Mechanistic study on the ferric chloride-based rapid cultivation and enhancement of aerobic granular sludge.

Aerobic granular sludge (AGS) can achieve simultaneous carbon, nitrogen and phosphorus removal owing to its three-dimensional oxygen gradient structure. However, long start-up period and poor operational stability restrict its application and promotion. A novel rapid granulation strategy, viz., the short-term (7 days) addition of ferric chloride at the commissioning stage, was developed and verified in this study. The granulation period was shortened by 9 days, and the formed granules were compact and dense with an Fe3+ concentration of 250 mg L-1. The addition of flocculant not only maintained a high sludge concentration during the initial stages of granulation (5.3 g L-1), but also stimulated the secretion of TB-EPS and increased protein and polysaccharide contents, thereby expediting granule formation. Additionally, ferric chloride induced a diverse microbial community in granules, resulting in the emergence of new genera, such as Thaurea, Brevundimonas and Kinneretia, which improved pollutant removal performance and flocculent aggregation. The removal efficiencies of COD, PO43--P, and NH4+-N stabilized at 94.2, 62.4, and 71.3%, respectively. Therefore, it has been demonstrated that short-term ferric chloride dosing has a synergistic effect on aerobic granulation.

Granular activated carbon and exogenous hydrogen enhanced anaerobic digestion of hypersaline phenolic wastewater via syntrophic acetate oxidation and hydrogenotrophic methanogenesis.

High salinity in phenolic wastewater inhibited anaerobes' metabolic activity, thereby affecting the anaerobic biotransformation of phenol. In this study, granular activated carbon (GAC) coupled with exogenous hydrogen (H2) was used to enhance the anaerobic digestion of phenol. The GAC/H2 group's accumulative methane production, coenzyme F420 concentration, and interspecies electron transfer system activity increased by 24 %, 53 %, and 16 %, respectively, compared with the control group. In the floc sludge of the GAC/H2 group, the relative abundance of syntrophic acetate-oxidizing bacteria such as Syntrophus and Syntrophorhabdus were 18.7 % and 1.1 % at genus level, respectively, which were around 93.5 and 7.5 times of that of the controlgroup. Moreover, Acinetobacter (77.6 %), Methanobacterium (44.0 %), and Methanosarcina (34.2 %) were significantly enriched on the GAC surface in GAC/H2 group. Therefore, the coupling of GAC and H2 provided a novel attempt at anaerobic digestion of hypersaline phenolic wastewater via syntrophic acetate oxidation and hydrogenotrophic methanogenesis pathway.

Response of anaerobic granular sludge to long-term loading of roxarsone: From macro- to micro-scale perspective.

Extensive use of organoarsenic feed additives such as roxarsone has caused organoarsenicals to occur in livestock wastewater and further within anaerobic wastewater treatment systems. Currently, information on the long-term impacts of roxarsone on anaerobic granular sludge (AGS) activity and the underlying mechanisms is very limited. In this study, the response of AGS to long-term loading of roxarsone was investigated using a laboratory up-flow anaerobic sludge blanket reactor spiked with 5.0 mg L-1 of roxarsone. Under the effect of roxarsone, methane production decreased by ∼40% due to the complete inhibition on acetoclastic methanogenic activity on day 260, before being restored eventually. Over 30% of the influent arsenic was accumulated in the AGS and the capability of AGS to prevent intracellular As(III) accumulation increased with time. The AGS size was reduced by ∼30% to 1.20‒1.26 mm. Based on morphology and confocal laser scanning microscopy analysis, roxarsone exposure stimulated the excretion of extracellular polymeric substances and the surface spalling of AGS. High-throughput sequencing analysis further indicated roxarsone initially altered the acidogenic pathway and severely inhibited the acetoclastic methanogen Methanothrix. Acetogenic bacteria and Methanothrix were finally enriched and became the main contributor for a full restoration of the initial methane production. These findings provide a deeper understanding on the effect of organoarsenicals on AGS, which is highly beneficial for the effective anaerobic treatment of organoarsenic-bearing wastewater.

