Nicky Eshtiaghi

Nicky Eshtiaghi
RMIT University | RMIT · School of Chemical, and Environmental Engineering

PhD in Chemical Engineering, FIEAust, FHEA CPEng, NER

About

127
Publications
50,269
Reads
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2,617
Citations
Additional affiliations
January 2018 - present
RMIT University
Position
  • Professor (Associate)
January 2014 - December 2017
RMIT University
Position
  • Professor (Associate)
January 2010 - December 2013
RMIT University
Position
  • Lecturer

Publications

Publications (127)
Article
Full-text available
Sustainable sludge management is becoming a major issue for wastewater treatment plants due to increasing urban populations and tightening environmental regulations for conventional sludge disposal methods. To address this problem, a good understanding of sludge behaviour is vital to improve and optimize the current state of wastewater treatment op...
Article
Full-text available
The elastic rheological properties of sludge are complex and evolve with time as a result of ageing and microbial activity. Due to the peculiar nature of sludge, this makes the measurement of physical parameters difficul. The challenge is to identify a reference material that can be used as a proxy for industrial process design or optimization. In...
Article
Full-text available
Optimising flow processes in wastewater treatment plants requires that designers and operators take into account the flow properties of the sludge. Moreover, due to increasingly more stringent conditions on final disposal avenues such as landfill, composting, incineration etc., practitioners need to produce safer sludge in smaller quantities. Anaer...
Article
Full-text available
Globally, wastewater treatment plants are under pressure to handle high concentration sludge in a sludge treatment line. Unawareness of the non-Newtonian behaviour of the thickened sludge has the potential to cause unexpected problems when the fluid behaviour changes from turbulent to laminar flow. In this study, sludge apparent viscosity was plott...
Article
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Liquid marbles are micro reservoirs of fluid surrounded by a powder shell. Their unique properties show promise for high-value technological applications in the medical, biotechnology, chemical and pharmaceutical industries. In this study, liquid marbles were prepared from six mixtures of water and glycerol by releasing droplets from different heig...
Article
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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 she...
Article
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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....
Article
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 diges...
Article
Increasing volume of Food waste (FW) and cardboard (CB) which are the two major fractions of municipal solid waste increases environmental concerns. This study evaluated the performance of a pilot-scale auto-fed continuous stirred tank reactor (CSTR) system for the solid-state anaerobic co-digestion (ACoD) of acetic acid rich food waste (FW) and ca...
Article
The aim of the present work is to investigate the impact of acetic acid assisted ultrasound pre-treatment of food waste (FW) and cardboard (CB) to overcome the barriers of substrate characteristics. Anaerobic co-digestion (ACoD) experiments were conducted with FW and CB in the mixing ratios of 100:0, 80:20, 60:40 and 50:50 at a food to inoculum (F/...
Article
Full-text available
The datasets included in this paper provide periodically measured physico-chemical and rheological properties of mesophilic batch anaerobic digesters’ content for 30 days biochemical methane potential tests (BMP). Waste activated sludge (WAS) and primary sludge (PS) were the main substrates and digested sludge from a large scale mesophilic anaerobi...
Article
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 204.1 mL/g VSS (volatile suspended solids) with PF dosage enhanced from 0 to 0.05 g/g TSS (tot...
Article
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...
Article
Liquid-liquid extraction of volatile fatty acids (VFA) from landfill leachate (LL) as well as synthetic solution (SS) whose concentration varied from 0.2 – 1 mol/L was investigated. The impact of extractant and feed VFA concentration on extraction efficiency (EE), distribution ratio (KD) and loading ratio (z) with the help of statistical analysis a...
Article
Full-text available
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 us...
Article
Rheology is known to have an impact on the performance of digesters, but the effect of additional substrates (co-digestion) is poorly understood. The main objective of this study was to investigate the effects of the addition of cellulose, protein and lipids to substrates on the rheological behaviour and biogas production of the mixture of primary...
Article
