Does a change in reactor loading rate affect activated sludge bioflocculation?

A collection of particles held together by different interparticle forces might eventually give rise to the formation of activated sludge flocs. This process is known as bioflocculation and is crucial for both conventional activated sludge systems and membrane bioreactors. Since industrial wastewater treatment plants generally face varying reactor loading rates due to varying production schemes in the facility, this paper investigates the impact of reactor loading rates on activated sludge bioflocculation. For this purpose, two reactors were initially operated at a nominal reactor loading rate (RLR) and afterwards changed to a high and low RLR. Based on the obtained results, it can be observed that sludge under low RLR conditions is prone to floc fragmentation due to an increase in water-soluble extracellular polymeric substances (EPS). The reactor under high RLR indicated increased floc erosion as a result of increased biomass concentration, which might imply more collisions between sludge flocs, releasing small sludge particles from the floc. In the high RLR reactor, no significant increase in EPS was observed. A distinction between the different (de)flocculation phenomena was made based on sludge volume index, effluent suspended solids and EPS data supplemented with microscopic image analysis.     

The use of a new mobile phase,with no multivalent cation binding properties,to differentiate extracellular polymeric substances (EPS), by size exclusion chromatography (SEC), from biomass used for wastewater treatment

The fingerprints of extracellular polymeric substances (EPS) extracted from different types of biomass used for wastewater treatment (i.e., activated sludge, filamentous activated sludge, anaerobic granular sludge, anaerobic flocculated sludge) were studied by size exclusion chromatography (SEC) with Amersham Biosciences Superdex 200 10/300 GL column with a theoretical resolving range of 10–600 kDa. A new mobile phase, which does not display binding properties for multivalent cations, was previously optimized. This mobile phase contained 75 mM Hepes buffer at pH 7 with 15% acetonitrile (v/v) and was selected to minimize ionic and hydrophobic interactions between the molecules that make up the EPS and the column packing.When EPS extracted from similar sludges is analyzed using different mobile phases, the number of chromatographic peaks obtained is quite similar, and differences are mainly observed in the relative absorbance of the chromatographic peaks. However, very different chromatograms (number and relative absorbance of chromatographic peaks) are obtained for EPS extracted from different types of sludges. Furthermore, when dysfunctions, such as filamentous bulking in the activated sludge, occur in a bioreactor, they also induce strong variations in chromatographic profiles.     

Comparative composition and characteristics of methanogenic granular sludges treating industrial wastes under different conditions

Comparative investigation of the components and characteristics of three types of fully developed granular sludges operating in full-scale and laboratory upflow anaerobic sludge blanket reactors under different conditions was qualitatively and quantitatively carried out. Extracellular polymeric material of granular sludges contained 1.7–2.7% carbohydrates, 2.5–5.1% nucleic acids and 8.3–16.3% proteins of total suspended solids (TSS). The ash content of the granular sludges varied from 11–21% and was an equal combination of metals—mainly calcium, sodium, magnesium, potassium, phosphorus and iron-and non metals in the form of clay. The results indicated that feed mineral concentration had an overall effect on the mineral composition of granular sludges and that specific uptake of preferred minerals such as magnesium, iron and phosphorus occurred depending upon the operational and environmental conditions. Significant variation was found in the dominant methanogenic groups.     

AMP deaminase from the gill of Salmo gairdnerii Richardson: effects of anions, cations and buffers

The AMP deaminase isoenzymes from trout gill were activated by sodium and potassium, sodium being the most efficient. The optimal concentration for activation was 30-50 mM. The enzyme was sensitive to ionic strength, and imidazole was an inhibitor at concentrations higher than 25 mM. A possible regulation of gill AMP deaminase by intracellular imidazole buffers is discussed. AMP deaminase activity was tested in the presence of physiological concentrations of sodium and potassium. When the concentration of one of these cations was varied around its physiological concentration, the enzyme activity was relatively stable, indicating that the intracellular AMP deaminase activity would be insensitive to changes in the concentrations of monovalent cations. The effects of the sodium salts of different inorganic and organic anions were tested. Except chloride and gluconate, all were inhibitors of gill AMP deaminase.     

