Sequencing Batch Reactor Research Articles

Enhancing propionic acid production in the anaerobic fermentation of high-strength starch wastewater facilitated by hydraulic retention time and FeCl3 under alkaline pH

With increasing market demand, anaerobic fermentation for propionic acid production has been attracting lots of interests. However, oriented propionic acid refining in an open environment is typically challenging because of the diversity of microorganisms involved and the complexity of the process. This study examined the effects of varying the pH, FeCl3 dosage, and operational hydraulic retention time (HRT) on the synthesis of propionic acid from fermentative wastewater containing high-strength starch in an anaerobic sequencing batch reactor. The results showed that the most favorable operational conditions for the enrichment of propionic acid were an HRT of 24 h, and pH of 8.0 with a FeCl3 dosage of 960 mg/L. Under this condition, the long-term fermentation system produced a maximum of 7009 mg COD/L of propionic acid, which accounted for approximately 70.74 % of the total VFAs (volatile fatty acids). Microbial analysis showed that the combined regulating strategy not only significantly enriched genera associated with propionic acid production, such as norank_f__Propionibacteriaceae, Bacteroides, Corynebacterium, Bifidobacterium, but also shifted to lactate-propionate for production of propionic acid. These results will guide enhancing propionic acid products' yield from anaerobic fermentation.

Inhibition of phosphorus removal performance in activated sludge by Fe(III) exposure: transitions in dominant metabolic pathways.

Simultaneous chemical phosphorus removal process using iron salts (Fe(III)) has been widely utilized in wastewater treatment to meet increasingly stringent discharge standards. However, the inhibitory effect of Fe(III) on the biological phosphorus removal system remains a topic of debate, with its precise mechanism yet to be fully understood. Batch and long-term exposure experiments were conducted in six sequencing batch reactors (SBRs) operating for 155 days. Synthetic wastewater containing various Fe/P ratios (i.e., Fe/P = 1, 1.2, 1.5, 1.8, and 2) was slowly poured into the SBRs during the experimental period to assess the effects of acute and chronic Fe(III) exposure on polyphosphate-accumulating organism (PAO) growth and phosphorus metabolism. Experimental results revealed that prolonged Fe(III) exposure induced a transition in the dominant phosphorus removal mechanism within activated sludge, resulting in a diminished availability of phosphorus for bio-metabolism. In Fe(III)-treated groups, intracellular phosphorus storage ranged from 3.11 to 7.67 mg/g VSS, representing only 26.01 to 64.13% of the control. Although the abundance of widely reported PAOs (Candidatus Accumulibacter) was 30.15% in the experimental group, phosphorus release and uptake were strongly inhibited by high dosage of Fe(III). Furthermore, the abundance of functional genes associated with key enzymes in the glycogen metabolism pathway increased while those related to the polyphosphate metabolism pathway decreased under chronic Fe(III) stress. These findings collectively suggest that the energy generated from polyhydroxyalkanoates oxidation in PAOs primarily facilitated glycogen metabolism rather than promoting phosphorus uptake. Consequently, the dominant metabolic pathway of communities shifted from polyphosphate-accumulating metabolism to glycogen-accumulating metabolism as the major contributor to the decreased biological phosphorus removal performance.

Synergistic role of powdered activated carbon (PAC) for aerobic granular sludge (AGS) formation and organic micropollutant (OMPs) removal

Aerobic granular sludge (AGS) is a spherical aggregate formed by the self-aggregation of activated sludge. AGS consists of diverse microbial groups, not only shortening the settling time but also enhancing treatment efficacy within a shorter reaction time. However, it necessitates a longer start-up time for granule formation. This study aims to investigate the synergistic effects of powdered activated carbon (PAC) on AGS formation in a sequencing batch reactor (SBR) and its potential for maintaining biodegradability in the presence of inhibitory organic micro-pollutants (OMPs). PAC substantially supported the formation of faster and more stable granule (PAC-AGS) with a very low sludge volume index (SVI < 50 mL/g). Morphological observation indicated that PAC-AGS is more compact than AGS without PAC addition, and PACs were broadly present inside and on the surface of PAC-AGS granules. Respirometric bioassay demonstrated that biodegradation of organic matter in the presence of OMP, e.g., diclofenac and isoproturon, was enhanced when PAC-AGS was used as seed instead of AGS due to the alleviated inhibition of those OMPs by PAC. The overall result illustrated that PAC has dual positive contributions to AGS reactor for wastewater treatment by accelerating the formation of AGS and enhancing removal performance even in the presence of inhibitory OMPs.

