (RO), respectively. Moreover, the high-throughput data showed that Aquabacterium accounted for a high proportion in the immobilized bioreactor, and the prediction of functional genes based on the KEGG database showed that the addition of IOW was closely related to the acceleration of nitrate transformation and the inflow and outflow of iron in cells.

Dynamics of Microbial Communities in Phototrophic Polyhydroxyalkanoate Accumulating Cultures

Phototrophic mixed cultures (PMC) are versatile systems which can be applied for waste streams, valorisation and production of added-value compounds, such as polyhydroxyalkanoates (PHA). This work evaluates the influence of different operational conditions on the bacterial communities reported in PMC systems with PHA production capabilities. Eleven PMCs, fed either with acetate or fermented wastewater, and selected under either feast and famine (FF) or permanent feast (PF) regimes, were evaluated. Overall, results identified Chromatiaceae members as the main phototrophic PHA producers, along with Rhodopseudomonas, Rhodobacter and Rhizobium. The findings show that Chromatiaceae were favoured under operating conditions with high carbon concentrations, and particularly under the PF regime. In FF systems fed with fermented wastewater, the results indicate that increasing the organic loading rate enriches for Rhodopseudomonas, Rhizobium and Hyphomicrobiaceae, which together with Rhodobacter and Chromatiaceae, were likely responsible for PHA storage. In addition, high-sugar feedstock impairs PHA production under PF conditions (fermentative bacteria dominance), which does not occur under FF. This characterization of the communities responsible for PHA accumulation helps to define improved operational strategies for PHA production with PMC.

Converting nitrogen and phosphorus wastewater into bioenergy using microalgae-bacteria consortia: A critical review

Conventional wastewater treatment using activated sludge cannot efficiently eliminate nitrogen and phosphorus, thus engendering the risk of water eutrophication and ecosystem disruption. Fortunately, a new wastewater treatment process applying microalgae-bacteria consortia has attracted considerable interests due to its excellent performance of nutrients removal. Moreover, some bacteria facilitate the harvest of microalgal biomass through bio-flocculation. Additionally, while stimulating the functional bacteria, the improved biomass and enriched components also brighten bioenergy production from the perspective of practical applications. Thus, this review first summarizes the current development of nutrients removal and mutualistic interaction using microalgae-bacteria consortia. Then, advancements in bio-flocculation are completely described and the corresponding mechanisms are thoroughly revealed. Eventually, the recent advances of bioenergy production (i.e., biodiesel, biohydrogen, bioethanol, and bioelectricity) using microalgae-bacteria consortia are comprehensively discussed. Together, this review will provide the ongoing challenges and future developmental directions for better converting nitrogen and phosphorus wastewater into bioenergy using microalgae-bacteria consortia.