Inverse Fluidized Bed Bioreactor Research Articles

Modelling selenite and chemical oxygen demand removal in an inverse fluidized bed bioreactor using genetic algorithm optimized artificial neural network

AbstractBACKGROUNDA genetic algorithm (GA) optimized artificial neural network (ANN) model was developed to simulate selenite removal efficiency (SRe) and chemical oxygen demand (COD) removal efficiency (CRe) in a single‐stage inverse fluidized bed reactor (IFBR) operated under different hydraulic retention time (HRT) (12–48 h), and inlet selenite concentration (12.7–635 mg L−1). Multi‐objective optimization for SRe and CRe with the ANN model was adopted to estimate the pareto optimal solutions in the bioreactor system.RESULTSGA optimized ANN topology suggested five neurons in the hidden layer, and the optimal data partitioning between training, test, and validation subsets (in 70:15:15 ratio) using cross‐validation. The average fitness for SRe and CRe of the resulting ANN model over training (R2 = 0.885), test (R2 = 0.967) and validation (R2 = 0.972) subsets were reasonably good. Sensitivity analysis suggested an increase in SRe and CRe with HRT, while an increase in inlet selenite concentration had a negative effect on SRe. Local interpretable model‐agnostic explanations and SHapley Additive exPlanations for the developed model suggested a positive coefficient of the predictors on CRe. Pareto optimal solution for SRe (92.87%–95.26%), and CRe (91.33%–99.35%) were suggested for HRT and inlet selenite concentration varying between 35.67 h and 36 h, and 0.1 g L−1 and 0.884 g L−1, respectively.CONCLUSIONSThe GA optimized ANN model could be exploited for the prediction of contaminant removal efficiencies in the bioreactor system with a fair degree of complexity (i.e., IFBR). Multiple objective pareto optimal solutions can identify the best operating conditions relevant for wastewater treatment. © 2023 Society of Chemical Industry (SCI).

Simultaneous removal of selenite and heavy metals from wastewater and their recovery as nanoparticles using an inverse fluidized bed bioreactor

Occurrence of selenium oxyanions and different heavy metals as co-pollutants in various waste streams is common from industries such as mining, coal burning, thermal power plants, petrochemical refinery, etc. Among the available technologies to treat such wastewater, biological removal using anaerobic microbes is one of the most advantageous. This study examined simultaneous removal and recovery of selenite and heavy metals using an inverse fluidized bed bioreactor (IFBR). The effect of commonly occurring heavy metals namely Zn, Cu and Cd on selenite removal was evaluated at 24 h hydraulic retention time (HRT). The maximum selenite removal of 93.9% was obtained in the absence of any heavy metals. The presence of heavy metals negatively impacted the selenite removal (45.8–85.3%), and the inhibitory effect due to Cu was the most significant among the three metals at 50 mg/L of influent concentration (47% lower). The heavy metal removal efficiency values were more than 70%, except in the case of Cd at 50 mg/L. The recovery values of selenium and heavy metals using the continuous bioreactor were in the range 45.1–73.9% and 59.2–69.8%, respectively, under different experimental conditions. Elemental selenium nanoparticles were formed inside the bioreactor due to selenite bioreduction and the nanoparticle size ranged from 50 to 300 nm. Furthermore, formation of small sized (<10 nm) metal selenide nanoparticles of the respective metals were detected during the bioreactor operation. Overall, this study clearly demonstrated the potential of the IFBR system for the removal of selenite and heavy metals from wastewater as well as their recovery as elemental selenium and metal selenide nanoparticles, respectively.

A review on hydrodynamic parameters and biofilm characteristics of inverse fluidized bed bioreactors for treating industrial wastewater