Effect of Carbon Source on Endogenous Partial Denitrification Process: Characteristics of Intracellular Carbon Transformation and Nitrite Accumulation

This study focused on the start-up and operating characteristics of the endogenous partial denitrification (EPD) process with different carbon sources. Two sequencing batch reactors (SBRs) with sodium acetate (SBR1#) and glucose (SBR2#) as carbon sources were operated under anaerobic/oxic (A/O) and anaerobic/anoxic/oxic (A/A/O) modes successively for 240 d. The results showed that COD removal efficiency reached 85% and effluent COD concentrations were below 35 mg/L in both SBRs. The difference was that faster absorption and transformation of sodium acetate was achieved compared to glucose (COD removal rate (CRR) was 7.54 &gt; 2.22 mgCOD/(L·min) in SBR1# compared to SBR2#). EPD could be started up with sodium acetate and glucose as carbon sources, respectively, and desirable high nitrite accumulations were both obtained at influent NO3−−N (NO3−-Ninf) increased from 20 to 40 mg/L with nitrate-to-nitrite transformation ratio (NTR) and specific NO3−-N deduction rate (rNa) of 88.4~90% and 2.41~2.38 mgN/(gVSS·h), respectively. However, at NO3−-N of 50~60 mg/L, both the NTR and rNa in SBR1# were higher compared to SBR2# (86.5% &gt; 83.9% and 1.58 &gt; 1.20 mgN/(gVSS·h), respectively). Hereafter, when NO3−-N was increased by 70~90 mg/L, lower NTR and rNa were observed in SBR1# than in SBR2# (72% and 78%, 1.16 and 1.32 mgN/(gVSS·h), respectively). Additionally, similar internal carbon transformations were observed to drive EPD for NO2−−N accumulation, especially for higher and faster carbon transformation with sodium acetate as carbon source compared to glucose. However, precise control of anoxic time as the peak point of nitrite (TNi,max) was still the key to achieve high NO2−−N accumulation.

Implementing a completely autotrophic nitrogen removal over nitrite process using a novel umbrella basalt fiber carrier.

The completely autotrophic nitrogen removal over nitrite (CANON) process is significantly hindered by prolonged start-up periods and unstable nitrogen removal efficiency. In this study, a novel umbrella basalt fiber (BF) carrier with good biological affinity and adsorption performance was used to initiate the CANON process. The CANON process was initiated on day 64 in a sequencing batch reactor equipped with umbrella BF carriers. During this period, the influent NH4+-N concentration gradually increased from 100 to 200 mg·L-1, and the dissolved oxygen was controlled below 0.8 mg L-1. Consequently, an average ammonia nitrogen removal efficiency (ARE) and total nitrogen removal efficiency (TNRE) of ∼90 and 80% were achieved, respectively. After 130 days, ARE and TNRE remained stable at 92 and 81.1%, respectively. This indicates a reliable method for achieving rapid start-up and stable operation of the CANON process. Moreover, Candidatus Kuenenia and Candidatus Brocadia were identified as dominant anammox genera on the carrier. Nitrosomonas was the predominant genus among ammonia-oxidizing bacteria. Spatial differences were observed in the microbial population of umbrella BF carriers. This arrangement facilitated autotrophic nitrogen removal in a single reactor. This study indicates that the novel umbrella BF carrier is a highly suitable biocarrier for the CANON process.

