Lab-scale Sequencing Batch Reactor Research Articles

Responses of activated sludge under a short-term exposure to facial scrub microbeads: implications from treatment performance and higher-life microbial population dynamics.

In this study, four identical laboratory-scale sequencing batch reactors (SBRs) were continuously operated with different concentrations of microbeads (MBs) (5,000-15,000 MBs/L) to investigate the stress-responses of activated sludge under the MB exposure. It was found that the overall treatment performance (organic removal) of SBRs was fairly affected by short-term exposure to low levels of MBs; however, it was adversely affected as the concentration of MBs increased. The average concentration of mixed liquor suspended solids and heterotrophic bacteria in the reactor fed with 15,000 MBs/L were 16 and 30% less than in the pristine control reactor, respectively. Batch experiments further demonstrated that fairly low concentrations of MBs favored the development of dense microbial structures. Further increasing the MB concentrations to 15,000 MBs/L, however, distinctly weakened the settling performance of sludge. Morphological observations revealed suppressed uniformity, strength, and integrity of flocs reactors with the addition of MBs. Microbial community analyses revealed that the abundance of protozoan species declined 37.5, 58, and 64%, respectively, when SBRs were exposed to 5,000; 10,000; and 15,000 MBs/L as compared with the control reactor. The present work provided new insight into the possible effects of MBs on the performances and operational parameters of activated sludge.

Biosorption and biotransformation behaviours of veterinary antibiotics under aerobic livestock wastewater treatment processes

To study the fate of veterinary antibiotics released from swine wastewater treatment plants (SWTP), 10 antibiotics were investigated in each unit of a local SWTP periodically. Over a 14-month period of field investigation into target antibiotics, it was confirmed that tetracycline, chlortetracycline, sulfathiazole, and lincomycin were used in this SWTP, with their presence observed in raw manure. Most of these antibiotics could be effectively treated by aerobic activated sludge, except for lincomycin, which was still detected in the effluent, with a maximum concentration of 1506 μg/L. In addition, the potential for removing antibiotics was evaluated using lab-scale aerobic sequencing batch reactors (SBRs) that were dosed with high concentrations of antibiotics. The SBR results, however, showed that both sulfonamides and macrolides, as well as lincomycin, can achieve 100% removal in lab-scale aerobic SBRs within 7 days. This reveals that the potential removal of those antibiotics in field aeration tanks can be facilitated by providing suitable conditions, such as adequate dissolved oxygen, pH, and retention time. Furthermore, the biosorption of target antibiotics was also confirmed in the abiotic sorption batch tests. Biotransformation and hydrolysis were identified as the dominant mechanism for removing negatively charged sulfonamides and positively charged antibiotics (macrolides and lincomycin) in SBRs. This is due to their relatively low sorption affinity (resulting in negligible to 20% removal) onto activated sludge in abiotic sorption tests. On the other hand, tetracyclines exhibited significant sorption behavior both onto activated sludge and onto soluble organic matters in swine wastewater supernatant, accounting for 70%–91% and 21%–94% of removal within 24 h, respectively. S-shape sorption isotherms with saturation were observed when high amounts of tetracyclines were spiked into sludge, with equilibrium concentrations ranging from 0.4 to 65 mg/L. Therefore, the sorption of tetracyclines onto activated sludge was governed by electrostatic interaction rather than hydrophobic partition. This resulted in a saturated sorption capacity (Qmax) of 17,263 mg/g, 1637 mg/g, and 641.7 mg/g for OTC, TC, and CTC, respectively.

Removal of 17α-ethinylestradiol and total phosphorus in a sequencing batch reactor under two different sludge retention-time conditions