Abstract Wastewater treatment processes play crucial role in keeping the human health and environment at proper hygiene. Currently, biological wastewater treatment methods are dominant in the effluent treatment process because of their cost-effectiveness in the treatment. However, the rapid increase in population has created a need for the implementation of highly efficient wastewater treatment methods. In the recent past, the treatment of wastewater through fluidized-bed bioreactor has proven as one of the best processes from the currently available methods of chemical and biochemical engineering fields. This review aims to explore and compile the methods of fluidization used for the treatment of wastewater in the recent past, majorly by the inverse fluidization method. In the inverse fluidization process, the density of solid particles utilized in the fluidization is lower than that of the liquid and compared to an up-flow fluidized bed bioreactor, and it is a very effective system for biological wastewater treatment. This review discusses the developments made in recent years with regard to aerobic inverse fluidized bed bioreactors, with more emphasis placed on the reported applications on treating industrial wastewaters. The influence of hydrodynamic parameters (minimum fluidization velocity, phase holdup, bed expansion, and bed height, pressure drop, superficial gas velocity, liquid velocity, hydraulic retention time, biofilm carriers and ratio of volume of settled bed to the volume of reactor) are highlighted in the discussion, and also the effect of these parameters on the biofilm and its subsequent effect on wastewater is included. Recent trends of application of aerobic inverse fluidized bed bioreactors for the removal of COD and scope of future study elements have been discussed in this manuscript.

Biological Removal of Selenate and Selenite from Wastewater: Options for Selenium Recovery as Nanoparticles

Different selenium species released into the environment by anthropogenic activities pollute surface and ground water resources and can cause severe damage to the environment and ecosystems due to bio-accumulation. Though several physico-chemical methods are available to treat selenium oxyanion-containing wastewater, biological methods have gained significant importance due to their capability to convert selenium oxyanions to elemental selenium nanoparticles. The purpose of this review is to summarize the literature available on biological removal of selenium oxyanions and their recovery as elemental selenium nanoparticles. In recent times, the capability of several bacterial and fungal strains to reduce selenate and selenite to form elemental selenium nanoparticles has been reported. The shape, size and location of these selenium nanoparticles along with the selenium oxyanion removal efficiency depend on the operating parameters. Moreover, bioreactor configurations and operation strategies greatly influence the selenium removal and recovery efficiency. Several conventional bioreactor systems can be used to remove selenate and selenite from wastewater and form selenium nanoparticles. However, the selenium nanoparticles are mostly entrapped in the biomass and require a secondary treatment to recover them. On the other hand, some novel bioreactors, viz. inverse fluidized bed bioreactor, rotating biological contractor, horizontal rotating packed bed bioreactor, moving bed biofilm reactor, and hybrid bioreactor, can possibly recover selenium nanoparticles following bioreduction of selenium oxyanions in a single stage system. Thus, this review will help in finding research gaps in this area and providing solutions for resource recovery from selenium oxyanion-containing wastewater.

Performance and bacterial community structure of a novel inverse fluidized bed bioreactor (IFBBR) treating synthetic municipal wastewater

The performance of a lab-scale integrated anoxic and aerobic inverse fluidized bed bioreactors (IFBBR) for biological nutrient removal from synthetic municipal wastewater was studied at chemical oxygen demand (COD) loading rates of 0.34–2.10 kg COD/(m3-d) and nitrogen loading rates of 0.035–0.213 kg N/(m3-d). Total COD removal efficiencies of >84% were achieved, concomitantly with complete nitrification. The overall nitrogen removal efficiencies were >75%. Low biomass yields of 0.030–0.101 g VSS/g COD were achieved. Compared with other FBBR systems, the energy consumption for this IFBBR system was an average 59% less at organic loading rates (OLRs) of 1.02 and 2.10 kg COD/(m3-d). Bacterial community structures of attached and suspended biomass revealed that the dominant phyla were Proteobacteria, Bacteroidetes, and Epsilonbacteraeota, etc. The relative abundance of ammonia-oxidizing bacteria (AOBs) and nitrite-oxidizing bacteria (NOBs) in the aerobic attached biomass were 0.451% and 0.110%, respectively. COD mass balance in the anoxic zone was closed by consideration of sulfate reduction, which was confirmed by the presence of genus Chlorobium (sulfate-reducing bacteria) in the anoxic attached biofilm with a relative abundance of 0.32%.

Selenite removal from wastewater using fungal pelleted airlift bioreactor.

