Activated Sludge Flocs Research Articles

Activated sludge floc morphology and nitrifier enrichment can explain the conflicting reports on the oxygen half‐saturation index for ammonium oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB)

AbstractBACKGROUNDAmmonium oxidizing bacteria (AOB) have been suggested to have a lower oxygen half‐saturation index than that of nitrite oxidizing bacteria (NOB), i.e. KO,AOB < KO,NOB. However, recent research has shown the opposite. We propose that biomass floc morphology and nitrifier enrichment are the causes of the conflicting reports, thus sludge samples with low NOB enrichment were ultrasonicated to produce samples with different floc diameters and tested for their KO,AOB and KO,NOB.RESULTSExperimental results showed that the apparent KO,NOB values stabilized at c. 0.20 mg O2 L−1 after the activated sludge sample was ultrasonicated and the medium floc diameter was reduced from c. 420 to 50 µm. In comparison, the apparent KO,AOB dropped significantly from c. 1.5 to 0.24 mg O2 L−1. Simulation results were in agreement with the experimental observations.CONCLUSIONSHigh floc diameter and low NOB enrichment were identified to be the reason for the reversion in the comparison of measured KO,AOB and KO,NOB. The study explains the conflicting reporting on the relative comparison of measured KO,AOB and KO,NOB. © 2017 Society of Chemical Industry

The use of waste mussel shells for the adsorption of dyes and heavy metals

AbstractBACKGROUNDWaste mussel shells present a significant environmental problem in the area of Northern Greece, since they are produced in vast quantities and there is no legislation for their appropriate disposal or use. In the present study the waste shells were used for the removal of dyes and heavy metals from aqueous solutions while powdered mussel shells were added into activated sludge processes for the removal of hexavalent chromium.RESULTSPowdered mussels shells were used in standard adsorption experiments for the removal of methyl blue and methyl red as well as for the removal of Cr (VI), Cd and Cu. Also they were added into laboratory scale activated sludge reactors treating synthetic wastewater with hexavalent chromium, in order to investigate the potential attribution to the treatment efficiency.CONCLUSIONAdsorption experiments indicated almost 100% color removal. High removal efficiencies were observed for the metals, especially in the case of chromium and cadmium reached concentrations even below 1 mg L−1. The addition of powdered mussel shells in the activated sludge processes enhanced the removal of chromium and phosphorus, while enabled the formation of heavier activated sludge flocs and thus enhanced the settling properties of the activated sludge. © 2017 Society of Chemical Industry

Effect of nitrifiers enrichment and diffusion on their oxygen half-saturation value measurements

It has been recognized that the size of activated sludge floc affected the measurement of substrate half-saturation value. The impact of bacteria enrichment on the half-saturation value measurement has not been studied. This study highlighted the importance of bacteria enrichment on the evaluation of the half-saturation values. Due to the critical importance of oxygen half-saturation value in achieving partial nitrification, the impact of floc diameter and nitrifier enrichment on the measurement of oxygen half-saturation value for AOB (KO,AOB) and NOB (KO,NOB) was evaluated both in experiment and in mathematical simulation. The experiment results showed low measured KO,AOB and KO,NOB values under small floc diameter and low nitrifiers concentration condition. The increase in floc diameter and nitrifiers enrichment caused a significant increase in the measured KO,AOB, while only slight increase in KO,NOB was noticed. The simulation results were consistent with the experiment results and indicated that the nitrifiers concentration and the floc diameter had higher impact on the KO,AOB measurement than on the KO,NOB measurement. The results could explain the conflicting reports on the measured KO,AOB and KO,NOB values.

Predation by Bdellovibrio bacteriovorus significantly reduces viability and alters the microbial community composition of activated sludge flocs and granules.

