Photo-sequencing Batch Reactors Research Articles

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.

Mechanistic insights into nitrification by microalgae-bacterial consortia in a photo-sequencing batch reactor under different light intensities

NH4+ removal by a consortium of microalgae, ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) was examined in a photo-sequencing batch reactor (PSBR) under various light intensities (150, 500, 1500 and 2000 μmol m−2 s−1). Nitrification performance revealed that the light stress tolerance of the consortium was up to 1500 μmol m−2 s−1 during the 12 h study. NH4+ removal efficiencies due to nitrification and microalgae uptake at 150, 500, 1500 and 2000 μmol m−2 s−1 light intensities are 100, 100, 6.2 and −2.2%, respectively. The nitrogen mass balance revealed that the microalgal-nitrifying (AOB and NOB) bacterial consortium utilized 19.89% of supplied ammonium for the growth and maintenance of microalgae, whereas 79.29% was eliminated through bacterial nitrification process at 150 μmol m−2 s−1. Ammonium uptake and bacterial nitrification were affected at light intensity ≥1500 μmol m−2 s−1, thus revealing that ammonium removal mechanism is strongly governed by the daily average light intensity (DALI). Based on the empirical equations to calculate the oxygen balance in PSBR the effect of DALI on nitrification performance was deduced as follows: (1) below 40 μmol m−2 s−1: insufficient O2 for nitrification; (2) at 40 μmol m−2 s−1: sufficient oxygen for nitrification with less than saturated dissolved oxygen; (3) 40–160 μmol m−2 s−1: sufficient oxygen for nitrification with significant dissolved oxygen; (4) above 160 μmol m−2 s−1: failure of nitrification, owing to inhibition of microalgal-bacterial consortia.

Enhanced removal of antibiotics and decreased antibiotic resistance genes in the photo-sequencing batch reactor during the aquaculture wastewater treatment

ABSTRACT The performance of photo-sequencing batch reactor (PSBR) in removing multiple antibiotics and nutrients from aquaculture wastewater as well as the antibiotic resistance genes (ARGs) proliferation were firstly investigated during the long-term experiments. The operational conditions (i.e. light intensity, light time, aeration and solid retention time) were optimised to realise the simultaneous removal of antibiotics and nutrients. It was found that, compared with traditional SBR, PSBR has similar nutrient removal rate and a 30% higher antibiotics removal rate due to the corporation of microalgae (Chlorella) and bacteria, and the absolute abundance of ARGs decreased by 78% in PSBR. Further investigation showed that PSBR had certain advantages in removing quinolones and the corresponding removal rate could reach up to 90%. In terms of the mechanisms, the possible metabolic pathway of antibiotic was analysed and the intermediate metabolites were different from that of the reported studies. The microbial communities were also affected by microalgae and the relative abundance of certain bacteria (such as members of the families Rhodocyclaceae and Burkholderiaceae), which were positively correlated with some ARGs, decreased in PSBR. This study provides an alternative and effective method to aquaculture wastewater treatment, which present high nutrients and antibiotics removal efficiencies and low ARGs transmission.

Photo-sequencing batch reactor with Klebsormidium nitens: a promising microalgal biotechnology for sustainable phosphorus management in wastewater treatment plants.

This study aims at improving the existing algal-based wastewater treatment technologies by overcoming some of the major drawbacks of these systems such as large required land area, culture contamination, and energy-intensive algal harvesting. The experiments were carried out in an open photo-sequencing batch reactor at a laboratory-scale for nearly 2 months. A specific strain ACUS00207 of the aeroterrestrial green microalga Klebsormidium nitens (Kützing) Lokhorst was used. The strain is native to Bulgaria and belongs to a species that has never been used before in suspended growth systems for wastewater treatment for phosphorus removal. The culture of K. nitens showed promising results: phosphorus removal rates ranging from 0.4 to 1 mg total phosphorus L-1 d-1, efficient settling properties, and resistance to culture contamination with native microalgae. On the basis of the observed phosphorus removal mechanism of biologically mediated chemical precipitation/phosphorus precipitation, an innovative working mode of the sequencing batch reactor is suggested for reducing the hydraulic retention time and the required land area.

