Nutrient Removal Efficiency Research Articles

Enhanced cultivation and lipid production of isolated microalgae strains using municipal wastewater

Cultivation of microalgae in wastewater is strongly related to the selection of suitable species for a specific type of wastewater. Thus, this study presented the cultivation of isolated microalgae strains, Acutodesmus obliquus CN01 and Desmodesmus maximus CN06 using municipal wastewater, along with Chlorella vulgaris NIES-1269 as the control species. The highest growth rate of 0.23/day was achieved by D . maximus CN06, while all species exhibited excellent nutrient removal efficiencies. High removal of NH 3 -N was demonstrated by all strains and complete total phosphorus removal was observed to be fastest in A. obliquus CN01 at 3.8 mg P/gDCW.day, followed by D . maximus CN06 and C. vulgaris NIES-1269, respectively. Lipid productivity was found to be highest in D . maximus CN06 at 3.43 mg/L.day which majorly consisted of hexadecanoic (C16:0) and oleic (C18:1) acids. The extracted fatty acids indicated good potential to be applied for biodiesel production. This study has shown that cultivation of isolated microalgae strain in municipal wastewater is beneficial for high nutrient removals and lipid accumulation. • Tropically isolated microalgae strains were cultivated in municipal wastewater. • Complete total phosphorus removal by all microalgae strains. • Highest growth rate and lipid accumulation by Desmodesmus maximus CN06. • Possible utilization of extracted FAME for biodiesel production.

Deciphering the effect of algae sources on the formation of algal-bacterial granular sludge: Endogenous versus exogenous algae

As a key factor affecting the granulation of symbiotic sludge , the evaluation of the influence of algae sources on the ABGS system is expected to further optimize the cultivation of ABGS. In this study, formation of algal-bacterial granular sludge (ABGS) cultivated with endogenous algae and exogenous algae was comparatively investigated. During ABGS formation, the presence of algae facilitated the settleability improvement and biomass growth. ABGS cultivated with endogenous algae achieved a faster granulation (39 days) than that with exogenous algae (46 days). Inoculating exogenous algae could significantly improve the nutrient removal efficiency at the start-up stage. Tightly-bound extracellular polymeric substances (TB-EPS) were crucial for ABGS formation and maintenance, especially protein (PN) components. More EPS enriched in the mature ABGS enhanced by endogenous algae. The spatial distribution of protein and α-D-glucopyranose was obviously affected by algal sources. During ABGS formation, there was a directional selection in algal species , and the operation condition of the system was the key factor affecting the structure of algae community. The effect of algae sources on the bacterial community structure of ABGS took time to manifest. Correlation analysis showed that endogenous algae contributed more to the metabolism and property improvement of sludge than exogenous algae. • ABGS cultivated by the endogenous algae achieved a faster granulation. • Inoculating EX-A obviously improved the nutrient removal at the initial stage. • Mature ABGS cultivated with endogenous algae could secrete more EPS. • Algae source was not the dominant factor in determining the algal community in ABGS. • The genes related to metabolism were more enriched by endogenous algae in mature ABGS.

Stable denitrification performance of a mesh rotating biological reactor treating municipal wastewater

The mesh rotating biological reactor (MRBR) is one of the advanced modifications of the rotating biological contactor. MRBRs have a high specific surface area for biomass in order to achieve efficient nutrient removal performance. This study evaluated the denitrification performance of an MRBR during municipal wastewater treatment. A laboratory-scale MRBR was continuously operated for approximately 550 days under ambient conditions, fed with actual sewage. Influent NO3−-N concentration was decreased from 27.8 ± 6.0 mg-N L−1 to an effluent value of 8.4 ± 4.8 mg-N L−1 at ≥20 ºC under 2 h of hydraulic retention time. The total nitrogen removal was 190 ± 130 g N m−3 d−1, compared to 860 ± 310 g N m−3 d−1 with added nitrate at ≥20 ºC and 100 ± 47 g N m−3d−1 compared to 830 ± 220 g-N m−3d−1 with added nitrate at ≤15 ºC. A batch test showed that soluble chemical and biological oxygen demand removal efficiencies were 87% and 93%, respectively, after 2 h of operation. While NO3−-N remained after 2 h, adding methanol to enhance denitrification resulted in 93% removal after 8 h. Microbial analysis was performed on samples taken from the surface and inside the mesh carrier. Comamonadaceae, Thiotrichaceae, and Rhodocyclaceae denitrifying bacteria dominated the bacterial community and accelerated the performance of the MRBR. The study revealed that water temperature changes have an insignificant effect on denitrification and that the process can be performed stably throughout the year.