Influences of extracellular polymeric substances (EPS) on the characteristics of activated sludge under non-steady-state conditions

Laboratory experiments were carried out on activated sludge (AS) to investigate the correlations between the content of extracellular polymeric substances (EPS) and the performance of biosolids–water separation, including sludge flocculation, sedimentation, compression, and dewatering, under non-steady-state conditions. On three stabilized AS reactors changes were made in sludge retention time (SRT), substrate composition, and loading rate, respectively, to bring about unstable operation to the reactors. A two-step heating method was used to extract from the sludge the easily extractable EPS, or loosely bound EPS (LB-EPS), and tightly bound EPS (TB-EPS), respectively. The experimental results demonstrate dynamic changes in sludge characteristic and EPS production under the non-steady-state conditions. During the early phase of transition after a change was imposed, the sludge became generally worse in flocculation, compressibility, and dewaterability. With the acclimatization of the biomass to the new process conditions, biosolids–water separation showed a general trend of improvement. Changes in AS process condition also resulted in considerable variations in EPS production. The change of the LB-EPS content appeared to be more significant than that of the TB-EPS. Throughout the non-steady-state operation, the sludge flocculating behavior, settleability, compressibility, and dewaterability had a positive correlation with the LB-EPS content; however, no correlation could be found between these properties and the TB-EPS content. The results suggest that although EPS is essential to biofloc formation, excessive EPS in the form of LB-EPS would weaken cell attachment and deteriorate the AS floc structure, resulting in poor biosolids–water separation.     

Quinone profiling of bacterial communities in natural and synthetic sewage activated sludge for enhanced phosphate removal

Respiratory quinones were used as biomarkers to study bacterial community structures in activated sludge reactors used for enhanced biological phosphate removal (EBPR). We compared the quinone profiles of EBPR sludges and standard sludges, of natural sewage and synthetic sewage, and of plant scale and laboratory scale systems. Ubiquinone (Q) and menaquinone (MK) components were detected in all sludges tested at molar MK/Q ratios of 0.455 to 0.981. The differences in MK/Q ratios were much larger when we compared different wastewater sludges (i.e., raw sewage and synthetic sewage) than when we compared sludges from the EBPR and standard processes or plant scale and laboratory scale systems. In all sludges tested a Q with eight isoprene units (Q-8) was the most abundant quinone. In the MK fraction, either tetrahydrogenated MK-8 or MK-7 was the predominant type, and there was also a significant proportion of MK-6 to MK-8 in most cases. A numerical cluster analysis of the profiles showed that the sludges tested fell into two major clusters; one included all raw sewage sludges, and the other consisted of all synthetic sewage sludges, independent of the operational mode and scale of the reactors and the phosphate accumulation. These data suggested that Q-8-containing species belonging to the class Proteobacteria (i.e., species belonging to the beta subclass) were the major constituents of the bacterial populations in the EBPR sludge, as well as in standard activated sludge. Members of the class Actinobacteria (gram-positive bacteria with high DNA G+C contents) were the second most abundant group in both types of sludge. The bacterial community structures in activated sludge processes may be affected more by the nature of the influent wastewater than by the introduction of an anaerobic stage into the process or by the scale of the reactors.     

Application of enzymes, sodium tripolyphosphate and cation exchange resin for the release of extracellular polymeric substances from sewage sludge. Characterization of the extracted polysaccharides/glycoconjugates by a panel of lectins

The study describes extraction of extracellular polymeric substances (EPS) from sewage sludge by applying enzymes and enzymes combined with sodium tripolyphosphate (STPP). Additionally, a systematic study of two non-enzymatic extraction agents is described. The assessment of the released products is made by colorimetrical methods and polysaccharides/glycoconjugates identification by the interaction with four immobilized lectins. Bio-sludge from Helsingborg (Sweden) and Damhus?en (Denmark) were used as two case studies for testing enzymatic extractability and thereby to make useful prediction of sludge bio-digestibility. From Helsingborg sludge the enzymes extracted about 40% more of EPS than from Damhus?en. The polysaccharides/glycoconjugates in both sludges maintained the same level, and showed substantial different interaction motifs with lectins panel. Damhus?en enzymatic extracted EPS had an enhanced amount of suspended material that was post-hydrolysed by the use of polygalacturonase and lysozyme resulting in pectin like polymers and petiptidoglycans. Petiptidoglycan is a marker from bacterial cell debris. STPP and cation exchange resin (CER) released different quantities of EPS. The CER released polysaccharides/glycoconjugates had higher molecular weight and stronger affinity towards Concanavalin A than the one released by the action of STPP. Independent of the extraction conditions, STPP released elevated amounts of polyvalent cations and humic substances in contrast to the very low amounts of released by CER.     