Anaerobic digestion model number 1 applied to the modeling of anaerobic digestion of residues generated in soluble coffee processing

The Anaerobic Digestion Model No. 1 (ADM1) was applied in this study to simulate the anaerobic digestion (AD) of wastewaters from soluble coffee processing in sequential batch reactors. As these substrates present considerable levels of phenolic compounds, modifications were made to the basic structure of the ADM1. Additionally, the Luong inhibition model replaced the Monod model to describe the consumption of soluble organic matter. On the other hand, the removal of phenolic compounds was carried out using the Haldane model, appropriate when the inhibition by excess substrate is present, taking into account in this case the quantification of phenols and benzoic acid as total phenols. The new ADM1-based model was calibrated with experimental data from the AD of post hydrothermal wastewater (PHWW) of spent coffee grounds (SCG) and validated with experimental data of the AD of effluents produced during the soluble coffee processing. The simulation results demonstrated that the new model moderately described the removal of phenolic compounds ( > 90 %), methane production (2.243 kgCODm−3 in calibration and 6.16 kgCODm−3 in validation), and the production and consumption of organic acids over time. However, in future research new metabolic pathways may be included in the model to improve its quality even more.

Impact of long-term temperature shifts on activated sludge microbiome dynamics and micropollutant removal

Micropollutants removal efficiency strongly vary across different aerobic wastewater treatment plants, resulting in their frequent detection in surface and ground waters. Seasonal temperature variation is a major factor influencing plant performance, but it is still unclear how prolonged periods of temperature change impact microbiome and micropollutant biotransformation. This work investigates the effect of long-term temperature variation on the microbial dynamics in an activated sludge system, and the impact on micropollutant biotransformation. Sequencing batch reactors were used as model system and 4–40 °C temperature range was studied. 16S rRNA amplicon sequencing showed that temperature drives microbial structure (gDNA) and activity (RNA), rather than time, and this was stronger below 15 °C and above 25 °C. The microbial community was richest and more diverse at 20 °C, while rarer and more specific taxa became predominant over time, at more extreme temperatures. This suggested that less abundant taxa might be responsible for maintaining the biotransformation capability in the activated sludge at extreme temperatures. Micropollutant biotransformation rates mostly deviated from the classic Arrhenius model below 15 °C and above 25 °C, indicating that prolonged exposure to temperature changes leads to temperature-induced taxonomic shifts, resulting in the emerging of different sets of biotransformation pathways over different temperature ranges.

Produced water treatment by semi-continuous sequential bioreactor and microalgae photobioreactor

Produced water (PW) from oil and gas exploration adversely affects aquatic life and living organisms, necessitating treatment before discharge to meet effluent permissible limits. This study first used activated sludge to pretreat PW in a sequential batch reactor (SBR). The pretreated PW then entered a 13 L photobioreactor (PBR) containing Scenedesmus obliquus microalgae culture. Initially, 10% of the PW mixed with 90% microalgae culture in the PBR. After the exponential growth of the microalgae, an additional 25% of PW was added to the PBR without extra nutrients. This study reported the growth performance of microalgae in the PBR as well as the reduction in effluent’s total organic carbon (TOC), total dissolved solids (TDS), electrical conductivity (EC), and heavy metals content. The results demonstrated removal efficiencies of 64% for TOC, 49.8% for TDS, and 49.1% for EC. The results also showed reductions in barium, iron, and manganese in the effluent by 95, 76, and 52%, respectively.

Moving Bed Sequenced Batch Reactor System in Tetracycline Antibiotic Removal from Real Hospital Wastewater

Background: Water contamination by synthetic organic chemicals like antibiotics is a major environmental issue. Tetracycline (TC), an antibiotic in a wide family, is notable. A moving bed sequenced batch reactor (MBSBR) is tested for treating hospital raw wastewater containing TC. Methods: A 35-L pilot system was constructed, with 30 L usable. PVC suspended carriers (Kaldnes K3) with 584.3 m2 /m3 specific surface area made about 70% of the functional volume. The independent variables in this study were hydraulic retention duration (1, 1.5, 2, and 2.5 hours) and starting TC concentration (5, 10, and 15 mg/L). Results: The findings of the study demonstrated satisfactory performance under the conditions of an initial TC concentration of 5 mg/L and an organic load of 350 mg/L. The overall removal efficiencies for TC, chemical oxygen demand (COD), and biological oxygen demand (BOD5 ) were 72.8%, 83%, and 93.9%, respectively. The optimal performance of the system was primarily observed during the initial phase, characterized by a TC concentration of 5 mg/L and a hydraulic retention time (HRT) of 2.5 hours. The experimental results also indicated that the maximum removal efficiency was 1.8 kg COD/m2 .day, as determined by a fitted surface loading rate (SLR). Furthermore, the food-tomicroorganism (F/M) ratio decreased from 0.101 to 0.038 as the HRT increased from 1 to 2.5 hours. Conclusion: The results of the study indicate that the MBSBR exhibits a high level of efficiency in removing TC from hospital wastewater.