Cost-effective treatment of sewage wastewater using microalgae Chlorella vulgaris and its application as bio-fertilizer

The present study lays an emphasis on microalgae-based treatment of sewage wastewater using Chlorella vulgaris to remove toxic pollutants and nutrients from the wastewater, making it safely dischargeable and reusable as bio-fertilizer, with simultaneous biomass and lipid production. The sewage treatment experiment was carried out in a 50 L capacity outdoor open syntax tank. The results exhibited the survival efficiency of C. vulgaris in sewage wastewater generating 0.67 g/L biomass and 0.26 g/L lipid yields. Crucial environmental factors like light intensity and temperatures have played a key role in biomass growth, lipid accumulation and nutrient removal efficiencies of C. vulgaris. The concentrations of significant nutrients like nitrates, COD and BOD were reduced up to 93%, 95% and 92% respectively. Other nutrients and parameters were removed up to 90% on an average. The treated sewage wastewater was then supplied as a bio-fertilizer to grow Solanum lycopersicum (tomato) plants as a comparative to chemical fertilizer grown plants. The results obtained from the comparative analyses showed that the tomato plant grown with treated sewage wastewater showed efficient growth and productivities as good as the chemical fertilizer aided yields. This study proved that sewage can be a successful replacement to the chemical fertilizers. The details are ornately discussed inside the paper.

Phycoremediation of textile and tannery industrial effluents using microalgae and their consortium for biodiesel production

The study reveals the treatment of textile and tannery effluents using freshwater microalgal strains, Chlorella vulgaris (NRMC-F 0128), Scenedesmus dimorphus (NRMC-F 0178), Coelastrella sp., (NRMC-F 0179) and Chlorococcum sp., (NRMC-F 0181) isolated from betel field. The physiochemical parameters of the textile and tannery effluents were analyzed prior to the experimentations. The nutrient removal efficiency of all the cultures was evaluated in both lab and outdoor conditions. Further, a consortium of two efficiently growing and lipid producing strains, Chlorella vulgaris (NRMC-F 0128), Scenedesmus dimorphus (NRMC-F 0178) was tested against effluent degradation under 30 L pond conditions. The levels of pH, TDS (total dissolved solids), EC and nitrite, nitrate, sodium, phosphate, calcium, magnesium, lead, iron, copper and cadmium of both the textile mill and tannery industrial effluents were reduced upon algae mediated remediation. Further, Chlorella vulgaris and Scenedesmus dimorphus consortium produced high amounts of lipid in lab conditions of about 31.20% and 29.50% using textile mill effluent and tannery industrial effluent, respectively; while in outdoor conditions, the lipid was 30.40% and 28.50% respectively. Eventually, the fatty acid analysis showed oleic acid as the major fatty acid in lipids of the consortium, which makes it a plausible candidate for biodiesel production.

Efficient removal of Imidacloprid and nutrients by algae-bacteria biofilm reactor (ABBR) in municipal wastewater: Performance, mechanisms and the importance of illumination