Light as a Novel Inhibitor of Nitrite-Oxidizing Bacteria (NOB) for the Mainstream Partial Nitrification of Wastewater Treatment

Conventional biological nutrient removal processes in municipal wastewater treatment plants are energy-consuming, with oxygen supply accounting for 45–75% of the energy expenditure. Many recent studies examined the implications of the anammox process in sidestream wastewater treatment to reduce energy consumption, however, the process did not successfully remove nitrogen in mainstream wastewater treatment with relatively low ammonia concentrations. In this study, blue light was applied as an inhibitor of nitrite-oxidizing bacteria (NOB) in a photo sequencing batch reactor (PSBR) containing raw wastewater. This simulated a biological nitrogen removal system for the investigation of its application potential in nitrite accumulation and nitrogen removal. It was found that blue light illumination effectively inhibited NOB rather than ammonia-oxidizing bacteria due to their different sensitivity to light, resulting in partial nitrification. It was also observed that the NOB inhibition rates were affected by other operational parameters like mixed liquor suspended solids (MLSS) concentration and sludge retention time (SRT). According to the obtained results, it was concluded that the process efficiency of partial nitrification and anammox (PN/A) could be significantly enhanced by blue light illumination with appropriate MLSS concentration and SRT conditions.

Rapid Start-Up of Photo-Granule Process in a Photo-Sequencing Batch Reactor Under Low Aeration Condition: Impact of Inoculum Ags Size

Rapid Start-Up of Photo-Granule Process in a Photo-Sequencing Batch Reactor Under Low Aeration Condition: Impact of Inoculum Ags Size

Behavior of algal-bacterial granular sludge in a novel closed photo-sequencing batch reactor under no external O2 supply

Algal-bacterial aerobic granular sludge (AB-AGS) as a symbiosis system possesses high potential for being operated without external O2 supply. In this study, a novel lab-scale closed photo-sequencing batch reactor (PSBR) was developed for AB-AGS operation under successively open (Phase Ⅰ) and closed (Phase Ⅱ) conditions. Results show that AB-AGS maintained almost 100% of organics removal, exhibiting higher removals of phosphate (63 ± 20%), K+ (19 ± 12%) and Mg2+ (26 ± 12%), and higher chlorophylls content during Phase II. Meanwhile, only O2 besides N2 was detectable in the headspace of PSBR. The change of granular structure and faster algae growth during Phase Ⅱ may contribute to the increase of microbial activity and phosphorus bioavailability, in which lower extracellular polymeric substances content may account for low biomass retention. Results from this closed PSBR imply that AB-AGS has the potential to reduce some greenhouse gases like CO2 and CH4 emission.

Novel shortcut biological nitrogen removal method using an algae-bacterial consortium in a photo-sequencing batch reactor: Process optimization and kinetic modelling

This study evaluated a novel shortcut nitrogen removal method using a mixed consortium of microalgae, enriched ammonia oxidizing bacteria (AOB) and methanol utilizing denitrifier (MUD) in a photo-sequencing batch reactor (PSBR) for treating ammonium rich wastewater (ARWW). Alternating light and dark periods were followed to obtain complete biological nitrogen removal (BNR) without any external aeration and with the addition of methanol as the sole carbon source, respectively. The results showed that influent NH4+ was oxidized to NO2− by AOB during the light periods at a rate of 8.09 mg NH4+-N L−1h−1. Subsequently, NO2− was completely reduced during the dark period due to the action of MUD in presence of methanol. The high activities of ammonia monooxygenase (AMO) and nitrite reductase (NIR) enzymes revealed the strong role of AOB and MUD for achieving shortcut nitrogen removal from the wastewater. The reduced activities of nitrate reductase (NR) and nitrite oxidoreductase (NOR) at a high concentration of DO, NH4+ and NO2−in the system further confirmed the nitrogen removal pathway involved in the process. The biomass produced from these experiments showed good settling properties with a maximum sedimentation rate of 0.7–1.8 m h−1, a maximum sludge volume index (SVI) of 193 ml g−1- 256 ml g−1and floc size of 0.2–1.2 mm. In order to describe the growth and interaction among the algae, AOB and MUD for nitrogen removal in the system, the experimental results were fitted to four metabolic models, which revealed best fit of the experimental data due to the models based on algae-AOB and algae-AOB-MUD activities than with the other two models.

