Relationship between flocculation of activated sludge and composition of extracellular polymeric substances

2003 ◽  
Vol 47 (12) ◽  
pp. 95-103 ◽  
Author(s):  
B.-M. Wilén ◽  
B. Jin ◽  
P. Lant
Keyword(s):  
Activated Sludge ◽  
Surface Properties ◽  
Negative Correlation ◽  
Extracellular Polymeric Substances ◽  
Treatment Plant ◽  
Volume Index ◽  
Physical Parameters ◽  
Floc Size ◽  
Flocculation Ability ◽  
Floc Properties

Activated sludge flocs are a flocculated mass of microorganisms, extracellular polymeric substances (EPS) and adsorbed organic and inorganic material. The structure of the flocs is very heterogeneous and flocs with very different properties and morphologies may occur, depending on the conditions in the activated sludge treatment plant and wastewater composition. Present thinking suggests that cations, such as calcium, create cationic bridges with EPS excreted by the bacteria and thereby hold the various floc constituents together. However, due to the complex and heterogeneous nature of activated sludge, the mechanisms have neither been thoroughly investigated nor successfully quantified. A better understanding and description of the biological flocculation process is necessary in order to establish more efficient operational strategies. The main aim of this study was to get a comprehensive and unique insight into the floc properties of activated sludge and to assess the relative impact of chemical and physical parameters. A variety of sludges from full scale treatment plants with different settling properties were characterised. The interrelationships between floc parameters such as composition of EPS, surface properties and floc structure, and their effect on the flocculation and separation properties were assessed. The results indicate that the EPS, both in terms of quantity and quality, are very important for the floc properties of the activated sludge. However, presence of filaments may alter the physical properties of the flocs considerably. The EPS showed positive correlations to sludge volume index (SVI) if only sludges with low or moderate numbers of filaments were included. The surface properties were more affected by the composition of the EPS than by the number of filaments. The EPS showed positive correlation to negative surface charge and a negative correlation to relative hydrophobicity and flocculation ability. The negative correlation between flocculation ability and amount of EPS was surprising. The shear sensitivity, measured as degree of erosion of flocs when subjected to shear, was more affected by floc size and number of filaments than amount of EPS.

Study of factors affecting simultaneous nitrification and denitrification (SND)

1999 ◽  
Vol 39 (6) ◽  
pp. 61-68 ◽  
Author(s):  
Klangduen Pochana ◽  
Jürg Keller
Keyword(s):  
Carbon Source ◽  
Activated Sludge ◽  
Physical Phenomenon ◽  
Treatment Plant ◽  
Batch Reactors ◽  
Sequencing Batch Reactors ◽  
Factors Affecting ◽  
Floc Size ◽  
Sludge Flocs ◽  
Activated Sludge Systems

Experiments have been performed to gain an understanding of the conditions and processes governing the occurrence of SND in activated sludge systems. Sequencing batch reactors (SBRs) have been operated under controlled conditions using the wastewater from the first anaerobic pond in an abattoir wastewater treatment plant. Under specific circumstances, up to 95% of total nitrogen removal through SND has been found in the system. Carbon source and oxygen concentrations were found to be important process parameters. The addition of acetate as an external carbon source resulted in a significant increase of SND activity in the system. Stepwise change of DO concentration has also been observed in this study. Experiments to determine the effect of the floc size on SND have been performed in order to test the hypothesis that SND is a physical phenomenon, governed by the diffusion of oxygen into the activated sludge flocs. Initial results support this hypothesis but further experimental confirmation is still required.

In situ detection of cell surface hydrophobicity of probe-defined bacteria in activated sludge

2001 ◽  
Vol 43 (6) ◽  
pp. 97-103 ◽  
Author(s):  
J. L. Nielsen ◽  
L. H. Mikkelsen ◽  
P. H. Nielsen
Keyword(s):  
Activated Sludge ◽  
Surface Properties ◽  
Treatment Plant ◽  
Cell Surface Hydrophobicity ◽  
Surface Hydrophobicity ◽  
Substrate Uptake ◽  
Filamentous Bacteria ◽  
In Situ Conditions ◽  
Bacterial Surfaces