Sewage treatment systems can prevent the direct discharge of endocrine disruptors, such as 17α-ethinylestradiol (EE2), into the environment. Treatment systems capable of promoting total phosphorus (TP) removal, such as sequencing batch reactors (SBRs), are promising in this regard. Two lab-scale SBRs with different sludge retention times (SRTs) were assessed for their EE2 and TP removal rates. Anaerobic/aerobic/anoxic phases with cycles of 6 h were used to treat sewage containing EE2 at a concentration of 5 μg L-1. The removal rates of chemical oxygen demand and TP were approximately 80% for both the SBRs. Partial nitrification was observed in the SBRs. Initially, concentrations of EE2 above 1.0 μg L-1 in the treated sewage were measured. These concentrations were smaller in SBR 1, which used lower SRTs; EE2 was removed by sludge sorption. After the 56th cycle, the concentrations of EE2 in the treated sewage were below 0.1 μg L-1 in both the SBRs, indicating that its removal may have occurred by biodegradation due to acclimation to the process. Therefore, both TP removal and nitrification seem to play an important role in EE2 removal by SBRs.
 Keywords: A2O SBR, EE2 and TP removal, sewage treatments.

Bioaugmentation and enhanced formation of biogranules for degradation of oil and grease: Start-up, kinetic and mass transfer studies

Biogranulation technology is an emerging biological process in treating various wastewater. However, the development of biogranules requires an extended period of time when treating wastewaters with high oil and grease (O&G) content. A study was therefore conducted to assess the formation of biogranules through bioaugmentation with the Serratia marcescens SA30 strain, in treating real anaerobically digested palm oil mill effluent (AD-POME), with O&G of about 4600 mg/L. The biogranules were developed in a lab-scale sequencing batch reactor (SBR) system under alternating anaerobic and aerobic conditions. The experimental data were assessed using the modified mass transfer factor (MMTF) models to understand the mechanisms of biosorption of O&G on the biogranules. The system was run with variable organic loading rates (OLR) of 0.69–9.90 kg/m3d and superficial air velocity (SAV) of 2 cm/s. After 60 days of being bioaugmented with the Serratia marcescens SA30 strain, the flocculent biomass transformed into biogranules with excellent settleability with improved treatment efficiency. The biogranules showed a compact structure and good settling ability with an average diameter of about 2 mm, a sludge volume index at 5 min (SVI5) of 43 mL/g, and a settling velocity (SV) of 81 m/h after 256 days of operation. The average removal efficiencies of O&G increased from 6 to 99.92%, respectively. The application of the MMTF model verified that the resistance to O&G biosorption is controlled via film mass transfer. This research indicates successful bioaugmentation of biogranules using the Serratia marcescens SA30 strain for enhanced biodegradation of O&G and is capable to treat real AD-POME.

Effect of Organic Loading Rates on Performance of Treating Dairy Wastewater in a Lab-Scale Sequencing Batch Reactor

This study aims to investigate, the effect of organic loading rates (OLRs), nutrient ratio addition, and sludge retention time (SRT) on treating dairy wastewater in a sequencing batch reactor (SBR) system. This investigation is verified by experiments conducted in 3 phases at 3 different OLRs (1.8, 1.2, and 0.9 kg/m3d, respectively). Urea ((NH2)2CO) is added to make a suitable (COD:N:P) ratio of (100:5:1) in dairy wastewater. The SRT is adjusted from 50 days to an appropriate value of 18 days. The obtained results show that the COD, TN, and TP removal efficiencies are increased with decreasing OLRs. Sludge concentration in the SBR tank is stable at 1100 mg/L after adding (NH2)2CO. In addition, the SBR operated at a suitable SRT (i.e. 18 days) helps the biomass stably, resulting in enhancement of COD, TN, and TP removal. The results are helpful to the design of SBR for treating dairy wastewater.

Impact of the anaerobic feeding mode on substrate distribution in aerobic granular sludge

There is a growing interest to implement aerobic granular sludge (AGS) in existing conventional activated sludge (CAS) systems with a continuous flow-through configuration. The mode of anaerobic contact of raw sewage with the sludge is an important aspect in the adaptation of CAS systems to accommodate AGS. It remains unclear how the distribution of substrate over the sludge by a conventional anaerobic selector compares to the distribution via bottom-feeding applied in sequencing batch reactors (SBRs). This study investigated the effect of the anaerobic contact mode on the substrate (and storage) distribution by operating two lab-scale SBRs; one with the traditional bottom-feeding through a settled sludge bed similar to full-scale AGS systems, and one where the synthetic wastewater was fed as a pulse at the start of the anaerobic phase while the reactor was mixed through sparging of nitrogen gas (mimicking a plug-flow anaerobic selector in continuous flow-through systems). The distribution of the substrate over the sludge particle population was quantified via PHA analysis, combined with the obtained granule size distribution. Bottom-feeding was found to primarily direct substrate towards the large granular size classes (i.e. large volume and close to the bottom), while completely mixed pulse-feeding gives a more equal distribution of substrate over all granule sizes (i.e. surface area dependant). The anaerobic contact mode directly controls the substrate distribution over the different granule sizes, irrespective of the solids retention time of a granule as an entity. Preferential feeding of the larger granules will enhance and stabilise the granulation compared to pulse-feeding, certainly under less advantageous conditions imposed by real sewage.