Promoting direct interspecies electron transfer and acetoclastic methanogenesis for enhancing anaerobic digestion of butanol octanol wastewater by coupling granular activated carbon and exogenous hydrogen.

Butanol octanol wastewater (BOW) generated from syngas conversion of coal contained abundant toxic organic pollutants. Anaerobic digestion is a promising technology for BOW, but abundant toxic substances would inhibit the activity of anaerobic microorganisms. Granular activated carbon (GAC) and exogenous hydrogen (EH2) were employed to enhance anaerobic digestion of BOW. The results indicated that methane production increased to 289.55 ± 17.43 mL CH4/g COD in EH2/GAC group, which was 1.07, 2.04, and 1.98 times of that in GAC, EH2, and control groups, respectively. In EH2/GAC group. The relative abundance of Geobacter and Methanosaeta increased rapidly to 25.36% and 52.81%, respectively, and the relative abundance of Clostridium was 9.78%. The underlying mechanism might be that GAC promoted the enrichment of Geobacter, and EH2 changed metabolic mechanism of Clostridium, stimulating the enrichment of Methanosaeta. Direct interspecies electron transfer was promoted by EH2/GAC, thus improving the methane production rate of BOW.

Three-dimensional multi-species mathematical model of the aerobic granulation process based on cellular automata theory.

Aerobic granular sludge is a kind of microbial polymer formed by self-immobilization under aerobic conditions. It has been widely studied because of its promising application in wastewater treatment. However, the granulation process of aerobic sludge is still a key factor affecting its practical application. In this paper, a three-dimensional (3D) multi-species mathematical model of aerobic granular sludge was constructed using the cellular automata (CA) theory. The growth process of aerobic granular sludge and its spatial distribution of microorganisms were studied under different conditions. The simulation results show that the aerobic granules were smaller under high shear stress and that the autotrophic bacterial content of the granular sludge interior was higher. However, the higher the dissolved oxygen concentration, the larger the size of granular sludge and the higher the content of autotrophic bacteria in the interior of the granular sludge. In addition, inhibition of toxic substances made the aerobic granule size increase more slowly, and the spatial distribution of the autotrophic bacteria and the toxic-substance-degrading bacteria were mainly located in the outer layer, with the heterotrophic bacteria mainly existing in the interior of the granular sludge.

Temperature dependence of bioelectrochemical CO2 conversion and methane production with a mixed-culture biocathode.

This study evaluated the effect of temperature on methane production by CO2 reduction during microbial electrosynthesis (MES) with a mixed-culture biocathode. Reactor performance, in terms of the amount and rate of methane production, current density, and coulombic efficiency, was compared at different temperatures. The microbial properties of the biocathode at each temperature were also analyzed by 16S rRNA gene sequencing. The results showed that the optimum temperature for methane production from CO2 reduction in MES with a mixed-culture cathode was 50°C, with the highest amount and rate of methane production of 2.06±0.13mmol and 0.094±0.01mmolh-1, respectively. In the mixed-culture biocathode MES, the coulombic efficiency of methane formation was within a range of 19.15±2.31% to 73.94±2.18% due to by-product formation at the cathode, including volatile fatty acids and hydrogen. Microbial analysis demonstrated that temperature had an impact on the diversity of microbial communities in the biofilm that formed on the MES cathode. Specifically, the hydrogenotrophic methanogen Methanobacterium became the predominant archaea for methane production from CO2 reduction, while the abundance of the aceticlastic methanogen Methanosaeta decreased with increased temperature.

Numerical simulation of filtration performance in submerged membrane bioreactors: effect of particle packed structure.