Short-term electrochemical stimulation induces sustained enhancement of extracellular pollutant degradation in anaerobic granular sludge

Electroactive bacteria (EAB) are advantageous for degrading the pollutants extracellularly, but the enrichment primarily restricts on the electrode surface of bioelectrochemical system and is challenging to scale up. To address this, a new strategy was proposed to electrochemically stimulate the anaerobic granular sludge (AGS) and employ the harvested electroactive granular sludge (EGS) to an electrode-free bioreactor for pollutant removal. Fast establishment of EGS was achieved after 7 days' electrochemical stimulation, with a maximum current output of 112.5 A/m3 achieved and the abundance of electroactive bacteria-like genera increased from 5% to around 20%. The electric conductivity of EGS improved by 1-fold, while the increased extracellular protein and humic acid substance but unchanged polysaccharide content in the extracellular polymeric substance suggested a more robust redox network. After assembling in a sequential batch reactor, the methylene orange (MO) and Cr(VI) removal rate by EGS was enhanced by 65–80% and 38–55%, respectively. Better oxygen tolerance was also observed. The comparative study with exogenous riboflavin and respiration inhibitors indicated the complete extracellular reduction achieved by EGS while almost half of MO was metabolically degraded by AGS, which was kinetically sluggish. More importantly, there is no performance and electroactivity decay in a 60 days' batch operation. Meanwhile, the characterization of microbial community revealed the further increased abundance of EAB-like genera (∼28%) but Acinetobacter became dominant (∼15%), suggesting the competition of EAB species in EGS. In brief, a simple 7-day electrochemical stimulation imposed diverse and sustained benefits on the performance and microbial community of granular sludge, which may inspire the application of EAB and their extracellular degradation capacity in real wastewater treatment.

Treatment of Wastewaters with Different Ammonium Concentrations in a Sequencing Batch Reactor by Nitritation and Denitritation Processes

In the treatment of industrial and municipal wastewaters, biological nitrification and denitrification processes have been widely applied methods. However, in recent years, experimental studies have been carried out on nitritation and denitritation processes in order to reduce the cost of wastewater treatment. In this study, the removal of synthetic wastewaters containing ammonium at various concentrations through nitritation and denitritation processes was investigated in a sequence batch reactor (SBR). The SBR was operated at a low dissolved oxygen concentration of 0.7±0.2 mg/L, while the initial pH level and temperature were kept constant at 7.5 and 25 ℃, respectively, which were below the defined optimal level for nitritation. For the initial concentrations of 100, 150, and 200 mg NH4-N/L, 91, 142, and 180 mg NOx-N were produced, respectively with the specific nitritation rates of 0.69, 0.95, and 0.81 mg NH4-N/mg MLVSS.hour. Considering the operating conditions of nitritation, approximately NO2-N/NOx-N ratio of 80% could be considered as successful with the combined effect of DO limitation and NH3 inhibition on the nitrite oxidizing bacteria. During the first days of nitritation and denitritation processes, change of nitrogen concentrations was negligible because the adaptation of organisms to the oxic and anoxic conditions. After completing nitritation stage, denitritation was carried out by using methanol as an electron donor for the initial concentrations of 91, 142, and 180 mg/L of NOx-N in 96, 120 and 264 hours of reaction times, respectively.

