Photo-sequencing Batch Reactors Research Articles

Conventional activated sludge vs. photo-sequencing batch reactor for enhanced nitrogen removal in municipal wastewater: Microalgal-bacterial consortium and pathogenic load insights

Municipal wastewater treatment plants are mostly based on traditional activated sludge (AS) processes. These systems are characterised by major drawbacks: high energy consumption, large amount of excess sludge and high greenhouse gases emissions. Treatment through microalgal-bacterial consortia (MBC) is an alternative and promising solution thanks to lower energy consumption and emissions, biomass production and water sanitation. Here, microbial difference between a traditional anaerobic sludge (AS) and a consortium-based system (photo-sequencing batch reactor (PSBR)) with the same wastewater inlet were characterised through shotgun metagenomics. Stable nitrification was achieved in the PSBR ensuring ammonium removal > 95 % and significant total nitrogen removal thanks to larger flocs enhancing denitrification. The new system showed enhanced pathogen removal, a higher abundance of photosynthetic and denitrifying microorganisms with a reduced emissions potential identifying this novel PSBR as an effective alternative to AS.

Inorganic carbon limitation decreases ammonium removal and N2O production in the algae-nitrifying bacteria symbiosis system

Ammonium removal by a symbiosis system of algae (Chlorella vulgaris) and nitrifying bacteria was evaluated in a long-term photo-sequencing batch reactor under varying influent inorganic carbon (IC) concentrations (15, 10, 5 and 2.5 mmol L−1) and different nitrogen loading rate (NLR) conditions (270 and 540 mg-N L−1 d−1). The IC/N ratios provided were 2.33, 1.56, 0.78 and 0.39, respectively, for an influent NH4+-N concentration of 90 mg-N L−1 (6.43 mmol L−1). The results confirmed that both ammonium removal and N2O production were positively related with IC concentration. Satisfactory ammonium removal efficiencies (>98 %) and rates (29–34 mg-N gVSS−1 h−1) were achieved regardless of NLR levels under sufficient IC of 10 and 15 mmol L−1, while insufficient IC at 2.5 mmol L−1 led to the lowest ammonium removal rates of 0 mg-N gVSS−1 h−1. The ammonia oxidation process by ammonia oxidizing bacteria (AOB) played a predominant role over the algae assimilation process in ammonium removal. Long-time IC deficiency also resulted in the decrease in biomass and pigments of algae and nitrifying bacteria. IC limitation led to the decreasing N2O production, probably due to its negative effect on ammonia oxidation by AOB. The optimal IC concentration was determined to be 10 mmol L−1 (i.e., IC/N of 1.56, alkalinity of 500 mg CaCO3 L−1) in the algae-bacteria symbiosis reactor, corresponding to higher ammonia oxidation rate of ∼41 mg-N gVSS−1 h−1 and lower N2O emission factor of 0.13 %. This suggests regulating IC concentrations to achieve high ammonium removal and low carbon emission simultaneously in the algae-bacteria symbiosis wastewater treatment process.

Algal-bacterial shortcut nitrogen removal model with seasonal light variations.

The algal-bacterial shortcut nitrogen removal (ABSNR) process can be used to treat high ammonia strength wastewaters without external aeration. However, prior algal-bacterial SNR studies have been conducted under fixed light/dark periods that were not representative of natural light conditions. In this study, laboratory-scale photo-sequencing batch reactors (PSBRs) were used to treat anaerobic digester sidestream under varying light intensities that mimicked summer and winter conditions in Tampa, FL, USA. A dynamic mathematical model was developed for the ABSNR process, which was calibrated and validated using data sets from the laboratory PSBRs. The model elucidated the dynamics of algal and bacterial biomass growth under natural illumination conditions as well as transformation processes for nitrogen species, oxygen, organic and inorganic carbon. A full-scale PSBR with a 1.2 m depth, a 6-day hydraulic retention time (HRT) and a 10-day solids retention time (SRT) was simulated for treatment of anaerobic digester sidestream. The full-scale PSBR could achieve >90% ammonia removal, significantly reducing the nitrogen load to the mainstream wastewater treatment plant (WWTP). The dynamic simulation showed that ABSNR process can help wastewater treatment facilities meet stringent nitrogen removal standards with low energy inputs.