It is widely known that the accumulation of solid matter forming a cake layer on the membrane surface is one of the major limitations of the filtration performance in submerged membrane bioreactors (SMBR). This study is focused on the influence of the cake porosity of different particle microscopic packed structures on the filtration performance of hollow fiber systems. An integrated model based on the finite element method to simulate numerically the flow in an SMBR is presented. The model coupled the Navier-Stokes and Darcy Brinkman equations to simulate a complete filtration run. The cake growth took into consideration not only the deposition with local filtration velocity but also the effect of aeration scouring. A novel solution of mesh deformation was adopted to investigate transient cake growth along the fiber. Comparisons between simulations and experiments are in good agreement. The results show that a higher porosity particle packed structure causes non-uniform filtration and cake thickness but also higher permeate flux. Meanwhile, the proportion of cake resistance to total resistance increases with the decrease of porosity.

Example study for granular bioreactor stratification: Three-dimensional evaluation of a sulfate-reducing granular bioreactor.

Recently, sulfate-reducing granular sludge has been developed for application in sulfate-laden water and wastewater treatment. However, little is known about biomass stratification and its effects on the bioprocesses inside the granular bioreactor. A comprehensive investigation followed by a verification trial was therefore conducted in the present work. The investigation focused on the performance of each sludge layer, the internal hydrodynamics and microbial community structures along the height of the reactor. The reactor substratum (the section below baffle 1) was identified as the main acidification zone based on microbial analysis and reactor performance. Two baffle installations increased mixing intensity but at the same time introduced dead zones. Computational fluid dynamics simulation was employed to visualize the internal hydrodynamics. The 16S rRNA gene of the organisms further revealed that more diverse communities of sulfate-reducing bacteria (SRB) and acidogens were detected in the reactor substratum than in the superstratum (the section above baffle 1). The findings of this study shed light on biomass stratification in an SRB granular bioreactor to aid in the design and optimization of such reactors.

Dielectric barrier discharge plasma induced degradation of aqueous atrazine.

Degradation of herbicide atrazine in aqueous solution was investigated using a plate type dielectric barrier discharge (DBD) plasma reactor. DBD plasma was generated at the gas-liquid interface of the formed water film. At discharge time of 14 min, atrazine was degradated effectively with a degradation rate of 99 % at the discharge power of 200 W. The experimental data fitted well with first-order kinetics and the energy efficiency for 90 % degradation of atrazine (G value) was calculated, obtaining a rate constant of 0.35 min(-1) and a G value of 1.27 × 10(-10) mol J(-1) (98.76 mg kW(-1) h(-1)) at a discharge power of 200 W, respectively. The addition of Fe(2+) increased the rate constant and G value dramatically, and a significant decrease of the rate constant and G value was observed with the addition of radical scavengers (tert-butyl alcohol, isopropyl alcohol, or Na2CO3). The generated aqueous O3 and H2O2 were determined, which promoted the degradation of herbicide atrazine. Dechlorination was observed and the experimentally detected Cl(-) was 1.52 mg L(-1) at a discharge time of 14 min. The degradation intermediates of atrazine were detected by means of liquid chromatography-mass spectrometry; dechlorination, hydroxylation, dealkylation, and alkyl oxidation processes were involved in the degradation pathways of atrazine.

Modeling and optimization of granulation process of activated sludge in sequencing batch reactors.

Aerobic granulation is a promising process for wastewater treatment, but this granulation process is very complicated and is affected by many factors. Thus, a mathematical model to quantitatively describe such a granulation process is highly desired. In this work, by taking into account all of key steps including biomass growth, increase in particle size and density, detachment, breakage and sedimentation, an one-dimensional mathematic model was developed to simulate the granulation process of activated sludge in a sequencing batch reactor (SBR). Discretization methodology was applied by dividing operational time, sedimentation process, size fractions and slices into discretized calculation elements. Model verification and prediction for aerobic granulation process were conducted under four different conditions. Four parameters indicative of granulation progression, including mean radius, biomass discharge ratio, total number, and bioparticle size distribution, were predicted well with the model. An optimum controlling strategy, automatically adjusted of settling time, was also proposed based on this model. Moreover, aerobic granules with a density higher than 120 g VSS/L and radius in a range of 0.4-1.0 mm were predicted to have both high settling velocity and substrate utilization rate, and the corresponding optimum operating conditions were be determined. Experimental results demonstrate that the developed model is appropriate for simulating the formation of aerobic granules in SBRs. These results are useful for designing and optimizing the cultivation and operation of aerobic granule process.