Analysis and Design of Sequencing Batch Reactor Basin for Sewage Treatment Plant by using Autocad

bstract: The objectives of this project are to review and evaluate sewage treatment technologies and propose a method to improve or select appropriate technology. Sequencing batch reactor (SBR) is a part of the secondary treatment process of sewage treatment. It is fill and draw-type of activated sludge system involving a single complicated mix reactor where all steps of an activated sludge process take place. The objectives of this project are to review and evaluate sewage treatment technologies and propose a method to improve or select appropriate technology. Sequencing batch reactor (SBR) is a part of the secondary treatment process of sewage treatment. It is fill and draw-type of activated sludge system involving a single complicated mix reactor where all steps of an activated sludge process take place.

Effects of Na+/H2O2 on nitrogen removal and sludge activity: Performance and mechanism

A large amount of wastewater containing Na+ and H2O2 was generated in the pharmaceutical, food and dyeing industries. After entering sewage treatment plant, they could interfere with the growth and metabolism of microorganisms. However, the effects of coexisting Na+/H2O2 on nitrogen removal and sludge flocculation were unclear. In this study, the effects of Na+/H2O2 on removal efficiencies of pollutants and sludge activity were investigated using sequencing batch reactor. The composition and structure of extracellular polymer substance (EPS) were analyzed, and the influencing mechanisms of Na+/H2O2 on the activated sludge were revealed. The results showed that when concentration ratio of Na+/H2O2 was 30, removal efficiencies of COD and TN were the highest values of 96 % and 68 %, ARE, NAR and SAOR were 56.9 %, 35.3 % and 24.08 mg N/(mg MLVSS·h), respectively. The level of oxidative stress was the lowest, and ROS and MDA were 30.78 % and 32.65 %, respectively. Zeta potential, particle size and flocculation capacity of the sludge reached the highest values of -4.1283 mV, 48.73 μm and 8.92 %, respectively. Na+ promoted the decomposition of H2O2, and ·OH, ·O2- and 1O2 produced improved denitrification rate. However, removal efficiencies of pollutants and sludge activity were decreased when Na+/H2O2 concentration ratio was higher and lower than 30. The coexisting Na+/H2O2 could promote the production of EPS and improve fluorescence intensity of protein and humic acids, but main components and functional groups of EPS were not changed. Therefore, removal efficiencies of pollutants and sludge flocculation could be improved by regulating influent concentration ratio of Na+/H2O2.

Hybrid peroxymonosulfate/activated carbon fiber-sequencing batch reactor system for efficient treatment of coking wastewater: Establishment and influential factors

Coking wastewater contains high concentrations of toxic and low biodegradable organics, causing long hydraulic retention times for its biological treatment process. This study developed a pretreatment method for coking wastewater by using activated carbon fiber (ACF) activated peroxymonosulfate (PMS) to improve the treatment performance of subsequent biological post-treatment process, sequencing batch reactor (SBR). The results showed that, after optimization of treatment processes, the removal efficiency of chemical oxygen demand (COD), phenol, and chroma in coking wastewater reached to 76, 98, and 98%, respectively, with a significantly improved biodegradability. Compared with the sole SBR system without any pretreatment that could remove 73% of COD, the ACF/PMS+SBR system removed over 97% of COD in coking wastewater. Moreover, this pretreatment method facilitated the growth of functional bacteria for organics biodegradation, indicating its high potential as a highly efficacious pretreatment strategy to improve the overall treatment efficiency of coking wastewater.

Anaerobic digestion of spoiled milk from dairy industry for biogas production – optimization of operating parameters and kinetic modeling of the pilot scale study

BackgroundSpoiled milk from the dairy industry was subjected to anaerobic treatment to produce biogas at 37℃ in this experiment. Parameters such as inoculum dosage, pH, Chemical Oxygen Demand (COD), and retention time were optimized in a laboratory-scale batch reactor for 90 days.MethodsThe anaerobic digestion of spoilt milk was carried out in a laboratory setting using a batch reactor. Then, using the recognized protocols of the APHA, the characteristics of the spoilt milk were assessed. In order to enhance the accuracy of predicting the reactor's performance, the research adopted two different models for kinetic analysis: the Stover-Kincannon model and the Grau second-order multi-component model. The reactor's improved performance, as indicated by evaluated kinetic parameters, was shown by the superior results from both of these models.ResultsThe results attained from the reactor’s performance were then used as a reference to improve biogas production in a 100 L Anaerobic Sequential Batch Reactor (ASBR) for 45 days. The ASBR achieved a high COD removal efficiency of 92.4% and produced a maximum of 70.4 L of biogas per liter of spoiled milk, equivalent to 69.6% methane content.ConclusionThe Stover-Kincannon model yielded kinetic parameters of Umax = 0.295 gCOD/L and KB = 12.87 gCOD/L, whereas the Grau second-order model presented kinetic coefficients a = 6.744 and b = 2.578. The results obtained from the two models suggest that the investigated kinetic coefficients could be improved upon to increase the reactor's capability for handling different substrates during the AD process.

