Azize Ayol

Aerobic and anaerobic bioprocessing of activated sludge: Floc disintegration by enzymes

Hydrolytic enzymes such as glucosidases, lipases, and proteases have an imperative function at the hydrolysis stage of complex organic structures in the degradation of biodegradable particulate organic matter. As a key factor, extracellular polymeric substances (EPS) control the extracellular hydrolytic enzymes in this degradation mechanism. A flocculated matrix of EPS bridging with bacteria holds back the dewaterability properties of the bioprocessed sludges. Disruption of the flocculated matrix leads to improved solubilization of sludge solids by attacking the hydrolytic enzymes to polymeric substances forming enzyme-substrate complexes. To determine the floc disintegration mechanisms by enzymes during aerobic and anaerobic bioprocessing of sludges, experimental data obtained from three aerobic digesters and three anaerobic digesters were evaluated. As part of a broader project examining the overall fate and effects of hydrolytic enzymes in biological sludge stabilization, this paper compares the performances of aerobic and anaerobic reactors used in this study and reports significant improvements in enzymatic treatment of activated sludge.

Fate and Effects of Fry-Drying Application on Municipal Dewatered Sludge

The present experimental investigation examined the applicability of fry-drying technology for municipal dewatered sludge by using waste engine oil for frying. The process was studied in a 100–180°C temperature range for 2 to 20 min frying times. The cakes were shaped in a diameter range of 1 to 3 cm with 3-cm-length prior to the frying. Experimental points were determined by the Box–Wilson experimental method. Statistical analysis was employed for determining the response function coefficients for variables. The response functions were as dry solids content (DS), volatile solids content (VS), and low heating value (LHV). Experimental and predicted results indicated good agreement with high correlation coefficients. The results showed that fry-drying is an alternative, fast process for sludge drying. In addition, it makes fry-dried sludge as a product with noteworthy LHV. This study provides further insight into the fry-drying of municipal dewatered sludges.

Rheological Characterization of Sludges during Belt Filtration Dewatering Using an Immobilization Cell

An immobilization cell was successfully coupled to a controlled stress rheometer to quantify rheological properties of a sludge during its dewatering. An anaerobically digested sludge and a synthetic sludge were analyzed and conditioned at various doses with a cationic flocculant. Direct strain-controlled oscillatory analyses could not be performed due to rapid dewatering, but controlled shear rate analysis quantified the increases in sludge viscosity as the solid’s concentration increased. Immobilization times determined by these experiments—viscosity versus dewatering time—agree with capillary suction times, since both indicate the time required for water removal ( r2 from 0.81 to 0.99). However, capillary suction time tests were more strongly influenced by filtrate viscosity at high polymer doses. The immobilization cell allowed quantified amounts of shear to be imposed during dewatering, with greater shearing found to provide more rapid immobilization. This finding is consistent with the design of bel...

Response Surface Methodological Approach for the Assessment of Thermal Drying of Dewatered Municipal Sludge

Thermal drying of dewatered municipal sludge was studied in the temperature range 50–180°C for different times from 10 to 120 min. The Box–Wilson response surface experimental method was used to investigate the effects of temperature and time on sludge drying. Statistical analysis using the methodology was employed to determine the response function coefficients for each variable: temperature and time. The response functions of the study were dry solids (DS) content, volatile solids (VS) content, and low heating value (LHV). Experimental and predicted results from the model indicated excellent agreements. Higher drying temperatures and time led to higher DS content. Higher temperatures increase the drying kinetics and longer drying times allow more time for water to evaporate. The elevated temperatures and time did not drastically change the VS content values. Only small-scale changes were observed regarding the increases in temperature and time. Higher shrinkage percentages were achieved via increased temperature and time. The drying kinetics exhibited increased drying rates depending on the decrease in water content. This study showed that the response surface methodology could be used as a tool for drying process optimization.

Gasification of yeast industry treatment plant sludge using downdraft Gasifier

Sludges produced in biological wastewater treatment plants have rich organic materials in their characteristics. Recent research studies have focused on the energy recovery from sludge due to its high organic content. The gasification process is a thermal conversion technology transforming the chemical energy contained in a solid fuel into thermal energy and electricity. The produced syngas as a mixture of CO, CH4, H2 and other gases can be used to generate electrical energy. The gasification of yeast industry sludge has been experimentally evaluated in a pilot scale downdraft-type gasifier as a route towards the energy recovery. The gasifier has 20 kg biomass/h fuel capacity. During gasification, the temperature achieved was more than 1,000°C in the gasifier, and then the syngas was transferred to the gas engine to yield the electricity. A load was connected to the grid box and approximately 1 kWh electrical power generation for 1 kg dry sludge was determined. The characteristics of residuals - ash, glassy material - were also analyzed. It was found that most of the heavy metals were fixed in the glassy material. Experimental results showed that the yeast industry sludge was an appropriate material for gasification studies and remarkable energy recovery was obtained in terms of power production by using syngas.