[Experimental and modeling research on the settlement of aerobic granular sludge].

Settling process of mature aerobic granules cultivated in sequencing batch reactor was investigated in this study. With the increase of settling height, the concentration of suspended solids increased from 0.24 mg x L(-1) to 6.07 mg x L(-1), mean size increased from 450 microm to 550 pm and roundness of granules increased by 12.67%. This indicated that big and regular granules have high settling velocity and can remain in the reactor after settling selection. A new parameter, selective coefficient is introduced based on the theory of selective pressure and settling experiments. Both experimental and simulated results showed that the selective coefficient increased with the increase of granule size and density, at any settling height. With the increase of settling height, selective coefficient of granules with radius above 600-800 microm increased, while that of smaller granules decreased. At high exchange ratio, bigger granules have higher selective coefficient and can accumulate more than smaller ones. At lower exchange ratio, the granulation process will slow down. Results of this study can provide foundation and instruction for the cultivation and stability of aerobic granular sludge reactors.

A generalized model for aerobic granule-based sequencing batch reactor. 1. Model development.

A generalized model was established for simulating an aerobic granule-based sequencing batch reactor (SBR) with considerations of biological processes, reactor hydrodynamics, mass transfer, and diffusion. Methodology of discretization was effectively used forthe model development and calculations. The activated sludge model no.1 was modified to describe the biological processes within the granules. Based on the difference between the calculated and measured results, the model structure was further improved through introducing simultaneous consumption of soluble substrates by storage and heterotrophs growth with a changeable reaction rate. Model calculations were conducted using a MATLAB program. The calculation results show the respective contributions of granules in different size fractions and slices to the overall change of model component concentrations. Moreover, oxygen concentration profiles within granules and oxygen consumption rate varied in one operating cycle. This confirms the applicability and validity of the discretization method and the model structure.

A generalized model for aerobic granule-based sequencing batch Reactor. 2. Parametric sensitivity and model verification.

The sensitivity of the effluent chemical oxygen demand, NH4+-N and volatile suspended solids concentrations toward the stoichiometric and kinetic coefficients, oxygen diffusivity, characteristics of granules, and operating parameters was analyzed. With such a parametric sensitivity analysis, calibration of the model, which was established for describing aerobic-granule-based sequencing batch reactor (SBR) in the accompanying paper, was performed by comparing the measured and predicted values for model components. Thereafter, the established model was verified with the experimental results for four aerobic-granule-based SBRs with different granule sizes and fed with different wastewaters. The verification results show that the model established in this work was applicable to simulating and predicting the performance of an aerobic-granule-based SBR.

Formation and characterization of aerobic granules in a sequencing batch reactor treating soybean-processing wastewater.

Aerobic granules were cultivated in a sequencing batch reactor (SBR) fed with soybean-processing wastewater at 25+/-1 degrees C and pH 7.0+/-0.1. The granulation process was described via measuring the increase of sludge size. The formation of granules was found to be a four-phase process, that is, acclimating, shaping, developing, and maturated. A modified Logistic model could well fit with the granule growth by diameter and could be employed to estimate the maximum diameter, lag time, and specific diameter growth rate effectively. Both normal and log-normal distributions proved to be applicable to model the diameter distribution of the granules. The granule-containing liquor was shear thinning, and their rheological characteristics could be described by using the Herschel-Buckley equation. The suspended solids concentration, pH, temperature, diameter, settling velocity, specific gravity, and sludge volume index all had an effect on the apparent viscosity of the mixed liquor of granules. The matured granules had fractal nature with a fractal dimension of 1.87+/-0.34. Moreover, 83% of matured granules were permeable with fluid collection efficiencies over 0.034. As compared to activated sludge flocs, the aerobic granules grown on the soybean-processing wastewater had better settling ability, mass transfer efficiency, and bioactivity.