Anaerobic digestion of liquid products following hydrothermal carbonisation of faecal sludge at different reaction conditions

The hydrothermal carbonisation (HTC) conversion of wet wastes, such as sewage sludge, generates a carbon-rich material (called ‘hydrochar’), and an aqueous fraction with a small release of gas. The liquid fraction is high in soluble chemical oxygen demand, from 10 to 50 g/L, and could not be discharged to the natural environment without treatment. This study investigates the anaerobic digestibility of this HTC liquid stream from different HTC temperatures and retention times (140°C–200°C for 30–240 min). It is focused on biogas production in order to improve the energy input of the HTC process and to improve process sustainability. The results demonstrated that liquid products from the lower HTC temperatures gave better biogas production. The biogas yield from the 140°C HTC filtrate digestion was 0.45–0.86 L/L reactor/d, while 0.33 L/L reactor/d was obtained from 170°C and 0.31–0.45 L/L reactor/d from 180°C HTC filtrates. The lowest anaerobic digestion (AD) efficiency was recorded for the treatment from 200°C with biogas yield of 0.07 L/L reactor/d. The data also show that low AD hydraulic retention time (HRT), typical of high rate fixed biomass digesters can be used to treat the HTC filtrate. Halving the AD HRT to 0.9 d resulted in 1.8–6.8 times greater biogas yield

Process energetics for the hydrothermal carbonisation of human faecal wastes

Hydrothermal carbonisation (HTC) has the capability to convert wet biomass such as sewage sludge to a lignite-like renewable solid fuel of high calorific value. However, to date assessment of the energy efficiency of the HTC process has not been fully investigated. In this work, mass and energy balances of semi-continuous HTC of faecal waste conducted at 200 °C and at a reaction time of 30 min are presented. This analysis is based on recovering steam from the process as well as energy from the solid fuel (hydrochar) and methane from digestion of the liquid product. The effect of the feedstock solids content and the quantity of feed on the mass and energy balance were investigated. The heat of reaction was measured at 200 °C for 4 h using wet faecal sludge, and the higher heating value was determined for the hydrochar. The results indicated that preheating the feed to 100 °C using heat recovered from the process would significantly reduce the energy input to the reactor by about 59%, and decreased the heat loss from the reactor by between 50% and 60%. For feedstocks containing 15–25% solids (for all feed rates), after the process is in operation, energy recycled from the flashing off of steam and combustion of the hydrochar and would be sufficient for preheating the feed, operating the reactor and drying the wet hydrochar without the need for any external sources of energy. Alternatively, for a feedstock containing 25% solids for all feed rates, energy recycled from the flashing off of steam and combustion of the methane provides sufficient energy to operate the entire process with an excess energy of about 19–21% which could be used for other purposes

Using statistical and artificial neural networks to predict the permeability of loosely packed granular materials

Well-known analytical equations for predicting permeability are generally reported to overestimate this important property of porous media. In this work, more robust models developed from statistical (multivariable regression) and Artificial Neural Network (ANN) methods utilised additional particle characteristics [‘fines ratio’ (x50/x10) and particle shape] that are not found in traditional analytical equations. Using data from experiments and literature, model performance analyses with average absolute error (AAE) showed error of ~40% for the analytical models (Kozeny–Carman and Happel–Brenner). This error reduces to 9% with ANN model. This work establishes superiority of the new models, using experiments and mathematical techniques

