Anaerobic Fluidized Bed Research Articles

Investigating membrane fouling associated with GAC fluidization on membrane with effluent from anaerobic fluidized bed bioreactor in domestic wastewater treatment.

Effect of mechanical scouring driven by granular activated carbon (GAC) fluidization on membrane fouling was investigated using a laboratory-scaled, fluidized membrane reactor filtering the effluent from anaerobic fluidized bed bioreactor (AFBR) in domestic wastewater treatment. The GAC particles were fluidized by recirculating a bulk solution only through the membrane reactor to control membrane fouling. The membrane fouling was compared with two different feed solutions, effluent taken from a pilot-scaled, AFBR treating domestic wastewater and its filtrate through 0.1-μm membrane pore size. The GAC fluidization driven by bulk recirculation through the membrane reactor was very effective to reduce membrane fouling. Membrane scouring under GAC fluidization decreased reversible fouling resistance effectively. Fouling mitigation was more pronounced with bigger GAC particles than smaller ones as fluidized media. Regardless of the fluidized GAC sizes, however, there was limited effect on controlling irreversible fouling caused by colloidal materials which is smaller than 0.1μm. In addition, the deposit of GAC particles that ranged from 180 to 500μm in size on membrane surface was very significant and accelerated fouling rate. Biopolymers rejected by the membranes were thought to play a role as binding these small GAC particles on membrane surface strongly.

Ultrasonically enhanced anaerobic digestion of thickened waste activated sludge using fluidized bed reactors

This study aimed at assessing the impact of ultrasonication on the anaerobic digestibility of thickened waste activated sludge (TWAS) in an anaerobic fluidized bed reactor (AnFBR). Two lab-scale AnFBRs treating TWAS were studied to explore the impact of ultrasonication (US) in the dispersing and reuse of scum for methane production. Our current work applied ultrasound energy at 120–600kJ/d for 2s per 30s corresponding to ultrasonication densities of 6–15.7MJ/kg dry-scum-d. At an organic loading rate (OLR) of 5.1kg COD/m3-d and US energy of 11.9MJ/kg dry-scum-d, scum decreased by 82% from 20.2gm/d to 3.7gm/d, and COD and VSS destruction efficiencies were 65% and 63%, respectively roughly 20% higher than the control reactor without US. Scum reduction varied linearly with US energy about 25kJ/g TS was required to break the scum. The energy balance also indicated that the aforementioned US energy of 11.9MJ/kg dry-scum-d was optimum because of energy neutrality. Specific methanogenic activity (SMA) tests showed that the activity-based sludge retention time (SRT) is higher for the ultrasonicated AnFBR (U-AnFBR) (7.1days) compared to AnFBR (5.1days). Furthermore, a higher rate of maximum specific biogas production (Rm) was observed in the U-AnFBR of 26.7ml/gmVSS-hr as compared to 15.7ml/gmVSS-hr for the control AnFBR, with respective suspended biomass activities of 2ml/gmVSS-hr and 4.1ml/gmVSS-hr i.e. confirming that US improved methanogenic activity in the reactor and reduced the detachment of active methanogens.

Simultaneous nitrogen and organics removal using membrane aeration and effluent ultrafiltration in an anaerobic fluidized membrane bioreactor

Dissolved methane and a lack of nutrient removal are two concerns for treatment of wastewater using anaerobic fluidized bed membrane bioreactors (AFMBRs). Membrane aerators were integrated into an AFMBR to form an aeration membrane fluidized bed membrane bioreactor (AeMFMBR) capable of simultaneous removal of organic matter and ammonia without production of dissolved methane. Good effluent quality was obtained with no detectable suspended solids, 93±5% of chemical oxygen demand (COD) removal to 14±11mg/L, and 74±8% of total ammonia (TA) removal to 12±3mg-N/L for domestic wastewater (COD of 193±23mg/L and TA of 49±5mg-N/L) treatment. Nitrate and nitrite concentrations were always low (<1mg-N/L) during continuous flow treatment. Membrane fouling was well controlled by fluidization of the granular activated carbon (GAC) particles (transmembrane pressures maintained <3kPa). Analysis of the microbial communities suggested that nitrogen removal was due to nitrification and denitrification based on the presence of microorganisms associated with these processes.