Impact of cationic polyelectrolytes on activated sludge morphology and biological wastewater treatment in a Sequential Batch Reactor (SBR)

The variability of the sedimentation characteristics of activated sludge is a phenomenon that often occurs in biological wastewater treatment plants. Deterioration of sedimentation properties requires the application of polyelectrolytes. They affect the morphology of sludge flocs, facilitating and accelerating their deposition. On the other hand, the type of reagent used and its dose may affect the quality of the treated wastewater. This study investigates the effect of dosing two different cationic polyelectrolytes on the properties of activated sludge and treated wastewater parameters in lab-scale sequencing batch reactors (SBRs). During studies, doses of polyelectrolytes that significantly changed activated sludge flocs' morphology were applied. It caused an improvement of the sludge volume index (SVI) from 42 to even 80 % in relation to the control reactor. However, polymers overdose resulted in the SVI increase by 10–14 % and obtaining sludge flocs with a highly branched structure, difficult to thicken. The applied polymers Praestol 855BS and Superfloc C-18530 did not affect the chemical characteristics of the treated wastewater. The only significant effect was observed for the turbidity of the wastewater. Polymers doses reduced the value of that parameter by 54–64 %. In addition, a simulation of a technological failure for several days was introduced to assess the durability of the produced flocs and their impact on the effectiveness of wastewater treatment. The experiment showed that Praestol formed stable and durable flocs, while for Superfloc polymer, a slight temporary deterioration of wastewater quality was observed due to the lower cohesion of the activated sludge.

Low C/N promotes stable partial nitrification by enhancing the cooperation of functional microorganisms in treating high-strength ammonium landfill leachate

Partial nitrification is an effective process for treating high-strength ammonium landfill leachate with low C/N ratio, for the cooperation with denitrification can save almost 40% carbon addition in biological nitrogen removal. However, high ammonia loading often causes the instability of partial nitrification process. Less carbon addition can promote the stability of partial nitrification and increase the nitrite accumulation ratio (NAR). Nevertheless, the microbial mechanisms within remain further elusive. In this study, two laboratory-scale sequencing batch reactors were constructed and operated for 125 days, which were fed with ammonia synthetic wastewater with C/N of 0.6 (CN system) and C/N of 0.0 as the control (N system). CN system performed more stably and had the highest NAR of 100%. Extracellular polymeric substances (EPS) generated from carbon source provided spatial and nutrient niches to tighten the cooperation of functional microorganisms, thus, enhanced the stability and efficiency of partial nitrification. Thauera was the dominant denitrifier in CN system. Nitrosomonas was one of the most important autotrophic ammonia oxidizing bacteria, while Paracoccus and Flavobacterium were the main heterotrophic nitrification-aerobic denitrification (HN-AD) bacteria in CN system. The enrichment of HN-AD bacteria outcompeted nitrite oxidizing bacteria (NOB), therefore leaded to higher nitrite accumulation in CN system. The findings of this study may be conducive to increasing the understanding of the microbial collaboration mechanisms of partial nitrification, thereby provides theoretical support for the improvement of biological nitrogen removal technology.