The surface hydrophobicity of different types of bacteria in activated sludge were investigated under in situ conditions by following the adhesion of fluorescent microspheres with defined surface properties to bacterial surfaces (the MAC-method). This technique was combined with identification of the bacteria with fluorescence in situ hybridization with rRNA-targeted oligonucleotides (FISH) and could thus be used for characterization of surface properties of probe-defined bacteria directly in a complex system without prior enrichment or isolation. This MAC-FISH technique could be used for single bacteria as well as filamentous bacteria. In the investigated activated sludge from an industrial wastewater treatment plant, two types of filamentous bacteria dominated. One morphotype consistently attracted only very few hydrophobic microspheres, indicating that the thin sheath of exopolymers around the cells had a hydrophilic surface. Use of a hierarchical set of gene probes revealed that these filaments were sulphide oxidising Thiothrix spp. The other predominating filamentous morphotype had a thick, very hydrophobic exopolymeric sheath. This filamentous bacterium was found to belong to the alpha-Proteobacteria. The relevance of the significant differences in surface hydrophobicity for the two morphotypes in respect to substrate uptake and floc formation is discussed.

Estimation of suspended solids concentrations in activated sludge settling tanks

1997 ◽  
Vol 35 (8) ◽  
pp. 127-135 ◽  
Author(s):  
Youngchul Kim ◽  
Wesley O. Pipes ◽  
Paul-Gene Chung
Keyword(s):  
Activated Sludge ◽  
Suspended Solids ◽  
Marked Effect ◽  
Treatment Plant ◽  
Accurate Method ◽  
Volume Index ◽  
Sludge Volume Index ◽  
Solids Concentration ◽  
Exponential Decrease ◽  
Sludge Settling

This is a report of a field study based on data from an activated sludge process in a wastewater treatment plant in Chester, Pennsylvania, USA. The objective was to develop an accurate method for estimation of the average suspended solids concentration (SSB) of the layer of sludge in the settling tanks (the “sludge blanket”). Plant operators estimated SSB by averaging the mixed liquor suspended solids (Sm) and the return sludge suspended solids (Su) concentrations. Measurement of SSB showed that averaging Sm and Su frequently overestimated SSB by a large amount. A different relationship between SSB and parameters which are normally measured for operational purposes was developed. The parameters are Su, the overflow rates and data from the sludge volume index (SVI) measurement. It was found that an increasing overflow rate will result in an exponential decrease in the ratio of SSB to Su. Also, the SVI has a marked effect on the ratio of SSB to Su and thus on the amount of suspended solids which can be stored in the settling tanks. The proposed estimation equation was found to be statistically superior to estimation by averaging the Sm and Su.

Removal of organic halogens (AOX) from municipal wastewater by powdered activated carbon (PAC)/activated sludge (AS) treatment

1997 ◽  
Vol 35 (10) ◽  
pp. 147-153 ◽  
Author(s):  
C. Bornhardt ◽  
J. E. Drewes ◽  
M. Jekel
Keyword(s):  
Activated Carbon ◽  
Activated Sludge ◽  
Municipal Wastewater ◽  
Activated Carbons ◽  
Treatment Plant ◽  
Volume Index ◽  
Enhancement Effect ◽  
Simultaneous Treatment ◽  
Volatile Solids ◽  
Organic Halogens

The effectiveness of different treatments with powdered activated carbons (PAC) to reduce the AOX-levels in municipal wastewater was investigated in a bench-scale activated sludge (AS) treatment plant. The PAC was added either directly to the aerated basin (simultaneous PAC-treatment), or to a partial stream of clarified effluent, which was treated with PAC in an agitated tank and recirculated to the aerated basin (subsequent PAC-treatment with recirculation). The standard advanced biological treatment reduced the AOX-content by 24%. In the pilot-plant, three types of powdered activated carbons were tested for a simultaneous treatment. The treatment with 100 mg/l PICA PCO Super produced an additional reduction of AOX by 20%, whereas a dosage of 50 mg/l NORIT W-20 showed no enhancement effect, and W-35 led to an additional AOX-removal of about 9%. Also, an improved removal of DOC, NH4-N and PO4-P was observed. In all cases, the PAC addition caused a significantly improved settling of the AS, reducing the sludge-volume-index, and increasing the content of volatile solids of the PAC-sludge. In general, no evidence of a synergistic effect of the PAC addition to activated sludge, nor bioregeneration of the activated carbon, could be observed. This suggests, that the observed effects probably are caused only by simple adsorption.