Examination into the gamma irradiation of activated sludge

This study has shown that the treatment of activated sludge by gamma irradiation resulted in a deterioration in the filterability, a decrease in the size of the floc particles and an increase in the organic matter present in the sludge supernatant. A significant difference was found between the results obtained for filamentous and non-filamentous sludges in relation to the amount of soluble polysaccharide produced.     

Effects of ammonia and phosphate limitation on the activated sludge treatment of calcium-containing chemical waste

Laboratory-scale biotreaters were used to study the effects of NH(3)-N and PO(4)-P nutrients on the activated sludge treatment of a chemical waste containing soluble calcium (1300 mg/L). Units receiving high or low levels of NH(3)-N and PO(4)-P were similar in their ability to remove organic compounds from the waste. Adaptation of sludges to low PO(4)-P levels (<0.1 mg/L effluent) resulted in a marked accumulation of CaCO(3) in the biosolids, whereas those receiving high PO(4)-P (2-4 mg/L effluent) had little CaCO(3). Microscopic observations of CaCO(3) containing sludges showed substantial amounts of CaCO(3) crystals imbedded in the biomass. These flocs also appeared to be enriched with nonfilamentous bacterial species in contrast to flocs devoid of CaCO(3) which had a floc structure of filamentous and nonfilamentous organisms. Scanning electron micrographs of flocs grown under low NH(3)-N showed a microbial fibrillar network of exocellular material interconnecting cells in the floc matrix. The sludges adapted to low NH(3)-N also produced higher amounts of extractable polysaccharide. CaCO(3) containing biosolids were more dense, larger, and settled better (low SVI, high ISV) than flocs devoid of the precipitates. It is not known from our experiments whether PO(4)-P or some inorganic or organic polymer produced by the floc bacteria are involved in inhibiting CaCO(3) precipitation in the activated sludge treatment of calcium-containing wastes.     

Relations between substrate feeding pattern and development of filamentous bacteria in activated sludge processes

Summary Laboratory scale activated sludge systems were operated under regimes of continuous or intermittent feeding of substrate. It was found that continuously fed systems repeatedly resulted in the development of filamentous bacteria and bulking of the sludge. Intermittently fed systems did form good settling sludges, without filamentous bacteria. The same results were found using different sludge loadings and different concentrations of mixed liquor suspended solids. High dissolved oxygen concentration did not prevent bulking in continuous systems while low dissolved oxygen concentration resulted in bulking with intermittently fed systems. It was found that the substrate removal rate of intermittently operated systems was always higher than for continuously fed systems. The hypothesis is formulated that intermittent feeding leads to higher substrate removal rates by floc forming bacteria and their predominance in intermittently fed systems, which can be compared to plug flow systems.     

Microbial composition and structure of aerobic granular sewage biofilms

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.     

Floc destruction and its impact on dewatering properties in the process of using flat-sheet membrane for simultaneous thickening and digestion of waste activated sludge

Floc destruction and its impacts on the dewatering properties in terms of capillary suction time (CST) in the process of using flat-sheet membrane for simultaneous thickening and digestion (MSTD) of waste activated sludge were investigated. A pilot-scale MSTD reactor was used to treat waste activated sludge, and extracellular polymeric substances (EPS), soluble biopolymers, dissolved cations and the dewatering properties were measured. The results indicated that the destruction mechanisms of the MSTD process could be divided into two phases due to the variation of dissolved oxygen (DO). Polysaccharides and proteins were released in both phases, but the release patterns were different. The concentration of polysaccharides was much greater than that of proteins in Phase 1, while the ratio of proteins to polysaccharides ranged from 1.5 to 1.7. The divalent cations in supernatant significantly increased in Phase 1, while the monovalent cations in supernatant rose in Phase 2. The dewatering properties in terms of CST significantly increased in the MSTD process, and the mixed liquor suspended solids (MLSS), particle size, and biopolymers in supernatant had significant effects on the dewatering properties.     

Comparison and Analysis of Membrane Fouling between Flocculent Sludge Membrane Bioreactor and Granular Sludge Membrane Bioreactor

The goal of this study is to investigate the effect of inoculating granules on reducing membrane fouling. In order to evaluate the differences in performance between flocculent sludge and aerobic granular sludge in membrane reactors (MBRs), two reactors were run in parallel and various parameters related to membrane fouling were measured. The results indicated that specific resistance to the fouling layer was five times greater than that of mixed liquor sludge in the granular MBR. The floc sludge more easily formed a compact layer on the membrane surface, and increased membrane resistance. Specifically, the floc sludge had a higher moisture content, extracellular polymeric substances concentration, and negative surface charge. In contrast, aerobic granules could improve structural integrity and strength, which contributed to the preferable permeate performance. Therefore, inoculating aerobic granules in a MBR presents an effective method of reducing the membrane fouling associated with floc sludge the perspective of from the morphological characteristics of microbial aggregates.     

