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A novel on-line method and system for characterisation of sludge flocs in view of improving sludge dewatering has been developed. The characterisation of sludge flocs was carried out after the conditioning or the flocculation process. The system uses a conventional CCD-line scan camera providing an on-line monitoring of the relative floc size distribution by image processing procedures. The image processing procedure has been re-evaluated and adapted to the practical dewatering results, obtained from a chamber filter press of 250 x 250 mm size. A good correlation between the calculated sensor signal and the sludge dewaterability of digested sludge in terms of the up-concentration factor was found. Although different sludge compositions and flocculation systems have been tested within the whole experimental period of six months, a good reproducibility of this correlation was also found. A well balanced floc size distribution is necessary showing that not too many but still some fine flocs and also not too large but compact flocs lead to improved dewaterability. This has been illustrated by an extended range of floc size measurements ranging between 50 microm and 29 mm. The conditioning monitoring system would be suitable for the control of production of good size-balanced flocs to compensate fluctuations in sludge characteristics of the sludge to be conditioned.

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An ultrasound (US)-assisted bioprocess for wastewater treatment for the food industry was developed in a three years EC-funded project (FAIR CT-3259). An improvement of biological activity by US was successfully demonstrated with lab scale reactors [Schläfer et al. Ultrasonics 38 (2000)]. Now a pilot scale optimisation with a 200 l bioreactor was carried out in co-operation with the Department of Industrial Acoustics, Technical University of Denmark and RESON A/S (Denmark). Batch experiments have been performed by measuring the degradation rate of organic compounds of wastewater. The process parameters were kept constant while varying the US-intensity. A significant increase of biological activity could be obtained only in a very narrow range of US-intensity. Very low US-power leads to a decrease of degradation rate down to the standard value if there is no US-intake. Implementation of too high level of US lead to drastically decreasing of the biological activity to a level far below the Standard value if there is no US-intake. The optimisation of this narrow US-power window needs to be carried out carefully for every investigated bioprocess. The most important aspect of the experimental results was that a more than 100% increase of the maximum biological degradation rate has been achieved by US-transduction with an optimum US-intensity of 1.5 W/l wastewater at 25 kHz. The developed bioprocess reduces the overall energy by use of low-energy US-irradiation below the cavitation level. The US-assisted biological degradation process would be presented together with its optimisation and the economical calculation.

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The world-wide increasing environmental awareness and its subsequent regulations have led to the application of improved technologies in wastewater purification plants. This has resulted in higher wastewater and sludge productions. Sludge is the by-product of such plants and it is not only rich in organic carbon and pathogens but also in heavy metals and other environmental pollutants. In Europe, agricultural application of dried sludge (bio-solids) is confronted with negative reactions from the citizens, governmental organisations, farmers and the food industry. Ultrasonic disruption of sludge is a popular mechanical disruption process in sludge treatment. During ultrasonic treatment, high frequency acoustic signals are used to initiate the cavitation process. The applied ultrasonic field leads to a breakdown of cohesive forces of the liquid molecules resulting in the generation of cavitation bubbles. A shock wave is released by the collapse of the cavitation bubbles and propagates in the surrounding medium forming jet streams that cause the disruption of cells in sludge. Disruption of sludge cells enables the release of light organic substances into the sludge water thereby exposing them for further anaerobic digestion. This paper presents results on the disruption of conventionally stabilised sludge through the application of the ultrasonic field. In order to reduce the specific energy input (i.e. ratio of the consumed energy during ultrasonic disruption to the input sludge mass) and improve biogas production, the total solids content of the stabilised sludge was increased before disruption. The anaerobic digestion of sludge samples was carried out in a set of specially constructed laboratory anaerobic digesters. Results showed that subsequent anaerobic digestion of the ultrasonically disrupted sludge could improve biogas production with reduced sludge quantity that is vital to the economic consideration of the wastewater treatment plants. This process encourages the exploitation of valuable materials and energy from stabilised sewage sludge just before its final disposal. The negative effects of mixing disrupted sludge with its separated sludge water are also shown in this paper. This expresses the microbiological instability of the anaerobic process caused by the mixing process.

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To elucidate possible mechanisms of activity in medicinal plants containing flavonoids, the inhibitory potency of twenty flavones, flavonols, flavanones, phenylacrylic acids and various hydroxylated phenylacetic acids on the activity of neutral endopeptidase (NEP; EC 3.4.24.11), angiotensin-converting enzyme (ACE; EC 3.4.15.1) and aminopeptidase N (APN; EC 3.4.11.2) was investigated in vitro. The screening generally resulted that inhibition of these enzymes requires free hydroxyl groups at the flavone molecule. Flavone and methoxylated compounds (sinensetin) were without effects. Flavonoids with free hydroxyl functions in position 3',4' and 5,7 inhibited the activity of NEP (quercetin, luteolin, fisetin), with myricetin (IC50 = 42 microM) as strongest inhibitor. Inhibition of ACE and APN did not depend on this class of compounds and substitution pattern. E.g. 3,4-dihydroxyphenylacetic acid and 4-methylcatechol (urinary metabolites of flavonoids) also inhibited both APN and ACE activity, but not NEP activity. The results demonstrate that some of the pharmacological activities of flavonoids might be related to the inhibition of metallopeptidases responsible for the splitting of regulatory neuropeptides.

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The triterpene betulinic acid inhibits the activity of aminopeptidase N (EC 3.4.11.2) in a dose-dependent manner. An IC50 of 7.3 +/- 1.4 microM was determined for betulinic acid. This inhibitory activity is higher than that of bestatin' (IC50 = 16.9 +/- 4.1 microM), a well known inhibitor of this enzyme. The finding supports the idea that betulinic acid acts as anti-melanoma agent via inhibition of aminopeptidase N activity.

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The tolerance induction in mice to human serum albumin (HSA) and bovine gamma globulin (BGG) by combined injections of antigen and 6-mercaptopurine is studied. After pretreatment with antigen and mercaptopurine specific unresponsiveness or hyporesponsiveness are observed both in inbred (CBA) and outbred mice. Under the experimental protocol HSA is more tolerogenic than BGG. In CBA-mice tolerance to BGG was only found on the level of IgG-antibodies. The factors which influence the development of a drug-induced immunological unresponsiveness (mice strain, quality of antigen and antigen dosage) and the role of test system are discussed.

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