Determination of some rheological parameters for the characterization of activated sludge

The rheological characterization of activated sludge originating from different aeration tanks and from a lab-scale plant was carried out using rotation tests. Two rheological parameters were used: limit viscosity (mu(infinity)) and reduced hysteresis area (rHa). Mu(infinity) was strongly influenced by the total suspended solids (TSS) content of sludge and an exponential relation was found between TSS and the rheological parameter mu(infinity). Significant differences in sludge viscosity were found for sludge of different origins, but all of 10 g/l TSS content, indicating ability of viscosity to show different sludge qualities. Marked changes in activated sludge microorganisms communities were shown to have an influence on rheological parameters. During aerobic digestion of sludge, variations in mu(infinity) were noticed, indicating change of sludge quality. An over-growth of filamentous bacteria species was shown to induce a particular rheological behavior which could be characterized by rHa. This parameter was proposed as an index of filamentous bacteria proliferation in activated sludge aeration tanks.     

Viscous cosolvent effect on the ultrasonic absorption of bovine serum albumin.

Protein-ligand binding and enzyme activity have been shown to be regulated by solvent viscosity, induced by the addition of viscous cosolvents. This was indirectly interpreted as an effect on protein dynamics. However, viscous cosolvents might affect dynamic, e.g., viscosity, as well as thermodynamic properties of the solution, e.g., activity of solution components. This work was undertaken to examine the effect of viscous cosolvent on the structural dynamics of proteins and its correlation with dynamic and thermodynamic solution properties. For this purpose we studied the effect of viscous cosolvent on the specific ultrasonic absorption, delta mu, of bovine serum albumin, at pH = 7.0 and at 21 degrees C, and frequency range of 3-4 MHz. Ultrasonic absorption (UA) directly probes protein dynamics related to energy dissipation processes. It was found that the addition of sucrose, glycerol, or ethylene glycol increased the BSA delta mu. This increase correlates well with the solvent viscosity, but not with the cosolvent mass concentration, activity of the solvent components, dielectric constant, or the hydration of charged groups. On the grounds of these results and previously reported findings, as well as theoretical considerations, we propose the following mechanism for the solvent viscosity effect on the protein structural fluctuations, reflected in the UA: increased solvent viscosity alters the frequency spectrum of the polypeptide chain movements; attenuating the fast (small amplitude) movements, and enhancing the slow (large amplitude) ones. This modulates the interaction strength between the polypeptide and water species that "lubricates" the chain's movements, leading to larger protein-volume fluctuation and higher ultrasonic absorption. This study demonstrates that solvent viscosity is a regulator of protein structural fluctuations.     

Feasibility of using ultrasonic irradiation to recover active biomass from waste activated sludge

Under typical operating conditions, the microbial fraction of activated sludge flocs is approximately 40% by weight. The objective of this research is to evaluate the feasibility of using ultrasonic irradiation to disrupt activated sludge flocs allowing for the subsequent separation of active and inactive fractions. If separation of floc components is possible, then methods may be incorporated into wastewater treatment plant operations whereby only the inactive fraction of floc is wasted (i.e., of waste activated sludge, WAS), which in turn could increase the overall effective biological solids retention time, leading to increased process robustness with no net increase in reactor size. The results indicate that ultrasonic irradiation of WAS at 800 Wl(-1) followed by 30 min of settling can produce a supernatant with heterotrophic specific oxygen uptake rates (SOURs) of over two times the SOUR measured in the bulk mixed liquor. Under these conditions 26% of the initial heterotrophic activity was recovered within only 11% of the initial volatile mass. Similarly, autotrophic analysis revealed that nitrifying organisms, while sensitive to the effects of ultrasonic irradiation, can be separated from the activated sludge floc and recovered. An irradiation density of 200 Wl(-1) with an exposure time between 1 and 2 min produced a supernatant with a specific ammonia removal rate of over two times the initial mixed liquor rate.     