We recently isolated and characterised a predatory Bdellovibrio bacteriovorus strain from activated sludge (Ulu Pandan Water Reclamation Plant, Singapore), and this strain, B. bacteriovorus UP, was able to prey upon a broad spectrum of bacterial isolates from the activated sludge when grown as planktonic cells or as biofilms. Here, we have tested the effect of Bdellovibrio predation on floccular and granular sludge to determine if the spatial organisation, loosely or tightly aggregated communities, was protective from predation. The effect of predation was assessed using a combination of biomass quantification, cellular activity measurement and microscopic image analysis to determine community viability. Additionally, changes in the microbial communities due to predation by B. bacteriovorus UP were analysed through total RNA sequencing. Predation led to a significant reduction in microbial activity and total biomass for both floccular and granular sludge communities. Predation was also associated with significant changes in the microbial community composition in both communities, with >90% of the community members reduced in relative abundance after 24 h. Of those community members, the dominant organisms, such as Proteobacteria and Bacteroidetes, were the most affected phylotypes. This suggests that predatory bacteria, which display indiscriminant feeding, could significantly shift the species composition and thus, may disturb the operational performance of wastewater treatment systems.

Modification of Rhodamine WT tracer tests procedure in activated sludge reactors

One of the tracers recommended for use in wastewater treatment plants and natural waters is Rhodamine WT, which is a fluorescent dye, allowing to work at low concentrations, but may be susceptible to sorption to activated sludge flocs and chemical quenching of fluorescence by dissolved water constituents. Additionally raw sewage may contain other natural materials or pollutants exhibiting limited fluorescent properties, which are responsible for background fluorescence interference. This paper presents the proposed modifications to the Rhodamine WT tracer tests procedure in activated sludge reactors, which allow to reduce problems with background fluorescence and tracer loss over time, developed on the basis of conducted laboratory and field experiments.

Optimization of air scouring for an effective control of membrane fouling in submerged MBR

A membrane module including grid was designed and introduced to MBR (membrane bio-reactor) for the purpose of better control of membrane fouling. It could be anticipated that the grid enhances the shear force of fluid-air mixture into the membrane surface by even-distributing the fluid-air to the membrane module. As MLSS concentration, packing density which is expressed in the ratio of the housing and the cross-sectional area of membrane fibers (Am/At) and air-flow rate were changed, membrane foulings were checked by monitoring fouling resistances. The total fouling resistance (Rc+Rf) without grid installation (i.e., control) was 2.13×1012 m-1 , whereas it was reduced to 1.69×1012 m-1 after the grid was installed. Regardless of the grid installation, the Rc+Rf increased as the packing density increased from 0.09 to 0.28, however, the increment of resistance for the grid installation was less than that of the control. Increase in the air flow rate did not always guarantee the reduction of fouling resistance, indicating that the higher air flow rate can partially de-flocculate the activated sludge flocs, which led to severer membrane fouling. Consequently, installation of grids inside the housing have brought a beneficial effect on membrane fouling and optimum air flow rate is important to keep the membrane lowering fouling.

Comparison of biomass from integrated fixed-film activated sludge (IFAS), moving bed biofilm reactor (MBBR) and membrane bioreactor (MBR) treating recalcitrant organics: Importance of attached biomass

This study compared microbial characteristics and oil sands process-affected water (OSPW) treatment performance of five types of microbial biomass (MBBR-biofilm, IFAS-biofilm, IFAS-floc, MBR-aerobic-floc, and MBR-anoxic-floc) cultivated from three types of bioreactors (MBBR, IFAS, and MBR) in batch experiments. Chemical oxygen demand (COD), ammonium, acid extractable fraction (AEF), and naphthenic acids (NAs) removals efficiencies were distinctly different between suspended and attached bacterial aggregates and between aerobic and anoxic suspended flocs. MBR-aerobic-floc and MBR-anoxic-floc demonstrated COD removal efficiencies higher than microbial aggregates obtained from MBBR and IFAS, MBBR and IFAS biofilm had higher AEF removal efficiencies than those obtained using flocs. MBBR-biofilm demonstrated the most efficient NAs removal from OSPW. NAs degradation efficiency was highly dependent on the carbon number and NA cyclization number according to UPLC/HRMS analysis. Mono- and di-oxidized NAs were the dominant oxy-NA species in OSPW samples. Microbial analysis with quantitative polymerase chain reaction (q-PCR) indicated that the bacterial 16S rRNA gene abundance was significantly higher in the batch bioreactors with suspended flocs than in those with biofilm, the NSR gene abundance in the MBR-anoxic bioreactor was significantly lower than that in aerobic batch bioreactors, and denitrifiers were more abundant in the suspended phase of the activated sludge flocs.