Neonicotinoids, such as Imidacloprid (IMI), are frequently detected in water and wastewater, posing a threat on both the environment and the health of living things. In this work, a novel algae-bacteria biofilm reactor (ABBR) was constructed to remove IMI and conventional nutrients from municipal wastewater, aiming to explore the removal effect and advantage of ABBR. Results showed that ABBR achieved 74.9% removal of IMI under 80 μmol m−2·s−1 light, higher than photobioreactor (PBR) without biofilm (61.2%) or ABBR under 40 μmol m−2·s−1 light (48.4%) after 16 days of operation. Moreover, it also showed that ABBR allowed a marked improvement on the removal of total dissolved nitrogen (TDN), total dissolved phosphorus (TDP) and soluble chemical oxygen demand (sCOD). ABBR showed different IMI removal efficiencies and bacterial communities under different light conditions, indicating that light played an important role in driving ABBR. The merits of ABBR are including (i) ABBR showed rapid pollutant removal in a short time, (ii) in ABBR, stable consortiums were formed and chlorophyll content in effluent was very low, (iii) compared with PBR, degradation products in ABBR showed lower biological toxicity. Our study highlights the benefits of ABBR on IMI removing from municipal wastewater and provides an effective and environment-friendly engineering application potential of IMI removal.

Efficient removal of Imidacloprid and nutrients by microalgae‐bacteria consortium in municipal wastewater: effects, mechanism, and importance of light

AbstractBACKGROUNDWith the rapid development of society, a large amount of wastewater and pesticides enter the water bodies globally, posing a threat to both the environment and the health of people and other living things. In this paper, an algal strain Scenedesmus sp. was isolated from a municipal wastewater treatment plant (WWTP); its interaction effect with wastewater bacteria on the removal of IMI and conventional pollutants in municipal wastewater was evaluated.RESULTSIn this study, an algae‐bacteria system was constructed with municipal wastewater, with the aim of exploring the removal effects and mechanisms of the consortium system on Imidacloprid (IMI, 20 mg L−1 and 60 mg L−1) and conventional nutrients from municipal wastewater. The results showed that no IMI was removed under 20 μmol m−2 s−1. However, under 60 μmol m−2 s−1, more than 90% of IMI was removed in the algae‐wastewater group (AWG) with Scenedesmus sp.; this value is much higher than the 50.4% (20 mg L−1) and 36.1% (60 mg L−1) achieved by the wastewater group (WG) without Scenedesmus sp. Meanwhile, the removal efficiency of nitrogen was 82.3% (20 mg L−1) and 71.9% (60 mg L−1) in AWG, both of which are higher than the 73.4% and 59.1% in WG, respectively. Moreover, Scenedesmus sp. TXH has a strong resistance to IMI and 4 degradation products (including IMI‐urea, 4(5)‐hydroxy‐IMI, Nitrosimine, and a substance with m/z of 176) were found in AWG.CONCLUSIONUsing consortium to treat municipal wastewater containing IMI is an effective and safe way. © 2022 Society of Chemical Industry (SCI).

Photo-induced biomitigation of sewage wastewater by new isolate of Rhodotorula glutinis ISO A1–lipid augmentation and profiling

Development of efficient wastewater treatment technologies along with circular economic approaches are the most imperative biotechnological attention presently. Thus, to add more value in this process, current study accessed a novel oleaginous yeast strain, R. glutinis ISO A1 for its biodegrading potential in sewage wastewater encompassing toxic formulations. To achieve improved performance light irradiance of various intensities (50 lux–150 lux) was applied during the cultivation period as an abiotic stress factor. All irradiances significantly stimulated nutrient removal efficiency of R. glutinis and improved growth rate but intracellular accumulation of carotenoids was found slightly inhibited. Boosted lipogenesis (lipid content ⁓40.66%) along with phenomenal reduction in COD (88.33 ± 1.88%), nitrate (73.2 ± 3.95%) and phosphate (85.1 ± 2.97%) was monitored with an optimum exposure condition at 100 lux. Cultures illuminated with light (50 lux–150 lux) also showed excellent tolerance for multiple heavy metals (Zn, Cd, Cr) and exhibited their complete removal. Further, analysis of fatty acid methyl esters (FAME) presented an increase in saturated fatty acids that reveal modulations in R. glutinis's membrane fluidity against stress generated due to the light exposure. Besides, estimated biodiesel properties of obtained FAME complying European and American fuel standards. These findings shed new light on the factors affecting wastewater bioremediation and successfully established a photo-induced biological treatment system in an oleaginous yeast for the very first time with an addition to successive lipid enhancement.