The relationship between rheological properties and the hydrolysis rate in anaerobic digestion (AD) is poorly understood. This study investigated AD of waste-activated sludge (WAS) in batch digesters of 2.10%, 3.40%, 4.10%, and 5.02%TS digester media (WAS mixed with inoculum). The digesters operated below ammonia inhibition levels and at the same f...
Article
Full-text available
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...
Article
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 volati...
Article
Full-text available
Bubble columns are intensively used in many different industries as multiphase contactors. The gas phase properties in the bubble column significantly impact on the hydrodynamics of the column which effects on heat and mass transfer rates within the column. In this paper, electrical resistance tomography together with dynamic gas disengagement tech...
Article
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Process intensification of agitated slurry vessels requires improving solid-liquid mass transfer beyond that can be achieved with agitation alone. As ultrasound has been shown to enhance solid-liquid mass transfer, this study aims to investigate whether process intensification can be achieved under combined (agitation + ultrasonic irradiation) cond...
Article
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....
Article
Full-text available
Millions of tonnes of leftover biosolids are increasingly stockpiled every year around the globe. Biosolids are a product of the wastewater sludge treatment process. Stockpiles necessitate the use of large areas of increasingly valuable land. Biosolids have many beneficial uses and are currently utilised in agricultural and land rehabilitation appl...
Article
Mesophilic batch anaerobic digesters fed by different substrates were set up to identify the role of substrate rheology in anaerobic digestion performance while operating below the toxic level. Five substrates of different rheological behaviour but at the same amount of organic matters were prepared by addition of different amount of an inert mater...
Article
Full-text available
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 o...
Article
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 re...
Article
Computational fluid dynamic (CFD) models were employed to investigate flow conditions inside a model reactor in which yield stress non‐Newtonian liquid is mobilized using submerged recirculating jets. The simulations results were found to agree well with the experimental results of active volume in 0.19 m diameter reactor obtained using flow visual...
Article
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...
Article
Sludge pumps in wastewater treatment plants are often oversized due to uncertainty in calculation of pressure drop. This issue costs millions of dollars for industry to purchase and operate the oversized pumps. Besides costs, higher electricity consumption is associated with extra CO2emission which creates huge environmental impacts. Calculation of...
Article
Liquid jet mixing is a common practice in industry when mechanical mixing becomes unfeasible due to the scale of mixing vessel required. The present study employed a flow visualization technique to investigate the agitation of a non-Newtonian fluid (0.5 wt% xanthan gum solution) using a submerged recirculating jet. Building on the work already publ...
Article
Full-text available
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...
Article
Full-text available
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 t...
Article
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. Thre...
Article
Inadequate mixing in anaerobic digesters fitted with gas sparging systems is caused by many factors, and leads to dead zones where sludge remains stagnant. The present study explores a range of gas sparging configurations that can be implemented to maximize active volume, and validates electrical resistance tomography (ERT) as an effective measurem...
Article
Process intensification of sonochemical reactions due to the addition of solids is studied using very high solids concentrations (up to 0.5 (v/v)). The impacts of particle size, surface roughness, and solids concentration on sonochemical yields were studied experimentally by measuring the concentration of I3⁻ formed in the cavitation of potassium i...
Article
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 origi...
Article
This paper provides experimental evidence supporting the idea that the transition to turbulent flow is governed by the ratio of the specific power input (SPI) and the term G/λ, where G is the viscoelastic modulus of the liquid and λ is the relaxation time, in a vessel containing a fluid agitated by sparged gas (air) at low superficial gas velocitie...
Article
Full-text available
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...
Article
In this study, we examined the efficiency of mixing due to liquid jets in a model anaerobic digester. Xanthan Gum Keltrol T (XGKT) solution which is transparent and has similar rheological characteristics to those of digested sludge was selected as the model liquid. Experiments were carried out using 0.15 and 0.4. wt% XGKT solutions. Four different...
Article