Stability and performance of algal-bacterial granular sludge in shaking photo-sequencing batch reactors with special focus on phosphorus accumulation

The granular stability, nutrients removal and phosphorus (P) accumulation of algal-bacterial aerobic granular sludge (AGS) was examined by using shaking photoreactors (at a fixed light/dark cycle of 12 h/12 h). During the 25 days’ operation, algal-bacterial AGS possessed good granular integrity (8.4 ± 0.6%), and excellent removals of dissolved organic carbon (94.8 ± 1.6%) and total nitrogen (71.1 ± 3.3%). More extracellular proteins (153.7 ± 2.3 mg/g) were excreted from the granules with a high proteins/polysaccharides ratio (∼7.4) on day 25, especially the tightly bound proteins mainly responsible for granular stability. Decrease in P content, especially non-apatite inorganic P relating to Fe-PO4 precipitates, was detected in the granules to some extent, although 54.8 ± 17.1% of total P removal was achieved during the light-on cycles. Still, high P bioavailability (92.0%) was kept in the algal-bacterial AGS throughout the test period. Further optimization of light-on/light-off cycle and hydraulic/sludge retention time is demanding for better and stable P accumulation in the algal-bacterial granules with high bioavailability.

Selection of cyanobacteria over green algae in a photo-sequencing batch bioreactor fed with wastewater

In this work, a strategy based on photo-sequencing batch operation was used to select cyanobacteria over unsettled green algae in a wastewater treatment system, evaluating for the first time the effect of hydraulic regimes on nutritional dynamics and microorganisms' competition. During 30 days of operation, an initial microalgae mixed consortia dominated by the green microalgae Scenedesmus sp. was cultivated in two different photo-sequencing batch reactors operated at hydraulic retention time (HRT) of 6 days (PSBR6) and 4 days (PSBR4) at a theoretical solids retention time (SRT) of 10 d. Both reactors were compared with a semi-continuous reactor (SC10) operated at 10 d of HRT and 10 days of SRT (used as a control). The results indicated that PSBR6 and PSBR4 decreased Scenedesmus sp. population by 88% and 48%, respectively. However, only PSBR6 provided suitable conditions to select cyanobacteria from an initial green algae dominated culture. These conditions included volumetric loads of 11.72 mg TN L−1 d−1, 2.04 mg TP L−1 d−1 and 53.31 mg TOC L−1 d−1. The remaining nutrients in the culture led also to a phosphorus limiting N:P ratio (34:1) that improved the increase of cyanobacteria from an initial 2% until 70% of the total population. In addition, PSBR6 reached a biomass production of 0.12 g L−1 d−1, while removing TN, TP and TOC by 58%, 83% and 85%, respectively. Conversely, the application of higher nutrients loads caused by lower HRT (PSBR4) led to an increase of only 13% of cyanobacteria while SC10 remained with the same biomass composition during all the experimental time. Thus, this study showed that the dominance of cyanobacteria in microalgal-based wastewater treatment systems can be controlled by the operational and nutritional conditions. This knowledge could contribute to control microalgae contamination from up-scaling cyanobacterial biomass production in wastewater treatment systems.

Laboratory-scale investigation on the role of microalgae towards a sustainable treatment of real municipal wastewater.

