Strong selection pressures impact the capacity of flocculating activated sludge bacteria to granulate

2013 ◽  
Vol 67 (8) ◽  
pp. 1678-1687 ◽  
Author(s):  
G. A. C. Ehlers ◽  
S. J. Turner
Keyword(s):  
Particle Size ◽  
Activated Sludge ◽  
Extracellular Polymeric Substances ◽  
High Rate ◽  
Volume Index ◽  
Size Analysis ◽  
Liquid Separation ◽  
Granule Formation ◽  
Selection Pressures ◽  
The Impact

The capacity of activated sludge (AS) microbial populations to form dense granules offers the potential to establish efficiently settleable biomass. This has the potential to circumvent problems around ineffective solids–liquid separation and sensitivity to variable chemical oxygen demand (COD) loads. Although a number of studies have evaluated aerobic laboratory granulation reactors as high-rate treatment systems, the biological processes involved in aerobic granulation are not fully understood. Concomitantly, the impact of operation parameters such as organic loading rates is also important for granulation. The ability of a flocculating AS community to granulate under different selection pressures was evaluated in a laboratory sequencing batch reactor by determining levels of extracellular polymeric substances (EPS) and particle size fractions that developed under feast (4.74 g COD L−1) and famine (0.42 g COD L−1) nutrient regimes. The efficiency of solid–liquid separation was also measured. Aggregation indices showed levels >94% and a sludge volume index factor of up to 0.94, which strongly suggested granule formation; however, microscopy evaluation showed a mixture of flocs and granules. Particle size analysis revealed binomial distribution patterns of particles in the reactor which shifted to smaller tightly bound particles (<200 μm) although large particles (>600 μm) were also measured during famine conditions. This coincided with increases in EPS levels although EPS quantities were low and it is postulated that this could have impacted granule formation: the EPS in the bacterial aggregates were consumed since the AS community was starved.

Comparison of Activated Sludge Technologies by Particle Size Analysis

2012 ◽  
Vol 223 (7) ◽  
pp. 4319-4331 ◽  
Author(s):  
J. J. Garcia-Mesa ◽  
F. Delgado-Ramos ◽  
M. M. Muñio ◽  
E. Hontoria ◽  
J. M. Poyatos
Keyword(s):  
Particle Size ◽  
Activated Sludge ◽  
Particle Size Analysis ◽  
Size Analysis

scholarly journals Microbial Composition and Structure of Aerobic Granular Sewage Biofilms

2007 ◽  
Vol 73 (19) ◽  
pp. 6233-6240 ◽  
Author(s):  
S. D. Weber ◽  
W. Ludwig ◽  
K.-H. Schleifer ◽  
J. Fried
Keyword(s):  
Activated Sludge ◽  
Laser Scanning ◽  
Extracellular Polymeric Substances ◽  
Phase 1 ◽  
Simultaneous Detection ◽  
Laser Scanning Microscopy ◽  
Confocal Laser ◽  
Microbial Composition ◽  
Granule Formation ◽  
Biofilm Development

ABSTRACT Aerobic activated sludge granules are dense, spherical biofilms which can strongly improve purification efficiency and sludge settling in wastewater treatment processes. In this study, the structure and development of different granule types were analyzed. Biofilm samples originated from lab-scale sequencing batch reactors which were operated with malthouse, brewery, and artificial wastewater. Scanning electron microscopy, light microscopy, and confocal laser scanning microscopy together with fluorescence in situ hybridization (FISH) allowed insights into the structure of these biofilms. Microscopic observation revealed that granules consist of bacteria, extracellular polymeric substances (EPS), protozoa and, in some cases, fungi. The biofilm development, starting from an activated sludge floc up to a mature granule, follows three phases. During phase 1, stalked ciliated protozoa of the subclass Peritrichia, e.g., Epistylis spp., settle on activated sludge flocs and build tree-like colonies. The stalks are subsequently colonized by bacteria. During phase 2, the ciliates become completely overgrown by bacteria and die. Thereby, the cellular remnants of ciliates act like a backbone for granule formation. During phase 3, smooth, compact granules are formed which serve as a new substratum for unstalked ciliate swarmers settling on granule surfaces. These mature granules comprise a dense core zone containing bacterial cells and EPS and a loosely structured fringe zone consisting of either ciliates and bacteria or fungi and bacteria. Since granules can grow to a size of up to several millimeters in diameter, we developed and applied a modified FISH protocol for the study of cryosectioned biofilms. This protocol allows the simultaneous detection of bacteria, ciliates, and fungi in and on granules.