This study investigated the removal of selenite from wastewater using the fungus Asergillus niger KP isolated from a laboratory scale inverse fluidized bed bioreactor. The effect of different carbon sources and initial selenite concentration on fungal growth, pellet formation and selenite removal was first examined in a batch system. The fungal strain showed a maximum selenite removal efficiency of 86% in the batch system. Analysis of the fungal pellets by field-emission scanning electron microscopy, field-emission transmission electron microscopy and energy-dispersive X-ray spectroscopy revealed the formation of spherical-shaped elemental selenium nanoparticles of size 65-100nm. An increase in the initial selenite concentration in the media resulted in compact pellets with smooth hyphae structure, whereas the fungal pellets contained hair like hyphae structure when grown in the absence of selenite. Besides, a high initial selenite concentration reduced biomass growth and selenite removal from solution. Using an airlift reactor with fungal pellets, operated under continuous mode, a maximum selenite removal of 94.3% was achieved at 10mgL-1 of influent selenite concentration and 72h HRT (hydraulic retention time). Overall, this study demonstrated very good potential of the fungal-pelleted airlift bioreactor system for removal of selenite from wastewater. Graphical abstract.

Biological removal of selenite from wastewater and recovery as selenium nanoparticles using inverse fluidized bed bioreactor

This study evaluated the performance of an inverse fluidized bed (IFB) bioreactor with anerobic biomass immobilized onto Kaldness-K1 media as the biosupport material for selenite removal and recovery as selenium nanoparticle from waste stream. The effect of different process parameter and nutrient supplement on selenium removal was first studied in a batch system using serum bottles. The results revealed that among the different nitrogen substrates, ammonium bicarbonate was most suitable, whereas, lactate was found to be the preferred carbon substrate with 98% selenite removal efficiency and 90% COD removal. Later studies with the continuously operated IFB bioreactor operated at different hydraulic retention time (HRT) and different influent selenite concentrations revealed an efficient removal of selenite at 24 h HRT and 1.0 mM of influent Se (IV). Furthermore, selenium nanoparticles formed at the bottom of the bioreactor were successfully recovered with a recovery efficiency in the range 35–58% with a maximum recovery obtained at 1.0 mM selenite concentration and 24 h HRT. The extracellular produced selenium nanoparticles were found to be spherical in shape with 90–150 nm in size. Fourier transform infrared (FTIR) spectroscopy confirmed the presence of extracellular polymeric substances (EPS) as capping agent on the outer surface of Se nanoparticles.

Role of zinc oxide nanoparticles for effluent treatment using Pseudomonas putida and Pseudomonas aureofaciens.

The biological treatment of textile effluent is enhanced by the use of zinc oxide (ZnO) nanoparticles for the reduction in chemical oxygen demand (COD) from its initial value of 1700ppm. The present research investigated the effect of ZnO nanoparticles when microbial cultures of Pseudomonas putida and Pseudomonas aureofaciens were used to treat textile effluent in three-phase inverse fluidized bed bioreactor. The parameters like-size of ZnO nanoparticles, static bed height, superficial gas velocities and solid media particle size-together affected the COD reduction and all of these were investigated in this paper. ZnO nanoparticles of 280nm reduced the maximum COD to 47ppm (97.24%) at low gas velocity of 0.0027m/s at 10% inoculum size and at a static bed height of 2.43cm.

Hydrodynamics and mathematical modelling in a low HRT inverse fluidized-bed reactor for biological sulphate reduction.

Biological reduction of sulphate at low hydraulic retention time (HRT) is presented in this paper. A sulphidogenic inverse fluidized-bed bioreactor (IFBB) was operated successfully at a progressively decreasing HRT from 1 to 0.125days for a total of 155days. Synthetic wastewater containing sulphate at a concentration of 745 (± 17)mg/L was used. COD was supplied as lactate in variable concentrations at COD/SO42- ratios of 1.2-2.4. The pH of the feed ranged between 5.2 and 6.2. The highest measured removal rates were 2646 and 4866mg SO42-/Lday at an HRT of 0.25 and 0.125days, respectively, using a COD/SO42- ratio of 2.3. The biological sulphate reduction was limited by the influent COD concentrations at a COD/SO42- ratio < 2.3. The IFBB ensured biomass retention at a maximum liquid residence time of θ = 3.84 (± 0.013), according to the residence time distribution analysis. Hydrodynamic studies were carried out at recirculation rates of 0, 200, 300, 350, 400, and 500L/h to measure the relative bed expansion, the mixing pattern, and the fluidization characteristics of the reactor. A dynamic model is also developed based on COD and sulphate as the two limiting substrates in a Monod-type kinetic equation describing the kinetics of lactate oxidation by SRB. A set of the following parameters [Formula: see text] = 0.23mg COD of VSS/mg lactate, µmax = 1.758day- 1, KCOD = 956mg COD of lactate/L, [Formula: see text] = 316mg SO42-/L, kd = 0.024day- 1, tres = 5.7days, and kexchange = 0.4day- 1 simulated adequately the residual effluent COD and sulphate concentrations, the produced sulphide concentration as well as the pH of the IFBB effluent. Low HRT values, shown efficient in this study, are prerequisite for industrial applicability and economic feasibility of the sulphur reduction process. In addition, the developed model can be used for optimum experimental design and further process upscale and development.

