Presence Of Flocs Research Articles

Iron-organic carbon coprecipitates reduce nitrification by restricting molybdenum in agricultural soils

Nitrification converts ammonium (NH4+) to nitrate (NO3−) using metalloenzymes, the activity of which depends on iron (Fe), molybdenum (Mo), and copper (Cu) availability. Iron-organic carbon coprecipitates (or Fe-OC flocs) are key byproducts of wastewater treatment industry and natural components of soil that may affect nitrification by changing the bioavailability of these metals. Here, we used flocs of different chemistry (aromatic and aliphatic) and known Fe and C composition to investigate their effects on nitrification in soils along a soil C gradient. Both aromatic and aliphatic flocs reduced net nitrification, but the magnitude of their effect was more pronounced in soils with low C content as opposed to those with high C content. Within each soil, both flocs reduced net nitrification similarly. In the presence of flocs, the bioavailability of Mo (assessed by changes in the concentration of water-soluble Mo) was dramatically decreased in low C soils, possibly because Mo was incorporated into or adsorbed to flocs or their decomposition products. In contrast, Mo bioavailability in high C soils was decreased to a lesser extent by flocs, likely because organic matter limited floc adsorption capacity and released Mo through mineralization. The depletion of bioavailable Mo by flocs in agricultural soils has the potential to impede soil nitrification and extend the residence time of NH4+ and its availability to plants and microbes.

Long-term effects of hydrocyclone operation on activated sludge morphology and full-scale secondary settling tank wet-weather operation in long sludge age WWTP

This paper presents the study concerning long-term effects of a full scale hydrocyclone unit implemented in a continuous flow long sludge age system, on sedimentation, treatment efficiency and sludge morphology. The research concentrates on identifying the mechanisms of sludge behaviour within the system. The gravimetric selection of activated sludge via a hydrocyclone is a recent development for enhancing sludge separation, where heavier flocs are retained in the system, and lighter ones are discarded as waste sludge. The effects of implementing hydroclyclones were analysed with the use of SEM imagining and fractal dimensioning through the frequent assessment of sludge settling capabilities, effluent quality, and floc properties. Over the course of 60 weeks of hydrocyclone operation, sedimentation efficiency varied significantly. Sludge volume index values of 40 mL/g, achieved during the warm season, were not sustained when the temperature decreased and an overgrowth of filamentous bacteria occurred. Good settling efficiency was also observed in batch tests, where settling velocity of experimental sludge was app. 1 m/h higher than for the reference train at the same concentrations. This was confirmed during wet weather, as the experimental train sustained safe sludge blanket height in secondary clarifiers. SEM imaging and fractal dimension analysis revealed that the underflow that returned to the system had a more compact and spherical shape, which led to an increased content of granule-like particles in the reactor. The presence of flocs with a diameter exceeding 900 μm in the underflow, which is not observed in the feed, indicated agglomeration within the hydrocyclone. This is contradictory to most of the literature data coming from laboratory experiments. This phenomenon was attributed to differences in the size and geometry of the used hydrocyclones, and the potential process mechanism was presented.

Ammonium-based aeration control improves nitrogen removal efficiency and reduces N2O emissions for partial nitritation-anammox reactors

This study deals with the effect of aeration control strategies on the nitrogen removal efficiency and nitrous oxide (N2O) emissions in a partial nitritation–anammox reactor with granular sludge. More specifically, dissolved oxygen (DO) control, constant airflow and effluent ammonium (NH4+) control strategies were compared through a simulation study. Particular attention was paid to the effect of flocs, which are deliberately or unavoidable present besides granules in this type of reactor. When applying DO control, DO setpoints had to be adjusted to the amount of flocs present in the reactor to maintain high nitrogen removal and reduce N2O emissions, which is difficult to realize in practice because of variable floc fractions. Constant airflow rate control could maintain a good nitrogen removal efficiency independent of the floc fraction in the reactor, but failed in N2O mitigation. Controlling aeration based on the effluent ammonium concentration results in both high nitrogen removal and relatively low N2O emissions, also in the presence of flocs. Fluctuations in floc fractions caused significant upsets in nitrogen removal and N2O emissions under DO control but had less effect at constant airflow and effluent ammonium control. Still, rapid and sharp drops in flocs led to a peak in N2O emissions at constant airflow and effluent ammonium control. Overall, effluent ammonium control reached the highest average nitrogen removal and lowest N2O emissions and consumed the lowest aeration energy under fluctuating floc concentrations.