Efficiency of Biological Phosphorus Removal by Filamentous Bacteria

Abstract Phosphorus removal in wastewater treatment plant is carried out by chemical precipitation, advanced biological treatment or a combination of both. One of the biggest problems with high concentration of phosphorus in water environment is eutrophication. Activated sludge flocs have a heterogeneous structure, which consist of a variety of microorganisms. Filamentous bacteria are normally present in the activated sludge and have ability to assimilation of phosphorus. In this study phosphorus accumulation by isolated filamentous bacteria from activated sludge foam was present.

Oxygen transfer dynamics and activated sludge floc structure under different sludge retention times at low dissolved oxygen concentrations

In activated sludge systems, the aeration process consumes the most energy. The energy cost can be dramatically reduced by decreasing the operating dissolved oxygen (DO) concentration. However, low DO may lead to incomplete nitrification and poor settling performance of activated sludge flocs (ASFs). This study investigates oxygen transfer dynamics and settling performances of activated sludge under different sludge retention times (SRTs) and DO conditions using microelectrodes and microscopic techniques. Our experimental results showed that with longer SRTs, treatment capacity and settling performances of activated sludge improved due to smaller floc size and less extracellular polymeric substances (EPS). Long-term low DO conditions produced larger flocs and more EPS per unit sludge, which produced a more extensive anoxic area and led to low oxygen diffusion performance in flocs. Long SRTs mitigated the adverse effects of low DO. According to the microelectrode analysis and fractal dimension determination, smaller floc size and less EPS in the long SRT system led to high oxygen diffusion property and more compact floc structure that caused a drop in the sludge volume index (SVI). In summary, our results suggested that long SRTs of activated sludge can improve the operating performance under low DO conditions.

Impact of cell cluster size on apparent half-saturation coefficients for oxygen in nitrifying sludge and biofilms

A three-dimensional (3-D) diffusion-reaction model was used to assess the effects of nitrifiers growing in cell clusters on the apparent oxygen half-saturation coefficients in activated sludge flocs. The model allows conciliation of seemingly contradictory reports by several research groups. Although intrinsic half-saturation coefficients (i.e., not affected by diffusion) show a better affinity for oxygen for ammonia oxidizing (AOB) than for nitrite oxidizing bacteria (NOB) (KO,AOB < KO,NOB), measurements in flocs often produced reversed apparent values (KO,AOB,app > KO,NOB,app), which can now be explained by the 3-D model with AOB and NOB microcolonies. This effect cannot be described with a conventional 1-D homogeneous model because the reversion of the AOB/NOB apparent KO is caused by the high biomass density and resulting concentration gradients inside the microcolonies. Two main factors explain the reversion of the half-saturation coefficients: the difference in oxygen yields (for NOB lower than for AOB) and the difference in colony size (NOB colonies are smaller than those of AOB). The strongest increase in the apparent half-saturation coefficients is linked to the colony size, rather than to the floc size. For high-density microbial aggregates (i.e., granular sludge), the need for a stratified population (AOB outer shell, NOB inner layers) was revealed in order to outcompete NOB. This study stresses the need for a more detailed description of the biomass distribution in activated sludge, granular sludge and biofilm reactors when elucidating the mechanisms for NOB repression.

Wastewater ammonia removal using an integrated fixed-film activated sludge-sequencing batch biofilm reactor (IFAS-SBR): Comparison of suspended flocs and attached biofilm

Integrated fixed-film activated sludge (IFAS) that combines the activated sludge (suspended flocs) and attached biofilm has been applied in municipal wastewater treatment to promote nitrification. This study investigated the changes in reactor performance and bacterial community structure in response to different organic loadings (500, 250, 150 mg/L COD) in an integrated fixed-film activated sludge (IFAS) reactor operated under sequencing batch mode. Changes of bacterial population in the suspended flocs and attached biofilm were compared. Biomass in the suspended flocs and in biofilm decreased as the organic loading decreased. The specific nitrification rate was highest when COD was only 150 mg/L in the feeding, which highlighted the effects of competition between heterotrophic bacteria and autotrophic bacteria over oxygen and space. Besides, lack of carbon sources limited denitrification activities. The percentages of nitrifying related genes over total genes were higher in biofilms as compared to those in activated sludge flocs, indicating biofilm was a more favorable habitat for nitrifiers. In addition, extracellular polymeric substance (EPS) in biofilm and suspended flocs changed differently in response to the organic loading changes, which might also be related to the microbial population changes.

