Rheology of a primary and secondary sewage sludge mixture: Dependency on temperature and solid concentration

The main objective of this study was to investigate the rheology of mixed primary and secondary sludge and its dependency on solid content and temperature. Results of this study showed that the temperature and solid concentration are critical parameters affecting the mixed sludge rheology. It was found that the yield stress increases with an increase in the sludge solid content and decreases with increasing temperature. The rheological behaviour of sludges was modelled using the Herschel-Bulkley model. The results of the model showed a good agreement with experimental data. Depending on the total solid content, the average error varied between 3.25% and 6.22%

A kinetic model of municipal sludge degradation during non-catalytic wet oxidation

Wet oxidation is a successful process for the treatment of municipal sludge. In addition, the resulting effluent from wet oxidation is a useful carbon source for subsequent biological nutrient removal processes in wastewater treatment. Owing to limitations with current kinetic models, this study produced a kinetic model which predicts the concentrations of key intermediate components during wet oxidation. The model was regressed from lab-scale experiments and then subsequently validated using data from a wet oxidation pilot plant. The model was shown to be accurate in predicting the concentrations of each component, and produced good results when applied to a plant 500 times larger in size. A statistical study was undertaken to investigate the validity of the regressed model parameters. Finally the usefulness of the model was demonstrated by suggesting optimum operating conditions such that volatile fatty acids were maximised

A review of wet air oxidation and thermal hydrolysistechnologies in sludge treatment

With rapid world population growth and strict environmental regulations, increasingly large volumes of sludge are being produced in today's wastewater treatment plants (WWTP) with limited disposal routes. Sludge treatment has become an essential process in WWTP, representing 50% of operational costs. Sludge destruction and resource recovery technologies are therefore of great ongoing interest. Hydrothermal processing uses unique characteristics of water at elevated temperatures and pressures to deconstruct organic and inorganic components of sludge. It can be broadly categorized into wet oxidation (oxidative) and thermal hydrolysis (non-oxidative). While wet air oxidation (WAO) can be used for the final sludge destruction and also potentially producing industrially useful by-products such as acetic acid, thermal hydrolysis (TH) is mainly used as a pre-treatment method to improve the efficiency of anaerobic digestion. This paper reviews current hydrothermal technologies, roles of wet air oxidation and thermal hydrolysis in sludge treatment, and challenges faced by these technologies

Analysis of biological wastewater treatment processes using multicomponent gas phase mass balancing

A reactor system using off-gas analysis was developed for analyzing wastewater treatment process reactions. Using a mass spectrometer for the gas analysis provides the ability to simultaneously measure several gas components (such as oxygen, nitrogen, carbon dioxide, and argon). One of the benefits of the reactor design was the precise control of the dissolved oxygen concentration, uncoupled from the system turbulence, which was controlled via a gas recycle loop. This feature allowed control of the turbulence within the reactor without any need for mechanical stirring. Using oxygen as the test gas, the reactor was shown to perform well in the measurement of oxygen uptake rate of nitrifying activated sludge. The oxygen uptake rate calculations were made using a simple calibration method developed for the reactor system. The reactor was able to provide precise and accurate results for this test case. Furthermore, the system was capable of measuring under dynamic process conditions, as well as when the process rates were constant (steady state). (C) 2001 John Wiley & Sons, Inc

Fungal based SBR: a Model Investigation in an Open Culture on the removal of glucose and on the effect of toxic compounds on the biomass

An investigation was performed to explore the capabilities of a filamentous fungus – Trichoderma viride, strain 8/90 - to aseptically grow in a glucose-fed Sequencing Batch Reactor system in extreme environmental conditions (pH 3.5). Microscopic investigations were carried out to assess fungal dominance in the open culture. Batch tests were carried out to characterize the ability of the biomass to resist to toxic shocks, in which gallic acid was dosed. The fungus showed a significant ability to grow and to remove all the organic load at the adopted feeding rate (2000 mgGlucose/l/d), attaining high biomass yields. Furthermore, it showed to be able to resist to concentrated (1 g L-1) gallic acid even though the biomass had not been exposed to it before. Further, the microbial biomass (about 2.5 gVSS L-1) was able to completely remove gallic acid in aerobic conditions in a timeframe of 12 h

Performance of a fungal based SBR under pH extreme and shock phenolic exposure

An investigation was performed to explore the capabilities of a filamentous fungal biomass to grow non-aseptically in a glucose-fed Sequencing Batch Reactor system in very extreme environment (pH 3.5) conditions. Trichoderma viride Pers: Fr. Isolate 8/90 was used as inoculum. Microscopic investigations were carried out to confirm fungal dominance in the open culture. In batch tests, the fungal biomass showed a significant ability to grow and remove the applied organic load (2000 mgGlucose/L d), with high biomass yields. Furthermore, the biomass showed an ability to resist gallic acid toxicity at high concentrations (1 g/L) without any pre-exposure acclimation of the biomass. The biomass (about 2.5 gVSS/l) demonstrated significant aerobic removal of gallic acid in a timeframe of 20 h from initial exposure. The robust characteristics of this SBR system demonstrate potential for future development of fungal based treatment for recalcitrant feedstocks or operation under extreme environmental conditions

Rheological characteristics of a mixture of primary and secondary municipal sludge

Municipal wastewater sludges are complex fluids displaying non-Newtonian characteristics. Whilst rheological properties of sludges are very important for the design and operation of wastewater treatment facilities, there is a lack of information regarding these properties, particularly for mixtures of primary and secondary sludges. The rheology of wastewater treatment sludge has been widely studied but most of the literature has concentrated on secondary or digested sludges alone. Therefore, the current study aimed to investigate the rheology of mixed primary and secondary sludge. A mixed sludge containing 40 % primary and 60 % secondary sludges, were collected from Rotorua wastewater treatment plant, Rotorua, New Zealand. The sludge was diluted to total solid contents of 4.3, 7.3 and 9.8 %, and the rheological properties were measured at different temperature. Results showed that the temperature and solid concentration are critical parameters affecting the mixed sludge rheology. It was found that the yield stress increases with an increase in the sludge solid content and decreases with increasing temperature

Model Investigation of Fungal Activity on a Synthetic Biorecalcitrant Wastewater

The remediation of those effluents containing pollutants which are hard to be metabolized (biorecalcitrant) is becoming an increasingly important enviromental problem, due to the complex nature of many wastewaters. An example is the class of polyphenols. In this work, the capability of the fungus Trihcoderma viride to act as bioremediation agent for the treatment of a synthetic wastewater containing glucose, acetic acid and gallic acid (chosen as phenolic model pollutant) was characterized. The investigation was carried out in a Sequencing Batch Reactor (SBR) with a Hydraulic Retention Time of 5 d. No settling phase was operated as this work is intended to be only a model study focused on the metabolic biomass performance (i.e., the removal of pollutant from the liquor). After few days, the organic load was completely removed, including the depletion of gallic acid from the medium. Furthermore, a 0.57 yield (C- mmol based) was achieved, thus indicating the absence of inhibition phenomena