Influent Acetate Concentration Research Articles

An extended bio-electrochemical model for wastewater treatment and water desalination: Insights into the performance of microbial desalination cells

This paper presents an extended mathematical model for a microbial desalination cell (MDC), integrating Haldane kinetics for substrate inhibition and proton translocation theory for substrate dissociation under dynamic flow. The model is capable of predicting exoelectrogenic and methanogenic biomass dynamics, acetate removal efficiencies, salt concentration changes, and current production. Notably, it can be used to explore the influence of operational parameters such as dilution rates, temperatures, and external resistances. Our simulations reveal the optimal conditions for maximizing exoelectrogen concentration (500 mg/L) with minimal methanogen presence (50 mg/L) in the anode chamber at an anolyte dilution rate of 0.5 d−1, a temperature of 20 °C, and an influent acetate concentration of 1500 mg/L. The model accurately predicts the salt reduction in the middle chamber (from 0.2 to 0.09 mol/L) with a salt dilution rate of 0.5 d−1 and an external resistance of 20 Ohm. The model predicts a peak power output of 2.5 mW at external resistances between 20 and 50 Ohm. The model was validated against a suite of experimental literature data, including our previously published lab-scale studies, verifying its accuracy in predicting organic and salt removal rates, current production, and desalination efficiency. This extended model is a valuable tool for understanding the complex interactions between factors that influence MDC performance and can guide the optimization of MDC design for wastewater treatment and desalination.

Effect of external acetate added in aquaculture wastewater on mixotrophic cultivation of microalgae, nutrient removal, and membrane contamination in a membrane photobioreactor

The mixotrophic cultivation of microalgae in wastewater has attracted extensive attention due to its many advantages. In this study, acetate, which can be prepared by hydrolysis of aquaculture waste, was used as exogenous organic matter to promote the growth of Chlorella pyrenoidosa cultured in aquaculture wastewater. Microalgae cultivation was carried out in a membrane photobioreactor (MPBR) with continuous inflow and outflow mode. The results showed that exogenous acetate greatly promoted the mixotrophic growth of C. pyrenoidosa. When the dosage of acetate reached 1.0 g L−1, the relative growth rate of microalgae in the logarithmic stage reached 0.31 d−1, which was 4.4 times that of the control. As a result, exogenous acetate also promoted the removal of nutrients from aquaculture wastewater. During the stable operation stage of the MPBR with acetate added in the influent, an average of 87.41%–93.93% nitrogen and 76.34%–88.55% phosphorus was removed from the aquaculture wastewater containing 19.41 mg L−1 total inorganic nitrogen and 1.31 mg L−1 total inorganic phosphorus. However, it was worth noting that adding exogenous acetate also led to an increase in the membrane resistance of the membrane module in the MPBR. Membrane resistance was mainly composed of internal resistance (Ri) and cake resistance (Rc), and with the increase of acetate content in the influent, their proportion in the total resistance gradually increased. Ri contributed the major membrane resistance and was most affected by acetate dosage. Ri reached 32.04 × 1012 m−1 with 1 g L−1 acetate, which accounted for 69.49% of total resistance. Moreover, with the increase of influent acetate concentration of the MPBRs, both the number of insoluble contaminants and dissolved organic contaminants in the membrane modules increased. In addition, the composition of proteins, polysaccharides, and humus in dissolved organic contaminants was close to that in extracellular polymeric substances and soluble microbial products secreted by microalgae. These results suggested that the membrane fouling of membrane modules was closely related to the algal biomass content in the MPBRs. The above results provided a theoretical basis for reducing membrane fouling of MPBR.

Adopting co-metabolism strategy for optimized biotreatment of ortho-hydroxytoluene and bioelectricity generation in microbial fuel cell: Transformation products and pathways