Composition and aggregation of extracellular polymeric substances (EPS) in hyperhaline and municipal wastewater treatment plants.

As important constituents of activated sludge flocs, extracellular polymeric substances (EPS) play significant roles in pollutants adsorption, the formation and maintenance of microbial aggregates, and the protection of microbes from external environmental stresses. In this work, EPS in activated sludge from a municipal wastewater treatment plant (M-WWTP) with anaerobic/anoxic/oxic (A2/O) process and a hyperhaline wastewater treatment plant (H-WWTP) with anaerobic/oxic (A/O) process were extracted by ultrasound method. The proteins and polysaccharides contents in EPS were determined by using a modified Lowry method and anthrone colorimetry respectively to analyze the detail differences in two types of WWTPs. Fourier transform-infrared spectroscopy and three-dimensional excitation-emission matrix fluorescence spectroscopy demonstrated proteins and polysaccharides were the dominant components of the two types of EPS, and the aromatic protein-like substances accounted for a larger proportion in EPS proteins. The results of the aggregation test indicated that EPS were good for the sludge aggregation, and the EPS in oxic sludge were more beneficial to sludge aggregation than that in anoxic sludge. Anoxic sludge EPS in H-WWTP showed a negligible effect on sludge aggregation. Comparative study on EPS of different tanks in the M-WWTP and H-WWTP was valuable for understanding the characteristics of EPS isolated from two typical wastewater treatment processes.

Population balance modeling of activated sludge flocculation: Investigating the influence of Extracellular Polymeric Substances (EPS) content and zeta potential on flocculation dynamics

Abstract Modeling activated sludge flocculation via particle population balances has been used to investigate the floc size distribution (FSD). The impact of shear rate on the FSD has been stated in previous studies, but the quantitative effect of the Extracellular Polymeric Substance (EPS) content and zeta potential on the aggregation and breakage of activated sludge flocs need to be further investigated. This study defined the balance factor, i.e. the ratio of the breakage rate coefficient to the collision efficiency, to evaluate the combined effect of the EPS content and the zeta potential on the aggregation and breakage of activated sludge, and introduced a binomial breakage function for more probable daughter-particles distributions after the breakage of flocs. The flocculation dynamic parameters were found to be linearly related to the EPS content and the zeta potential. The flocculation balance factor decreased with the increase of EPS content and the decrease of absolute zeta potentials. Smaller flocculation balance factor means better flocculation ability of flocs, leading to larger mean-size flocs. The binomial breakage function parameter values varied from 0.79 to 1.78 for activated sludge flocs with different EPS content, from 0.87 to 1.19 (Al3+ addition) and from 0.96 to 1.93 (Ca2+ addition) for flocs with different zeta potentials, which suggests that the flocs might possess different breakage. Although the increase of EPS content is beneficial to the aggregation of larger flocs, the flocs with high EPS content are susceptible to large-scale fragmentation resulting in more smaller-daughter-particles. Lower absolute values of zeta potentials would promote flocculation, and the activated sludge flocs showed strong stability with Al3+ additions but weak stability with Ca2+ additions.

Enzyme disintegration with spatial resolution reveals different distributions of sludge extracellular polymer substances.