Study of the hysteresis phenomenon in canine anterior cruciate ligaments

Preconditioning is now in common use in biomechanical testing of soft connective tissues. During the first few cycles the tissue behaviour is characterized by a decreasing hysteresis area. However, little is known about the changes occurring during the preconditioning process. The purpose of this study was to investigate the hysteresis phenomenon of ligaments as it is influenced by preconditioning and in vitro enzymatic treatment. Canine anterior cruciate ligament (ACL) was chosen because its mechanical properties and microstructure are relatively well known. A series of experiments were conducted to clarify some of the hysteresis features by combining mechanical testing, enzymatic digestions and pH variations. The area within the hysteresis loops (energy absorption, EA) was measured before and after each treatment. The results showed that the EA before preconditioning is not modified by elastase treatment, however, it was significantly reduced after preconditioning. The fractional EA lost during the preconditioning process increased significantly as compared to the controls. This may be explained by the destruction of elastin, which plays a significant role in the elasticity of ligaments. It was found that hyaluronidase treatment did not significantly affect the hysteresis of preconditioned ligaments. However, the EA during the first cycle decreased significantly as a result of uronic acid digestion leading probably to an exhaustion of the viscous component of the tissue. Hyaluronidase treatment seems to have the same effect as preconditioning on the hysteresis area.     

Entomotoxicity,protease and chitinase activity of Bacillus thuringiensis fermented wastewater sludge with a high solids content

This study investigated the production of biopesticides, protease and chitinase activity by Bacillus thuringiensis grown in raw wastewater sludge at high solids concentration (30 g/L). The rheology of wastewater sludge was modified with addition of Tween-80 (0.2% v/v). This addition resulted in 1.6 and 1.3-fold increase in cell and spore count, respectively. The maximum specific growth rate (μ_max) augmented from 0.17 to 0.22 h⁻¹ and entomotoxicity (Tx) increased by 29.7%. Meanwhile, volumetric mass transfer coefficient (k_La) showed marked variations during fermentation, and oxygen uptake rate (OUR) increased 2-fold. The proteolytic activity increased while chitinase decreased for Tween amended wastewater sludge, but the entomotoxicity increased. The specific entomotoxicity followed power law when plotted against spore concentration and the relation between Tx and protease activity was linear. The viscosity varied and volume percent of particles increased in Tween-80 amended wastewater sludge and particle size (D₅₀) decreased at the end of fermentation. Thus, there was an increase in entomotoxicity at higher suspended solids (30 g/L) as Tween addition improved rheology (viscosity, particle size, surface tension); enhanced maximum growth rate and OUR.     

Mechanics on myocardium deficient in the N2B region of titin: the cardiac-unique spring element improves efficiency of the cardiac cycle

Titin (also known as connectin) is an intrasarcomeric muscle protein that functions as a molecular spring and generates passive tension upon muscle stretch. The N2B element is a cardiac-specific spring element within titin's extensible region. Our goal was to study the contribution of the N2B element to the mechanical properties of titin, particularly its hypothesized role in limiting energy loss during repeated stretch (diastole)-shortening (systole) cycles of the heart. We studied energy loss by measuring hysteresis from the area between the stretch and release passive force-sarcomere length curves and used both wild-type (WT) mice and N2B knockout (KO) mice in which the N2B element has been deleted. A range of protocols was used, including those that mimic physiological loading conditions. KO mice showed significant increases in hysteresis. Most prominently, in tissue that had been preconditioned with a physiological stretch-release protocol, hysteresis increased significantly from 320 ± 46 pJ/mm²/sarcomere in WT to 650 ± 94 pJ/mm²/sarcomere in N2B KO myocardium. These results are supported by experiments in which oxidative stress was used to mechanically inactivate portions of the N2B-Us of WT titin through cysteine cross-linking. Studies on muscle from which the thin filaments had been extracted (using the actin severing protein gelsolin) showed that the difference in hysteresis between WT and KO tissue cannot be explained by filament sliding-based viscosity. Instead the results suggest that hysteresis arises from within titin and most likely involves unfolding of immunoglobulin-like domains. These studies support that the mechanical function of the N2B element of titin includes reducing hysteresis and increasing the efficiency of the heart.     