Potential causes of partial-denitrification (PD) granular sludge breakdown under high nitrate loading rates

The granule instability has been frequently reported during the operation of high loading rates. While, there no research was performed on the recently developed anoxic partial-denitrification (PD) granules, a novel pathway in producing nitrite from nitrate for anammox process. Herein, this work, for the first time, investigated the influence of nitrate loading rates on the instability of PD granules and identified the key causes. Two lab-scale sequencing batch reactors (SBRs) were operated with nitrate loading rates (NLR) increased from 0.48 to 3.84 kg N/m3/d (R1, 8 cycles/d), and 0.96 to 7.68 kg N/m3/d (R2, 16 cycles/d) by gradually elevating the influent nitrate concentration. Results showed that nitrite production rates increased with the NLRs, with a maximal value of 5.26 kg N/m3/d obtained. However, the compact regular PD granules were not stable and broke down when NLR was above 3.84 kg N/m3/d, which resulted in serious sludge washing out from SBR. The high NLRs led to the extracellular polymeric substances (EPS) transformation in terms of its composition and structure, which the protein content in the EPS and the tightly bound EPS (T-EPS) fraction was significantly decreased, this was supposed to be the major reason causing the breakdown of PD granules. Besides, it was found the PD granule in R2 was more deteriorated than that in R1 under the same high NLR, suggesting the short starvation (idle) times in SBR cycle was likely another reason impairing the stability of PD granules. Overall, this research provides useful information in development of granule-based PD systems and sheds light on achieving high-rate nitrite production in SBR with great stability.

In-situ sludge reduction based on Mn2+-catalytic ozonation conditioning: Feasibility study and microbial mechanisms

To improve the sludge conditioning efficiency without increasing the ozone dose, an in-situ sludge reduction process based on Mn2+-catalytic ozonation conditioning was proposed. Using ozone conditioning alone as a control, a lab-scale sequencing batch reactor coupled with ozonated sludge recycle was evaluated for its operating performance at an ozone dose of 75 mg O3/g VSS and 1.5 mmol/L Mn2+ addition. The results showed a 39.4% reduction in MLSS and an observed sludge yield of 0.236 kg MLSS/kg COD for the O3+Mn2+ group compared to the O3 group (15.3% and 0.292 kg MLSS/kg COD), accompanied by better COD, NH4+-N, TN and TP removal, improved effluent SS and limited impact on excess sludge properties. Subsequently, activity tests, BIOLOG ECO microplates and 16S rRNA sequencing were applied to elucidate the changing mechanisms of Mn2+-catalytic ozonation related to microbial action: (1) Dehydrogenase activity reached a higher peak. (2) Microbial utilization of total carbon sources had an elevated effect, up to approximately 18%, and metabolic levels of six carbon sources were also increased, especially for sugars and amino acids most pronounced. (3) The abundance of Defluviicoccus under the phylum Proteobacteria was enhanced to 12.0% and dominated in the sludge, they had strong hydrolytic activity and metabolic capacity. Denitrifying bacteria of the genus Ferruginibacter also showed an abundance of 7.6%, they contributed to the solubilization and reduction of sludge biomass. These results could guide researchers to further reduce ozonation conditioning costs, improve sludge management and provide theoretical support.

Amyloid adhesin production in activated sludge is enhanced in lab-scale sequencing batch reactors: Feeding regime impacts microbial community and amyloid distribution

Amyloid adhesins are β-sheet-rich extracellular proteins thought to contribute to bioflocculation. They are present in activated sludge to varying extent. However, it remains unclear which operational conditions promote their production. To this end, the abundance and distribution of amyloids and their potential producers were monitored in two lab-scale reactors operated in sequencing batch mode with an unaerated and aerated reaction phase. Various feeding regimes ranging from feast-famine to nearly continuous feeding were applied. Thioflavin T staining revealed more amyloids in the lab-scale reactors during all operational stages compared to the full-scale industrial and municipal inocula. Furthermore, the feeding regime impacted the distribution of produced amyloids from dense clusters during feast-famine conditions towards a dispersed distribution during nearly continuous feeding. This dispersed presence did not negatively impact the bioflocculation (towards average floc size and shear sensitivity). 16S rRNA sequencing detected several known EPS and amyloid producers. More continuous and, hence, partially aerobic feeding promoted the relative abundance of denitrifiers. Sequential Thioflavin T staining and fluorescence in situ hybridization identified Zoogloea and Ca. Competibacter as potential amyloid producers under the applied conditions. This experiment confirms that amyloid producers need to be triggered for production and that the feeding regime impacts the microbial community composition, which in turn influences the amyloid production and distribution.