Acetate Degradation at 70 degrees C in Upflow Anaerobic Sludge Blanket Reactors and Temperature Response of Granules Grown at 70 degrees C

Anaerobic acetate degradation at 70 degrees C and at 55 degrees C (as a reference) was studied by running laboratory upflow anaerobic sludge blanket (UASB) reactors inoculated with mesophilic granular sludge. In UASB reactors fed with acetate-containing media (3 g of chemical oxygen demand [COD] per liter, corresponding to 47 mM acetate) approximately 50 days was needed at 70 degrees C and less than 15 days was needed at 55 degrees C to achieve an effluent COD of 500 to 700 mg/liter. In the UASB reactors at both 70 and 55 degrees C up to 90% of the COD was removed. Batch assays showed that sludges from two 70 degrees C UASB reactors, one run at a low effluent acetate concentration and the other run at a high effluent acetate concentration, exhibited slightly different responses to temperatures in the range from 37 to 70 degrees C. Both 70 degrees C sludges, as well as the 55 degrees C sludge, produced methane at temperatures of 37 to 73 degrees C. The 55 degrees C sludge exhibited shorter lag phases than the 70 degrees C sludges and higher specific methane production rates between 37 and 65 degrees C.     

Relation between substrate feeding pattern and development of filamentous bacteria in activated sludge processes: Part III. applications with industrial waste waters

Summary Laboratory scale activated sludge systems were operated under regimes of continuous or intermittent feeding of the waste water. Industrial waste waters from breweries, a dairy plant and a petro-chemical plant were investigated. The systems were started up with sludge from a municipal waste water plant or more often with sludges obtained from the corresponding industrial waste water treatment plants. It was found that intermittently fed systems produced sludges with better settleability characteristics than systems that were continuously supplemented with waste water. Our previous hypothesis that in intermittent systems floc forming bacteria become dominant as a result of higher substrate uptake rates was confirmed and may thus be extended to waste waters containing readily available substrates such as carbohydrates (brewery-and dairy waste water) or acids (petro-chemical waste water). Supplementation of brewery waste water with urea had a negative influence on sludge settleability, especially in continuously operated systems.     

Influence analysis for the behavior of dewaterability of excess sludge in a two-stage vermifilter

To improve excess sludge dewaterability, a two-stage vermifilter was developed to qualitatively and quantitatively analyze sludge physico-chemical properties (fractal dimension, zeta potential, extracellular polymeric substances (EPS), particle size distribution, etc.) and to correlate them with sludge dewatering characteristics (specific resistance to filtration (SRF) and capillary suction time (CST)). Results demonstrated that sludge dewatering performance was significantly improved after the primary vermifilter VF₁ and the second-stage vermifilter VF₂. In addition, the further VF₂ treatment exhibited higher effects on sludge dewatering performance. The particle boundary of sludge after VF₂ treatment was clearer and smoother than VF₁ sludge (VF₁S), apart from the fact that sludge morphological structure got denser and more compact. Comparing with VF₁S, the fractal dimension D₁ calculated within 1D topological space was closer to 1 after VF₂ treatment, and the fractal dimension D₂ within 2D topological space closer to 2, indicating a better dewatering performance after VF₂ treatment. Additionally, the changes of sludge floc surface properties (such as zeta potential and EPS) resulted in small particles agglomerating into larger ones and then the increase of particle diameter. In summary, the two-stage vermifilter got a better sludge dewatering performance, and thus beneficial for subsequent processing of sludge.