Modeling of organic substrate transformation in the high-rate activated sludge process

2015 ◽  
Vol 71 (7) ◽  
pp. 971-979 ◽  
Author(s):  
Thomas Nogaj ◽  
Andrew Randall ◽  
Jose Jimenez ◽  
Imre Takacs ◽  
Charles Bott ◽  
...  
Keyword(s):  
Activated Sludge ◽  
Extracellular Polymeric Substances ◽  
Oxygen Demand ◽  
Organic Substrate ◽  
High Rate ◽  
State Variables ◽  
Modified Model ◽  
Soluble Substrate ◽  
Substrate Model ◽  
Dual Substrate

This study describes the development of a modified activated sludge model No.1 framework to describe the organic substrate transformation in the high-rate activated sludge (HRAS) process. New process mechanisms for dual soluble substrate utilization, production of extracellular polymeric substances (EPS), absorption of soluble substrate (storage), and adsorption of colloidal substrate were included in the modified model. Data from two HRAS pilot plants were investigated to calibrate and to validate the proposed model for HRAS systems. A subdivision of readily biodegradable soluble substrate into a slow and fast fraction were included to allow accurate description of effluent soluble chemical oxygen demand (COD) in HRAS versus longer solids retention time (SRT) systems. The modified model incorporates production of EPS and storage polymers as part of the aerobic growth transformation process on the soluble substrate and transformation processes for flocculation of colloidal COD to particulate COD. The adsorbed organics are then converted through hydrolysis to the slowly biodegradable soluble fraction. Two soluble substrate models were evaluated during this study, i.e., the dual substrate and the diauxic models. Both models used two state variables for biodegradable soluble substrate (SBf and SBs) and a single biomass population. The A-stage pilot typically removed 63% of the soluble substrate (SB) at an SRT <0.13 d and 79% at SRT of 0.23 d. In comparison, the dual substrate model predicted 58% removal at the lower SRT and 78% at the higher SRT, with the diauxic model predicting 32% and 70% removals, respectively. Overall, the dual substrate model provided better results than the diauxic model and therefore it was adopted during this study. The dual substrate model successfully described the higher effluent soluble COD observed in the HRAS systems due to the partial removal of SBs, which is almost completely removed in higher SRT systems.

Effect of phosphorus limitation on microbial floc structure and gene expression in activated sludge

2006 ◽  
Vol 54 (1) ◽  
pp. 247-255 ◽  
Author(s):  
J.R. Liu ◽  
C.T. Liu ◽  
E.A. Edwards ◽  
S.N. Liss
Keyword(s):  
Gene Expression ◽  
Activated Sludge ◽  
Extracellular Polymeric Substances ◽  
Morphological Changes ◽  
Cell Structure ◽  
Operating Conditions ◽  
P Limitation ◽  
Floc Structure ◽  
The Impact ◽  
Log Ratio

The effect of limiting phosphorus (P) in activated sludge was investigated in laboratory-scale sequencing batch reactors (SBRs). Correlative microscopy revealed that P-limitation (COD:N:P=100:5:0.05) leads to morphological changes in floc structure and the composition of extracellular polymeric substances (EPS). This was found to be accompanied by expression of quorum-sensing in an acyl homoserine lactone bioassay. Differential gene expression in relation to P-limitation was examined in a global profile using the Affymetrix™ Escherichia coli antisense genomic microarray. Three separate experiments were conducted where the impact of P-limitation was examined under batch conditions and in SBRs at stable operating conditions and within 3–7 days following a down-shift in P. Significant changes in open reading frames (ORF) and intergenic regions based on the E. coli microarray were observed. Several genes associated with cell structure, including slt, wbbH, fimH, amB, rfaJ and slp were found to be expressed. Quorum regulated genes were also found to be expressed including psiF which is known to be induced by P-starvation (92% confidence level; 1.45 log ratio).

scholarly journals Recent Advances in Magnesia Blended Cement Studies for Geotechnical Well Construction—A Review

2021 ◽  
Vol 8 ◽  
Author(s):  
Weiqing Chen ◽  
Salaheldin Elkatatny ◽  
Mobeen Murtaza ◽  
Ahmed Abdulhamid Mahmoud
Keyword(s):  
Mechanical Properties ◽  
Particle Size ◽  
Portland Cement ◽  
Supplementary Cementitious Materials ◽  
Research Progress ◽  
Size Analysis ◽  
Strength Testing ◽  
Cement Material ◽  
The Impact ◽  
Caustic Magnesia