Background To understand the intrinsic role of hydrolytic enzymes in sludge treatment, particularly their effect on the digestibility and dewaterability of sludge, activated sludge flocs were disintegrated using various techniques that included different enzymes (amylase, cellulase, proteinase, DNase, and polygalacturonase), pH adjustment, and temperature adjustment. The effectiveness of each enzyme treatment was pinpointed by quantifying the spatial distribution of each type of organic matters (protein, polysaccharide, DNA, fluorescent organics) in outer layer extracellular polymeric substances (EPS), inner layer EPS, and cells. ResultsMost hydrolytic enzymes functioned only owing to a temperature or pH effect. The release of organic matter from the interior fraction of EPS to the exterior fraction was prompted under high pH and temperature even without enzyme addition. The effectiveness of enzyme addition was only significant for cellulase and polygalacturonase treatments. Polygalacturonase unexpectedly increased the total EPS polysaccharides up to seven times, accompanied with improved dewaterability, while the amount of EPS proteins was almost unchanged. Combining chemical and morphological evidence, a new conceptual model considering the spatial distribution of polygalacturonic acid-like matter, proteins, cellulose, and other organics in EPS was proposed.ConclusionsPolygalacturonic acid-like matter hydrolysis caused significant release of polysaccharides. Polygalacturonase released polysaccharides while keeping proteins unreleased. Temperature and pH adjustment were as effective as enzyme at sludge disintegration. Cellulose hydrolysis led to massive release of all kinds of organic matters. A new conceptual sludge structure model regarding organic components is proposed.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-016-0444-y) contains supplementary material, which is available to authorized users.

Suspended and immobilized biomass in individual wastewater treatment systems SBR and SBBR

The small wastewater treatment plant is a device or group of devices which—through mechanical, biological, and chemical processes—reduces the pollution load to the values specified in the Regulation of the Minister of the Environment. The aim of this research is to show the relationship between the growth of the biomass and the effectiveness of removing contaminants from wastewater in individual wastewater treatment systems. The results of activated sludge volume after 30 min settling, microscopic analysis, and quantitative and qualitative parameters of biomass in the aeration chambers were analyzed in this article. During the research, one of the reactors was converted into a hybrid reactor (SBR filled with plastic carriers, which support the process of nitrification). A microscopic analysis of the biomass was conducted to evaluate the operation of activated sludge and biofilm. Flocs of activated sludge in the SBR were characterized by irregular shape and high biodiversity. The appearance of rotifers testified about the good condition of the sludge. The microscopic analysis of biomass of the hybrid reactor showed a negative effect of the applied biopreparation. Microorganisms such as bacteria and ciliates were observed in the biomass. In summary, the structure of the biofilm and activated sludge floc is very sensitive to the system parameters and external factors. Biofilm develops more slowly than the activated sludge. Introduction of the moving bed into the reactor of activated sludge should be made in the summertime.

Aerobic Granular Sludge

Aerobic Granular Sludge has recently received growing attention by researchers and technology developers, worldwide. Laboratory studies and preliminary field tests led to the conclusion that granular activated sludge can be readily established and profitably used in activated sludge plants, provided ‘correct’ process conditions are chosen. But what makes process conditions ‘correct’? And what makes granules different from activated sludge flocs? Answers to these question are offered in Aerobic Granular Sludge. Major topics covered in this book include: Aerobic Granular Sludge provides up-to-date information about a rapidly emerging new technology of biological treatment. This title belongs to Water and Environmental Management Series (WEMS) ISBN: 9781843395096 (Print) ISBN: 9781780402055 (eBook)

Local adaptive approach toward segmentation of microscopic images of activated sludge flocs

Activated sludge process is a widely used method to treat domestic and industrial effluents. The conditions of activated sludge wastewater treatment plant (AS-WWTP) are related to the morphological properties of flocs (microbial aggregates) and filaments, and are required to be monitored for normal operation of the plant. Image processing and analysis is a potential time-efficient monitoring tool for AS-WWTPs. Local adaptive segmentation algorithms are proposed for bright-field microscopic images of activated sludge flocs. Two basic modules are suggested for Otsu thresholding-based local adaptive algorithms with irregular illumination compensation. The performance of the algorithms has been compared with state-of-the-art local adaptive algorithms of Sauvola, Bradley, Feng, and c-mean. The comparisons are done using a number of region- and nonregion-based metrics at different microscopic magnifications and quantification of flocs. The performance metrics show that the proposed algorithms performed better and, in some cases, were comparable to the state-of the-art algorithms. The performance metrics were also assessed subjectively for their suitability for segmentations of activated sludge images. The region-based metrics such as false negative ratio, sensitivity, and negative predictive value gave inconsistent results as compared to other segmentation assessment metrics.