This study investigated the effects of carbon source availability and concentrations, external loads (Rload), and cathode conditions on the overall removal rate of ortho-hydroxytoluene and bioelectricity generation characteristics in anti-gravity flow microbial fuel cell (AGF-MFC) through co-metabolism approach. Sodium acetate outperformed sucrose, glucose and carbamide, and the optimum influent acetate concentration (1000 mg L−1) significantly enhanced the o-hydroxytoluene degradation by 13.41 % (98.71 %), output voltage by 15.14 % (609.25 mV) and power generation by 30.96 % (159.44 mW m−2). The results demonstrated that there were prominent differences in MFC performances under different Rload (p < 0.05). Different external load conditions resulted in varying electron transfer reactions, and thus affecting the removal efficiency and power responses of MFC system. A complete removal of o-hydroxytoluene and highest power density of 173.10 mW m−2, with a Chemical Oxygen Demand (COD) removal of 93.56 % were obtained with the Rload of 230 Ω, where the Rload approaches the cell design point. Hysteresis phenomenon was detected in the dynamic polarization during Rload variations. Moreover, it was observed that the removal efficiency of o-hydroxytoluene was significantly enhanced with aeration rate of 50 mL min−1, and dissolved oxygen concentration of 5.4 mg L−1. Conversely, higher aeration rate (400 mL min−1) had caused a decline of 26 % in power generation, ascribed to the limited active surface area for oxygen reduction reaction. Additionally, the degradation pathway of o-hydroxytoluene was proposed based on the identified intermediates.

The Rational Design of a Financially Viable Microbial Electrolysis Cell for Domestic Wastewater Treatment

Microbial electrolysis cells (MECs) are yet to achieve commercial viability. Organic removal rates (ORR) and capital costs dictate an MEC’s financial competitiveness against activated sludge treatments. We used numerical methods to investigate the impact of acetate concentration and the distance between opposing anodes’ surfaces (anode interstices width) on MEC cost-performance. Numerical predictions were calibrated against laboratory observations using an evolutionary algorithm. Anode interstices width had a non-linear impact on ORR and therefore allowable cost. MECs could be financially competitive if anode interstices widths are carefully controlled (2.5 mm), material costs kept low (£5–10/m2-anode), and wastewater pre-treated, using hydrolysis to consistently achieve influent acetate concentrations &amp;gt;100 mg-COD/l.

New insights in the competition of polyphosphate-accumulating organisms and glycogen-accumulating organisms under glycogen accumulating metabolism with trace Poly-P using flow cytometry

In enhanced biological phosphorus removal (EBPR) from wastewater, the metabolism pathway of polyphosphate accumulating organisms (PAOs) converted from polyphosphate accumulating metabolism (PAM) to glycogen accumulating metabolism (GAM) under a high ratio of carbon to phosphorus (C/P). This study investigated the competition mechanism between PAOs and glycogen accumulating organisms (GAOs) under GAM pathway. Low acetic acid (HAC) concentration made the GAM of PAOs outcompete GAOs in high C/P ratio (100:1), and the effect of influent acetate concentration on GAOs was stronger than PAOs. “Candidatus Accumulibacter” clades IIC and IID were the main dominant PAOs, and Thiothrix caldifontis (potential PAOs) was discovered and significantly increased from 0.53% to 5.75%. Flow cytometry results indicated that PAOs had higher specific surface area and lower nucleic acid content than GAOs, and high C/P promoted GAM rather than GAOs growth, which maybe important reasons causing PAOs dominant growth. PAOs dominance under GAM ensured stable performance of EBPR when C/P ratio in real wastewater increased.

A simple power management circuit for microbial fuel cell operation with intermittent electrical load connection

AbstractPractical implementation of microbial fuel cell (MFC)‐based power sources requires stable MFC performance regardless of the variations in the composition and quantity of a carbon source (fuel). This study describes a simple power management circuit (PMC) utilizing low and high voltage boundaries for intermittent MFC connection and disconnection to the electrical load. The PMC performance is demonstrated during MFC operation at carbon source‐replete and carbon source‐deplete conditions. In spite of MFC operation at external resistance values significantly below the estimated internal MFC resistance (e.g., 5.5 versus 24.5 Ω, respectively), the proposed PMC optimized MFC performance at all tested influent acetate concentrations, resulting in a volumetric power output of up to 56 mW · L−1. Furthermore, MFC operation with an up‐converter is tested and approaches for optimizing the voltage boundaries are discussed. The robustness and simplicity of the proposed PMC algorithm allows for its implementation in a standalone microprocessor with ultralow energy consumption, which enables MFC application as an autonomous power source.