Biological treatment of benzophenone-type UV filter wastewater in a sequencing batch reactor (SBR)

Benzophenone-n (BPs) is an emerging endocrine-disrupting contaminant that can be applied to different commercial products including UV-filters. BPs are toxic to microorganisms, coral, and animals. This study aims to demonstrate the use of laboratory-scale SBR to remove 2,4-dihydroxybenzophenone (BP-1) and oxybenzophenone (BP-3) and to investigate extracellular polymeric substance (EPS) production and functions under different hydraulic retention time (HRT) and operating stages. HRT period focused on removal of BPs and different stages focused on EPS content. The results show that the removal of BPs is high when HRT is increased from 8 (68.9% for BP-1/78.5% for BP-3) to 48 h (96.8%/98.0%, respectively); and favoured in reaction stage (aerobic condition) (80.33%/90.23%, respectively). In the view of EPS, protein (EPS-PN) content increases from 57.8 μg/L to 119.8 μg/L when HRT is increased from 8 to 48 h; however, polysaccharides (EPS-PS) show no relationship with HRT. In different stages, both EPS content reach the maximum (132.2 μg/L and 194.2 mg/L, respectively) during idle stage, and fluctuate in first 3 h of reaction stage and later recover to 117.1 μg/L and 160.6 mg/L, respectively. The next-generation sequencing (NGS) results show that different HRTs promote different dominant strains, but both communities are similar at different stages.

Simultaneous nitrification, denitrification, and phosphorus removal from municipal wastewater at low temperature

A lab-scale sequencing batch reactor was employed to study simultaneous nitrification, denitrification, and phosphorus removal (SNDPR) when treating municipal wastewater at 10 °C for 158 days. An anaerobic/aerobic configuration that had previously been effective when treating synthetic wastewater was explored, however, these conditions were relatively ineffective for real municipal wastewater. Incorporation of a post-anoxic phase (i.e., anaerobic/aerobic/anoxic) improved nitrogen and phosphorus removals to 91.1 % and 92.4 %, respectively while achieving a simultaneous nitrification and denitrification efficiency of 28.5 %. Activity tests indicated that 15.8 % and 56.0 % of nitrogen were removed by denitrifying phosphorus accumulating organisms in the aerobic phase and heterotrophs using hydrolyzed carbon in the post-anoxic phase, respectively. 16S rRNA gene analysis and stoichiometric ratios indicated the system was rich in phosphorus accumulating organisms (Dechloromonas and Ca. Accumulibacter). Overall, implementation of the post-anoxic phase eliminated carbon uptake for denitrification in the anaerobic phase and was essential to maintaining SNDPR at low temperatures.

Physical Characteristics and Removal Performance of Aerobic Granular Sludge in Biological Treatment of Domestic Wastewater

This study aims to demonstrate the formation of aerobic granular sludge (AGS) for domestic wastewater treatment applications in hot climate and low humidity conditions (e.g. Saudi Arabia) as well as to characterize and examine the bioreactor performance in removing organic matter and nutrients. Based on the study, aerobic granular sludge (seeded with domestic activated sludge from Al-Madina Wastewater Treatment Plant and fed with synthetic wastewater with an organic loading rate (OLR) of 1.6 kg COD m−3d−1) was successfully cultivated with average size ranging from 1 to 2 mm in a laboratory scale sequencing batch reactor (SBR) system operated at 30 days with a complete cycle time of 3 h and at the working temperature of 30 ± 1°C. Results also showed that the aerobic granular sludge formed had excellent settling ability (settling velocity, 38.98 mh−1 and MLSS, 7.8 gL−1) and great removal performance of COD and nutrient (i.e. more than 90%).

Rapid method of aerobic granular sludge bioreactor start-up for domestic wastewater treatment

This study presents a rapid method on how to speed up aerobic granular sludge (AGS) cultivation and ensure excellent and stable removal performance during bioreactor operation for domestic wastewater treatment. This new strategy consists of start-up the bioreactor using only anaerobic granular sludge (AnGS) as a seed and feeding with crude sewage extracted from a full-scale Extended Aeration Plant. This experiment used a 2.5 L lab-scale sequencing batch reactor (SBR). The bioreactor operated at low dissolved oxygen (DO) concentration controlled at the value of 2.0 mg/L and below. After 60 days of operation, it clearly showed that almost 90% of AnGS seeds turned from black color to brown. The physical characterization analysis showed that the average sizes were unchanged, and the granules remained compact. Also, the SBR operation monitored with brown granules showed stable removal performance. Average removal efficiencies during steady-state cycles at room temperature of COD, ammoniacal nitrogen, and phosphate reached 84%, 92%, and 100%, respectively.