We provide experimental demonstration that the spread of tracer elements in a tank containing a viscoelastic liquid and agitated by a submerged jet pointing to the base of the tank can be influenced by the relaxation time of the liquid. We analyzed the temporal spreading of the boundary of a tracer-front in two dimensions using flow visualization a...
Article
The effects of high volumetric solids concentration (CV), impeller type, and baffles on the impeller power input required for solids suspension and dispersion, and the solid-liquid mass transfer coefficient (kSL) were studied in this work using an agitated vessel with dual impellers for the purpose of process intensification. It was found that at C...
Article
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. The effects of treatment temp...
Article
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 s...
Article
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. Moreover, sludge rheology is easier to measure than chem...
Article
Full-text available
In a wastewater treatment process, energy is mainly used in sludge handling and heating, while energy is recovered by biogas production in anaerobic digestion process. Thermal pre-treatment of sludge can change the energy balance in a wastewater treatment process since it reduces the viscosity and yield stress of sludge and increases the biogas pro...
Article
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A biofilm developed on polyurethane packing in a trickle bed bioreactor was used to effectively remove formaldehyde from contaminated air. Formaldehyde removal depended on the retention time of the gas in the bed as well as on the gas-liquid mass transfer coefficient. Both retention time and the mass transfer coefficient depended on the gas flow ra...
Article
The extensive amount of available information on global warming suggests that this issue has become prevalent worldwide. Majority of countries have issued laws and policies in response to this concern by requiring their industrial sectors to reduce greenhouse gas emissions, such as CO2. Thus, introducing new and more effective treatment methods, su...
Article
Compositional change in sewage sludge due to thermal treatment drives rheological changes in the sludge. In this study, the viscoelastic characteristics of waste activated sludge (WAS) was investigated by measuring viscoelastic properties of sludge, the storage (G′) and loss (G″) moduli over 1 h thermal treatment at different temperatures ranging f...
Conference Paper
Full-text available
Sludge exhibits different flow properties at different concentration, temperature and pressure. Knowledge of real time sludge rheology is extremely important for the efficient and optimised operation of sludge treatment process. The aeration in activated sludge process has a significant influence on fluid properties and which in turn influences mas...
Article
This study employs electrical resistance tomography and flow visualisation techniques to monitor the spread of a tracer in a vessel containing complex non-Newtonian media agitated using submerged recirculating liquid jets. The experimental media are aqueous solutions of xanthan gum with varying concentrations. One of the solutions posses a yield st...
Article
In anaerobic digesters operated in a municipal wastewater plant, submerged recirculating jet streams are often used for the purpose of agitating sludge. However, due to the complex rheology of the sludge, large portions of the digester can remain stagnant and the stagnant volume changes slowly with time. The rate of change varies with time which is...
Article
Full-text available
We report a simple method for on-demand continuous processing of composite liquid marbles with the aid of a 3D printed slide platform, which offers the potential for engineering novel functional surfaces for the production of combination drug therapies, particle-based barcode biomarkers and smart membranes, among other applications. Unlike other at...
Article
Predicting the flow behaviour, most notably, the apparent viscosity and yield stress of sludge mixtures inside the anaerobic digester is essential because it helps optimize the mixing system in digesters. This paper investigates the rheology of sludge mixtures as a function of digested sludge volume fraction. Sludge mixtures exhibited non-Newtonian...
Article
Full-text available
This study aims to investigate the mixing characteristics of a transparent sludge simulant in a mechanically agitated model digester using flow visualisation technique. Video images of the flow patterns were obtained by recording the progress of an acid-base reaction and analysed to determine the active and inactive volumes as a function of time. T...
Article
The legal banning of conventional sludge disposal methods such as landfill has led to a global movement towards achieving a sustainable sludge management strategy. Reusing sludge for energy production (biogas production) through the anaerobic digestion of sludge can provide a sustainable solution. However, for the optimum performance of digesters w...