Lignocellulosic biowastes as carrier material and slow release electron donor for sulphidogenesis of wastewater in an inverse fluidized bed bioreactor

Industrial wastewaters containing high concentrations of sulphate, such as those generated by mining, metallurgical and mineral processing industries, require electron donor for biological sulfidogenesis. In this study, five types of lignocellulosic biowastes were characterized as potential low-cost slow release electron donors for application in a continuously operated sulphidogenic inverse fluidized bed bioreactor (IFBB). Among them, natural scourer and cork were selected due to their high composition of volatile solids (VS), viz. 89.1 and 96.3%, respectively. Experiments were performed in batch (47days) and in an IFBB (49days) using synthetic sulphate-rich wastewater. In batch, the scourer gave higher sulphate reduction rates (67.7mgSO42-L-1day-1) in comparison to cork (12.1mgSO42-L-1day-1), achieving >82% sulphate reduction efficiencies. In the IFBB packed with the natural scourer, the average sulphate reduction efficiency was 24 (±17)%, while the volumetric sulphate reduction rate was 167 (±117)mgSO42- L-1day-1. The long incubation time in the batch experiments (47days) allowed higher sulphate reduction efficiencies in comparison to the short hydraulic retention time (24h) in the IFBB. This suggests the hydrolysis-fermentation was the rate-limiting step and the electron donor supply (through hydrolysis of the lignocellulosic biowaste) was limiting the sulphate reduction. Lignocellulose as carrier material and slow release electron donor for sulphidogenesis.

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,

Coupled Inverse Fluidized Bed Bioreactor with Advanced Oxidation Processes for Treatment of Vinasse

Vinasse is the wastewater generated from ethanol distillation; it is characterized by high levels of organic and inorganic matter, high exit temperature, dissolved salts and low pH. In this work the treatment of undiluted vinasse was achieved using sequentially-coupled biological and advanced oxidation processes. The initial characterization of vinasse showed a high Chemical Oxygen Demand (COD, 32 kg m -3 ), high Total Organic Carbon (TOC, 24.5 kg m -3 ) and low pH (2.5). The first stage of the biological treatment of the vinasse was carried out in an inverse fluidized bed bioreactor with a microbial consortium using polypropylene as support material. The fluidized bed bioreactor was kept at a constant temperature (37 ± 1oC) and pH (6.0 ± 0.5) for 90 days. After the biological process, the vinasse was continuously fed to the photoreactor using a peristaltic pump 2.8 × 10 -3 kg of FeSO 4 •7H 2 O were added to the vinasse and allowed to dissolve in the dark for five minutes; after this time, 15.3 m 3 of hydrogen peroxide (H 2 O 2 ) (30% w/w) were added, and subsequently, the UV radiation was allowed to reach the photoreactor to treat the effluent for 3600 s at pH = 3. Results showed that the maximum organic matter removed using the biological process, measured as COD, was 80% after 90 days. Additionally, 88% of COD removal was achieved using the photo-assisted Fenton oxidation. The overall COD removal after the sequentially-coupled processes reached a value as low as 0.194 kg m -3 , achieving over 99% of COD removal as well as complete TOC removal.

