Filament Index Research Articles

Microbiological aspects of the aeration tanks of an activated sludge treatment plant in dysfunction: Consequences on its treatment performance

The present study was conducted in a sewage treatment plant, called "El Kouwaer", located in the department of Mascara, North-West of Algeria. Mainly, the objective of this investigation is to evaluate the relevant settling and pollution parameters and to assess the proliferation level of filamentous microbial communities during the dysfunction period to further the effectiveness of the operative treatment. Sludge parameter values were estimated such us Settling Test, Diluted Sludge Volume Index (DSVI), and Total Suspended Solids (TSS) content to set up the sludge classification, the performance analysis of treatment was conducted by computing pollution indicators and removal efficiencies of organic pollution, as well as the Principal Component Analysis (PCA) of dysfunction parameters. The results showed that in aeration tanks 65% of samples represented a maximum Filament Index (FI) of 6. Diluted Sludge Volume Index (DSVI) was greater than 300 mg/L in 23% of samples. A high level of filamentous bacteria biodiversity was also noted during the assessment of the (FI) including Microthrix parvicella, Bogiotae, and Sphaerotilus natans. The effluent in the biological unit was characterized by BOD5/COD ratio of 0.17 and COD removal efficiency of 53.32%. Those results demonstrated that the sewage treatment plant is frequently affected by bulking problems. This study had confirmed the importance of continuous monitoring of different process parameters like Wastewater Biodegradability Index, Dissolved Oxygen, filamentous flora, and Dilute Sludge Volume Index (DSVI) to avoid irreversible damage at the level of a wastewater treatment plant.

Quantifying the Effect of COD to TN Ratio, DO Concentration and Temperature on Filamentous Microorganisms’ Population and Trans-Membrane Pressure (TMP) in Membrane Bio-Reactors (MBR)

Using moderate populations of filaments in the biomass of Membrane Bio-Reactors (MBRs) is a biological anti-fouling method which has been increasingly applied over the last few years. This study aims to quantify the effect of COD to TN ratio, Dissolved Oxygen (DO) concentration and temperature on filaments’ population and Trans-Membrane Pressure (TMP) in a pilot-scale MBR, with a view to reducing membrane fouling. The novelty of the present work concerns the development of a mathematical equation that correlates fouling rate (dTMP/dt) with the population of filamentous microorganisms, assessed by the Filament Index (FI), and with the concentration of the carbohydrate fraction of Soluble Microbial Products (SMPc). Apart from TMP and SMPc, other fouling-related biomass characteristics, such as sludge filterability and settleability, were also examined. It was shown that at high COD to TN ratio (10:1), low DO concentration in the filaments’ tank (0.5 ± 0.3 mg/L) and high temperature (24–30 °C), a moderate population of filaments is developed (FI = 1–2), which delays the TMP rise. Under these conditions, sludge filterability and settleability were also enhanced. Finally, TMP data analysis showed that the fouling rate is affected by FI and SMPc concentration mainly in the long-term fouling stage and increases exponentially with their increase.

The Use of Natural Minerals in a Pilot-Scale MBR for Membrane Fouling Mitigation

This study examines the effect of bentonite and zeolite concentration (0.25–5 g/L) on the membrane fouling of a fully automated, pilot-scale membrane bioreactor (MBR) treating high-strength synthetic municipal wastewater. Reversible fouling was estimated by sludge filterability measurements and irreversible fouling was estimated by the reduction of the carbohydrate fraction of soluble microbial products (SMPc), which are considered to be significant MBR foulants. Both minerals were added to biomass samples (during batch-mode experiments) which were obtained from the system’s aeration tank. Results showed that the optimal bentonite and zeolite concentrations were 3.5–4 g/L and 2.5–3.5 g/L, respectively. Interestingly, above these values, the addition of both minerals increased the examined fouling indices, i.e., the measured filterability times and the SMPc concentration, implying that they might act as foulants at high concentrations. Optical microscopy images of the biomass samples showed that the addition of minerals at the optimal concentrations did not affect significantly filamentous microorganisms, since filament index (FI) was practically unaffected (~2). Finally, regarding the system’s treating performance, it was found that the pilot-scale MBR can operate successfully with high-strength synthetic municipal wastewater, since remarkable behaviour was exhibited in terms of organics (BOD5, COD) and ammonium (NH4+-N) removal (>98%).