Energy-efficient sludge sonication: power and sludge characteristics

This paper improves the energy efficiency for sludge treatment using ultrasound. The sludge organic content, solid concentration, ultrasonic intensity, and time were optimized. A new index, kWh/kgSCOD-increase, was used to evaluate the energy efficiency that covers both sludge characteristics and lysis effectiveness. The results showed that the energy efficiency of sludge sonication was in the range of 102-347kWh/kgSCOD-increase. Higher VS/TS ratio gave higher energy efficiency. Optimal solid concentration (TS) was found to be 20g/L; low TS (5.0g/L) consumed 137% more energy; while higher TS might assimilate the sound energy and decrease the efficiency. The cavitation threshold for sludge was 20-30W/cm(2), below which no sludge lysis was observed. The lowest effective sound intensity (31.4W/cm(2)) was best and saved 20-35% energy compared to higher intensities. The initial first minutes of sonication were most effective; hence intensive-short treatment was preferred.     

Dewaterability of waste activated sludge with ultrasound conditioning

This study investigated the potential benefits of ultrasound-conditioned sludge dewatering treatments with specific energy dosages from 0 to 35,000 kJ/kg total solids (TS). Capillary suction time (CST) and specific resistance of filtration (SRF) were used to evaluate sludge dewaterability. Sludge water distribution was measured by the drying test and mechanical separation methods. Both extracellular polymeric substance (EPS) content and sludge particle size were determined in an attempt to explain the observed changes in sludge dewaterability. The results indicated that application of low specific energy dosages (<4400 kJ/kg TS) slightly enhanced sludge dewaterability, but larger specific energy dosages (>4400 kJ/kg TS) significantly deteriorated sludge dewaterability. The optimal specific energy to give maximal dewaterability characteristics was found to be 800 kJ/kg TS, which generated sludge with optimal EPS concentration (400-500 mg/l) and particle size distribution (80-90 microm diameter). Subjecting sludge to a combination of cationic polymer and ultrasound pretreatments did not present any clear advantages over polymeric conditioning alone for improving sludge dewaterability. The effects of cationic polymer treatment predominated over those of ultrasound pretreatment when both were used together.     

Did psychrophilic enzymes really win the challenge?

Organisms living in permanently cold environments, which actually represent the greatest proportion of our planet, display at low temperatures metabolic fluxes comparable to those exhibited by mesophilic organisms at moderate temperatures. They produce cold-evolved enzymes partially able to cope with the reduction in chemical reaction rates and the increased viscosity of the medium induced by low temperatures. In most cases, the adaptation is achieved through a reduction in the activation energy, leading to a high catalytic efficiency, which possibly originates from an increased flexibility of either a selected area of or the overall protein structure. This enhanced plasticity seems in return to be responsible for the weak thermal stability of cold enzymes. These particular properties render cold enzymes particularly useful in investigating the possible relationships existing between stability, flexibility, and specific activity and make them potentially unrivaled for numerous biotechnological tasks. In most cases, however, the adaptation appears to be far from being fully achieved.     

Effect of low power ultrasonic radiation on anaerobic biodegradability of sewage sludge

The effect of low power ultrasonic radiation on anaerobic biodegradability of sewage sludge was investigated. For this purpose, soluble substances and variation of microbial system of sewage sludge subjected to low power ultrasonic radiation were tested. The well known hydromechanical shear forces and heating effect of low frequency ultrasound plays a major role in the sludge pre treatment process. More, the increase of soluble substance may partly result from the destruction of microbial cell by excess ultrasonic pretreatment, which will inhibit the anaerobic process. By orthogonal tests, the optimal parameters were found to be an exposure time of 15 min, ultrasonic intensity of 0.35 W/cm² and ultrasonic power density of 0.25 W/ml. Under the optimal condition, anaerobic biodegradability of sewage sludge (R_(vss/ss) %) was increased by 67.6%. Consequently, it can be concluded that low power ultrasonic pretreatment is a valid method for improving anaerobic biodegradability of sewage sludge.     