A toilet system based on hydrothermal carbonization

We are developing a toilet system that converts faecal material to an aqueous suspension of carbonised material that is safe to handle, and readily separated from the remaining liquid. It will also extract useful salts from the liquid. The system is aim to be the new generation universally appealing toilet and it will be of particular and urgent interest to areas where no (or very crude) sanitation exists. The system is designed to be self-sufficient in terms of energy input and to scale for a number of users in the range a few tens to a thousand or more. In parallel with our engineering development we are designing the system to provide users with a positive and comfortable experience. Hydrothermal carbonisation (HTC) has received attention recently as a way to convert biomass - including sewerage - into coal like material. It involves heating the start material in water at high temperatures and pressures. Depending on the conditions used the process can produce hydrocarbon gases or liquids or coal like particles. Most HTC work involving sewerage treatment is currently aimed at replacing established large-scale treatment plants i.e. for places with well-developed sewerage services. Our system, using HTC, is aimed at bringing the process at a decentralized household ( including combination of households) level so that the new generation toilet become accessible to all and particularly to those areas where none currently exists. Using HTC for toilets on continuous basis for such a small scale is the key innovation of our proposed system. We will describe our work to characterise the energetics of the HTC process in order to optimise the process in terms of total energy input and how we have used this information to develop a continuous system based on a plug flow reactor. The material produced by the system can be easily separated from the remaining liquid and used to generate heat and power (via a generator including solar) in order to maintain the process. The solids are safe to handle, and look, feel and smell much like coffee grounds. In situations where electrical (or renewable energy like solar) power is available the solid material can be used either as a fuel for heating and cooking, as a soil conditioner and possibly for carbon capture. We will discuss the possibility of including other waste material (food, sanitary waste etc.) into the system. In order to minimize the amount of water required to flush material away from the toilet bowl and to help maintain high sanitary standards we have been investigating anti-fouling coatings for the system. We will describe the results of studies of a nano-coating based on a responsive polymer that significantly enhances the rate at which water flushes away material that adheres to the toilet surface

Microfluidic systems for the analysis of the viscoelastic fluid flow phenomena in porous media

In this study, two microfluidic devices are proposed as simplified 1-D microfluidic analogues of a porous medium. The objectives are twofold: firstly to assess the usefulness of the microchannels to mimic the porous medium in a controlled and simplified manner, and secondly to obtain a better insight about the flow characteristics of viscoelastic fluids flowing through a packed bed. For these purposes, flow visualizations and pressure drop measurements are conducted with Newtonian and viscoelastic fluids. The 1-D microfluidic analogues of porous medium consisted of microchannels with a sequence of contractions/ expansions disposed in symmetric and asymmetric arrangements. The real porous medium is in reality, a complex combination of the two arrangements of particles simulated with the microchannels, which can be considered as limiting ideal configurations. The results show that both configurations are able to mimic well the pressure drop variation with flow rate for Newtonian fluids. However, due to the intrinsic differences in the deformation rate profiles associated with each microgeometry, the symmetric configuration is more suitable for studying the flow of viscoelastic fluids at low De values, while the asymmetric configuration provides better results at high De values. In this way, both microgeometries seem to be complementary and could be interesting tools to obtain a better insight about the flow of viscoelastic fluids through a porous medium. Such model systems could be very interesting to use in polymer-flood processes for enhanced oil recovery, for instance, as a tool for selecting the most suitable viscoelastic fluid to be used in a specific formation. The selection of the fluid properties of a detergent for cleaning oil contaminated soil, sand, and in general, any porous material, is another possible application

Emotional behavior in aquatic organisms? Lessons from crayfish and zebrafish

Experimental animal models are a valuable tool to study the neurobiology of emotional behavior and mechanisms underlying human affective disorders. Mounting evidence suggests that various aquatic organisms, including both vertebrate (e.g., zebrafish) and invertebrate (e.g., crayfish) species, may be relevant to study animal emotional response and its deficits. Ideally, model organisms of disease should possess considerable genetic and physiological homology to mammals, display robust behavioral and physiological responses to stress, and should be sensitive to a wide range of drugs known to modulate stress and affective behaviors. Here, we summarize recent findings in the field of zebrafish- and crayfish-based tests of stress, anxiety, aggressiveness and social preference, and discuss further perspectives of using these novel model organisms in translational biological psychiatry. Outlining the remaining questions in this field, we also emphasize the need in further development and a wider use of crayfish and zebrafish models to study the pathogenesis of affective disorders. © 2019 Wiley Periodicals, Inc.MCS is currently supported by National Funds through FCT ‐ Foundation for Science and Technology. AVK is supported by the Russian Science Foundation grant 19‐15‐00053. KAD is supported by the Fellowship of the President of Russia and SPSU Rector Productivity Fellowship for PhD Students. CM is supported by CNPq/Brazil under Edital Universal 2016 (400726/2016‐5). PMA and FB are supported by the strategic plan of MARE ‐ Marine and Environmental Sciences Centre (UID/MAR/04292/2019)