Engineered microalgal-bacteria consortia are an attractive solution towards a low-cost and sustainable wastewater treatment that does not rely on artificial mechanical aeration. In the research conducted for this study, a bench-scale photo-sequencing-batch reactor (PSBR) was operated without external aeration. A spontaneous consortium of microalgae and bacteria was developed in the PSBR at a concentration of 0.8-1.7 g TSS/L. The PSBR ensured removal efficiency of 85 ± 8% for chemical oxygen demand (COD) and 98 ± 2% for total Kjeldahl nitrogen (TKN). Nitrogen balance revealed that the main mechanisms for TKN removal was autotrophic nitrification, while N assimilation and denitrification accounted for 4% and 56%, respectively. The development of dense microalgae-bacteria bioflocs resulted in good settleability with average effluent concentration of 16 mgTSS/L. The ammonium removal rate was 2.9 mgN L-1 h-1, which corresponded to 2.4 mgN gTSS-1 h-1. Although this specific ammonium removal rate is similar to activated sludge, the volumetric rate is lower due to the limited total suspended solids (TSS) concentration (three times less than activated sludge). Therefore, the PSBR footprint appears less competitive than activated sludge. However, ammonium was completely removed without artificial aeration, resulting in a very cost-effective process. Only 50% of phosphorus was removed, suggesting that further research on P uptake is needed.

Effects of light intensity on oxygen distribution, lipid production and biological community of algal-bacterial granules in photo-sequencing batch reactors

The effects of light intensity (0–225 µmol m−2 s−1) on oxygen distribution, lipid production and biological community structure of algal-bacterial granules were investigated in six identical photo-sequencing batch reactors (with a dark/light cycle of 12 h/12 h). Typically green algal-bacterial granules could be developed at a light intensity of ≥135 µmol m−2 s−1. The lipid content was significantly increased under higher light intensity, while the percentage of saturated fatty acid methyl esters was remarkably decreased. Results showed that light intensity ≥90 µmol m−2 s−1 yielded enough O2 production from algae, creating aerobic/anoxic zone (0.3–0.6 mg-O2/L) in the core of granules and thus efficient algal-bacterial symbiosis system. Enhanced nitrogen and phosphorus removals were achieved in the reactors with stronger light illumination, probably attributable to the enrichment of ammonia oxidizing bacteria (Comamonadaceae and Nitrosomonadaceae) and algae (Navicula and Stigeoclonium). Illuminance ≥180 µmol m−2 s−1 was found to be unfavorable for Nitrospiraceae.

Nitrogen removal in photo sequence batch reactor using algae-bacteria consortium

In this study, photo-sequencing batch reactors (PSBR) were setup to evaluate the effect of photoperiod (i.e. 24 h’ illumination and 16 h/8 h light-dark cycle) on NH4+-N removal performance of algae-bacteria consortium under long-term low-light intensity condition. It was observed that constant NH4+-N removal rate of 60 mg N/L/d was achieved in both photoperiods at low light intensity (LI) of 1000 lx. Longer photoperiod favored higher production of biomass. The photoperiod of 16 h/8 h light-dark cycle condition produced less biomass but exhibited same nitrification rate and slightly higher denitrification efficiency (30 mg/L) than the reactor that was operated at 24 h illumination. The results of this study demonstrated that using algae-bacteria consortia could be a sustainable and cost-effective method to treat NH4+-N-loaded wastewater.

Natural sunlight induced rapid formation of water-born algal-bacterial granules in an aerobic bacterial granular photo-sequencing batch reactor

Wastewater treatment by means of algal-bacterial granules has become a hot topic worldwide recently. Rapid granulation of algal-bacterial granules was achieved in an aerobic bacterial granular sequencing batch reactor (SBR) under natural sunlight exposure. Occurrence of abundant filamentous bacteria bridging the water-born algae, and overproduction of extracellular polymeric substances (EPS) (especially polysaccharides (PS), tryptophan & protein-like, and humic acid-like substances) were observed on the first 3 days, while the algae grew into the inner side of the granules and mature granules were obtained on day 7. The growth of the water-born algae slightly decreased the settleability, mean sizes of the granules, but stimulated the bioactivity significantly. Whereas, the biomass retention decreased before day 3, and got stable soon with the maturation period with symbiotic growth of algal-bacterial biomass. Illumina results revealed that the introduction of algae reduced the richness and diversity of bacterial community. Besides, few changes in structure and some compositions shifts in bacterial communities were found, while the predominant algae shifted from Diatomea to green algae Chlorophyceae. The possible mechanism for natural sunlight induced granulation of algal-bacterial granules was thus proposed based on the interactions between algae and bacteria.