Surface Modification of Polyurethane Sponge with Zeolite and Zero-Valent Iron Promotes Short-Cut Nitrification.

Partial nitrification-Anammox (PN-A) is a cost-effective, environmentally friendly, and efficient method for removing ammonia (NH4+-N) pollutants from water. However, the limited accumulation of nitrite (NO2--N) represents a bottleneck in the development of PN-A processes. To address this issue, this study developed a composite carrier loaded with nano zero-valent iron (nZVI) and zeolite to enhance NO2--N accumulation during short-cut nitrification. The modified composite carrier revealed electropositive, hydrophilicity, and surface roughness. These surface characteristics correlate positively with the carrier's total biomass adsorption capacity; the initial adsorption of microorganisms by the composite carrier was increased by 8.7 times. Zeolite endows the carrier with an NH4+-N adsorption capacity of 4.50 mg/g carrier. The entropy-driven ammonia adsorption process creates an ammonia-rich microenvironment on the surface of the carrier, providing effective inhibition of nitrite-oxidizing bacteria (NOB). In tests conducted with a moving bed biofilm reactor and a sequencing batch reactor, the composite carrier achieved a 95% NH4+-N removal efficiency, a NO2--N accumulation efficiency of 78%, and a doubling in total nitrogen removal efficiency. This composite carrier enhances NO2--N accumulation by preventing biomass washout, inhibiting NOB, and enriching PN-A functional bacteria, suggesting its potential for large-scale, stable PN-A applications.

Aerobic granulation and resource production under continuous and intermittent saline stress

Three sequential batch reactors (SBR) were operated to evaluate salt addition's impact on granulation, performance, and biopolymer production in aerobic granular sludge (AGS) systems. System R1 was fed without adding salt (control); system R2 operated with saline pulses, i.e., one cycle with salt (2.5 g NaCl/L) addition followed by another without salt; and R3 received continuous supplementation of 2.5 g NaCl/L. The results indicated that the reactors supplemented with salt presented higher concentrations of mixed liquor volatile suspended solids (MLVSS) and better settleability than R1, showing that osmotic pressure contributed to biomass growth, accelerated granulation, and improved physical characteristics. The faster granulation occurred in R2, thus proving the beneficial effects of intermittent salt addition through alternating pulses. Salt addition did not impair the simultaneous removal of carbon, nitrogen, and phosphorus. In fact, R2 showed better carbon removals. In conclusion, continuous or intermittent (pulsed) supplementation of 2.5 g NaCl/L did not lead to increased production of extracellular polymeric substances (EPS) and alginate-like exopolymers (ALE). This outcome could be attributed to the low saline concentration employed, a higher food-to-microorganism (F/M) ratio observed in R1, and possibly greater endogenous consumption of biopolymers in the famine period in R2 and R3 due to the greater solids retention time (SRT). Therefore, this study brings important results that contribute to a better understanding of the effect of salt in continuous dosing or in pulses as a selection pressure strategy to accelerate granulation, as well as the behavior of the AGS systems for saline effluents.

