An accurate and robust method for intensification of wastewater sludge pipe flow.

Globally, environmental impacts and population growth are driving the process intensification of wastewater treatment plants (WWTPs) via transition from conventional (2-3 wt% solids) to highly concentrated (4-6 wt% solids) wastewater sludges (HCWS). This presents an industrial challenge as HCWS are complex, non-Newtonian materials whose viscosity increases nonlinearly with solids concentration. This viscosity increase is particularly relevant for sludge pipe flow as it leads to considerable pumping pressure that ultimately limits the feasibility of pipe flow transportation.

Process modelling and techno-economic analysis of anaerobic digestion of sewage sludge integrated with wet oxidation using a gravity pressure vessel and thermal hydrolysis.

Anaerobic digestion (AD) of sewage sludge is used to biodegrade sewage sludge into biomethane and digestate. With the addition of thermal processes such as thermal hydrolysis (TH) and wet oxidation (WO), AD biodegradability generally improves. Implementation of additional treatment is challenging due to the limitation in the mass and energy balances.

Impact of volatile solids destruction on the shear and solid-liquid separation behaviour of anaerobic digested sludge.

Systematic and comprehensive characterisation of shear and solid-liquid separation properties of sludge across a wide range of solids concentration and volatile solids destruction (VSD) is critical for design and optimization of the anaerobic digestion process. In addition, there is a need for studies at the psychrophilic temperature range as many unheated anaerobic digestion processes are operated under ambient conditions with minimal self-heating. In this study, two digesters were operated at different combinations of operating temperature (15-25 °C) and hydraulic retention time (16-32 d) to ensure a wide range of VSD in the range of 0.

Arsenic immobilization in soil affected by mining waste using waste-derived functional hydrochar and iron-encapsulated materials.

Arsenic (As) contamination is a widespread problem. Continued and concerted effort in exploring sustainable remediation strategies is required, with in situ immobilization emerging as a promising option. This work valorized a waste by-product from olive (Olea europaea L.

Shear and solid-liquid separation behaviour of anaerobic digested sludge across a broad range of solids concentrations.

Due to the non-homogeneous and multiphase nature of anaerobic lagoon constituents, CFD modelling for process optimisation requires continuous functions for shear and solid-liquid separation properties across a large range of solids concentrations. Unfortunately, measurement of existing material properties of anaerobic sludges is limited to only shear or solid-liquid separation, or to a limited solids concentration. In this work, the shear properties of an anaerobic sludge were measured from 0.

Formation mechanisms and mechanical properties of anaerobic lagoon scum.

The formation of a floating scum layer on the liquid surface of covered anaerobic lagoons prevents optimal and efficient lagoon operation. Scum can reduce hydraulic retention time, inhibit biogas capture and cause damage to lagoon covers. Managing the negative impact of scum requires understanding what scum is, how it forms and how it consolidates.

Characterising sedimentation velocity of primary waste water solids and effluents.

Sedimentation in waste water is a heavily studied topic, but mainly focused on hindered and compression settling in secondary sludge, a largely monodispersed solids, where bulk sedimentation velocity is effectively described by functions such as double Vesilind (Takacs). However, many waste water solids, including primary sludge and anaerobic digester effluent are polydispersed, for which application of velocity functions is not well understood. These systems are also subject to large concentration gradients, and poor availability of settling velocity functions has limited design and computational fluid dynamic (CFD) analysis of these units.

Revealing the mechanisms for potassium ferrate affecting methane production from anaerobic digestion of waste activated sludge.

This study investigated the issue of potassium ferrate (PF) affecting anaerobic methane generation from sludge by a set of experimental and model analyses. Experimental results indicated that the methane production was significantly promoted from 164.7 to 204.

Constitutive modelling and pipeline flow of thixotropic viscoplastic wastewater sludge.

Due to the inherent rheological complexity of wastewater sludges, conventional sludge pipeline design based on simplified rheological models can result in inefficient sludge transportation systems. These inefficiencies are further exacerbated by a global need for the processing of more concentrated wastewater sludges that have a more pronounced non-Newtonian character, and hence require greater energy for transportation. However, the complex rheology of these materials (typically visco-elastic and thixotropic) requires sophisticated methods for constitutive modelling that are impractical to implement for complex materials such as sewerage sludges.

Impact of methodological artifact on digested sludge flow curve measurement.

Inconsistent experimental procedures have been used to characterize sludge rheology in literature. This often has resulted in proposing different rheological models for sludge as well as non-comparable data. Any collected rheological data needs to be interpreted considering the methodology used for its collection because otherwise they cannot be used by engineers for design and troubleshooting.

Synergy of combined free nitrous acid and Fenton technology in enhancing anaerobic digestion of actual sewage waste activated sludge.

In this study, actual swage waste activated sludge in batch reactors was employed to assess the synergistic effect of free nitrous acid and Fenton pre-treatments on enhancing methane production in the anaerobic digestion process. In addition to methane enhancement, the mechanisms driving the enhancement were also investigated via measuring enzymes activity and solubilisation of organic matter. This study revealed that the combined pre-treatments solubilised organic matter significantly more than the bioreactors pre-treated with individual FNA and Fenton.

Comparison of mesophilic and thermophilic methane production potential of acids rich and high-strength landfill leachate at different initial organic loadings and food to inoculum ratios.