Effect of pH on the Performance of Sulfate and Thiosulfate-Fed Sulfate Reducing Inverse Fluidized Bed Reactors

AbstractSulfate-reducing bacteria (SRB)–based technologies have gained a lot of attention in the field of wastewater treatment, especially to treat metal-contaminated wastewaters. An inverse fluidized bed (IFB) bioreactor is a versatile bioreactor configuration that uses SRB technology for metal removal and recovery from wastewater. Apart from sulfate, which is commonly used as an electron acceptor, thiosulfate is another potential candidate for this process. In this study, the performance of two IFB bioreactors that were operated at pH 7.0 (R1) and 5.0 (R2) using sulfate and thiosulfate as the electron acceptors were evaluated. The electron donor used in this study was ethanol and the chemical oxygen demand (COD) to electron acceptor ratio (SO42− or S2O32−) was kept constant at 1.0. By using sulfate as the electron acceptor, the average COD removal efficiency was 75.0 and 58.0% at pH 7.0 and 5.0, respectively, while the sulfate removal efficiency was 74.4 and 50.4%, respectively. The average sulfide prod...

Modeling and optimization by response surface methodology and neural network–genetic algorithm for decolorization of real textile dye effluent using Pleurotus ostreatus: a comparison study

This study focuses on the modeling and optimization of the decolorization procedure of real textile dye. The percentage of decolorization of effluent in the Erlenmeyer flask level, as obtained by both response surface methodology (RSM) and artificial neural network (ANN), was determined and subjected to comparative evaluation. The effect of independent variables such as pH (5–8), self-immobilized Pleurotus ostreatus, bead volume (30–50%) (Vb/Vr), and initial effluent concentration (50–100%) was examined using three-level Box–Behnken design. A similar design was utilized to train a feed-forward multilayered perceptron with back-propagation algorithm. Errors were computed using error functions, and the values obtained for RSM and ANN were compared. The maximum percentage decolorization and COD reduction of effluent under optimized conditions over a 24-h period were observed as 89 and 72%, respectively. The parameters optimized in the flask level were adapted in an inverse fluidized bed bioreactor of 6 l working volume, in which the quantity of decolorization and COD reduction over a 24-h period was observed as 92 and 76%, respectively.

Effect of Parameters on Treatment of Industrial Effluents Using Inverse Fluidized Bed Bioreactor: Statistical Analysis

Phenolic wastewater (effluents from steel plant) was treated in an inverse fluidized bed (IFB) bioreactor. Effects of different system parameters (viz. residence time (t), settled bed to bioreactor volume ratio (Vb/Vr), water flow rate, static bed height, and gas flow rate) on removal of chemical oxygen demand (COD) were studied to determine the optimum conditions. Optimal conditions corresponding to the largest COD removal were obtained at Vb/Vr ratio of 0.55 and gas flow of 40 LPH with time period greater than 62 h. COD removal was also measured with the addition of mineral salts in the wastewater. The results thus obtained with and without the addition of mineral salt to the wastewater were compared. Addition of nutrient salts to the wastewater yielded better percentage of COD removal. The effect of different types of salts on COD removal was also studied with respect to the biomass growth. Experiments were also carried out by continuous culturing of biomass samples. Conversions greater than 68% and 84% were achieved with batch and continuous mode operation respectively, implying that IFB bioreactor can be used successfully for the treatment of industrial effluents.

Studies on Performance Analysis and Computer Aided Design of Inverse Fluidized Bed Bioreactors with Nanosupport Particles

Abstract Attempts have been made to propose a modified design of inverse fluidized bed bioreactor (IFBBR) that utilizes immobilized enzyme nanosilica particles. The substrate solution is mixed uniformly with nanosilica particles, and the resultant slurry flows down the reactor keeping particles in suspension. The performance characteristics of the bioreactor of proposed design have been analysed both mathematically and experimentally. In the mathematical analysis, dispersed flow of suspension down the reactor tubes has been assumed. The mathematical results (from the developed software package) agree closely with the experimental results, the maximum deviation being 9.5%. The bioreactor provides high fractional conversion at high substrate flow rates, but demands low reactor volume. In addition, the operating cost of the reactor is substantially low. In reactors of this kind, resistance to substrate transfer into the support particles (nanoparticles) is negligible, and the global rate is essentially equal to the intrinsic rate (as the computed value of effectiveness factor is equal to unity for different types of kinetic equations and within wide range of substrate concentration). This must be attributed to the nanosize and consequent large specific surface of support particles. The present design of IFBBR is thus anticipated to be quite attractive for successful industrial adaptation.