The current paper presents a literature review on the studies of incorporation of magnesia (magnesium oxide) into Portland cement material from the geotechnical well construction perspective. Starting with a comparison of application conditions between civil construction and geotechnical well cementing, this work reviewed the Portland cement categorizations, magnesia manufacturing routes at first. Then, the physical-chemical-mechanical properties were investigated which includes the reactivity of magnesia, expansion influence from its hydration, and carbonation/dehydroxylation of magnesia blended Portland cement. The development of cement material hydration modeling methods is also summarized. Moreover, the experimental characterization methods have also been elucidated including composition determination, particle size analysis, volumetric variation measurement, compressive strength testing, shear-bond strength testing, transition state analysis, etc. Meanwhile, the results and conclusions were extracted from the literature. Through this route, a comprehensive understanding of the scientific research progress on magnesia blended Portland cement development for geotechnical well construction is derived. Additionally, it is concluded that incorporating magnesia into Portland cement can provide benefits for this material utilization in geotechnical well constructions provided the reasonable tuning among the characteristics of magnesia, the downhole surrounding conditions, and the formulation of the cement slurry. Satisfying these pre-conditions, the effective expansion not only mitigates the micro-annulus issues but also increases the shear bonding strength at the cementing interfaces. Moreover, the caustic magnesia introduction into Portland cement has the potential advantage on carbon dioxide geological sequestration well integrity compared with the Portland cement sheath without it because of the denser in-situ porous matrix evolvement and more stable carbon fixation features of magnesium carbonate. However, since the impact of magnesia on Portland cement strongly depended on its properties (calcination conditions, particle size, reactivity) and the aging conditions (downhole temperature, pressure, contacting medium), it should be noted that some extended research is worth conducting in the future such as the synchronized hydration between magnesia and Portland cement, the dosage limit of caustic magnesia in Portland cement in terms of CO2 sequestration and the corresponding mechanical properties analysis, and the hybrid method (caustic magnesia, Portland cement, and other supplementary cementitious materials) targeting the co-existence of the geothermal environment and the corrosive medium scenario.

Granulation in an upflow anaerobic sequencing batch reactor treating disintegrated waste activated sludge

2005 ◽  
Vol 52 (12) ◽  
pp. 105-111 ◽  
Author(s):  
K.Y. Park ◽  
D.Y. Kim ◽  
T.H. Chung
Keyword(s):  
Activated Sludge ◽  
Batch Reactor ◽  
Spherical Shape ◽  
Granular Sludge ◽  
Gas Production ◽  
High Rate ◽  
Waste Activated Sludge ◽  
Batch Mode ◽  
Granule Formation ◽  
Methanogenic Activity

An upflow anaerobic reactor operated with a sequencing batch mode to enhance high rate digestion of raw and thermally disintegrated waste activated sludge with formation of granules. The gas production rate doubled when disintegrated waste activated sludge was introduced. Gradual granulation took place and the dispersed particles become coarse granulation as the operation continued. The granular sludge showed relatively higher specific methanogenic activity than the dispersed sludge. Bacterial morphology by a scanning electron microscope showed diversity of bacteria such as filamentous, rod and spherical shape in the section of granules. Filamentous bacteria, which might support the frame of a granule, were observed as long chains at the outer surface. Meanwhile, rod and spherical bacteria, which might play a role in the initial stage of granule formation, were observed from the inner surface of the granule. High rate digestion of sludge along with efficient liquid–solids separation was achieved due mainly to development of sludge granules within the upflow reactor.

Upgrading performance of an activated sludge process through addition of talqueous powder

1996 ◽  
Vol 34 (5-6) ◽  
pp. 75-83 ◽  
Author(s):  
J. Cantet ◽  
E. Paul ◽  
F. Clauss
Keyword(s):  
Activated Sludge ◽  
Control Unit ◽  
Physical Structure ◽  
Experimental Models ◽  
Volume Index ◽  
Liquid Separation ◽  
Floc Structure ◽  
Rapid Effect ◽  
Solid Liquid ◽  
Solid Liquid Separation