Algal-bacterial granular sludge for simultaneous denitrification and yttrium removal

This study investigated the performance and stability of algal-bacterial granular sludge (ABGS) for the treatment of inorganic wastewater containing ammonia and Y(III), which aimed to shed light on efficient treatment of yttrium-rich rare earth mine wastewater. By seeding heterotrophic granules and dosing exogenous algae, cationic polyacrylamide and sodium acetate in a photo-sequencing batch reactor, the algal and granular symbiosis system was successfully established on Day 50, and mature ABGS was harvested on Day 165. When the concentration of Y(III) was no more than 4 mg/L, the system showed good performance for simultaneous removal of nitrogen and Y(III). However, further increasing the Y(III) concentration to 30 mg/L in Days 144–210 gradually inhibited the bacterial activity and killed most of the functional algae, resulting in significant decrease of the activity of bacteria and chlorophyll a content after Days 135 and 180, as well as the oxygen yield rate of the algae and ammonia oxidation rate after Days 140 and 95. The removal efficiency of total inorganic nitrogen maintained mostly above 90% in Days 46–153, and gradually decreased to approximately 50% in Days 154–210. The Y(III) removal efficiency remained above 98% in Days 96–125, and gradually decreased to approximately 60% in Days 126–210. Most of the algal genera disappeared on Day 210. Conversely, the increase of the relative abundance of Nitrosomonas and Thauera was observed. The nitrogen removal pathways included denitrification and algal assimilation. However, the contribution rate of algae gradually decreased from 22% to 4% due to the accumulation of Y.

Highly efficient and rapid removal of Malathion using non-aerated algae bacteria consortia: Performance, kinetic, and microbial mechanisms

The frequent use of pesticides in human activities introduce Malathion into water， which caused serious environmental pollutants. However, the treatment of these wastewaters is expensive and inefficiency. In this study, two photo-sequencing batch reactors (PSBRs) were established to treat Malathion-containing wastewater using algae bacteria consortia (ABC) in aerated (R1) and non-aerated (R2) conditions, respectively. The removal rates of Malathion by ABC in R1 and R2 after stabilization were 83.6 % and 71.9 %, respectively. The microbial community analysis results indicated that Burkholderia was the dominant population in ABC, which was response for the main Malathion degradation. Furthermore, the investigation of degradation pathways of Malathion discovered that the ABC converted Malathion into inorganic phosphorus. The conversion rates of inorganic phosphorus in the two reactors were 16.9 % and 21.6 %. The results demonstrated that non-aerated ABC have a strong potential adaption on Malathion stress and can removal Malathion from wastewater economically and efficiently.

Characteristics of algal-bacterial aerobic granular sludge treating real wastewater: Effects of algal inoculation and alginate-like exopolymers recovery

Limited information is available on the characteristics of algal-bacterial aerobic granular sludge (AGS) treating real wastewater, especially on its alginate-like exopolymers (ALE) production. In addition, the effect of target microalgae species inoculation on the system performance has not been fully understood. This study aimed to reveal the effect of microalgae inoculation on the characteristics of algal-bacterial AGS and its ALE production potential. Two photo-sequencing batch reactors (PSBR) were employed, namely R1 with activated sludge and R2 with Tetradesmus sp. and activated sludge being inoculated, respectively. Both reactors were fed with locally sourced municipal wastewater and operated for 90 days. Algal-bacterial AGS were successfully cultivated in both reactors. No significant difference was observed between the performances of R1 and R2, reflecting that the inoculation of target microalgae species may not be crucial for the development of algal-bacterial AGS when treating real wastewater. Both reactors achieved an ALE yield of about 70 mg/g of volatile suspended solids (VSS), indicating that a substantial amount of biopolymer can be recovered from wastewater. Interestingly, boron was detected in all the ALE samples, which might contribute to granulation and interspecies quorum sensing. The enrichment of lipids content in ALE from algal-bacterial AGS treating real wastewater reveals its high resource recovery potential. Overall, the algal-bacterial AGS system is a promising biotechnology for simultaneous municipal wastewater treatment and resource (like ALE) recovery.