Activated Sludge Treatment of Wastewater from a Nylon 6 Manufacturing Plant

1988 ◽  
Vol 20 (10) ◽  
pp. 49-55 ◽  
Author(s):  
Masao Kageyama ◽  
Kosuke Tomita
Keyword(s):  
Activated Sludge ◽  
Treatment Plant ◽  
Nylon 6 ◽  
Volume Index ◽  
Manufacturing Plant ◽  
Sludge Treatment ◽  
Treated Water ◽  
Sedimentation Basin ◽  
Basic Studies ◽  
Achromobacter Sp

The activated sludge treatment of wastewater containing ɛ-caprolactam from a Nylon 6 manufacturing plant was investigated by basic studies and operation of a full-scale treatment plant. Activated sludges were obtained from several municipal and industrial wastewater sources, or were prepared by mixing ɛ-caprolactam-utilizing bacteria (Bacillus sp. and Achromobacter sp.) with a municipal activated sludge. However, bulking phenomena were soon observed in the acclimatization of ordinary activated sludges, even when started from a very low concentration of ɛ-caprolactam. On the other hand, the activated sludge synthesized from ɛ-caprolactam-utilizing bacteria showed better results as regards sludge volume index (SVI), BOD removal, and transparency of treated water. Wastewater from the Nylon 6 manufacturing plant, which contained ɛ-caprolactam, was treated by this synthesized activated sludge in a bench-scale apparatus consisting of a 4 m3 aeration basin and a 1.4 m3 sedimentation basin. The optimum BOD loading was estimated to be 0.35-0.40 kg BOD/kg MLSS/day for this wastewater. Production of excess activated sludge was 10% of the BOD loaded. In 1974, based on this preliminary experiment, a wastewater treatment facility consisting of a 2,500 m3 aeration basin and a 1,250 m3 sedimentation basin was constructed near the Uji Nylon 6 manufacturing plant (Unitika Ltd), to treat 5,000 m3 of wastewater (BOD 300-400 mg/l) per day. The treatment plant operates successfully, producing treated water with a BOD below 10 mg/l.

The main wastewater treatment plant of Vienna: an example of cost effective wastewater treatment for large cities

2006 ◽  
Vol 54 (10) ◽  
pp. 79-86 ◽  
Author(s):  
G. Wandl ◽  
H. Kroiss ◽  
K. Svardal
Keyword(s):  
Wastewater Treatment ◽  
Activated Sludge ◽  
Nitrogen Removal ◽  
Nutrient Removal ◽  
Process Management ◽  
Wastewater Treatment Plants ◽  
Treatment Plant ◽  
Single Stage ◽  
Volume Index ◽  
Two Stage

Two-stage activated sludge plants succeed in stable treatment efficiency concerning carbon removal and nitrification with far less reactor tank volume than conventional single stage systems. In case of large treatment plants this fact is of great economic relevance. Because of the very small specific volume of these two-stage treatment plants in comparison with low loaded single-stage plants, internal cycles have to be applied to ensure sufficient nitrogen removal. Due to these internal cycles two stage activated sludge plants offer many possibilities in terms of process management which results in new process optimisation procedures as compared to conventional single-stage nutrient removal treatment plants. The proposed extension concept for the Main Treatment Plant of Vienna was validated with pilot plant investigations especially with regard to nitrogen removal where it proved to comply with the legal requirements. The operation of the treatment plant can easily be adapted to changes in temperature and sludge volume index occurring in full scale practice. Sludge retention time and aerobic volume in the second stage are controlled in order to secure sufficient nitrification capacity and to optimise nitrogen removal by means of the variation of the loading conditions for the two stages. The investigations confirmed that the specific two-stage activated sludge concept applied in Vienna is an economically advantageous alternative for large wastewater treatment plants with stringent requirements for nitrification and nutrient removal.

scholarly journals Influence of road salt thawing peaks on the inflow composition and activated sludge properties in municipal wastewater treatment

2021 ◽  
Author(s):  
J. Tauber ◽  
B. Flesch ◽  
V. Parravicini ◽  
K. Svardal ◽  
J. Krampe
Keyword(s):  
Wastewater Treatment ◽  
Activated Sludge ◽  
Municipal Wastewater ◽  
Wastewater Treatment Plants ◽  
Road Salt ◽  
Volume Index ◽  
Municipal Wastewater Treatment ◽  
Floc Size ◽  
Floc Structure ◽  
Autotrophic Biomass