Sulfide response analysis for sulfide control using a pS electrode in sulfate reducing bioreactors

Step changes in the organic loading rate (OLR) through variations in the influent chemical oxygen demand (CODin) concentration or in the hydraulic retention time (HRT) at constant COD/SO42− ratio (0.67) were applied to create sulfide responses for the design of a sulfide control in sulfate reducing bioreactors. The sulfide was measured using a sulfide ion selective electrode (pS) and the values obtained were used to calculate proportional–integral–derivative (PID) controller parameters. The experiments were performed in an inverse fluidized bed bioreactor with automated operation using the LabVIEW software version 2009®. A rapid response and high sulfide increment was obtained through a stepwise increase in the CODin concentration, while a stepwise decrease to the HRT exhibited a slower response with smaller sulfide increment. Irrespective of the way the OLR was decreased, the pS response showed a time-varying behavior due to sulfide accumulation (HRT change) or utilization of substrate sources that were not accounted for (CODin change). The pS electrode response, however, showed to be informative for applications in sulfate reducing bioreactors. Nevertheless, the recorded pS values need to be corrected for pH variations and high sulfide concentrations (>200mg/L).

Oxygen transfer in three phase inverse fluidized bed bioreactor during biosurfactant production by Bacillus subtilis

Production of microbial biosurfactants requires development of bioreactors enabling sufficient oxygen supply and foaming control. Gas–liquid mass transfer in a three-phase inverse fluidized bed reactor designed for biosurfactant production by Bacillus subtilis was studied. The influence of main parameters on kLa was investigated in model and real fermentation conditions. Oxygen transfer increased up to 175% and up to 24% with the increase of superficial gas and liquid velocities, respectively. The oxygen transfer obtained in the TPIFB bioreactor (kLa up to 0.015s−1) was higher than in the other bioreactors used for biosurfactant production. A significant decrease of kLa (up to 27%) was measured during fermentation process. It was shown that this decrease of kLa was a result of surface tension decrease due to the production of biosurfactants. However the oxygen transfer remained important and allowed a correct oxygen supply for the aerobic B. subtilis strains. A correlation based on dimensional analysis was proposed to estimate kLa in function of the influencing parameters, integrating surface tension effects. This correlation allowed estimating correctly kLa in the presence or not of solid particles. The correlation being based on dimensionless numbers, it could help for further process control and scale-up considerations.

Fluid bed porosity mathematical model for an inverse fluidized bed bioreactor with particles growing biofilm

A new mathematic model to estimate bed porosity as a function of Reynolds and Archimedes numbers was developed based in experimental data. Experiments were performed using an inverse fluidized bed bioreactor filled with polypropylene particles, Lactobacillus acidophillus as the immobilized strain and fluidized with a Man-Rogosa-Sharpe culture medium under controlled temperature and pH conditions. Bed porosity was measured at different flow rates, starting from 0.95 to 9.5 LPM. The new model has several advantages when compared with previously reported. Among them, advantages such as standard deviation values ≤ 1% between experimental and calculated bed porosity, its applicability in traditional and inverse fluidization, wall effects do not take account, it gives excellent agreement with spherical particles with or without biofilm, and inertial drag coefficient allow extend the new model a non-spherical particles.

Starch Wastewater Treatment in a Three Phase Fluidized Bed Bioreactor with Low Density Biomass Support

Aerobic digestion of starch industry wastewater was carried out in an inverse fluidized bed bioreactor using low density (870 kg/m3) polypropylene particles. Experiments were carried at different initial substrate concentration of 2250, 4475, 6730 and 8910mg COD/L and forvarious hydraulic retention time 40, 32, 24, 16 and 8h. Degradation of organic matter was studied at different organic loading rate by varying the hydraulic retention time and initial substrate concentration. From the results it was observed that the maximum COD removal of 95.6% occurs at an organic loading rate of 1.35 kg COD/m3/d and a minimum of 51.8% at an OLR of 26.73 kg COD/m3/d. The properties of biomass accumulation on the surface of particles were also studied. It was observed that a constant biomass loading was achieved over the entire period of operation