Eco-efficiency analysis of non-potable water systems in domestic buildings

Energy efficiency in water systems contributes significantly towards achieving sustainable water management. Decentralized anaerobic fluidized bed membrane bioreactor (AFMBR) systems with energy recovery have been proposed for greywater recycling in domestic buildings for non-potable uses, such as toilet flushing. This study developed an eco-efficiency analysis (EEA) framework with the integration of life-cycle assessment (LCA) and economic analysis for the evaluation of different water systems. Four water management scenarios including (1) freshwater flushing system, (2) seawater flushing system, (3) greywater flushing system adopting aerobic membrane bioreactor (MBR), and (4) greywater flushing system adopting AFMBR, were analyzed in a case study in Hong Kong. The EEA results reveal the AFMBR greywater reuse scenario to be the most eco-efficient option as the system is capable of energy recovery, recycling of water resource and reduction of sewage treatment loadings. This study has demonstrated that the EEA framework is an effective tool to guide water management towards sustainability and provides a basis for further research on the application of greywater recycling systems on a larger scale.

Two phases fermentative process for hydrogen and methane production from cassava wastewater

Introduction: Hydrogen and methane production was investigated in two phases of fermentative process. Objective: At the acidogenic phase, an anaerobic fluidized bed reactor was fed with cassava wastewater producing hydrogen. Methods: Expanded clay was used as a support material for biomass immobilization. The reactor was operated with HRT ranging from 8-1 h. Results: The best hydrogen yield production was 1.91 mol H2/mol glucose at HRT of 2 h. At the methanogenic phase, the acidogenic process effluent fed a fixed-bed reactor producing methane. Conclusion: Sururu (Mytella falcata) shells was used as support acted as pH neutralizer in the fixed-bed reactor, yielding best (0.430±0.150 Lmethane/gCOD) with 12h HRT phase.

Effect of inoculum pretreatment on the microbial community structure and its performance during dark fermentation using anaerobic fluidized-bed reactors

The effect of two different inoculum pretreatments, thermal and cell wash-out (A1 and A2, respectively) on the performance of anaerobic fluidized bed reactors for hydrogen production was determined. The reactors were operated for 112 days under the same operational conditions using glucose as substrate at increasing organic loading rates and decreasing hydraulic retention times. Both treatments were effective avoiding methanogenesis. Reactor A2 showed better performance and stability than reactor A1 in each one of the different operational conditions. Cell wash-out treatment produced higher hydrogen volumetric production rates and yields than thermal treatment (7 L H2/L-d, 3.5 mol H2/mol hexose, respectively). DGGE analysis revealed that the microbial communities developed were affected by the inoculum treatment. Organisms from the genera Clostridium and Lactobacillus predominated in both reactors, with their relative abundances linked to hydrogen production. Resilience was observed in both reactors after a period of starvation.

Low energy single-staged anaerobic fluidized bed ceramic membrane bioreactor (AFCMBR) for wastewater treatment

An aluminum dioxide (Al2O3) ceramic membrane was used in a single-stage anaerobic fluidized bed ceramic membrane bioreactor (AFCMBR) for low-strength wastewater treatment. The AFCMBR was operated continuously for 395days at 25°C using a synthetic wastewater having a chemical oxygen demand (COD) averaging 260mg/L. A membrane net flux as high as 14.5–17L/m2h was achieved with only periodic maintenance cleaning, obtained by adding 25mg/L of sodium hypochlorite solution. No adverse effect of the maintenance cleaning on organic removal was observed. An average SCOD in the membrane permeate of 23mg/L was achieved with a 1h hydraulic retention time (HRT). Biosolids production averaged 0.014±0.007gVSS/gCOD removed. The estimated electrical energy required to operate the AFCMBR system was 0.039kWh/m3, which is only about 17% of the electrical energy that could be generated with the methane produced.