Abstract Operational data over 2 years from three large Austrian wastewater treatment plants (WWTPs) with design capacities of 4 million, 950,000 and 110,000 population equivalent (PE) were examined. Salt peaks, due to thawing road salt were detected and quantified by electrical conductivity, temperature and chloride measurement in the inflow of the WWTPs. Daily NaCl inflow loads up to 1,147 t/d and PE-specific loads of 0.26–0.5 kg NaCl/(PE · y) were found. To mimic the plants' behaviour in a controlled environment, NaCl was dosed into the inflow of a laboratory-scale activated sludge plant. The influence of salt peaks on important activated sludge parameters such as sludge volume index, settling velocity and floc size were investigated. Influent and effluent were sampled extensively to calculate removal rates. Respiration measurements were performed to quantify activated sludge activity. Particle size distributions of the activated sludge floc sizes were measured using laser diffraction particle sizing and showed a decrease of the floc size by approximately two-thirds. The floc structure was examined and documented using light microscopy. At salt concentrations below 1 g/L, increased respiration was found for autotrophic biomass, and between 1 and 3 g NaCl/L respiration was inhibited by up to 30%.

Effects of different coagulants on flocculation performance and floc properties in northwest China raw water treatment

2015 ◽  
Vol 15 (3) ◽  
pp. 599-605
Author(s):  
Jian Liu ◽  
Junguo He ◽  
Yixing Yuan ◽  
Jie Zhang
Keyword(s):  
Water Treatment ◽  
Low Temperature ◽  
Size Distribution ◽  
Treatment Plant ◽  
Northwest China ◽  
Quality Standard ◽  
Tibet Plateau ◽  
Floc Size ◽  
Melt Water ◽  
Floc Properties

The water of northwest China, characterized by low turbidity, low temperature, and micro-pollution, has posed difficult problems for water treatment plants. This study deployed a pilot-scale grid flocculation system to treat melt water from the Qinghai-Tibet Plateau in northwest China. A range of traditional coagulants were used on the low temperature, low turbidity, and micro-polluted melt water, to investigate the effect of coagulant types on flocculation performance and floc properties. Flocculation performance varied, depending upon the coagulant used. Turbidity and organic matter were removed with the greatest efficiency by polyaluminum chloride (PAC), followed by polyaluminum ferric chloride, followed by aluminum sulfate (alum). At a PAC dosage of 25 mg/L, the settled water's residual turbidity was lower than 1 NTU, meeting the Chinese national water-quality standard. Floc fractal dimensions of the three coagulants initially decreased, and then increased as the flocculation process yielded larger particles. This suggested that low turbidity could significantly affect the floc fractal dimension. Studying floc size distribution indicated that floc size in the grid flocculation tank was relatively uniform; the floc size distribution of PAC was the narrowest. The results could be used to inform operations of the Xining water treatment plant.

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.

Monitoring and troubleshooting of non-filamentous settling and dewatering problems in an industrial activated sludge treatment plant

2001 ◽  
Vol 44 (2-3) ◽  
pp. 155-162 ◽  
Author(s):  
B. V. Kjellerup ◽  
K. Keiding ◽  
P. H. Nielsen
Keyword(s):  
Wastewater Treatment ◽  
Activated Sludge ◽  
Wastewater Treatment Plants ◽  
Monitoring Program ◽  
Treatment Plant ◽  
Industrial Plant ◽  
Floc Strength ◽  
Floc Properties ◽  
One Year ◽  
Solid Liquid

A large industrial activated sludge wastewater treatment plant had temporary problems with settling and dewatering of the sludge. Microscopical investigations revealed that the poor settling properties were not due to presence of filamentous bacteria, but poor floc properties. In order to characterise the changes in floc properties that led to settling and dewatering problems and to find reasons for this taking place, a comprehensive monitoring program was conducted during more than one year. The monitoring program included various measurements of floc settleability, floc strength and sludge dewaterability. The monitoring program revealed that a deterioration of the floc strength and the settling properties in the process tanks was closely connected to downstream dewatering problems and poor effluent quality. Particularly severe problems were observed a few weeks after the production at the factory had started after summer closedown. Possible reasons for the changes in floc properties in the process tanks were found by a) analysing change in wastewater composition by evaluating the different production lines in the industrial plant, b) evaluating the operation of the plant, and c) performing short-term laboratory experiments testing factors that could potentially affect floc properties (absence of oxygen, presence of sulphide, detergents, etc). Among several measured parameters, the use of floc strength measurements in particular proved useful to monitor the activated sludge floc properties at this industrial plant. The described strategy can be useful in general to find and solve many solid/liquid separation problems in activated sludge wastewater treatment plants.

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