Achievement and microbial profiles of non-aerated partial nitrification in photo sequencing batch and continuous flow reactors

Nitrite accumulation could be achieved in algal-bacterial consortia without energy-intensive aeration, which could be a sustainable alternative for wastewater treatment. However, few studies focused on the achievement of partial nitrification in different non-aerated algal-bacterial systems and the related microbial mechanisms are still unclear. Here two different algal-bacterial systems (photo-sequencing batch reactor (PSBR) and up-flow sludge blanket bioreactor (PUSB)) were operated for anaerobic effluent treatment and the non-aerated partial nitrification was evaluated. Results showed that the nitrite accumulation rates in the PSBR and PUSB were 92.70 ± 7.81 % and 81.44 ± 11.28 %, respectively, which was constant with microbial activities. Denser algal-bacterial granules were observed in the PSBR, whereas looser algal-bacterial flocs were in the PUSB. Phormidium and Leptolyngbya (i.e., two filamentous cyanobacteria) were enriched in the PSBR and PUSB, respectively, and the higher enrichment of Nitrosomonas and complete inhibition of Nitrospira contributed to better partial nitrification of PSBR. The PUSB had more intensive interspecific interactions and more cooperative behavior in microbial network. Metagenomic analysis revealed that partial denitrification might partially contribute to the nitrite accumulation in the PUSB owing to higher nitrate reductase gene expressions. Overall, this study advances our understandings of the partial nitrification process and nitrite accumulation by algal-bacterial consortia.

Bioremediation of coastal aquaculture effluents spiked with florfenicol using microalgae-based granular sludge – a promising solution for recirculating aquaculture systems

Aquaculture is a crucial industry in the agri-food sector, but it is linked to serious environmental problems. There is a need for efficient treatment systems that allow water recirculation to mitigate pollution and water scarcity. This work aimed to evaluate the self-granulation process of a microalgae-based consortium and its capacity to bioremediate coastal aquaculture streams that sporadically contain the antibiotic florfenicol (FF). A photo-sequencing batch reactor was inoculated with an autochthonous phototrophic microbial consortium and was fed with wastewater mimicking coastal aquaculture streams. A rapid granulation process occurred within ca. 21 days, accompanied by a substantially increase of extracellular polymeric substances in the biomass. The developed microalgae-based granules exhibited high and stable organic carbon removal (83-100%). Sporadically wastewater contained FF which was partially removed (ca. 5.5-11.4%) from the effluent. In periods of FF load, the ammonium removal slightly decreased (from 100 to ca. 70%), recovering 2 days after FF feeding ceased. A high-chemical quality effluent was obtained, complying with ammonium, nitrite, and nitrate concentrations for water recirculation within a coastal aquaculture farm, even during FF feeding periods. Members belonging to the Chloroidium genus were predominant in the reactor inoculum (ca. 99%) but were replaced from day-22 onwards by an unidentified microalga from the phylum Chlorophyta (>61%). A bacterial community proliferated in the granules after reactor inoculation, whose composition varied in response to feeding conditions. Bacteria from the Muricauda and Filomicrobium genera, Rhizobiaceae, Balneolaceae, and Parvularculaceae families, thrived upon FF feeding. This study demonstrates the robustness of microalgae-based granular systems for aquaculture effluent bioremediation, even during periods of FF loading, highlighting their potential as a feasible and compact solution in recirculation aquaculture systems.

Rapid establishment of algal-bacterial granular sludge system by applying mycelial pellets in a lab-scale photo-reactor under low aeration conditions: Performance and mechanism analysis