活性污泥中电活性微生物的富集筛选研究进展

活性污泥含有多种微生物,是废水处理系统中污染物降解转化的重要驱动者。电活性微生物(Electroactive microorganisms,EAMs)是活性污泥的重要微生物类群,在废水资源化与能源化中发挥着核心关键作用。本文概括了活性污泥中EAMs的富集和筛选方法,整理总结了目前已从活性污泥中获得的EAMs菌种资源信息,在此基础上分析了从活性污泥中富集和筛选EAMs所存在的问题,并进一步展望了未来的研究方向,以期加速EAMs菌种资源的挖掘,促进以EAMs为主导的废水资源化与能源化技术发展。     

Effect of hydraulic retention time on membrane fouling and biomass characteristics in submerged membrane bioreactors

In this paper, three identical membrane bioreactors (MBRs) were operated in parallel in order to specify the influence mechanism of hydraulic retention time (HRT) on MBR. The results showed that the removal efficiency of chemical oxygen demand (COD) was stable though it decreased slightly as HRT decreased, but biomass activity and dissolved oxygen (DO) concentration in sludge suspension decreased as HRT decreased. The filamentous bacteria grew easily with decreasing HRT. The extracellular polymeric substances (EPS) concentration and sludge viscosity increased significantly as filamentous bacteria excessively grew. The over growth of filamentous bacteria, the increase of EPS and the decrease of shear stress led to the formation of large and irregular flocs. Furthermore, the mixed liquid suspended solids (MLSS) concentration and sludge viscosity increased significantly as HRT decreased. The results also indicated that sludge viscosity was the predominant factor that affecting hydrodynamic conditions of MBR systems.     

Shear Viscosity Investigation on Mango Juice with High Frequency Longitudinal Ultrasonic Waves and Rotational Viscosimetry

Ultrasonic velocity and attenuation measurements were performed on mango juices at 25 MHz in order to estimate longitudinal viscosity. Juices were extracted from fruits, removed periodically from fruit batches undergoing ripening for 3 weeks under controlled conditions. The correlation between longitudinal viscosity and apparent dynamic shear viscosity, obtained from flow tests, showed that up to 12–13 wt.% of Soluble Solids Content (SSC), the juices presented a Newtonian behavior. In this case the relation between longitudinal viscosity measured by ultrasound and shear viscosity measured by flow tests was very simple leading to the conclusion that ultrasound could replace rotating viscosimeters for specific applications. Over this limit, the results were also clearly correlated but the correlation depended on the shear rate because of the shear thinning behavior of the juices certainly due to soluble pectins. The use of longitudinal ultrasonic waves as a tool for viscosity determination on large batches of samples is discussed at the end of this communication.     

Observations on an ATP-sensitive protein system from the plasmodia of a myxomycete