Effects of light source and inter-species mixed culture on the growth of microalgae and bacteria for nutrient recycling and microalgae harvesting using black odorous water as the medium.

To achieve the sustainable and effective removal efficiency of nutrients in black odorous water, light source, inter-species microalgae mixed culture, and the harvesting effect were all explored. The results showed that under a LED light source, the addition of interspecific soluble algal products (SAP) promoted the growth of Haematococcus pluvialis (H. pluvialis) M1, and its maximum specific growth rate was 1.76 times that of H. pluvialis cultivated alone. That was due to the hormesis effect between the two kinds of microalgae, the SAP produced by Scenedesmus could stimulate the growth of H. pluvialis. The algae and bacteria symbiotic system with black odorous water as the medium showed excellent performance to treat nutrients, where the concentration of ammonia nitrogen (NH3-N) and total phosphorus (TP) (0.84, 0.23mg/L) met the requirements of landscape water. The microbial diversity analysis revealed that the introduction of microalgae changed the dominant species of the bacterial community from Bacteroidota to Proteobacteria. Furthermore, timely microalgae harvesting could prevent water quality from deteriorating and was conducive to microalgae growth and resource recycling. The higher harvest efficiency (98.1%) of H. pluvialis was obtained when an inoculation size of 20% and 0.16g/L FeCl3 were provided.

Comparison of single strain, natural algal communities and a native algal bloom: Application for wastewater treatment and biomass generation in cassava biogas effluent

AbstractPhycoremediation of Chlorella sorokiniana P21 as indigenous strain (P21), four algal communities from different wastewater treatment ponds (P1, P2, P3 and P4) and a native algal bloom (CTRL) were examined to treat cassava biogas effluent wastewater (CBEW) and generate algal biomass. All cultures showed higher biomass production in unsterilized CBEW than in the sterilized CBEW, whereas nutrient removal efficiency was not significantly different in both conditions for all cultures. Verhulst kinetics models showed P21 culture has the highest maximum biomass (1440.94 mg L−1), whereas P3 showed the highest growth rate (0.68 day−1). The removal efficiencies of these cultures for nitrate, phosphate and chemical oxygen demand were above 75%. Iron coagulants attained the removal to be more than 90% only in P21 culture. Indigenous and algal community cultures had similar potencies to treat wastewater, and thus, this result showed vast potency of phycoremediation using various inoculum sources.

The use of microalgae-microbial fuel cells in wastewater bioremediation and bioelectricity generation

Synthetic wastewater bioremediation and bioelectricity production were assessed in a bench-scale microalgae-microbial fuel cell (MMFC) system. The experiments were conducted in triplicate for 7 days with 3 different combinations: MMFC1 (Escherichia coli + Desmodesmus subspicatus), MMFC2 (Pseudomonas aeruginosa + D. subspicatus), and MMFC3 (E. coli + Pseudokirchneriella subcapitata). The pH range (6–8) was ideal for microbial growth. The MMFC 1 had a higher bioelectricity production than MMFC 2 and MMFC 3, with 560 mV (p < 0.05) on the 7th day of operation. The microalgae showed a high bioremediation efficiency, with a significant reduction (p < 0.05) of the total phosphorous (TP) and total organic carbon (TOC) after 7 days. In conclusion, the MMFC 1 containing E. coli in the anodic chamber and D. subspicatus in the cathodic chamber was most effective in the bioelectricity generation. All the system combinations were promising for the bioremediation, with average nutrient removal efficiencies of 55.5%, 39.2%, and 64.5%, for TP, TN, and TOC, respectively. The studied systems could simultaneously produce bioelectricity and remediate wastewater.

The Biological Performance of a Novel Electrokinetic-Assisted Membrane Photobioreactor (EK-MPBR) for Wastewater Treatment.