Analysis of organic compounds’ degradation and electricity generation in anaerobic fluidized bed microbial fuel cell for coking wastewater treatment

ABSTRACTA single-chambered packing-type anaerobic fluidized microbial fuel cell (AFBMFC) with coking wastewater (CWW) as fuel was built to treat CWW, which not only has high treating efficiency, but also can convert organic matter in wastewater into electricity. AFBMFC was constructed by using anaerobic sludge that was domesticated as inoculation sludge, which was used to biochemically treat CWW. The organic compounds in CWW were extracted by liquid–liquid extraction step by step every day. The extraction phase was concentrated by a rotary evaporator and a nitrogen sweeping device and was analyzed by GC–MS. And the electricity-generation performances of AFBMFC were investigated. The results show that the composition of CWW was complicated, which mainly contains hydrocarbons, phenols, nitrogenous organic compounds, alcohols and aldehydes, esters and acids and so on. After a cycle of anaerobic biochemical treatment, the content of organic compounds in the effluent decreased significantly. After the treatment of AFBMFC, 99.9% phenols, 98.4% alcohol and aldehydes and 95.3% nitrogenous compounds were biodegraded. In the effluent, some new compounds (such as tricosane and dibutyl phthalate) were produced. The chemical oxygen demand (COD) of CWW decreased from 3372 to 559 mg/L in the closed-circuit microbial fuel cell, and the COD removal was 83.4 ± 1.0%. The maximum power density of AFBMFC was 2.13 ± 0.01 mW m−2.

Influence of C/P and C/N ratios and microbial characterization in hydrogen and ethanol production in an anaerobic fluidized bed reactor

The aim of this study was to evaluate the influence of C/P and C/N ratios on the production of hydrogen and ethanol in four anaerobic fluidized bed reactors: R1 (C/N = 100), R2 (C/N = 150), R3 (C/N = 200), and R4 (C/N = 250). The hydraulic retention time (HRT) was maintained at 2 h, and the C/P ratios varied from 300 to 1100. Reactors were filled with grounded tire and fed with synthetic substrate containing glucose (5000 mg L−1). The effluent pH was around 3.7. The highest values for hydrogen yield (HY) and hydrogen production rate (HPR) were obtained at a C/P = 700 ratio in all reactors. The best performance was achieved at R3 (C/N = 200): HY of 0.76 mol H2 mol−1 glucose and HPR of 0.70 L h−1 L−1. The highest value for ethanol yield was obtained at C/P = 700 in R1 (1.5 mol EtOH mol−1 glucose). Ethanol- and hydrogen-producing fermenters, such as Ethanoligenens sp. and Clostridium sp. were identified by molecular analysis. Lactobacillus sp. was also identified in this study.

Macroscopic approach to develop fouling model under GAC fluidization in anaerobic fluidized bed membrane bioreactor

Abstract A mathematical model was presented to understand membrane fouling in anaerobic fluidized bed membrane bioreactor (AFMBR). Assuming three fouling mechanisms, the cake formation, progressive porosity reduction and the pore blocking, the model describes the effect of granular activated carbon (GAC) on fouling resistance and mechanisms. The model shows satisfactory description of transmembrane pressure with R 2 ≈ 99%. Using GAC particles (2–3 mm) allows a better fouling mitigation by removing cake deposit while long term fouling is due to pore blocking. The fluidized small GAC particles (0.18–0.5 mm) foster the cake formation by their deposit on membrane surface.

BIOHYDROGEN PRODUCTION FROM CASSAVA WASTEWATER AND DOMESTIC SEWAGE IN AN ANAEROBIC FLUIDIZED BED REACTOR

This study addresses hydrogen production in two anaerobic fluidized bed reactors (AFBRs) that were fed with cassava wastewater and domestic sewage. The reactors were operated at hydraulic retention times of 4-3 h (AFBR 1) and 4 h (AFBR 2). The maximum hydrogen yields (HY) and the maximum hydrogen production rate (HPR) were, respectively, 0.93 mol H2.mol glucose-1 and 1.69 L.h-1.L-1 (AFBR 1) for the AFBR 1, and 2.03 mol H2.mol glucose-1 and 0.95 L.h-1.L-1 for AFBR 2. The hydrogen content ranged from 2.25 to 23.25% (AFBR 1) and from 7 to 50.75% (AFBR 2). The hydrogen content increased significantly when the amount of domestic sewage decreased, that is, higher concentrations of cassava wastewater in the substrate favors the hydrogen production. Acetic acid was the predominant metabolite that was soluble in both reactors, indicating that the hydrogen production rate and the hydrogen yield made the acetic acid pathway predominant. The association between cassava wastewater and domestic sewage favored biohydrogen production satisfactorily.