1. Extracts of the plasmodia of the myxomycete, Physarum polycephalum, exhibit reversible decreases in viscosity in response to the addition of ATP under appropriate conditions. The protoplasm material prepared by extraction with KCl solution can apparently exist in either a high or a low viscosity state. As prepared, it is in the low viscosity condition. Rapid and extensive increases in viscosity of the extract are brought about by addition of AMP, inorganic phosphate, or, under certain conditions, of ATP. Only after the high viscosity state has been attained does addition of appropriate quantities of ATP cause a reversible decrease in viscosity. 2. The active principle of crude plasmodial extracts may be concentrated by fractional precipitation with ammonium sulfate and is found in the fraction precipitated between 30 and 40 per cent saturation. This material possesses a higher viscosity than does the original crude extract and is apparently in the high viscosity state since the addition of ATP causes an immediate reversible decrease in viscosity. 3. The ATP-sensitive fraction of myxomycete plasmodia possesses a viscosity which is dependent upon its previous thermal treatment. Extracts incubated at 0° for a period of a few hours increase greatly in viscosity when they are returned to 24.5°. This increased viscosity is structural in nature, is destroyed by mechanical agitation of the solution, and may be reversibly destroyed by addition of ATP. 4. It is suggested that the ATP-responsive protein of myxomycete plasmodia may be related to sol-gel transformations which have been observed in intact plasmodia and may participate in the protoplasmic streaming of the intact organism. This suggestion is based upon the following facts: (a) the protoplasmic streaming of myxomycete plasmodia is increased by microinjection of ATP; (b) the gel portion of the cytoplasm at the site of the microinjection of ATP is extensively converted to the sol state. The changes in structure of the intact cytoplasm are thus similar in nature to the changes exhibited in response to ATP by the purified ATP-sensitive protein. 5. The ATP-sensitive protein of myxomycete plasmodia appears to undergo reversible aggregation to form a high viscosity state. The function of ATP is to break down the aggregates thus formed. Since a specific ATPase activity is associated with the purified material, added ATP is gradually destroyed and recovery of viscosity attends the spontaneous reconstitution of aggregates.     

The Responses of Cytochrome Redox State and Energy Metabolism to Dehydration Support a Role for Cytoplasmic Viscosity in Desiccation Tolerance

To characterize the depression of metabolism in anhydrobiotes, the redox state of cytochromes and energy metabolism were studied during dehydration of soaked cowpea (Vigna unguiculata) cotyledons and pollens of Typha latifolia and Impatiens glandulifera. Between water contents (WC) of 1.0 and 0.6 g H₂O/g dry weight (g/g), viscosity as measured by electron spin resonance spectroscopy increased from 0.15 to 0.27 poise. This initial water loss was accompanied by a 50% decrease in respiration rates, whereas the adenylate energy charge remained constant at 0.8, and cytochrome c oxidase (COX) remained fully oxidized. From WC of 0.6 to 0.2 g/g, viscosity increased exponentially. The adenylate energy charge declined to 0.4 in seeds and 0.2 in pollen, whereas COX became progressively reduced. At WC of less than 0.2 g/g, COX remained fully reduced, whereas respiration ceased. When dried under N₂, COX remained 63% reduced in cotyledons until WC was 0.7 g/g and was fully reduced at 0.2 g/g. During drying under pure O₂, the pattern of COX reduction was similar to that of air-dried tissues, although the maximum reduction was 70% in dried tissues. Thus, at WC of less than 0.6 g/g, the reduction of COX probably originates from a decreased O₂ availability as a result of the increased viscosity and impeded diffusion. We suggest that viscosity is a valuable parameter to characterize the relation between desiccation and decrease in metabolism. The implications for desiccation tolerance are discussed.     

Using acoustic cavitation to improve the bio-activity of activated sludge

This paper studied a new method to improve the microbial activity of the activated sludge for wastewater treatment. Concentrated sludge was sonicated in an extra chamber for short period and then returned to the activated sludge system. The results showed that the bio-activity of the activated sludge, expressed as oxygen utilization rate (OUR), could be enhanced by ultrasonic irradiation. Powerful ultrasound (in the magnitude of W/ml) was much more effective than weak ultrasound (in the magnitude of W/L) in stimulating the activated sludge, but too strong sonication (power density higher than 0.5 W/ml) disintegrated the sludge and thus decreased the sludge activity. Low frequency (25 kHz) was more effective than higher ones (80 kHz and 150 kHz), indicating that mechanical effects, instead of free radicals, were responsible for the bio-activity enhancement. The optimal sonication conditions were sound frequency of 25 kHz, power density of 0.2 W/ml and duration of 30s; under which the sludge OUR increased by 28%, the bio-mass growth rate increased by 12.5%, and the wastewater chemical oxygen demand (COD) and total nitrogen removal efficiency increased by 5-6%.     