Comparison of Hydrometer Analysis and Laser Diffraction Method for Measuring Particle and Floc Size Distribution Applied to Fine Coal Refuse

Abstract Traditional grain size distribution measurement techniques assume that the measured particle diameters are of individual grains. However, for suspended particulate materials, particles may be dispersed or associated in flocs. Further, particle-level associations depend on the surrounding fluid chemistry, which may change over time. The purpose of this study is to compare two different methods of grain size analysis for detecting particle and floc sizes in suspensions of fine coal refuse (FCR): hydrometer analysis, the well-known traditional method, and laser diffraction, a lesser known method. The influence of background solution—flocculant, dispersant, or distilled water—on the apparent grain size of FCR was also investigated. Analogous slurry suspensions made from a well-characterized kaolin were analyzed for comparison. Results from the grain/floc size analysis indicate that there are several advantages of laser diffraction over hydrometer analysis including a short measurement period, small sample size requirement, and the ability to measure a wide range of particle sizes in the same analysis. Moreover, this study highlights the ability of the particle size analyzer (PSA) to accurately measure changes in apparent particle size over time for the same suspension and thereby indicate the presence of flocs. Finally, the PSA has the capability of capturing dynamic particle interactions—flocculation and deflocculation—in real time.

A novel strategy to alleviate ultrafiltration membrane fouling by rotating membrane module

Integrated ultrafiltration (UF) membrane technology has attracted extensive attention in drinking water treatment due to its excellent performance and small footprint. However, membrane modules normally are static in membrane tanks, which cause a gradual increase in the cake layer thickness over time, thus resulting in severe membrane fouling. To overcome this shortcoming, we report an effective strategy to regulate cake layer thickness by rotating the membrane module in the presence of flocs. The results showed that the cake layer thickness can be effectively reduced because of the floc looseness, resulting in the alleviation of membrane fouling. The higher the module rotation speed, the higher the flow velocity in the membrane tank and the larger the shearing force on the cake layer surface. As a result, the membrane fouling was considerably mitigated, and it was interesting that the pollutant removal efficiency was hardly influenced. With module rotation, we found that acid solutions displayed a better performance in removing pollutants (even low molecular weight pollutants) and alleviating membrane fouling compared to the alkaline conditions because of the smaller floc size, larger floc specific surface area, and higher floc positive charge. Additionally, an excellent UF membrane performance was also observed with the raw water taken from the South-North water in China. Collectively, this study demonstrated that floc-based cake layers can be effectively regulated with module rotation, which has a great potential in drinking water treatment application, particularly in small water plants.

Crescimento e sobrevivência do camarão-rosa (<em>Farfantepenaeus paulensis</em>) na fase de berçário em meio heterotrófico

The objective of the present study was to evaluate the potential of a heterotrophic rearing media (microbial flocs) on the growth and survival of Farfantepenaeus paulensis reared in the nursery phase. For 30 days, F. paulensis postlarvae (0.019 +- �� 0.01g) were reared in nine 40-liter plastic tanks at the density of 500 postlarvae m-2 . Three treatments with three replicates each were used: rearing in the presence of microbial flocs with ration supply (FLOC + R); rearing in the sole presence of flocs - no ration supplied (FLOC); and rearing in clear water plus with ration supply (AC + R). The presence of microbial flocs had no significant effect on growth and survival in the nursery rearing of F. paulensis .

Effect of extraction and enzymatic esterification of ethanol on glucose consumption by two Saccharomyces cerevisiae strains: a comparative study

AbstractExtractive alcoholic fermentations of high glucose concentrations (300 and 400 g dm−3) using a flocculent (saké) and a non‐flocculent (DER24) Saccharomyces cerevisiae strain were compared. The introduction of a Rhizomucor miehei lipase, in the extractive fermentations of 300 g dm−3 of glucose, increased the ethanol extraction due to its esterification with oleic acid, allowing complete glucose consumption at an organic solvent/fermentation medium phase ratio of 1. In these conditions, an increase of ethanol yield was observed. Total glucose consumption was also obtained in enzymatic extractive fermentations of 400 g dm−3 of glucose, but only when oleic acid was added at the exponential growth phase. From the comparison of the extractive fermentation performances obtained using the two yeast strains it was observed that the flocculent strain led to a lower glucose metabolisation rate. This behaviour was related to the highest diffusional limitations that occur in the presence of flocs. The developed processes showed that the association of alcoholic fermentation with enzymatic extraction led to the reduction of inhibitory effects as well as to the simultaneous production of fatty esters which are compounds with several commercial applications.© 2001 Society of Chemical Industry

Production of cellulose microfibrils by Rhizobium.

Electron microscope examination of Rhizobium spp. revealed microfibrils produced by flocculating strains but not by nonflocculating strains. The microfibrils from R. trifolii (NA30) were isolated and identified as cellulose by enzymatic, X-ray diffraction, and infrared spectral analyses. Both infective and noninfective strains of R. trifolii flocculated and produced microfibrils. More infection threads were observed in clover root hairs growing in the presence of flocs in comparison with root hairs where single bacterial cells predominated.

Production of Cellulose Microfibrils by Rhizobium1

Electron microscope examination of Rhizobium spp. revealed microfibrils produced by flocculating strains but not by nonflocculating strains. The microfibrils from R. trifolii (NA30) were isolated and identified as cellulose by enzymatic, X-ray diffraction, and infrared spectral analyses. Both infective and noninfective strains of R. trifolii flocculated and produced microfibrils. More infection threads were observed in clover root hairs growing in the presence of flocs in comparison with root hairs where single bacterial cells predominated.