Forecasting the effect of feast and famine conditions on biological sulphate reduction in an anaerobic inverse fluidized bed reactor using artificial neural networks

Abstract The longevity and robustness of bioreactors used for wastewater treatment is determined by the activity of the microorganisms under steady and transient loading conditions. Two identical continuously operated inverse fluidized bed bioreactors (IFB), IFB R1 and IFB R2, were tested for sulphate removal under the same operating conditions for 140 d (Periods I–IV). Later, IFB R1 was used as the control reactor (Period V), while IFB R2 was operated under feast (Period V-A) and famine (Period V-B) feeding conditions for 66 d. The sulphate removal efficiency was comparable in both IFB,

CFD study on the hydrodynamics of fluidized granular activated carbon in AnFMBR applications

Abstract The anaerobic fluidized bed membrane bioreactor (AnFMBR) utilizes the fluidization of granular activated carbon (GAC) particles as an unsteady-state shear means for mitigating membrane fouling. In this study, a two-fluid model (TFM) was validated against experimental results and used to obtain a comprehensive landscape of local water and particle velocities and concentrations throughout the reactor. The results provided interesting insights. Firstly, both water and particle velocities tended to be non-uniform vertically and laterally, which indicate that the extent of fouling across the membrane would be non-uniform. Secondly, to attain the same water shear stress or particle momentum values, the power required was greater for the larger particles, which indicate that smaller particles were more energy-efficient. Thirdly, at the same power input, the water shear stress or particle momentum values for the different particle diameters overlapped, which indicates that other parameters can be manipulated to improve performance even when particle diameter has been fixed. Fourthly, generally negative correlations existed between fouling rate and the hydrodynamics of both phases, but fouling rate and power input were poorly correlated, which suggests surprisingly that increasing power would not improve the fouling mitigation.

Bacterial resistance in sanitary sewage sludge in different treatment systems

PurposeThe purpose of this paper is to assess the occurrence and risk of dispersion in the environment of antibiotic-resistant microorganisms from sanitary sewage sludge produced in two conventional wastewater treatment systems adopted in the West of the State of Paraná, Brazil.Design/methodology/approachThe sludge samples were collected for three months from two wastewater treatment plants, totaling six sample points, and sent to the laboratory where the physical-chemical and biological determinations were performed.FindingsThis work made possible to find that the sludge produced in the sewage treatment plants presents potential risks related to the spread of microorganisms due to the occurrence of resistant isolates of Escherichia coli and Salmonella sp. It was also possible to detect that the largest concentrations of metal ions in the sludge favored the occurrence of bacterial resistance to antibiotics. The occurrence of pathogens, heavy metals and other emerging pollutants in sewage indicates that the sludge requires proper treatment, to provide safe agricultural reuse or disposal.Practical implicationsThe techniques applied for monitoring sludge were effective to check the risk of resistant microorganisms input into the environment. Studies concerning sewage treatment plants’ final effluents can bring additional data about the incorporation of such microorganisms into aquatic environments.Originality/valueThe results made possible to observe the need to provide post-treatment for the sludge, especially of the sludge obtained from the anaerobic fluidized bed reactor, since the removal of pathogens, as well as the nutrients, is not satisfactory.

Simultaneous determination of anionic and nonionic surfactants in commercial laundry wastewater and anaerobic fluidized bed reactor effluent by online column-switching liquid chromatography/tandem mass spectrometry.