Light-driven algal-bacterial granular sludge (ABGS) is an innovative low-carbon technology with significant merits in treating municipal wastewater, but how to shorten the photogranulation process, especially under low aeration conditions, is largely unknown. Herein, two strategies were proposed to accelerate the start-up of the ABGS system in photo-sequencing batch reactors (PSBRs) with a low superficial gas velocity of 0.5 cm/s. Compared to directly dosing mycelial pellets (MPs), applying MPs to flocculate algae and using the formed algal-mycelial pellets (AMPs) as carriers enhanced the establishment of the algal-bacterial symbiosis. The ABGS system developed rapidly within 20 days, with a large particle diameter (mean diameter of 321 μm) and excellent settleability (SVI30 of 55.4 mL/g). More importantly, this system could be stably operated for at least 100 days, mainly attributed to the reinforced secretion of protein with unique secondary structure and elevated hydrophobic functional groups. As for the reactor performance, the average removal efficiencies of the ABGS system were 97.8% for organic matter, 80.0% for total nitrogen, and 84.4% for phosphorus. The enrichment of functional bacteria and algae, and the up-regulation of functional genes and enzymes involved in electron production and transport processes likely drove the transformation of the pollutants, underlining the inherent mechanism for the excellent nutrient removal performance. This study provides a promising approach to solve the problem of a long ABGS start-up period and unstable granular structure under low aeration conditions, which is significant for achieving effective wastewater treatment without energy intensive aeration.

Exploring the effects of organic loading rate and domestic wastewater treatment by algal‐bacterial granules under natural daylight conditions

Algal-bacterial granules or phototrophic granules (PGs) comprising phototrophic microorganisms and bacteria are explored in wastewater treatment for achieving both environmental and economic sustainability. This study describes development of PGs and their use in biological treatment of synthetic and real domestic wastewater (sewage) under natural daylight conditions and low organic loading rate (OLR). Development of PGs was sequentially recorded in a photobioreactor operated in photo-sequencing batch reactor (photo-SBR) mode at a low OLR of 1 kgCOD.m-3 .day-1 and the developed PGs was evaluated for treating synthetic wastewater and real municipal wastewater with 0.14 kg COD m-3 .day-1 . PGs formed in the photo-sequential batch reactor (SBR) were compact and dense and exhibited excellent settling properties. The removal efficiencies were determined to be up to 95%, 93%, 97%, 72%, and 88% for turbidity, COD, TOC, NH4 + -N, and NO2 - -N/NO3 - -N, respectively. Additionally, a reduction in total viable bacterial counts and fecal coliform bacteria up to 1.7 × 103 and 7.8 × 102 cfu.mL-1 , respectively, during treatment of real municipal wastewater was achieved. This study demonstrated cultivation of algal-bacterial granules or PGs and their application for treating real municipal wastewater under natural daylight and tropical climate conditions. Further studies are needed on understanding interactions among phototrophic, autotrophic, and heterotrophic microorganisms of complex algal-bacterial consortium for emerging applications in bioremediation and wastewater treatment. PRACTITIONER POINTS: Phototrophic granules (PGs) were cultivated from algal consortium and activated sludge inoculum in photo sequencing batch reactors. Granular photobioreactor was operated at low OLR of 1 kgCOD.m3 .day-1 for developing well-settling algal-bacterial granules. PGs were stable and showed efficient biological treatment of synthetic wastewater and real sewage. Removals for turbidity, pathogens, and ammonium were at 95%, 3-log, and 72%, respectively, from real sewage.

Development of microalgal-bacterial aerobic granules for ammonium removal from wastewater in a photo sequencing batch reactor

Aerobic granular sludge was applied in a method with photo sequencing batch reactor (PSBR) under a constant light/dark cycle (18/6 h). Rapid aggregation of microalgae and bacterial biomass with the increasing production of extracellular polymeric substances (EPS) was recorded. EPS induced microalgal-bacterial growth led to the formation of microalgal-bacterial aerobic granules. Microalgal-bacterial aerobic granules showed maximum ammonium removal of 3.3 mg NH4+-N/L/h, equal to 333 mg NH4+-N/m2/h or 637 mg NH4+-N/mol photon or 0.05 mol NH4+-N/mol photon. Ammonium-nitrogen oxidation was carried out by oxygen produced from the microalgal photosynthesis, with simultaneous nitrification and denitrification in the aerobic and anaerobic zones, respectively. From this study it was observed that the microalgal-bacterial aerobic granules developed in a stirred PSBR and can treat domestic wastewater without external air supply, although the process of granules formation discontinued over time.