     

Sorption of Cd(II) and Pb(II) by exopolymeric substances (EPS) extracted from activated sludges and pure bacterial strains: Modeling of the metal/ligand ratio effect and role of the mineral fraction

The present study deals with the sorption of Cd(II) and Pb(II) by exopolymeric substances (EPS) extracted from activated sludges or pure bacterial strains. The percentage of sorbed metal increases with the concentration of the EPS–water solution. Pb(II) always presents a higher affinity than Cd(II) for EPS. For the EPS extracted from pure bacterial strains, only one global binding constant from a simple equilibrium sorption model, may be used to assess the effect of microbial products such as EPS on Cd(II) and Pb(II) speciation or mobility in the environment. However, for EPS extracted from activated sludges, the wide variation of the global binding constants determined for Cd(II) and Pb(II) do not permit such a simple approach. The differences in sorption to metals between the two types of EPS (bacterial, activated sludges) could be explained by the differences in EPS composition: organic macromolecules, as well as the nature of the mineral fraction.     

Bismuth dimercaptopropanol (BisBAL) inhibits formation of multispecies wastewater flocs

Aims: To determine the ability of a bismuth thiol to control floc formation in a multispecies population of micro‐organisms obtained from the activated sludge unit of a wastewater treatment plant. The molecular level mechanisms by which bismuth‐2‐3‐dimercapto‐1‐propanol (BisBAL) inhibits bioaggregation are also elucidated. Methods and Results: Micro‐organisms were grown over a 3‐day period in a batch system by adding glucose as an electron donor to stimulate short‐term heterotrophic activity. Extracellular polymeric substances (EPS) produced by activated sludge micro‐organisms during exponential and stationary growth phases in the presence and absence of BisBAL were characterized using colorimetry, X‐ray photoelectron spectroscopy (XPS), and Fourier transform infrared (FTIR) spectroscopy. BisBAL at its minimum inhibitory concentration (MIC, 10 μmol l^?1) was most effective in suppressing microbial floc formation. The principal effect of sub‐inhibitory concentrations of BisBAL was to decrease total EPS production while largely preserving homology. Conclusions: Antifouling and bactericidal properties of BisBAL arise from its ability to reduce EPS expression and preferentially suppressing acidic and O‐acetylated carbohydrates and certain protein secondary structures viz. β‐structures, random coils, and α‐and 3‐turn helices. As micro‐organisms exhibited a much weaker tendency to aggregate at lower concentrations of these specific EPS components, they also appear to be important for the formation of microbial flocs and bioaggregates. Significance and Impact of the Study: BisBAL was shown to be highly effective against multispecies microbial aggregation. Novel bismuth‐based biocides could also be potentially employed to control excess sludge production in wastewater treatment systems by inhibiting EPS expression.     

The effect of monovalent cations on calcium efflux in yeasts

The properties of the calcium efflux system in the yeast Saccharomyces cerevisiae were investigated. After growing the cells overnight in medium containing ⁴⁵Ca, the cells were transferred to medium containing glucose, Hepes buffer (pH 5.2) and monovalent cations. The presence of potassium or sodium in the medium induced efflux of calcium from the cells. The magnitude of the efflux was dependent on the concentration of these cations in the medium. The time course of calcium efflux was analyzed, and two types of exchangeable calcium pools, which turned over at different rates, were detected: ‘Fast turnover’ and ‘slow turnover’. Increase in the concentration of monovalent cations in the medium caused an increase in the fraction of cellular calcium which turned over at a fast rate, and activation of calcium efflux from the ‘slow turnover’ calcium pool. The specific changes in the parameters of calcium efflux induced by monovalent cations were different from those reported previously to be induced by divalent cations. Both processes, i.e. activation of calcium efflux by monovalent and by divalent cations, were found to be additive, indicating that they operate via different mechanisms. Experiments using the respiratory inhibitor Antimycin A, showed that stimulation of calcium efflux by monovalent cations is energy dependent. Lanthanum ions which are known to inhibit calcium influx into yeast cells, inhibitted the activation of calcium efflux by both divalent and monovalent cations. Determination of the cationic composition of the cells indicated that the stimulation of calcium efflux was accompanied by influx of potassium or sodium into the cells.     

Aerobic Heterotrophic Bacterial Populations of Sewage and Activated Sludge: IV. Adaptation of Activated Sludge to Utilization of Aromatic Compounds 1

An activated sludge from a sewage treatment plant and a laboratory activated sludge developed on an artificial waste were compared for their ability to utilize 11 aromatic compounds. There were several significant differences between them. The laboratory sludge contained higher numbers of organisms and metabolized the aromatics to a greater extent. Laboratory activated sludges acclimated to utilization of the aromatics differed from each other in population structure and the pattern of oxygen consumption with aromatic substrates. The oxidative patterns of uncontrolled mixed populations were unreliable for investigating metabolic pathways. Extracts of the various sludges elevated the plate counts of the sludges.