Nitrification–Autotrophic Denitrification Using Elemental Sulfur as an Electron Donor in a Sequencing Batch Reactor (SBR): Performance and Kinetic Analysis

Simultaneous nitrification and autotrophic denitrification (SNAD) has received attention as an efficient biological nitrogen removal alternative. However, SNAD using elemental sulfur (S0) has scarcely been studied. Thus, the main objective of this research was to study the behavior of a simultaneous nitrification–autotrophic denitrification operation in a sequential batch reactor (SNAD-SBR) at a lab scale using S0 as an electron donor, including its kinetics. Two-scale reactors were operated at lab scales in cycles for 155 days with an increasing nitrogen loading rate (NLR: 0.0296 to 0.0511 kg N-NH4+/m3/d) at 31 °C. As a result, simultaneous nitrification–autotrophic denitrification using S0 as an electron donor was performed successfully, with nitrification efficiency of 98.63% and denitrification efficiency of 44.9%, with autotrophic denitrification as the limiting phase. The kinetic model adjusted for ammonium-oxidizing bacteria (AOB) was the Monod-type kinetic model (µmax = 0.791 d−1), while, for nitrite-oxidizing bacteria (NOB), the Haldane-type model was employed (µmax = 0.822 d−1). For denitrifying microorganisms, the kinetic model was adjusted by a half order (k1/2v = 0.2054 mg1/2/L1/2/h). Thus, we concluded that SNAD could be feasible using S0 as an electron donor, with kinetic behavior similar to that of other processes.

Integrated partial nitrification and Tribonema minus cultivation for cost-effective ammonia recovery and lipid production from slaughterhouse wastewater

High ammonium content in untreated anaerobic digestion (AD) wastewater can inhibit microalgal growth, hindering both bioremediation and biomass/lipid productivity. This study investigated the potential of partial nitrification (PN) as a pretreatment step for AD effluent before cultivating the oleaginous microalga Tribonema minus for bioremediation and lipid production. The PN process transforms inhibitory ammonium into nitrate, a nitrogen form that microalgae can effectively utilize, thereby reducing ammonia toxicity. The results showed remarkable resilience in T. minus, with the species being able to tolerate high ammonium levels (≤120 mg/L) when combined with nitrate in synthetic wastewater. However, when ammonium was the sole nitrogen source (>30 mg/L), its inhibitory effect on T. minus growth became evident. Nevertheless, successful cultivation of T. minus was achieved in PN effluent from slaughterhouse AD using a Sequencing Batch Reactor (SBR) (25 °C and hydraulic retention time (HRT) of 1.5 h) containing 190 mg/L ammonium, achieving 51.25 % lipid accumulation. Additionally, cultivation with 125 mg/L NH4+-N in the PN effluent resulted in removal rates exceeding 95 % for NH4+-N. This approach, therefore, delivered the dual advantage of not only mitigating the environmental risks associated with wastewater but also fostering renewable biomass production for cleaner energy.

Simultaneous nitrification and denitrification pattern in aerated moving-bed sequencing batch reactor: Choosing appropriate SRT for different COD/N ratios

ABSTRACT The effect of chemical oxygen demand (COD)/N ratio and sludge retention time (SRT) on the simultaneous nitrification and denitrification (SND) process in an aerated moving-bed sequencing batch reactor (A-MBSBR), for treating synthetic municipal wastewater, was studied. Three lab-scale reactors with SRTs of 5, 10, and 15 days were operated under COD/N ratios of 10 (phase 1) and 20 (phase 2). The high correlation coefficients between nitrification and denitrification efficiencies in both phases demonstrated that the denitrification efficiency in A-MBSBRs was strongly affected by nitrification efficiency (nitrate concentration). A high COD/N ratio of 20 in phase 2 provided suitable conditions for the increase and dominance of the population of heterotrophic bacteria over autotrophic nitrifiers, which led to weak nitrification (29.6–39.1%) and consequently weak denitrification (15.8–27.9%) in all reactors. In phase 2, increasing SRT from 5 to 15 days was beneficial for both nitrification and denitrification reactions. Therefore, the optimal SND efficiency in phase 2 was expected to be achieved under SRTs higher than 15 days. Under the COD/N ratio of 10 in phase 1, a better balance between the population of heterotrophs and autotrophs resulted in higher nitrification and denitrification efficiencies (44.4–62.7% and 26.3–42.8%, respectively). In phase 1, the highest and the lowest nitrification and denitrification efficiencies were obtained at SRTs of 10 and 5 days, respectively.