This study is intended to induce better performance of existing activated sludge wastewater plants without modifying the physical structure of the plant. The process consists in injecting a specific mineral powder into the aeration stage with two precise purposes: firstly to improve floc structure and thus facilitate solid/liquid separation in the clarifier, and secondly to reduce nitrogenous pollution. By means of two experimental models the indisputable and rapid effect of talc/chlorite blend on the solid/liquid separation was established (with a sludge volume index improvement by a factor of 2 to 3 within a few days) compared with a control unit. The increase in nitrification capacity of the system is also clearly shown with nitrification yields being increased by 30%. These results lead us to believe that it is possible to use this process of enhanced nitrification for running a plant reliably without dysfunctioning. Problems linked to hydraulic or biological excess loading can be solved this way. Moreover, the addition of talqueous powder improves sludge dewaterability.

Particle size analysis and sedimentation properties of activated sludge flocs

1997 ◽  
Vol 36 (4) ◽  
pp. 167-175 ◽  
Author(s):  
Dieter Hilligardt ◽  
Erhard Hoffmann
Keyword(s):  
Particle Size ◽  
Activated Sludge ◽  
Shape Analysis ◽  
Particle Size Analysis ◽  
Size Analysis ◽  
Organic Loading ◽  
Sludge Characteristics ◽  
Sludge Flocs ◽  
Factors Influencing ◽  
Differential Sedimentation

Activated sludge is one of the best investigated and understood suspensions. But up to now we still lack the factors influencing the sedimentation velocities concerning the main sludge characteristics/properties to describe the settleability of different sludges. Different in terms of SVI, organic loading, sludge retention time, composition, content of polymers, iron or aluminium, density, porosity and particle size distribution. But for the design of clarifiers most of these parameters are disregarded, of none importance or neglectable. With the help of PSD and particle shape analysis we can improve our knowledge of the settleability of activated sludge flocs. The measurements, done with the CIS show the influence of the differential sedimentation in comparison to the effluent of the secondary clarifiers under different conditions. Calculating the sedimentation velocities, the behaviour of activated and precipitated sludge could be explained and conclusions can be drawn to optimize the solid flux in secondary clarifiers.

scholarly journals The Impact of Aluminium Salt Dosing for Chemical Phosphorus Removal on the Settleability of Activated Sludge

Environments ◽  
2018 ◽  
Vol 5 (8) ◽  
pp. 88 ◽  
Author(s):  
Peter Ojo ◽  
Augustine Ifelebuegu
Keyword(s):  
Activated Sludge ◽  
Settling Velocity ◽  
Treated Wastewater ◽  
Volume Index ◽  
Sem Images ◽  
Sludge Flocs ◽  
Floc Structure ◽  
Aluminium Salt ◽  
Dose Concentration ◽  
The Impact

The use of metal salts like aluminium in the precipitation of phosphorus in activated sludge plants has increased considerably in recent years due to the need to achieve tighter discharge consents for phosphorus in treated wastewater effluent. The impact of aluminium salt (Al3+) dosing on the settleability of activated sludge as a function of zone settling velocity (ZSV) and stirred specific volume index (SSVI) were investigated in batch settleability tests over a three-year period. The results showed that ZSV increased with increasing dose of aluminium salt as SSVI decreased. This trend was observed for dosing concentrations of less than 100 mg/L. At a dose concentration >100 mg/L, the trend was reversed as ZSV decreased and SSVI increased. At dose concentrations of <100 mg/L, Al3+ helped in the bioaggregation of dispersed activated sludge flocs, thereby improving settleability. The surface morphology from the scanning electron microscope (SEM) images indicated that the initial potential of interfloc bridging, open floc formation, and spindly bulking noticed in the undosed activated sludge flocs were remarkably reduced as the flocs became more compacted after Al3+ treatment. At >100 mg/L of Al3+, the sludge settleability started to disintegrate due mainly to surface charge reversal linked to the formation of aluminium hydroxides and the resultant disintegration of the activated sludge floc structure.

The role of extracellular polymeric substances on carbon capture in a high rate activated sludge A-stage system

2017 ◽  
Vol 322 ◽  
pp. 428-434 ◽  
Author(s):  
Maureen N. Kinyua ◽  
Matthew Elliott ◽  
Bernhard Wett ◽  
Sudhir Murthy ◽  
Kartik Chandran ◽  
...  
Keyword(s):  
Activated Sludge ◽  
Carbon Capture ◽  
Extracellular Polymeric Substances ◽  
High Rate ◽  
Stage System
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