Development of Microalgae-Bacteria Aerobic Granular Sludge for Landfill Leachate Treatment

Over the past few decades, aerobic granular sludge has become favorable biotechnology in wastewater treatment. Combining the AGS process with microalgae technology is desired to achieve higher treatment efficiency, especially for high-strength wastewater. This study aims to investigate the effectiveness of microalgae-bacteria AGS in treating landfill leachate. The photo-sequencing batch reactor, inoculated with Acutodesmus obliquus, was fed with old synthetic leachate, and run for 30days. The result showed that chemical oxygen demand (COD) removal up to 96%. The initial ammonia concentration was 130mg/L and achieved an efficiency of up to 80.77%. At the same time, the average removal of the phosphorus was 19.5mg/L, equal to 48.68%. The result of microalgae-bacteria AGS can produce the fast-settling properties of the granules throughout the experiment.

Development and characteristics of microalgae-bacteria aerobic granules treating low strength municipal wastewater

This study aims to assess the feasibility of cultivating microalgae-bacteria aerobic granular sludge using low-strength municipal wastewater (<200 mg COD/L) as a substrate. A laboratory-scale photo-sequencing batch reactor was inoculated with activated sludge and fed with municipal wastewater. The development and characteristics of microalgae-bacteria aerobic granular sludge were observed for 90 days. The average COD removal efficiency of this system was 71%. The granulation process was observed to occur on day 28, indicated by a high biomass accumulation and decreasing sludge volume index (SVI). After 90 days of cultivation, MLSS value was found to be 3.7 g/L and SVI30 at 18.9 mL/g. In addition, the diameter of the granules was significantly increased. Mature microalgae-bacteria aerobic granules were developed with an average and a maximum diameter of 0.65 mm and 6 mm, respectively. Moreover, cocci-shaped bacteria and microalgae cells were observed to reside on the granular surface during observation using field emission scanning electron microscopy (FESEM). The granules exhibited an excellent settling velocity at 80 m/h. The findings suggest the possibility of using low-strength wastewater to develop microalgae-bacteria aerobic granular sludge.

Simultaneous nitritation, denitritation and phosphorus removal in an algal-bacterial consortium system treating low-strength mariculture wastewater

Mariculture wastewater is characterized by high salinity and low concentration of pollutants, which poses a great challenge to the conventional wastewater treatment processes. In this study, an algal-bacterial consortium process for simultaneous organic carbon, nitrogen and phosphorus removal from such wastewater was investigated in a red-blue (4:1) LED photo-sequencing batch reactor (PSBR). Simultaneous bacterial ammonium oxidation (70 %) and algal ammonium assimilation (30 %) was obtained in the photo phase. In the dark phase, a weak ammonium assimilation was also observed. In the PSBR with an influent COD/N of 5:1, the nitrogen removal pathway was identified to be simultaneous nitritation and denitritation probably due to low-rate oxygenation of algae at a light luminance of 500 lx. In addition, the average COD and phosphorus removal efficiencies reached 82.4 % and 68.2 % with a removal activity of 0.63 mg PO43−-P/(L·d). High-throughput sequencing results showed that Nitrosomonus and Nitrospina were the dominant nitrifying genera using oxygen released by Cyanobacteria and Bacillariophyta. Therefore, it is feasible to efficiently remove nitrogen and phosphorus from mariculture wastewater by the algal-bacterial consortium, which opens a new window for the treatment of high-salinity and low-strength wastewater.

Storage strategy of aerobic algae-bacteria granular consortia in photo-sequencing batch reactor