Wastewater Sludge Pre-treatment for Enhancing Entomotoxicity Produced by Bacillus thuringiensis var. kurstaki

Summary Wastewater sludge is a complex raw material for fermentation and requires pre-treatment in order to transform less biodegradable compounds into more easily degradable ones. In this study, sludge was treated by thermo-alkaline and oxidative pre-treatment methods and subjected to Bacillus thuringiensis fermentation in bench scale fermentors under controlled conditions. Thermo-alkaline treatment was found to be an effective process in order to enhance the entomotoxicity tested against spruce budworm. The total cell and spore counts were improved by 40 and 46%, respectively as compared to that using the untreated sludge. The final entomotoxicity potency increased from 12.3 × 10⁹ SBU/l of the raw sludge to 16.6 × 10⁹ SBU/l of the thermo-alkaline pre-treated sludge. The improvement of the process performance was attributed to a better oxygen transfer due to decrease in media viscosity and an improvement of nutrient availability due to the sludge solubilization and biodegradability.     

Effects of physico-chemical factors on the viscosity evolution of anaerobic granular sludge

The rheological properties of anaerobic granular sludge samples from four full-scale and one lab-scale anaerobic bioreactors were characterized by determining their “limit viscosity” values. These values were deducted from the evolution of the apparent viscosity of granular sludge samples (20 mL) at steady shear rate (200 s⁻¹) recorded using rotation tests with a wings type measurement cell stirrer Anton-Parr reference: ST24-1D/2V-Q0. The limit viscosity values depended on the applied shear rate, indicating a non-Newtonian behavior of the anaerobic granular sludge types investigated. The effect of variations of physico-chemical parameters such as pH (involving surface charge change), size, surface roughness and TSS content on the evolution of the limit viscosity of an anaerobic granular sludge suspension was investigated. This showed the importance of both quantitative (number of particles in a given volume) as well as qualitative (surface charge or shape) granule-granule interactions on this rheological parameter. Moreover, the origin of the granular sludge strongly influenced the limit viscosity value according with different granules characteristics. This work confirms the ability of the rheological parameter “limit viscosity” as an overall parameter to describe the physico-chemical characteristics (TSS, granulometry, origin, and charge) of anaerobic granular sludge and showed this holds for both sieved (500 μm) and unsieved sludges.     

Measurement of interfacial areas in aerobic fermentations by ultrasonic pulse transmission

The penetration of ultrasonic waves through opaque media and the large difference in the acoustic properties between air bubbles and the fermentation broth were used to measure the energy attenuation of pulsed ultrasound by the bubbles as the waves passed through the broth. This leads to an on-line determination of the specific interfacial area provided information is available about the holdup or bubble mean diameter. This article gives the principle of the method and demonstrates how the measured interfacial area may be used in evaluating the mass transfer coefficient of a fermentation system in a bubble column.     

Microwave, ultrasonic and chemo-mechanical pretreatments for enhancing methane potential of pulp mill wastewater treatment sludge

Microwave (2450 MHz, 1250 W), ultrasonic (20 kHz, 400 W) and chemo-mechanical (MicroSludge® with 900 mg/L NaOH followed by 83,000 kPa) pretreatments were applied to pulp mill waste sludge to enhance methane production and reduce digester sludge retention time. The effects of four variables (microwave temperature in a range of 50-175 °C) and sonication time (15-90 min), sludge type (primary or secondary) and digester temperature (mesophilic and thermophilic) were investigated. Microwave pretreatment proved to be the most effective, increasing specific methane yields of WAS samples by 90% compared to controls after 21 days of mesophilic digestion. Sonication solubilized the sludge samples better, but resulted in soluble non-biodegradable compounds. Based on the laboratory scale data, MicroSludge® was found the least energy intensive pretreatment followed by sonication for 15 min alternative with net energy profits of 1366 and 386 kWh/tonne of total solids (TS), respectively. Pretreatment benefits were smaller for thermophilic digesters.