Developing an effective phycoremediation system, especially by utilizing microalgae, could provide a valuable approach in wastewater treatment for simultaneous nutrient removal and biomass generation, which would help control environmental pollution. This research aims to study the impact of low-voltage direct current (DC) application on Chlorella vulgaris properties and the removal efficiency of nutrients (N and P) in a novel electrokinetic-assisted membrane photobioreactor (EK-MPBR) in treating synthetic municipal wastewater. Two membrane photobioreactors ran in parallel for 49 days with and without an applied electric field (current density: 0.261 A/m2). Mixed liquid suspended soils (MLSS) concentration, chemical oxygen demand (COD), floc morphology, total phosphorus (TP), and total nitrogen (TN) removals were measured during the experiments. The results showed that EK-MPBR achieved biomass production comparable to the control MPBR. In EK-MPBR, an over 97% reduction in phosphate concentration was achieved compared to 41% removal in the control MPBR. The control MPBR outperformed the nitrogen removal of EK-MPBR (68% compared to 43% removal). Induced DC electric field led to lower pH, lower zeta potential, and smaller particle sizes in the EK-MPBR as compared with MPBR. The results of this novel study investigating the incorporation of Chlorella vulgar is in an electrokinetic-assisted membrane photobioreactor indicate that this is a promising technology for wastewater treatment.

Towards biomass production and wastewater treatment by enhancing the microalgae-based nutrients recovery from liquid digestate in an innovative photobioreactor integrated with dialysis bag

Microalgae-based nutrients recovery from liquid anaerobic digestate of swine manure has been a hotspot in recent decades. Nevertheless, in consideration of the high NH4+-N content and poor light penetrability exhibited by the original liquid digestate, uneconomical pretreatment on liquid digestate including centrifugation and dilution are indispensable before microalgae cells inoculation. Herein, aiming at eliminating the energy-intensive and freshwater-consuming pretreatment on liquid digestate and enhancing microalgae growth, the dialysis bag which permits nutrients transferring across its wall surface whereas retains almost all matters characterized by impeding light transmission within the raw liquid digestate was integrated into a column photobioreactor (DB-PBR). Consequently, light availability of microalgae cells in DB-PBR was elevated remarkably and thus contributed to a 357.58% improvement on microalgae biomass concentration in DB-PBR than the conventional PBR under 80 μmol m−2 s−1. Likewise, superior nutrients removal efficiencies from liquid digestate were obtained in DB-PBR (NH4+-N: 74.84%, TP: 63.75%) over the conventional PBR (NH4+-N: 30.27%, TP: 16.86%). Furthermore, higher microalgae biomass concentration (1.87 g L−1) and nutrients removal efficiencies (NH4+-N: 95.12%, TP: 76.87%) were achieved in the DB-PBR by increasing the light intensity to 140 μmol m−2 s−1. More importantly, the DB-PBR may provide a simple and greener solution to purify other kinds of wastewater.

Unravelling the biodegradation performance and mechanisms of acid orange 7 by aerobic granular sludge at different salinity levels

Azo dyes wastewater is characterized by high-salinity, however, the biodegradation performance and mechanisms of azo dyes by aerobic granular sludge (AGS) under different salinity levels are still unclear. Herein, the results showed that the reactor performance was almost unaffected at low-salinity levels (0.5%-1.0% salinity), and the removal efficiency of acid orange 7 (AO7) was increased by 2.6%-19.1%, possibly due to the excessive secretion of extracellular polymeric substances (EPS) and the enrichment of functional bacteria. Nevertheless, the microbial cell viability was negatively affected by high-salinity level (2.0% salinity), leading to the deterioration of AO7 and nutrient removal efficiencies. The AO7 removal was achieved by rapid adsorption and slow biodegradation. The biodegradation pathway indicated that AO7 was gradually mineralized in the AGS system through desulfurization, deamination, decarboxylation and hydroxylation. Altogether, this work provides an important reference for the application of AGS technology for treating saline azo dye wastewaters.