Wastewater Treatment and Online Chemical Oxygen Demand Estimation in a Cascade of Microbial Fuel Cells

This study demonstrates degradation of synthetic wastewater in two MFCs hydraulically connected in series. To maximize chemical oxygen demand (COD) removal, external resistance of each MFC is optimized using a perturbation–observation maximum power point algorithm. Under optimal operating conditions a removal efficiency over 90% is achieved at an influent acetate concentration of 750 mg L–1 and organic loading rates ranging from 0.75 to 3.0 g L–1 day–1. Furthermore, regression analysis is used to correlate current and power output of each MFC with the analytically measured COD concentrations, thus providing a means for online COD estimations. The accuracy of online COD estimations is further improved by developing a model-based soft-sensor.

Material flow analysis of feedstock for enhancing its conversion efficiency during continuous photo‐hydrogen production

AbstractThe practical application of photofermentative hydrogen production process has been generally limited by the low feedstock conversion efficiency. In this work, material flow analysis (MFA) was applied into continuous photohydrogen to investigate the material flow of feedstock. Maximum feedstock utilization for hydrogen production (31.87%) was obtained at an hydraulic retention time of 60 h and influent acetate concentration of 40 mmol l−1, corresponding to maximum hydrogen yield of 1.89 mol H2 mol−1 acetate. MFA showed that due to the poor flocculation, photofermentative bacteria (PFB) cannot be efficiently separated from supernatant and rushed out with effluent continuously. To replenish the biomass washout, most of feedstock was continuously utilized for cell growth rather than hydrogen production, which caused low feedstock conversion efficiency. The results showed that poor flocculation of PFB resulting in low biomass retention capacity of photobioreactor was the origin of low feedstock conversion efficiency. Therefore, enhancing flocculation of PFB and using high biomass retaining operation modes are essential to further develop photofermentative hydrogen production process.

Porous anodes with helical flow pathways in bioelectrochemical systems: The effects of fluid dynamics and operating regimes

Bioelectrochemical systems (BES) and/or microbial fuel cell (MFC) mass transport and associated over-potential limitations are affected by flow regimes, which may simultaneously increase the power and pollution treatment capacities. Two electrodes with helical flow channels were compared in the same tubular MFC reactor. 1). A machined monolithic microporous conductive carbon (MMCC). 2). A layered carbon veil with spoked ABS former (LVSF); both presented helical flow channel. Anode performances were compared when subject to temperature, substrate concentration and flow rate variations. The MMCC maximum power increased from 2.9 ± 0.3 to 7.6 ± 0.7 mW with influent acetate concentration, from 1 to 10 mM (with 2 mL min−1), but decreased power to 5.5 ± 0.5 mW at 40 mM, implicated localized pH/buffering. Flow rate (0.1 to 7.5 mL min−1) effects were relatively small but an increase was evident from batch to continuous operation at 0.1 mL min−1. The LVSF configuration showed improved performance in power as the flow rate increased, indicating that flow pattern affects BES performance. Computational fluid dynamics (CFD) modelling showed less uniform flow with the LVSF. Thus flow regime driven mass transfer improves the power output in continuously fed system operation. These results indicate that electrode configuration, flow regime and operating condition need consideration to optimize the bioelectrochemical reaction.

Feasibility studies on continuous hydrogen production using photo-fermentative sequencing batch reactor

A novel photo-fermentative sequencing batch reactor (PFSBR) process assisted by activated carbon fibers (ACFs) was used to continuously produce hydrogen gas by Rhodopseudomonas faecalis RLD-53. Feasibility of continuous hydrogen production in PFSBR operation at different hydraulic retention times (HRTs) (48, 96, 144 and 192 h) and influent acetate concentrations (20, 40, 60 and 80 mmol/l) was investigated. The rate and yield of hydrogen production increased with HRTs from 48 to 144 h, and then decreased with the HRTs from 144 to 192 h. Regulation of the proper influent acetate concentration (60 mmol/l) not only increased hydrogen production by PFSBR, but also maintained quality of the effluent with high substrate removal efficiency (97.70%). Free R. faecalis RLD-53 was adsorbed on the surface of ACFs, initially isolated cells, then monolayer, and finally mature biofilm with three dimensional multilayers structures. The PFSBR reached a maximum hydrogen yield (3.12 mol H2/mol acetate), and achieved a steady state when mature biofilm developed on ACFs. Therefore, photo-fermentative sequencing batch reactor was a promising process for continuous photo-fermentative hydrogen production.