Effect of carriers on sludge characteristics and mitigation of membrane fouling in attached-growth membrane bioreactor

This study aims to investigate the effect of carriers on membrane fouling. Three sets of submerged membrane bioreactors (MBRs), including one suspended-growth MBR, called SMBR, and two attached-growth MBRs (one called AMBR, and another with baffles called AMBRb) were operated at various media volume fractions. The results indicated that the membrane-fouling rates of AMBR and AMBRb were lower than that of SMBR. Moreover, the operation times of AMBR and AMBRb were 4.2 and 3.5 times longer, respectively, than that of SMBR at an optimum media volume fraction of 30%. The biochemical effects of carriers on sludge suspension significantly affected membrane fouling, unlike the physical effects of carriers. Further studies on sludge characteristics indicated that particle size, soluble microbial product (SMP), sludge volume index (SVI) and filament index (FI) did not remarkably affect membrane fouling, whereas the protein in bound EPS primarily contributed to membrane fouling.

Impact of biological constituents and properties of activated sludge on membrane fouling in a novel submerged membrane bioreactor

A 12-l submerged membrane bioreactor was developed to remove carbon and nitrogen simultaneously using synthetic wastewater. In this study, the main objective was to investigate the impact of activated sludge properties on membrane fouling in the novel submerged MBR. The activated sludge properties were characterized by biological constituents (mixed liquor suspended solids (MLSS), extracellular polymeric substances (EPS) and soluble microbial products (SMPs)), morphological parameters (filament index (FI), volume equivalent diameter ( D (4,3)) and fractal dimension ( D f )) and rheological properties (apparent viscosity (η a )). The influences of activated sludge properties on membrane fouling were quantified using statistical methods. The results showed that D f and EPS have strong and moderate positive effects on the membrane fouling resistance respectively, while MLSS was inversely correlated to the membrane fouling resistance. This study indicated that D f , EPS and MLSS were the predominant factors affecting the membrane fouling resistance.

Impact of filamentous bacteria on properties of activated sludge and membrane-fouling rate in a submerged MBR

This study presents the results from the continuous microfiltration of activated sludge with different filamentous bacteria density (expressed as filament index (FI)) in a submerged membrane bioreactor (MBR). During the entire experimental duration of 120 days, the filamentous bacteria density increased gradually from FI = 2 to 6 in the beginning, thereafter maintained at a plateau of FI = 6 for about 20 days, and decreased to FI = 4 at the end of the experiment. The relationship between FI and other properties of activated sludge were analysed using statistical analysis. It was found that filamentous bacteria density has no significant effect on bound extracellular polymeric substances (bound EPS, r p = −0.343, p = 0.080) and soluble microbial products (SMPs, r p = 0.221, p = 0.267). However, it has an important impact on floc size ( r p = 0.944, p = 0.000) and floc structure ( r p = −0.752, p = 0.000). High FI favored the formation of bigger flocs with a loose structure, and vice versa. Further studies on the impact of the activated sludge properties on membrane-fouling rate indicated that variations of the bound EPS may be the major factor contributing to the membrane-fouling rate. Although filamentous bacteria have the ability to change the floc morphology, the effect on the membrane-fouling rate may be negligible.

Identification of Type and Causes of Filamentous Bulking under Mediterranean Conditions

A national survey to identify the most common filamentous microorganisms in Greek wastewater treatment plants, to assess the extent of filamentous bulking phenomenon and to correlate the occurrence of these bacteria to specific operating parameters, was carried out for five years. According to the conclusions of this survey filamentous bulking is a widespread phenomenon in Greek wastewater treatment plants. Almost 70% of the sludge samples examined exhibited filament indices greater than 4 during the winter period. The most common filamentous species found in a decreasing order were M. parvicella, Type 0092, GALOs, Type 0041 and N. limicola. A seasonal variation of the composition of the biomass was observed. M. parvicella is the dominant species during winter periods, while T0092 is the dominant species during summer conditions. This seasonal pattern of biomass composition was followed by a similar seasonal variation of the settling characteristics in terms of Filament Index (FI) and Sludge Volume Index (SVI) values. M. parvicella's proliferation is favored in Carrousel and oxidation ditches systems especially when primary settling stage was preceeded, whereas its growth is also highly stimulated in intermittent aeration systems, even in the absence of primary settling tanks. Finally there is evidence that Bio-P systems without primary sedimentation inhibit its growth.