Effects of applying different carbon substrates on nutrient removal and greenhouse gas emissions by constructed wetlands treating carbon-depleted hydroponic wastewater

The addition of external carbon sources is crucial for effective biological treatment of nutrient-rich but carbon-depleted hydroponic wastewater using constructed wetlands. In this study, we examined the effects of applying three types of carbon substrates, namely sucrose, hydroponic kale residues, and common reed litter, on the nutrient removal efficiency and greenhouse gas emission rate of vertical flow constructed wetlands. The addition of sucrose and common reed litter was shown to perform equally well in enhancing the removal of total nitrogen (84.9–93.5%), nitrate (98.3–99.8%) and phosphate (53.8–55.2%) as compared to the control. Moreover, the application of common reed litter led to significantly lower mean CH4 and N2O emissions than that of kale residues. These findings suggested that Phragmites reed litter, which is easily found in wetlands worldwide, could be an effective, low-cost and climate-friendly carbon substrate to be applied in constructed wetlands for hydroponic wastewater treatment.

Effect of Operating Parameters and Energy Expenditure on the Biological Performance of Rotating Biological Contactor for Wastewater Treatment

The rotating biological contactor (RBC) is resistant to toxic chemical and shock loadings, and this results in significant organic and nutrient removal efficiencies. The RBC system offers a low-energy footprint and saves up to 90% in energy costs. Due to the system’s low-energy demand, it is easily operable with renewable energy sources, either solar or wind power. An RBC was employed to degrade pollutants in domestic wastewater through biodegradation mechanisms in this study. The high microbial population in the RBC bioreactor produced excellent biological treatment capacity and higher effluent quality. The results showed that the RBC bioreactor achieved an average removal efficiency of 73.9% of chemical oxygen demand (COD), 38.3% of total nitrogen (TN), 95.6% of ammonium, and 78.9% of turbidity. Investigation of operational parameters, disk rotational speed, HRT, and SRT, showed the biological performance impact. Disk rotational speed showed uniform effluent quality at 30–40 rpm, while higher values of disk rotational speed (&gt;40 rpm) resulted in lower effluent quality in COD, TN, and turbidity. The longer hydraulic retention time and sludge retention time (SRT) facilitated higher biological performance efficiency. The longer SRTs enabled the higher TN removal efficiency because of the higher quantity of microbial biomass retention. The longer SRT also resulted in efficient sludge-settling properties and reduced volume of sludge production. The energy evaluation of the RBC bioreactor showed that it consumed only 0.14 kWh/m3, which is significantly lower than the conventional treatment methods; therefore, it is easily operable with renewable energy sources. The RBC is promising substitute for traditional suspended growth processes as higher microbial activity, lower operational and maintenance costs, and lower carbon foot print enhanced the biological performance, which aligns with the stipulations of ecological evolution and environment-friendly treatment.

Highly enhanced removal of nutrients and benzo[a]pyrene in a siphon constructed wetland with magnetite: Performance and mechanisms

Due to its limited dissolved oxygen concentration, constructed wetland (CW) could not remove nutrients and benzo[a]pyrene (B[a]P) effectively. Therefore, in this study, a siphon was applied in CW (Si-CW) to create tidal flow to achieve efficient removal of nutrients and B[a]P, and the removal mechanism was explored. The results showed that the NH4+ and TP removal values for the Si-CW were 55.95% ± 7.75% and 20.79% ± 8.39%, which exceeded those for the conventional CW (CCW). Alternative anaerobic and aerobic environments formed by siphon also enabled magnetite in Si-CW to form the iron cycle (Fe2+/Fe3+ cycle), which promoted the occurrence of simultaneous nitrification and denitrification and hydrogen-utilizing autotrophic denitrification and improved nitrogen removal significantly. The mass balance showed that microbial degradation was the main mechanism of B[a]P removal (39.0% – 54.0%). Si-CW possessed better oxygen conditions and iron cycles, favoring the propagation and growth of B[a]P-degrading bacteria (i.e., Pseudoxanthomonas) while enhancing the proportion of microbial degradation of B[a]P. Metagenomic analysis indicated that Si-CW had a higher TC.FEV.OM gene expression of Pseudoxanthomonas, which could regulate the siderophores produced by Pseudoxanthomonas through the metabolic pathway (K02014) of the iron complex outer-membrane receptor protein to achieve efficient B[a]P removal.