Mechanism of Activated Sludge Floc Disintegration Induced by Excess Addition of NaCl

Abrupt salt intrusion in municipal wastewater treatment plants has triggered serious disturbances and deteriorated the biological treatment process from steady state into unsteady state. The effects of sodium (Na+) concentration on the structure and properties of activated sludge during the shock period were investigated in this paper. A floc disintegration characterized as the decreased floc size and increased porosity in the floc matrix was found when excess Na+ was added to the bioreactor. Increased Na+ resulted in a slight decrease in the normalized capillary suction time. About 53–57% of the total extracellular polymeric substances (EPS) derived from activated sludge was protein, at Na+ concentrations &lt;150.74 mmol/L, and this value even reached 68% at 286.04 mmol/L Na+. Over 50% of Na+ in EPS was found in the loosely bound EPS (LB‐EPS). The Na+ sorbed in LB‐EPS followed Langmuir model with a maxium sorption capacity of 2.086 mmol/g VSS. With the increase of Na+ concentration in LB‐EPS, the Mg2+ concentration in LB‐EPS decreased until reaching equilibrium while there was no significant change of Ca2+ concentration. A concept model is proposed for the first time targeting to improve the understanding of sodium ion effects on activated sludge.

Protein and polysaccharide content of tightly and loosely bound extracellular polymeric substances and the development of a granular activated sludge floc

A full-scale (FS) activated sludge system treating wastewater from a meat rendering plant with a long history of sludge management problems (pin-point flocs; >80% of floc <50 μm diameter; poor settling) was the focus of a study that entailed characterization of floc properties. This was coupled with parallel well-controlled lab-scale (LS) sequencing batch reactors (SBRs) treating the same wastewater and operated continuously over 1.5 years. Distinct differences in the proportion of proteins and polysaccharides associated with extracellular polymeric substances (EPS) were observed when comparing the properties of flocs from the FS and the LB systems. Further differences in the proportion of tightly bound (TB) and loosely bound (LB) fractions of EPS were also observed for flocs derived from conditions where differences in settling and dewatering properties of flocs occurred (i.e. FS and LS systems). FS flocs contained higher levels of EPS along with a higher proportion of LB than TB EPS, and possessing characteristics associated with non-filamentous bulking (SVI >150 mL/g). Floc formed in the LS system, following inoculation from sludge taken from the FS system, was markedly larger in size (>70% of floc >300 μm diameter), spherical in shape, compact and firm, and appeared to be granular in form. Flocs formed in the LS system, when an anoxic phase was introduced into the react stage of the SBR cycle, were found to be more hydrophobic and contained more TB and less loosely bound (LB) EPS when compared to the FS floc. TB-EPS contained a greater amount of protein, whereas the polysaccharide content of LB-EPS was larger. Protein was predominantly localized in the core region of granular flocs where cells were compactly packed. When assessing the operating conditions of the FS and LS systems parameters that appear to impact the floc properties and the transition to a granular form include dissolved oxygen (DO) concentration and food to microorganism (F/M) ratio.

Assessment of total bacterial cells in extended aeration activated sludge plants using flow cytometry as a microbial monitoring tool.

The extended aeration activated sludge (EAAS) process is one of the most applied biological processes in small towns. Here, we study the abundance and viability of total bacterial cells in two wastewater treatment plants (WWTPs) operating with an EAAS process. We use flow cytometry (FCM) combined with SYTO13 and propidium iodide (PI) dyes as a rapid, easy, reliable and accurate microbial monitoring tool. A disaggregation procedure with an ultrasonic bath was designed to detach total bacterial cells from activated sludge flocs for subsequent FCM analysis. This procedure permitted the recovery of total bacterial cells from sludge flocs without affecting bacterial viability, as indicated by bacterial strain controls. Since FCM is a multi-parameter technique, it was possible to determine total bacterial abundance and their viability in the activated sludge. As a comparative method, epifluorescence microscopy was also used to quantify total bacterial cells; both methods produced similar results. The FCM analysis revealed relative microbial stability in both the WWTPs. The total bacterial abundance quantified by FCM in the two plants studied was 1.02-6.23 × 10(11) cells L(-1) with 70-72% viability, one logarithm less than that reported in the literature for WWTPs using the conventional activated sludge process. This can be explained by the difference in the operational parameters between the conventional plant and EAAS, mainly the organic loading rate.