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Abstract

The factor which essentially affects sludge biodegradation rate is the degree of fluidization of insoluble organic polymers to the solved form, which is a precondition for availability of nutrients for microorganisms. The phases which substantially limit the rate of anaerobic decomposition include hydrolytic and methanogenic phase. Subjecting excess sludge to the process of initial disintegration substantially affects the effectiveness of the process of anaerobic stabilization. As a result of intensification of the process of hydrolysis, which manifests itself in the increase in the value and rate of generating volatile fatty acids (VFA), elongation of methanogenic phase of the process and increase in the degree of fermentation of modified sludge can be observed. Use of initial treatment of sewage sludge i.e. thermal disintegration is aimed at breaking microorganisms' cells and release of intracellular organic matter to the liquid phase. As a result of thermal hydrolysis in the sludge, the volatile fatty acids (VFA) are generated as early as at the stage of the process of conditioning. The obtained value of VFA determines the course of biological hydrolysis which is the first phase of anaerobic stabilization. The aim of the present study was to determine the effect of thermal disintegration of excess sludge on the effectiveness of the process of hydrolysis in anaerobic stabilization i.e. the rate of production of volatile fatty acids, changes in the level of chemical oxygen demand (COD) and increase in the degree of reduction in organic matter. During the first stage of the investigations, the most favourable conditions of thermal disintegration of excess sludge were identified using the temperatures of 50°C, 70°C, 90°C and heating times of 1.5 h - 6 h. The sludge was placed in laboratory flasks secured with a glass plug with liquid-column gauge and subjected to thermal treatment in water bath with shaker option. Another stage involved 8-day process of anaerobic stabilization of raw and thermally disintegrated excess sludge. Stabilization was carried out in mesophilic temperature regime i.e. at 37°C, under periodical conditions. In the case of the process of anaerobic stabilization of thermally disintegrated excess sludge at the temperature of 50°C and heating time of 6 h (mixture B) and 70°C and heating time of 4.5% (mixture C), the degree of fermentation of 30.67% and 33.63%, respectively, was obtained. For the studied sludge, i.e. mixture B and mixture C, maximal level of volatile fatty acids i.e. 874.29 mg CH3COOH/dm3 and 1131.43 mg CH3COOH/dm3 was found on the 2nd day of the process. The maximal obtained value of VFA was correlated on this day with maximal COD level, which was 1344 mg O2/dm3 for mixture B and 1778 mg O2/dm3 for mixture C.
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Abstract

The paper presents the investigations aimed at the determination of the effect of time and wavelength of ultrasound field on the value of capillary suction time (CST), sludge thickening and dry matter of the excess sludge subjected to the process of stabilization. The investigations were carried out on the excess sludge which comes from communal waste treatment plant. The sludge was exposed to ultrasound field, using ultrasound generator with power of 1500 W, frequency of 20 kHz and amplitude 39.42 μm (which corresponded to the amplitude of 100%). Sonication of the sludge was carried out for different amplitudes and sonication times. The non-conditioned sludge and the sludge initially conditioned with ultrasound field were subjected to the process of stabilization in laboratory flasks (V = 0.5 dm3) for the period of 10 days. On each day, sludge thickening and dewatering capacities were determined. The sludge subjected to the effect of ultrasound field exhibited elevated levels of CST. However, the sonication time had positive effect on the increase in the degree of thickening for each of the amplitudes studied. Also, the process of stabilization positively affected final thickening and dewatering of the sludge.
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Abstract

The study was undertaken to determine the effect of continuation or changes of the diet on the morphometry and histomorphometry of bone in male and female Wistar rats with experimen- tally induced obesity by high energetic diet. Sixty-four 90-day-old Wistar rats obtained from obese parents (16 male, 16 female) and control parents (16 male, 16 female) were used in this study. After 21 days of the baby period, rats were divided into four groups: obese rats fed with high energy feed (F/F), control rats fed with a standard diet (C/C), obese rats with changed diet from high energy diet to control diet (F/C) and control rats with changed diet from control diet to high energy diet (C/F). After 90 days of experimental feeding, the rats were sacrificed. Thereafter, body weight and the isolated humerus were measured and next, the histological stainings and counts were done. Our results revealed that change in the parent’s diet from F to C in the female leads to increased bone growth length and reduction of body weight in female and male. Reverse diet changes (from C to F) lead to decreased bone length only in the female. Moreover, the con- tinuation by offspring of both sexes with a high-energy diet contributes to a reduction in osteo- cytes, reduction in bone marrow cavity and cortical expansion, but a change in nutrition from parents’ standard diet to high-energy diet leads to increase in osteocytes dimensions. The contin- uation of feeding with F diet promotes the accumulation of adipocytes in the bone marrow in female and male, and correction of nutrition from F to standard diet leads to a reduction in their number in the bone marrow compared to groups continuing feeding with high-energy diet.
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