Influence of detachment on substrate removal and microbial ecology in a heterotrophic/autotrophic biofilm

Competition between heterotrophic bacteria oxidizing organic substrate and autotrophic nitrifying bacteria in a biofilm was evaluated. The biofilm was grown in a tubular reactor under different shear and organic substrate loading conditions. The reactor was initially operated without organic substrate in the influent until stable ammonia oxidation rates of 2.1 g N/(m 2 d) were achieved. A rapid increase of fluid shear in the tubular reactor on day 156 resulted in biofilm sloughing, reducing the biofilm thickness from 330 to 190 μm. This sloughing event did not have a significant effect on ammonia oxidation rates. The addition of acetate to the influent of the reactor resulted in decreased ammonia oxidation rates (1.8 g N/(m 2 d)) for low influent acetate concentrations (17 mg COD/L) and the breakdown of nitrification at high influent acetate concentrations (55 mg COD/L). Rapidly increasing fluid shear triggered biofilm sloughing in some cases—but maintaining constant shear did not prevent sloughing events from occurring. With the addition of acetate to the influent of the reactor, the biofilm thickness increased up to 1350 μm and individual sloughing events removed up to 50% of the biofilm. Biofilm sloughing had no significant influence on organic substrate removal or ammonia oxidation. During 325 days of reactor operation, ammonia was oxidized only to nitrite; no nitrate production was observed. This lack of nitrite oxidation was confirmed by fluorescent in situ hybridization (FISH) analysis, which detected betaproteobacterial ammonia oxidizers but not nitrite oxidizers. Mathematical modeling correctly predicted breakdown of nitrification at high influent acetate concentrations. Model predictions deviated systematically from experimental results, however, for the case of low influent acetate concentrations.

Column Study Simulating In Situ Bioremediation of Perchlorate Using Acetate as an Organic Substrate

Perchlorate, which is highly soluble and is persistent in the environment, is being identified increasingly as a groundwater contaminant. Because perchlorate is biodegradable, a column study was conducted investigating the feasibility of in situ biodegradation of perchlorate using acetate as an organic substrate, which was necessary to stimulate biodegradation of perchlorate. Degradation of the perchlorate was rapid, with a minimal lag phase, once acetate was added to the column. By 72 h, complete removal of the perchlorate occurred (from 10 to <0.05mg∙L−1) within the first 15 cm of the column. The column was then allowed to reach steady-state degradation with an influent perchlorate concentration of 50mg∙L−1 and an influent acetate concentration of 100mg∙L−1. The perchlorate was removed in the first 7.5 cm of the column. Then, the acetate was removed. This study indicated that, although acetate is needed to stimulate perchlorate removal, residual activity remains as the acetate is removed, retarding the decline in performance. Upon the reintroduction of 10mg∙L−1 of acetate in the influent, rapid removal of perchlorate was quickly reestablished. Steady-state operation was compared at three loading rates. In each case, the perchlorate was degraded below 0.05mg∙L−1 within the first 7.5 cm of the column. Volumetric degradation rates for perchlorate were as high as 102.6g∙m−3∙day−1, and the rate was completely dependent on the concentration for the loading rate tested. The column effluent was tested using analytical techniques with a method detection limit of 1μg∙L−1. For each loading, the effluent, on average, met the California action level of 6μg∙L−1.

AOC removal and accumulation of bacteria in experimental sand filters

Using small sand filets under well defined laboratory conditions, filtration experiments were performed with tap water supplemented with acetate. The objective of these experiments was to determine the effect of different acetate concentrations on (i) the removal of easily assimilable organic carbon (AOC) in the filter (ii), the clogging of the tiller and (iii) the bacteriological quality of the filtrate. The results of the experiments revealed that the reduction capacity of biological filtration processes for acetate is relatively high. Acetate removal resulted in an increased microbiological activity in the top layer (&lt; 1cm) of the filter bed and accumulation of bacterial matter was observed at an influent AOC concentration as low as 0.005 mg of ac-C eq/l. Clogging of the filter bed occurred at an influent acetate concentration of 0.01 mg C/l. Based on these observations it was concluded that the AOC concentration of water used for infiltration in recharge wells should be less thon 0.01 mg ac-C eq/l. This level is similar to the level advised for biologically-stable drinking water. A linear relationship was found between the acetate removal in the experimental filters and the colony count in the filtrate. It was recommended that the AOC load in the final filtration process in water treatment therefore should be limited to prevent high colony counts in the filtrate, thus leading to the use of post disinfection.

