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 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

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

Removal of hexavalent chromium-contaminated water and wastewater: A review

Cr(VI) is a well-known highly toxic metal, considered a priority pollutant. Industrial sources of Cr(VI) include leather tanning, cooling tower blowdown, plating, electroplating, anodizing baths, rinse waters, etc. This article includes a survey of removal techniques for Cr(VI)-contaminated aqueous solutions. A particular focus is given to adsorption, membrane filtration, ion exchange, and electrochemical treatment methods. The primary objective of this article is to provide recent information about the most widely used techniques for Cr(VI) removal

TiO 2/Al 2O 3 membrane reactor equipped with a methanol recovery unit to produce palm oil biodiesel

In this study, the central composite design of the response surface methodology was employed to investigate the effects of reaction temperature, catalyst concentration and cross flow circulation velocity on the production of biodiesel in a TiO 2/Al 2O 3 membrane reactor. High-quality palm oil biodiesel was produced by combination of alkali transesterification and separation processes in the ceramic membrane reactor. The optimum conditions for the conversion of palm oil to biodiesel in the ceramic membrane reactor were as follows: 70°C reaction temperature, 1.12wt catalyst concentration and 0.211cms - 1 cross flow circulation velocity. The physical and chemical properties of the produced biodiesel were determined and compared with the standard specifications. © 2010 John Wiley & Sons, Ltd

Viscosities and densities of binary and ternary blends of palm oil plus palm biodiesel plus diesel fuel at different temperatures

Vegetable oil-based fuels are promising alternative fuels for diesel engines because of their environmental and strategic advantages. In this work, binary and ternary blends of palm oil, biodiesel, and diesel fuel were prepared, and dynamic viscosities and densities of blends were measured as functions of temperature. The binary and tertiary blends demonstrate a temperature-dependent behavior, and viscosities and densities decreased nonlinearly and linearly with temperature, respectively. The evaluation of the measured viscosities of binary and tertiary blends was completed, and the hest correlation was obtained by a polynomial regression

Rheological characterisation of biologically treated and non-treated putrescible food waste

Food waste is gaining increasing attention worldwide due to growing concerns over its environmental and economic costs. Understanding the rheological behaviour of food waste is critical for effective processing so rheological measurements were carried out for different food waste compositions at 25, 35 and 45 °C. Food waste samples of various origins (carbohydrates, vegetables and fruits, and meat), anaerobically digested and diluted samples were used in this study. The results showed that food waste exhibits shear-thinning flow behaviour and viscosity of food waste is a function of temperature and composition. The composition of food waste affected the flow properties. Viscosity decreased at a given temperature as the proportion of carbohydrate increased. This may be due to the high water content of vegetable & fruits as the total solids fraction is likely to be a key controlling factor of the rheology. The Herschel-Bulkley model was used successfully to model food waste flow behaviour. Also, a higher strain was needed to break down the structure of the food waste as digestion time increased

A packed bed membrane reactor for production of biodiesel using activated carbon supported catalyst

In this study, a novel continuous reactor has been developed to produce high quality methyl esters (biodiesel) from palm oil. A microporous TiO2/Al2O3 membrane was packed with potassium hydroxide catalyst supported on palm shell activated carbon. The central composite design (CCD) of response surface methodology (RSM) was employed to investigate the effects of reaction temperature, catalyst amount and cross flow circulation velocity on the production of biodiesel in the packed bed membrane reactor. The highest conversion of palm oil to biodiesel in the reactor was obtained at 70 degrees C employing 157.04 g catalyst per unit volume of the reactor and 0.21 cm/s cross flow circulation velocity. The physical and chemical properties of the produced biodiesel were determined and compared with the standard specifications. High quality palm oil biodiesel was produced by combination of heterogeneous alkali transesterification and separation processes in the packed bed membrane reactor. (C) 2010 Elsevier Ltd. All rights reserved

Rheological Characterization Of Thermal Hydrolysed Waste Activated Sludge

Rheological properties are important in the design and operation of sludge-handling process. Despite this, the rheology of sludge in thermal hydrolysis processes (TH) is not well described. In-situ measurements were performed to characterize the flow behaviour of various concentrations (7-13 wt%) of waste activated sludge (WAS) at TH conditions. Equations were presented for predicting in situ rheological parameters (high-shear viscosity, eta(infinity,i), consistency index, k(i), and yield stress, sigma(c,i)) under various treatment conditions, which are useful for design of process units. The equations enable convenient estimation of in-situ properties based on ambient rheological measurements. Results suggested that the proportion of sludge solubilization and its rate were unaffected by varying sludge concentration. Thermally treated sludge still exhibited gel-like, viscoelastic characteristics similar to untreated sludge; however, the storage (G') and loss (G '') moduli decreased with higher treatment temperatures. Frequency and creep responses were described by a fractional derivatives Kelvin-Voigt (FKV) model, which showed increasing viscous characteristics of treated sludge. These equations can be utilised in CFD models. Results obtained from oscillatory measurements can also approximate steady-shear behaviour by comparing dynamic viscosity, eta'(omega), and steady-shear viscosity, eta(gamma'), whose values were very similar. This enables convenient estimation of steady-shear behaviour of sludge from oscillatory measurements, which is found to be a non-destructive technique for measuring flow behaviour of highly concentrated sludge. Yield stress can also be predicted from the product of modified Cox-Merz shift factors and storage modulus (G'). Practical engineering implications of the rheological observations were discussed