Aeration control strategy design based on dissolved oxygen and redox potential profiles for nitrogen and phosphorus removal from sewage in a sequencing batch reactor

Oxygen availability during different stages of biological nutrient removal (BNR) plays utmost critical role in all wastewater treatment techniques. Inadequate aeration control results in low treatment efficiencies and may lead to significantly higher costs. Hence, a strategically designed aeration scheme is very crucial. This study was carried out with the objective of maximising nitrogen and phosphorus removal from sewage by implementing an optimised aeration strategy. To achieve this, a 4-hour Anaerobic/Aerobic/Anoxic (AOA) cycle based on dissolved oxygen (DO) and oxidation-reduction potential (ORP) values was strategically designed, implemented and monitored in a 4.5 l laboratory-scale Sequencing Batch Reactor (SBR). On an average, feed waste consisted of 170 mg/l of biological oxygen demand (BOD), 228 mg/l of chemical oxygen demand (COD), 64 mg/l of total nitrogen (TN) and 33 mg/l of ortho-phosphate (PO43−). The average BOD, COD, TN and PO43− loading rates of 0.510, 0.684, 0.192 and 0.099 kg/(m3-d), respectively were applied to the reactor. During the 90-day operation of the SBR, it was observed that BOD, COD, TN and PO43− removal were achieved with 91%, 93%, 90% and 75% efficiencies, with removal rates of 0.477, 0.614, 0.173 and 0.075 kg/(m3-d), respectively. Also, the cycle study revealed that P removal occurred during the aerobic phase, while N removal occurred during the anoxic phase through denitrification. A mass balance analysis for N also revealed that denitrification and microbial uptake accounted for 59% and 41% of nitrogen removal, respectively. Study revealed that nutrient removal was achieved successfully while avoiding any unnecessary extended aeration costs. Such aeration strategy based on DO and ORP values could be deployed not only to optimise the aeration phase lengths, but could also be used for dynamic process control to manage fluctuations in influent characteristics and system conditions.

Rapid cultivation of aerobic granular sludge in laboratory scale sequencing batch reactor

Aerobic granular sludge (AGS) is known as excellent biological treatment for wastewater industry, high organic load wastewater and adsorption of heavy metal. AGS have some advantages such as higher density, higher biomass retention, simultaneous nutrient removal and higher tolerance to toxicity. The aim of this research is to use sequencing batch reactor (SBR) to cultivate AGS in the short time (28 days) in laboratory scale. Experimental condition that we use to cultivate AGS are based on this parameter: 1.5 hours of total cycle time, 50 % of exchange ratio, 3 hours of HRT and 3 l/min air flow rate. Even the AGS cultivation successfully achieve in 28 days with pH around 7-9, DO 3.6 mg/l, SVI 232.6 mg/l, and MLSS 500 mg/l, it is still need more time to generate more mature AGS to breakdown organic molecule in the wastewater.

A novel cross-flow honeycomb bionic carrier promotes simultaneous nitrification, denitrification and phosphorus removal in IFAS system: Performance, mechanism and keystone species