This study presents a new method developed for the simultaneous determination of anionic surfactant (linear alkylbenzene sulfonate - LAS, 4 homologs) and nonionic surfactant (linear alcohol ethoxylate - LAE) in commercial laundry wastewater. The surfactants were identified and quantified using online column-switching solid-phase extraction (SPE) coupled with liquid chromatography/tandem mass spectrometry (LC-MS/MS). Ten and three transitions (m/z) were identified for LAS and LAE, respectively. The detection and quantification limits were 75 and 200μg/L for LAS, respectively, and 75μg/L for LAE. This method was applied to the determination of the surfactants in the influent and effluent of an anaerobic fluidized bed reactor that was used for the treatment of commercial laundry wastewater. After 480days of operation with a hydraulic retention time (HRT) of 18h, the removal of 45.9±5.6% LAS and 99.2±4.3% LAE from an influent with surfactant concentrations of 26.1±12.9mg/L and 23.8±6.8mg/L, respectively, was obtained. Under these conditions, the breakage of longer-chain LAS homologs with the release of carbon units was observed with an increase in the number of shorter homolog chains. This SPE online sample treatment method is simple, fast and effective for the analysis of both surfactants. This technique is pioneering in its simultaneous measurement of two surfactant categories in anaerobic fluidized bed reactors.

Continuous thermophilic hydrogen production from cheese whey powder solution in an anaerobic fluidized bed reactor: Effect of hydraulic retention time and initial substrate concentration

The focus of this study is the use of an anaerobic fluidized bed reactor (AFBR) to continuously produce hydrogen under thermophilic conditions (55 °C) using a range of cheese whey (CW) concentrations and hydraulic retention times (HRTs). The following combinations of tests parameters were evaluated: a fixed concentration of 4900 ± 200 mg lactose L−1 and HRTs of 8, 6, 4, 2, 1 and 0.5 h in AFBR1 and a fixed HRT of 6 h and influent CW concentrations of 2800 ± 100, 4900 ± 200, 6800 ± 300, 9800 ± 300 and 14,600 ± 300 mg lactose L−1 in AFBR2. For AFBR1, the maximum hydrogen production rate (HPR) obtained was 4.1 ± 0.2 L H2 h−1 L−1 in the HRT of 0.5 h, and maximum hydrogen yield (HY) of 3.67 ± 0.59 mol H2 mol lactose−1 in the HRT of 4 h. For AFBR2, the maximum HPR was 0.85 ± 0.12 L H2 h−1 L−1 at a concentration of 6800 ± 300 mg lactose L−1, and the maximum HY was 2.64 mol H2 mol lactose−1 at a concentration of 2800 ± 100 mg lactose L−1. In both reactors, the main metabolic products were acetic acid and butyric acid. Based on 16S rRNA clone analysis of the bacterial community, the identified sequences were affiliated with relative abundances of 48.42% (Thermoanaerobacterium and Thermohydrogenium kirishiense) and 75.53% (Thermoanaerobacterium thermosaccharolyticuum and T. kirishiense) in AFBR1 and AFBR2, respectively.

Single-stage versus two-stage anaerobic fluidized bed bioreactors in treating municipal wastewater: Performance, foulant characteristics, and microbial community

This study examined the receptive performance, membrane foulant characteristics, and microbial community in the single-stage and two-stage anaerobic fluidized membrane bioreactor (AFMBR) treating settled raw municipal wastewater with the aims to explore fouling mechanisms and microbial community structure in both systems. Both AFMBRs exhibited comparable organic removal efficiency and membrane performances. In the single-stage AFMBR, less soluble organic substances were removed through biosorption by GAC and biodegradation than those in the two-stage AFMBR. Compared to the two-stage AFMBR, the formation of cake layer was the main cause of the observed membrane fouling in the single-stage AFMBR at the same employed flux. The accumulation rate of the biopolymers was linearly correlated with the membrane fouling rate. In the chemical-cleaned foulants, humic acid-like substances and silicon were identified as the predominant organic and inorganic fouants respectively. As such, the fluidized GAC particles might not be effective in removing these substances from the membrane surfaces. High-throughout pyrosequencing analysis further revealed that beta-Proteobacteria were predominant members in both AFMBRs, which contributed to the development of biofilms on the fluidized GAC and membrane surfaces. However, it was also noted that the abundance of the identified dominant in the membrane surface-associated biofilm seemed to be related to the permeate flux and reactor configuration.

Continuous Hydrogen Production from Agricultural Wastewaters at Thermophilic and Hyperthermophilic Temperatures.