Bioremediation of Perchlorate-Contaminated Groundwater Using a Packed Bed Biological Reactor

ABSTRACT The objective of this study was to assess the efficacy of a bench-scale, acetate-fed, packed bed bioreactor (PBR) to treat low concentrations (>1 mg L−1) of perchlorate (ClO4 −) in groundwater collected from an impacted site. The PBR consisted of a cylindrical plexiglass column packed with Celite, a diatomaceous earth product, as a solid support medium. The reactor was inoculated with a ClO−4 −-reducing bacterial isolate, perclace. Results showed that with influent ClO4 − concentrations of approximately 800 μg L−1, nondetectable effluent concentrations (>4 μg L−1) were achieved with the PBR/perclace system at residence time as low as 0.3 h. Influent acetate concentrations of less than 500 mg L−1 yielded nondetectable effluent ClO− 4 concentrations, and acetate concentrations generally less than 50 mg L−1 were present in the effluent. Nitrate (NO− −3) was also removed in this system, while sulfate (SO4 2−) reduction was not observed. The pH remained relatively constant during the process.

Effect of upward velocity and sulphide concentration on volatile fatty acid degradation in a sulphidogenic granular sludge reactor

During anaerobic treatment of sulphate-containing wastewaters, sulphate-reducing bacteria (SRB) compete with methane-producing bacteria (MPB) for the available electron-donors. In this work, the anaerobic treatment of a synthetic wastewater, consisting of a mixture of acetate, propionate and butyrate and high concentrations of sulphate (COD: sulphate ratio 0·5) was studied in an upflow anaerobic granular sludge bed reactor. The influence of the superficial upward liquid velocity ( v up ), the influent composition and reactor pH on the competition between SRB and MPB was investigated. At a v up of 2 m h −1 and pH 8, 93–97% of the COD was degraded by SRB. With increasing v up - values , COD removal efficiencies decreased, while at a v up of 6 m h −1 the fraction of COD removed by MPB rose to 23%. Elevation of the influent acetate concentrations, by decreasing the v up (lower recirculation) or by the use of an influent volatile fatty acid mixture with a higher acetate content, resulted in an increase of methanogenesis up to 41% of the total COD removal. In contrast, elevated levels of propionate and butyrate in the influent favoured the sulphate reducing process. A decrease of pH from 8 to 7 resulted in free hydrogen sulphide concentrations higher than 200 mg litre −1. This strongly inhibited methanogenesis while SRB were hardly affected, with a subsequent decrease of the COD removed by MPB from 41 to 7% as a result.

Modeling of volatile fatty acids degradation kinetics and evaluation of microorganism activity

Particular cases of Monod kinetics (zero order and exponential growth) were used for the description of VFA degradation by acetate and glucose pregrown inocula measured by Aguilar et al. (1995), and kinetic constants were evaluated. The equations with inhibition were used for description of the degradation kinetics of VFA mixtures measured by Mawson et al. (1991) and by Ozturk (1991). A good agreement between the model and the batch data with synthetic media and molasses pregrown inoculum was obtained and microorganism activity was evaluated. Using the generalized 〈 METHANE〉 model of anaerobic digestion described earlier, the Monod and Haldane kinetics were tested for the experimental data of Noike et al. (1985), where mesophilic conversion of acetate was studied in a continuous-flow reactor under a wide range of acetate-loading values. The system failed at high influent acetate concentration because of pH inhibition for Monod kinetics and of unionized-acetate inhibition for Haldane kinetics. However, the model could not describe the change of effluent acetate concentration. To describe that, the corrected Monod and Haldane function with changeable half-saturation coefficients was introduced.

Performance of Expanded‐Bed Methanogenic Reactor

A completely mixed, expanded-bed, anaerobic granular activated carbon reactor was operated continuously on synthetic wastewaters in which acetate was the only organic carbon source. Steady-state performance was achieved for four influent acetate concentrations, namely: 800, 1600, 3200, and 6400 mg/l. Steady-state removal efficiencies of acetate, COD, and DOC exceeded 98, 97 and 98%, respectively. Biological utilization was the major removal mechanism for acetate in the anaerobic filter. This process was demonstrated to be capable of purifying low strength wastewaters down to levels that are acceptable for final discharge. 16 references.