Inorganic nutrient removal efficiency of a constructed wetland before discharging into an urban eutrophic estuary

This study investigated the nutrient removal efficiency of a constructed wetland (CW) piloted to treat urban runoff before entering an estuary. Physico-chemical, dissolved inorganic nutrient (DIN and DIP), and stormwater inflow volume data were measured. The CW removal efficiency of DIN was negligible (5% uptake), while it acted as a consistent source of DIP (68% efflux) to the receiving estuarine waters. There was low water residency within the small CW (0.8 ha) that has been compounded by a 10-fold increase in flow volume since 2016. The surface area of the CW would need to be increased to 46 ha to cope with current daily inputs (ca. 6300 m3 d−1). The lack of maintenance (e.g., macrophyte harvesting, sediment desludging) has reduced nutrient uptake and increased autochthonous inputs. The conversion of an abandoned saltpan into an extension of the CW has been considered to manage the high flow volume and remove nutrients.

Partial Nitrification and Enhanced Biological Phosphorus Removal in a Sequencing Batch Reactor Treating High-Strength Wastewater.

Complex and high levels of various pollutants in high-strength wastewaters hinder efficient and stable biological nutrient removal. In this study, the changes in pollutant removal performance and microbial community structure in a laboratory-scale anaerobic/aerobic sequencing batch reactor (SBR) treating simulated pre-fermented high-strength wastewater were investigated under different influent loading conditions. The results showed that when the influent chemical oxygen demand (COD), total nitrogen (TN), and orthophosphate (PO43−-P) concentrations in the SBR increased to 983, 56, and 20 mg/L, respectively, the COD removal efficiency was maintained above 85%, the TN removal efficiency was 64.5%, and the PO43−-P removal efficiency increased from 78.3% to 97.5%. Partial nitrification with simultaneous accumulation of ammonia (NH4+-N) and nitrite (NO2−-N) was observed, which may be related to the effect of high influent load on ammonia- and nitrite-oxidising bacteria. The biological phosphorus removal activity was higher when propionate was used as the carbon source instead of acetate. The relative abundance of glycogen accumulating organisms (GAOs) increased significantly with the increase in organic load, while Tetrasphaera was the consistently dominant polyphosphate accumulating organism (PAO) in the reactor. Under high organic loading conditions, there was no significant PAO–GAO competition in the reactor, thus the phosphorus removal performance was not affected.

Impact of primary sedimentation on granulation and treatment performance of municipal wastewater by aerobic granular sludge process

Aerobic granules contain microorganisms that are responsible for carbon, nitrogen, and phosphorus removal in aerobic granular sludge (AGS) process in which aerobic/anoxic/anaerobic layers (from surface to core) occur in a single granule. Optimizing the aerobic granular sludge (AGS) process for granulation and efficient nutrient removal can be challenging. The aim of this study was to examine the impact of settling prior to AGS process on granulation and treatment performance of the process. For this purpose, synthetic wastewater mimicking municipal wastewater was fed directly (Stage 1), and after primary sedimentation (Stage 2) to a laboratory-scale AGS system. In full-scale wastewater treatment plants, primary sedimentation is used to remove particulate organic matter and produce primary sludge which is sent to anaerobic digesters to produce biogas. Performances obtained in both stages were compared in terms of treatment efficiency, granule settling behavior, and granule morphology. Granulation was achieved in both stages with more than 92% chemical oxygen demand (COD) removal efficiencies in each stage. High nutrient removal was obtained in Stage 1 since anaerobic phase was long enough (i.e., 50 min) to hydrolyze particulate matter to become available for PAOs. Primary sedimentation caused a decrease in influent organic load and COD/N ratio, as a result, low nitrogen and phosphorus removal efficiencies were observed in Stage 2 compared to Stage 1. With this study, the effect of the primary sedimentation on the biological removal performance of AGS process was revealed. COD requirement for nutrient removal in AGS systems should be assessed by considering energy generation via biogas production from primary sedimentation sludge.