The objective of this study was to investigate the effects of hydraulic retention time (HRT) (8 to 0.5h) and temperature (55 to 75°C) in two anaerobic fluidized bed reactors (AFBR) using cheese whey (AFBR-CW=10,000mg sugars L-1) and vinasse (AFBR-V=10,000mg COD L-1) as substrates. Decreasing the HRT to 0.5h increased the hydrogen production rates in both reactors, with maximum values of 5.36±0.81L H2 h-1 L-1 in AFBR-CW and 0.71±0.16L H2 h-1 L-1 in AFBR-V. The optimal conditions for hydrogen production were the HRT of 4h and temperature of 65°C in AFBR-CW, observing maximum hydrogen yield (HY) of 5.51±0.37mmol H2 g COD-1. Still, the maximum HY in AFBR-V was 1.64±0.22mmol H2 g COD-1 at 4h and 55°C. However, increasing the temperature to 75°C reduced the hydrogen production in both reactors. Methanol and butyric, acetic, and lactic acids were the main metabolites at temperatures of 55 and 65°C, favoring the butyric and acetic metabolic pathways of hydrogen production. The increased productions of lactate, propionate, and methanol at 75°C indicate that the hydrogen-producing bacteria in the thermophilic inoculum were inhibited under hyperthermophilic conditions.

Start-up of an anaerobic fluidized bed reactor treating synthetic carbohydrate rich wastewater

The present work studied the start-up process of a mesophilic (37 ± 2 °C) anaerobic fluidized bed reactor (AFBR) operated at a hydraulic retention time (HRT) of 20 days using synthetic carbohydrate rich wastewater. Anox Kaldness-K1 carriers were used as biofilm carrier material. The reactor performance and biofilm formation were evaluated during the process. The start-up process at lower liquid recirculation flow rate enhanced the biofilm formation and reactor performance. The organic substrate composition had a major impact on early colonization of methanogenic archaea onto the surface of the Kaldness carriers during the start-up process. Specific organic substrates favouring the growth of methanogenic archaea, such as acetate, are preferred in order to facilitate the subsequent biofilm formation and AFBR start-up. The supply of ‘bio-available’ nutrients and trace elements, in particular iron, had an important role on optimal methanogenic activity and speeding-up of the biofilm development on the Kaldness carriers. This paper provides possible strategies to optimize the various operational parameters that influence the initial biofilm formation and development in an AFBR and similar high rate anaerobic reactors, hence can be used to reduce the long time required for process start-up.

Effect of fluidized granular activated carbon (GAC) on critical flux in the microfiltration of particulate foulants

The fluidization of Granular Activated Carbon (GAC) particles has received much attention in recent years as a promising method for mitigating membrane fouling particularly in membrane bioreactors (MBRs). In particular, the fluidized GAC particles are acknowledged to be beneficial in terms of adsorption of organic foulants, and mechanical scouring and surface shear of the membrane surface. Both lab-scale and pilot-scale studies have affirmed the efficacy of GAC fluidization in maintaining a depressed extent of membrane fouling in anaerobic fluidized bed - membrane bioreactors (AnFMBRs). More in-depth studies have also correlated the hydrodynamics of fluidized GAC particles with the effectiveness of membrane fouling mitigation. This study aimed at understanding the improvement of fine (micron-sized) particle critical flux in the presence of fluidized GAC via the Direct Observation Through the Membrane (DOTM) technique. The model foulant was a suspension of polystyrene particles (5µm sized), and the parameters investigated included GAC particle diameter (dp), superficial liquid velocity (Ul) and thereby power requirement (Pr), and height along the vertically aligned membrane. Results indicate that: (i) fluidized GAC increased the critical flux by an order-of-magnitude relative to that with tangential liquid shear alone; (ii) the overall critical flux (Jcritical, overall) expectedly increased with power input (Pr), but the relationship between local critical flux (Jcritical) and power input (Pr) depended on the position along the membrane height; (iii) at the same Pr, although the larger GAC particles were more effective locally (i.e., higher Jcritical) due to greater particle inertia, the smaller GAC particles were more effective overall (i.e., higher Jcritical, overall) due to greater bed expansion enabling scouring of more membrane heights; and (iv) a higher power input (Pr) was required for sufficient bed expansion to enable more consistent critical flux (Jcritical) values over the whole membrane height.