Valorising Activated Sludge Biomass Waste via Low temperature Processing towards a Circular Economy.

   Hydro Nation Scholars Programme

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  Dr A Escudero, Dr A Pickard  No more applications being accepted  Competition Funded PhD Project (Students Worldwide)

About the Project

The project is based on a synergistic collaboration across four institutions (Glasgow Caledonian University: GCU, UK Centre for Ecology & Hydrology: UKCEH, University of Strathclyde: UoS and Heriot-Watt University: HWU) via the Hydro Nation Chair Research and

Innovation Programme (

Wastewater treatment plants in Scotland produce large quantities of sewage sludge from both small to large scale treatment plants. Most of the sludge in Scotland is marketed for agricultural use, land reclamation and incineration. However, regulations on sludge usage are set to become stricter, which will reduce the volume of sludge recycled and used in agriculture and land reclamation. This is a worldwide problem, and with the prospect of more sludge being produced and wasted because of these new regulations, there has been a recent surge in valorisation projects to find alternative uses for sludge in today’s modern society. One potential route of valorisation is to stabilise the biomass into a carbon-dense form.

Torrefaction is a process used to improve biomass properties, the products from which have been used, since the 1930’s, as fuels or reducing agents. Due to the milder processing conditions used in torrefaction, compared with those used in the manufacture of biochars, with temperatures between 200-300°C and atmospheric pressure routinely used, the final character of torrefied carbons is aimed at calorific value rather than textural development, hence, torrefaction has not been used for the development of materials to displace biochars. Torrefaction processing can be dry or wet, the latter is also referred to as hydrothermal carbonisation and gives rise to hydrochars; such wet processing can result in significant disruption of the biomass structure, producing chars with well-developed porous character for a range of potential applications. While torrefaction has been extensively studied for materials with high cellulosic contents, e.g. woods, less research has been conducted using sludge wastes, the latter focussing primarily on animal and food wastes with little work on sewage sludge. A handful of recent publications have looked at the application of torrefaction to process sewage sludge, but these have all involved a dewatering step, which consumes additional energy and produces associated emissions. Given that beneficial gains can be achieved, in terms of textural character of chars created using wet torrefaction, then processing wet sludge has the potential to create an improved material with reduced energy penalty compared with traditional biochar processing. There is also scope for further gains by the inclusion of additives to the solution matrix, hence, there is potential value in developing hydrochars from we-torrefaction of sewage sludge, which can be deployed in a range of applications, including soil amendment, water remediation and as construction media.

In this context, the main objectives of this project are: 1) to understand current modes of biomass processing and develop wet torrefaction methods for sludges; 2) to investigate wet torrefaction as an alternative route for sewage sludge valorisation and determine optimised production routes; 3) to identify the different applications and markets available for the product obtained from low-temperature processing of sewage sludge; and 4) to examine technical issues associated with deploying this technology at a national scale and working with industrial partners to understand the feasibility of such an approach.

To achieve the PhD objectives, key activities will include reviewing and synthesizing the available literature on current sewage sludge valorisation practices and low-temperature processes. Sludge processing will be undertaken using furnace and auto-clave facilities (UoS) and the resulting materials characterized for textural as well as thermo-hydro-chemo-mechanical properties (GCU, HWU, UoS) and tested for a range of applications (all partners); in particular, construction (e.g., water treatment, soil improvement and development of innovative building materials) and agriculture applications. There are potential hazards associated with the valorised sludge product production, transport and use in land application. The PhD student will work closely with UKCEH’s policy placement researcher, who is involved in developing the updated version of the Biochar Quality Mandate – risk assessment to ensure that potential hazards are recognised, and processes managed to mitigate against them. The student will be hosted at GCU with periods of training at UKCEH, UoS and HWU.

Applicants should hold a first degree (at least a 2.1) ideally in Environmental or Chemical or Process or Civil Engineering or a closely related discipline. 

Environmental Sciences (13)

Funding Notes

The Hydro Nation Scholars Programme is an open competition for PhD Scholars to undertake approved projects, hosted within Scottish Universities and Research Institutes. This project will be hosted by the Glasgow Caledonian University. Full funding is available from the Scottish Government (to host institutions via the Scottish Funding Council). The funding available will be in line with the UKRI doctoral stipend levels and indicative fees. Applicants should have a first-class honours degree in a relevant subject or a 2.1 honours degree plus Masters (or equivalent). Shortlisted candidates will be interviewed on 26th or 27th January 2023.
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