Landfill leachate (LL), which can contaminate both ground and surface water is a major global environmental issue. The aim of the present study was to investigate the biomethane potential (BMP) of a high-strength LL with low pH (5.0), high solids concentration (16%), and high organic matter (170 g/L of chemical oxygen demand (COD); 55 g/L of volatile fatty acids (VFA)) with ammonia nitrogen (NH-N) (17 g/L).

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.

Improvement of anaerobic digestion of sewage mixed sludge using free nitrous acid and Fenton pre-treatment.

Background: Recently, it has been indicated that free nitrous acid (FNA) and Fenton pre-treatment of waste activated sludge can enhance methane production in anaerobic digestion of waste activated sludge. In addition, it has been revealed that the substances used in these pre-treatments are both eco-friendly and economically attractive because not only are they produced in anaerobic digestion, but they are also low priced. Since primary sludge and waste activated sludge are mixed prior to anaerobic digestion in the majority of wastewater treatment plants, this study aims to assess the influence of combined FNA and Fenton on the anaerobic digestion of mixed sludge.

Impact of gas injection on physicochemical properties of waste activated sludge: A linear relationship between the change of viscoelastic properties and the change of other physiochemical properties.

Aeration process in the waste activated sludge treatment accounts for 75% of total energy consumption of the treatment plant. The main purpose of the aeration process is to enhance the biodegradation of the liquid waste. Gas bubbles, rising through the liquid, improves mixing, reduces inhomogeneities in the treatment tank and enhances biological reactions.

Control of the mixing time in vessels agitated by submerged recirculating jets.

Submerged recirculating jet mixing systems are an efficient and economical method of agitating large tanks with a high hydraulic residence time. Much work has been carried out in developing design correlations to aid the predictions of the mixing time in such systems, with the first such correlation being developed nearly 70 years ago. In most of these correlations, the mixing time depends directly on the volume of the vessel and inversely on the injection velocity of the submerged jet.

Influence of gas injection on viscous and viscoelastic properties of Xanthan gum.

Xanthan gum is widely used as a model fluid for sludge to mimic the rheological behaviour under various conditions including impact of gas injection in sludge. However, there is no study to show the influence of gas injection on rheological properties of xanthan gum specifically at the concentrations at which it is used as a model fluid for sludge with solids concentration above 2%. In this paper, the rheological properties of aqueous xanthan gum solutions at different concentrations were measured over a range of gas injection flow rates.

A study of gas emissions during the firing process from bricks incorporating biosolids.

This paper investigates the five different gas emissions during the firing process of clay bricks and bricks incorporating biosolids. In this study, three different biosolids produced at the Western Treatment Plant and Eastern Treatment Plant, Melbourne, were used as an alternative raw material to the conventional brick soil to produce bricks. Three sets of bricks were manufactured incorporating 25% of biosolids by weight.

Evaluation of single and two stage anaerobic digestion of landfill leachate: Effect of pH and initial organic loading rate on volatile fatty acid (VFA) and biogas production.

This work aims to evaluate the impact of pH and initial organic load (IOL) in terms of Chemical Oxygen Demand (COD) of landfill leachate for the production of value added products during single and two stage anaerobic digestion (AD). It was observed that at an optimal IOL of 48 g/L, acetic acid was dominant at pH 5.5 whereas it was butyric acid at pH of 5.

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 & fruits, and meat), anaerobically digested and diluted samples were used in this study.

Comparison between classical Kelvin-Voigt and fractional derivative Kelvin-Voigt models in prediction of linear viscoelastic behaviour of waste activated sludge.

Appropriate sewage sludge rheological models are essential for computational fluid dynamic simulation of wastewater treatment processes, in particular aerobic and anaerobic digestions. The liquid-like behaviour of sludge is well documented but the solid-like behaviour remains poorly described despite its importance for dead-zone formation. In this study, classical Kelvin-Voigt model, commonly used for sludge in literature, were compared with fractional derivative Kelvin-Voigt model regarding their predictive ability for describing the solid-like behaviour.

Evaluation of thermal hydrolysis efficiency of mechanically dewatered sewage sludge via rheological measurement.

In this study, laboratory tests of both low temperature (60-90 °C) and high temperature (120-180 °C) thermal hydrolysis (LTHP and HTHP) were performed on mechanically dewatered high-solid sludges (at total solid of 14.2 wt% and 18.2 wt%) to evaluate the extent of organic solubilization through rheological measurements.

Impact of gas injection on the apparent viscosity and viscoelastic property of waste activated sewage sludge.

Gas injection is known to play a major role on the particle size of the sludge, the oxygen transfer rate, as well as the mixing efficiency of membrane bioreactors and aeration basins in the waste water treatment plants. The rheological characteristics of sludge are closely related to the particle size of the sludge floc. However, particle size of sludge floc depends partly on the shear induced in the sludge and partly on physico-chemical nature of the sludge.

Rheological measurements as a tool for monitoring the performance of high pressure and high temperature treatment of sewage sludge.

Hydrothermal processing plays a significant role in sewage sludge treatment. However, the rheological behaviour of sludge during these processes is not fully understood. A better understanding of the sludge rheology under hydrothermal processing conditions can help improve process efficiency.