A novel mechanistic model for nitrogen removal in algal-bacterial photo sequencing batch reactors

A comprehensive mathematical model was constructed to evaluate the complex substrate and microbial interaction in algal-bacterial photo sequencing batch reactors (PSBR). The kinetics of metabolite, growth and endogenous respiration of ammonia oxidizing bacteria, nitrite oxidizing bacteria and heterotrophic bacteria were coupled to those of microalgae and then embedded into widely-used activated sludge model series. The impact of light intensity was considered for microalgae growth, while the effect of inorganic carbon was considered for each microorganism. The integrated model framework was assessed using experimental data from algal-bacterial consortia performing sidestream nitritation/denitritation. The validity of the model was further evaluated based on dataset from PSBR performing mainstream nitrification. The developed model could satisfactorily capture the dynamics of microbial populations and substrates under different operational conditions (i.e. feeding, carbon dosing and illuminating mode, light intensity, influent ammonium concentration), which might serve as a powerful tool for optimizing the novel algal-bacterial nitrogen removal processes.

Nutrients and biomass dynamics in photo-sequencing batch reactors treating wastewater with high nutrients loadings

The present study investigates different strategies for the treatment of a mixture of digestate from an anaerobic digester diluted and secondary effluent from a high rate algal pond. To this aim, the performance of two photo-sequencing batch reactors (PSBRs) operated at high nutrients loading rates and different solids retention times (SRTs) were compared with a semi-continuous photobioreactor (SC). Performances were evaluated in terms of wastewater treatment, biomass composition and biopolymers accumulation during 30 days of operation. PSBRs were operated at a hydraulic retention time (HRT) of 2 days and SRTs of 10 and 5 days (PSBR2-10 and PSBR2-5, respectively), whereas the semi-continuous reactor was operated at a coupled HRT/SRT of 10 days (SC10-10). Results showed that PSBR2-5 achieved the highest removal rates in terms of TN (6.7 mg L−1 d−1), TP (0.31 mg L−1 d−1), TOC (29.32 mg L−1 d−1) and TIC (3.91 mg L−1 d−1). These results were in general 3–6 times higher than the removal rates obtained in the SC10-10 (TN 29.74 mg L−1 d−1, TP 0.96 mg L−1 d−1, TOC 29.32 mg L−1 d−1 and TIC 3.91 mg L−1 d−1). Furthermore, both PSBRs were able to produce biomass up to 0.09 g L−1 d−1, more than twofold the biomass produced by the semi-continuous reactor (0.04 g L−1 d−1), and achieved a biomass settleability of 86–92%. This study also demonstrated that the microbial composition could be controlled by the nutrients loads, since the three reactors were dominated by different species depending on the nutritional conditions. Concerning biopolymers accumulation, carbohydrates concentration achieved similar values in the three reactors (11%), whereas < 0.5% of polyhydrohybutyrates (PHB) was produced. These low values in biopolymers production could be related to the lack of microorganisms as cyanobacteria that are able to accumulate carbohydrates/PHB.

Enhanced nitrogen removal and energy saving in a microalgal–bacterial consortium treating real municipal wastewater