Aerobic algae-bacteria granular consortia (AAG) is a novel biotechnology for wastewater treatment , although the optimal storage operation is in favor of practical application and commercial production of AAG, the information about the performance response and microbial community evolution of AAG during storage process and activation process are still sparse. This experiment selected temperature, time and illumination condition as target parameters to firstly study the influence of storage process on the AAG. The results indicated that AAG could maintain the integrated granular structure under different storage conditions, yet the influence of storage conditions on the properties of AAG was significant. After storage and activation process, the specific removal rates of total phosphorus and ammonia nitrogen of AAG that stored at 25 °C were 1.41–1.98 mg/g SS and 15.44–17.92 mg/g SS, respectively, which were significantly higher than those stored at 4 °C and −25 °C (0.88–1.16 mg/g SS and 8.46–14.14 mg/g SS). The stored time showed significant negative relationship with the EPS concentration (R = −0.47, P < 0.001) and the polysaccharides/protein ratio (R = −0.50, P < 0.001) of AAG, while illumination was conducive to maintain the polysaccharides/protein ratio of AAG (R = 0.43, P < 0.05). In term of target microalgae viability ( Scenedesmus obliquus ), temperature and illumination were the significant factors explaining the change of its relative abundance in AAG at the end of activation process (P < 0.05), which contributed 64.9% and 33.1% of the variation, respectively. Holistic evaluation of seven storage strategies in this study by analytic hierarchy process furtherly indicated that the storage strategy with 25 °C of operational temperature, 30 d of storage time and protect from illumination was preferable for AAG (total weight score = 0.188), while cryopreservation was the least desirable (total weight score = 0.077). • Illumination and shorter stored time are in favor of granular structure stability. • Temperature that is conducive to algae survival can ensure nutrient removal rate. • Normal temperature and illumination deficiency can guarantee Scenedesmus viability. • Optimal storage strategy for AAG was determined based on holistic evaluation by AHP.

How weak static magnetic field contributes to rapid granulation and better performance of microalgal-bacterial granular sludge?

Microalgal-bacterial granular sludge (MBGS) has received considerable attention as an emerging sustainable process for wastewater treatment, whereas achieving rapid granulation is still challenging. Herein, we applied a static magnetic field (5 mT) to accelerate MBGS granulation in photo-sequencing batch reactors (PSBRs). Results showed that complete granulation of MBGS in the reactor with magnetic field (RM) was achieved 20 days before that in the control reactor (RC). The magnetic field significantly promoted microbial growth, sludge settleability and granule density. The treatment performance for COD (84.1 %–96.7 %), ammonium (91.7 %–100 %) and phosphorus (71.5 %–83.3 %) was efficient and similar in both reactors. However, the volumetric removal rate for total nitrogen (TN) was greatly improved by magnetic field due to increased nitrogen assimilation and denitrification. Moreover, mature MBGS in RM showed higher specific oxygen production rate (SOPR) and specific oxygen uptake rate (SOUR), approximately 90 % and 16 % greater than those in RC. The accumulation of metal ions (iron and calcium), the enhanced production of extracellular polymeric substances (EPS, especially proteins (PN)), and the enrichment of functional bacteria (EPS producers and potential denitrifiers) and phototrophs (Tetradesmus, Monoraphidium and Desmodesmus) contributed to rapid granulation and better performance of MBGS. This study provides an economic, effective and environmental-friendly method for rapid cultivation of MBGS, which would be helpful for large scale applications of MBGS.

Dynamic model of algal-bacterial shortcut nitrogen removal in photo-sequencing batch reactors

This study investigated algal-bacterial shortcut nitrogen removal (SNR) in photo-sequencing batch reactors (PSBRs) for treatment of high ammonium strength wastewater using both experimental and modeling approaches. Bench-scale PSBR studies were carried out under alternating light and dark cycles, provided aerobic and anoxic conditions that promoted nitritation/ denitritation. Total nitrogen removal efficiencies >90% were achieved when favorable operating conditions, including solids retention time (SRT) and organic and inorganic carbon availability, were applied for the functional microorganisms. A dynamic model was developed to simulate conversions of species and the activity of algae, ammonia oxidizing, nitrite oxidizing and heterotrophic bacteria. In addition, biomass wasting during each cycle was estimated by the model to maintain the targeted SRT. The model was able to capture the dynamics of nitrogen removal, substrate utilization and biomass generation under varying operating conditions and can potentially be used for large scale PSBR design and optimization.

Mechanism and regulation of filamentous algal-bacterial symbiosis based on microbiological quorum sensing.