Simultaneously achieving efficient nitrogen (N) and phosphorus (P) removal without adding external carbon source is vital for carbon-neutral wastewater treatment. In this study, a novel cross-flow honeycomb bionic microbial carrier (CF) was developed to improve the efficiency of simultaneous nitrification, denitrification, and P removal (SNDPR) in an integrated fixed-film activated sludge (IFAS) system. A parallel laboratory-scale sequencing batch reactor with the commercialized microbial carriers (CM) (CM-IFAS) was performed as the comparative system for over 233 d The results demonstrated that CF-IFAS exhibited a more consistent N removal efficiency and better performance than CM-IFAS. In the CF-IFAS, the highest N and P removal efficiencies were 95.40% and 100%, respectively. Typical cycle analysis revealed that nitrate was primarily removed by the denitrifying glycogen-accumulating organisms in the CF-IFAS and by denitrifying phosphate-accumulating organisms in the CM-IFAS. The neutral community model showed that the microbial community assembly in both the reactors was driven by deterministic selection rather than stochastic factors. Compared to those in CM-IFAS, the microorganisms in CF-IFAS were more closely related to each other and had more keystone species: norank_f_norank_o_norank_c_OM190, SM1A02, Defluviicoccus, norank_f_ Saprospiraceae, and norank_f_Rhodocyclaceae. The absolute contents of the genes associated with N removal (bacterial amoA, archaeal amoA, NarG, NapA, NirS, and NirK) were higher in CF-IFAS than in CM-IFAS; the N cycle activity was also stronger in the CF-IFAS. Overall, the microecological environment differed between both systems. This study provides novel insights into the potential of bionic carriers to improve SNDPR performance by shaping microbial communities, thereby providing scientific guidance for practical engineering.

Impact of nitrite and oxygen on nitrous oxide emissions from a granular sludge sequencing batch reactor

Maximizing nutrient removal and minimizing greenhouse gas (GHG) emissions is imperative for the future of wastewater treatment. As municipalities focus on minimizing their carbon footprints, future permits could regulate GHG emissions from wastewater treatment plants. This study investigates how nitrous oxide (N2O) emissions are affected by dissolved oxygen and nitrite concentrations, providing potential strategies to meet possible gaseous emission permits. A lab-scale sequencing batch reactor (SBR) was enriched with aerobic granular sludge (AGS) capable of phosphate removal and simultaneous nitrification-denitrification (SND). N2O emissions were tracked at varying dissolved oxygen (DO) and nitrite (NO2−) concentrations, with >99% SND efficiency and 93%–100% phosphate removal efficiency. Higher DO and NO2− concentrations were associated with higher N2O emissions. Emissions were minimized at a DO concentration of 1 mg L−1, with an average emission factor of 0.18% of oxidized NH3–N emitted as N2O–N, which is lower than factors from many full-scale treatment plants (Vasilaki et al., 2019) and similar to a Nereda® full-scale AGS SBR (van Dijk et al., 2021). This challenges assertions that AGS emits more N2O than conventional activated sludge, although more research at full-scale with influent quality variations is required to confirm this trend. Molecular analyses revealed that the efficient SND was likely achieved with shortcut nitrogen removal facilitated by a low presence of nitrite oxidizing bacteria and a large population of denitrifying phosphate accumulating organisms, which far outnumbered denitrifying glycogen accumulating organisms.

Sequencing batch reactor (SBR) and anoxic and oxic process (A/O) display opposite performance for pollutant removal in treating digested effluent of swine wastewater with low and high COD/N ratios

Sequencing batch reactor (SBR) and anoxic/oxic process (A/O) are the predominant process for the treatment of digested effluent of swine wastewater. However, which is optimal process for their treatment? The question remains unclear. In this study, lab-scale SBR and A/O anoxic/oxic process were employed to treat digested effluent with addition of different proportion (v/v 10%–40%) of raw swine wastewater in order to make clear performance difference of the pollutant removal. The results showed that the NH4+-N and TN removal efficiencies of the A/O were more than 5.5 and 6.0 percentage points higher than that of the SBR respectively when the proportion of added raw wastewater was 20% (low COD/N ratios), due to the limitations caused by the low BOD5 concentration and the higher dissolved oxygen concentration during the anoxic phase. While, the NH4+-N and TN removal efficiencies of the SBR were more than 3.3 and 14.3 percentage points higher than that of the A/O respectively when the added raw wastewater proportion was 40% (high COD/N ratios), owing to limitation by the lower mixed liquor recycling ratio in the A/O. The sludge activity tests and microbial community analysis showed that the SBR displayed higher ammonia-oxidizing and anammox activity, whereas the A/O revealed higher denitrifying activity. These results uncovered that there are differences when A/O and SBR were employed to treat digested effluent and provide good insights for process selection when treating different C/N ratios wastewater.