The optimization of total nitrogen removal from municipal wastewater was investigated in a laboratory-scale photo-sequencing batch reactor (PSBR) operated with a mixed microalgal-bacterial consortium spontaneously acclimatized to real wastewater. No external aeration was provided in the PSBR to reduce energy consumption: oxygen was only supplied by the microalgal photosynthesis. The enhancement of total nitrogen removal was achieved through: (1) feeding of wastewater in the dark phase to provide readily biodegradable COD when oxygen was not produced, promoting denitrification; (2) intermittent use of the mixer to favor simultaneous nitrification-denitrification inside the dense flocs and to achieve 41% energy saving with respect to continuous mixing. Efficient COD removal (86 ± 2%) was observed, obtaining average effluent concentrations of 37 mg/L and 22 mg/L of total COD and soluble COD, respectively. TKN removal was 97 ± 3%, with an average effluent concentration of 0.5 ± 0.7 mg NH4 +-N/L. Assimilation of nitrogen by heterotrophic bacteria accounted only for 20% of TKN removal, whilst the major part of TKN was nitrified. In particular, the nitrification rate was 1.9 mgN L-1 h-1 (specific rate 2.4 mgN gTSS-1 h-1), measured with dissolved oxygen near zero, when the oxygen demand was higher than the oxygen produced by photosynthesis. Total nitrogen of 6.3 ± 4.4 mgN/L was measured in the effluent after PSBR optimization.

Evolution of real municipal wastewater treatment in photobioreactors and microalgae-bacteria consortia using real-time parameters

In the treatment of real municipal wastewater with photo-sequencing batch reactors (PSBR), operating strategies able to achieve high levels of pollutant removal, but reduce the hydraulic retention time (HRT), are imperative for making microalgae-bacteria consortia more competitive than conventional activated sludge systems. In regard to real-time monitoring, on-line probes like Dissolved Oxygen (DO), pH and oxidation–reduction potential (ORP) are cheap and reliable, but their exploitation has been largely overlooked in PSBRs. This paper proposes the use of DO, pH and ORP profiles to reveal the evolution of wastewater treatment in a PSBR treating real municipal wastewater with a mixed consortium of microalgae and bacteria. The PSBR ensured removal efficiency of 87 ± 5% for COD and 98 ± 2% for TKN without external aeration; indeed, photosynthesis was the only driver of the oxygen production. Considering the combined effects of photosynthetic oxygenation and microbial oxygen consumption, some practical information was gathered to understand the complex profiles of the on-line parameters. During dark and light phases, Zero-DO values, DO and pH raises, and their relative peaks were discussed to evaluate correctly the conclusion of the wastewater treatment and therefore to adjust the duration of the PSBR cycle. In particular: (1) two simultaneous “characteristic points”, “Ammonia valley” (pH profile) and “DO breakpoint” (DO profile), detected univocally the complete ammonium removal; (2) the absolute peaks of DO, pH and ORP at maximum irradiance revealed that wastewater treatment was complete and the cycle could be concluded. In this way, these characteristic points were exploited for the optimization of the PSBR cycle, which was concluded after 15–26 h, reducing the HRT by more than 45%.

The mechanism of enhanced wastewater nitrogen removal by photo-sequencing batch reactors based on comprehensive analysis of system dynamics within a cycle

To understand the mechanism of enhanced nitrogen removal by photo-sequencing batch reactors (photo-SBRs), which incorporated microalgal photosynthetic oxygenation into the aerobic phases of a conventional cycle, this study performed comprehensive analysis of one-cycle dynamics. Under a low aeration intensity (about 0.02 vvm), a photo-SBR, illuminated with light at 92.27 μ·mol·m−2·s−1, could remove 99.45% COD, 99.93% NH4+-N, 90.39% TN, and 95.17% TP, while the control SBR could only remove 98.36% COD, 83.51% NH4+-N, 78.96% TN, and 97.75% TP, for a synthetic domestic sewage. The specific oxygen production rate (SOPR) of microalgae in the photo-SBR could reach 6.63 fmol O2·cell−1·h−1. One-cycle dynamics shows that the enhanced nitrogen removal by photo-SBRs is related to photosynthetic oxygenation, resulting in strengthened nitrification, instead of direct nutrient uptake by microalgae. A too high light or aeration intensity could deteriorate anoxic conditions and thus adversely affect the removal of TN and TP in photo-SBRs.

Nutrients and biomass dynamics in photo-sequencing batch reactors treating wastewater with high nutrients loadings

Nutrients and biomass dynamics in photo-sequencing batch reactors treating wastewater with high nutrients loadings