In algae-bacteria symbiotic systems, algae and bacteria work cooperatively to reduce aeration demand and carbon emissions during wastewater treatment. However, controlling and stabilizing microbial communities in the conventional algae-bacteria symbiotic systems are complicated and unstable. We, therefore, developed a novel sewage treatment system based on a filamentous algae-bacterial symbiotic granule system (AB) in a photo-sequencing batch reactor (PSBR). The exogenous signal molecules (i.e., N-acyl-homoserine lactones [AHLs]) were applied to promote the algae-bacteria consortia formation. The characteristics and performance of the mature algae-bacterial granular consortia were investigated and then compared with that of the activated sludge (AS) system under identical operating conditions. The chemical oxidation demand (COD) removal efficiencies were greater than 90% in the dynamic synergistic investigation, even without aeration. However, the addition of AHLs (5, 50, and 200 nmol/L) had a negligible effect on treatment performance. In static conditions, 10-9 nmol/L of AHLs can significantly regulate the algae-bacteria symbiotic system, and AHLs (<50 nmol/L) improved COD and NH4 + removal efficiencies by up to 90%. Moreover, the addition of AHLs augmented polysaccharide secretion but had little effect on protein secretion. In comparison to the AS system, the AB system demonstrated promise in terms of pollution removal efficiency and microbial diversity enhancement. PRACTITIONER POINTS: Oscillatoria can serve as an excellent biological carrier for immobilizing bacteria. AHLs (10-9 mol/L) regulated the operation state of algae-bacteria symbiotic system. AHLs altered the composition and content of EPS in the algae-bacteria system.

Rapid start-up of photo-granule process in a photo-sequencing batch reactor under low aeration conditions: Effect of inoculum AGS size

The photo-granule process is an effective and economically feasible alternative for wastewater treatment, but little information is available regarding how to speed up the photo-granulation process. In this study, the effect of inoculum aerobic granular sludge (AGS) size on the start-up of the photo-granule process was investigated under low aeration conditions (superficial gas velocity of 0.5 cm/s). For this purpose, the inoculum AGS was sorted into various size-categories (0.4–0.8 mm, 0.8–1.4 mm, 1.4–2.2 mm, and > 2.2 mm) to serve as individual inoculum sludge. The excellent settling properties (SVI5 of 39.3 mL/g), strong mechanical strength, efficient nutrient removal (COD: 94.2–97.1%; TN: 80.1–84.8%; TP: 60.4–91.5%), and high biodiesel yields (12.11 mg/g MLSS) were rapidly achieved in the system inoculated with 0.8–1.4 mm AGS. The granulation process was facilitated by filamentous algae as the nucleus, extracellular polymeric substances as the backbone, and the enrichment of functional bacteria (such as Thauera and Sphingorhabdus). Furthermore, the inherent influencing mechanisms of inoculum AGS size on the photo-granulation were revealed from cellular hydrophobicity, surface thermodynamics, and sludge aggregation behavior. This study provides a novel start-up approach of the photo-granule process by inoculating with the optimal AGS size, which is convenient, practically feasible and significantly reduced the aeration consumption.

Uncertainty and sensitivity analysis of algal-bacterial model under different ranges of parameter variation

Based on the Activated Sludge Model No.3, a comprehensive model consisting of autotrophic bacteria, algae, and heterotrophic bacteria was presented in this work to describe the relationship among microorganisms and substrates in photo-sequencing batch reactors. The proposed model, which is called the algal-bacteria model, has involved a total of 31 parameters. The standard regression coefficient method was used to conduct global sensitivity analysis of the algal-bacteria model proposed was used to reduce the experiment time and energy of the experimenters, which determined that eight sensitivity parameters from analysis results according to the absolute value of sensitivity indices SRC. Analyzing the influence of different parameter value ranges on the sensitivity analysis, it provides a reference for the parameter sensitivity and uncertainty analysis of the algae-bacteria model. The results show that the algal-bacteria model simulates the removal process of complex nutrients well, and the parameter values affect the sensitivity analysis, but the identification of the most sensitive parameters will not be affected. Moreover, in terms of predicting the removal of dissolved oxygen and pollutants, the simulation results were proved to be in good agreement with the experimental data. It was demonstrated that the established model could be used as a valuable tool for optimizing the parameters of photo-sequencing batch reactors. Key findings of this paper include (1) representation of a comprehensive model to describe the interactions among bacteria, algae, and substrates; (2) assessment of the reliability of model parameters; (3) adoption of a novel method to estimate the most sensitive parameters and evaluate the influence of the change of parameters on the sensitivity analysis results. Our findings suggest that the application of the algal-bacterial consortia system may provide a viable technology in wastewater treatment.