Hydrothermal Processing (HTP) – Converting Wet Biomass Feedstocks to Biogas, Bioliquid, and Char
Over the past year Earth Systems has been actively investigating the use of high temperature pyrolysis (~700ºC) in order to increase eco-efficiency, reduce carbon footprints, and value-add to solid waste streams, such as biosolids.
Large volumes of biosolids are generated at sewage treatment plants and through both adsorption and absorption can contain complex mixtures of chemicals as well as pathogens and viruses. This can present a disposal problem – their usage as a furnace fuel being a particular problem on account of heavy metal content. These stockpiles can also consume a large amount of space especially if they are dispersed for sun drying.
HTP presents a solution to these problems with a range of beneficial outcomes:
- Generation of a crude bio-oil from which biodiesel could be produced;
- Production of fuel gas to assist in driving the pyrolysis process and/or running other facilities;
- The production of stable biochar for carbon sequestration and/or soil improvement;
- Physical compaction of on-site stockpiles; and
- Pyrolysis of biosolids represents a tangible means for a water authority to offset its carbon budget.
Earth Systems has undertaken a scoping study to:
Evaluate the characteristics of particular biosolid feedstocks (originating in Australia and overseas), their behaviour in the HTP environment, and the relevant characteristics of the products generated (in particular, the bio-oil component).
Perform a feasibility study with Melbourne Water in using their biosolids for beneficial reuse, in particular for energy production (especially gas with high methane content) that is suitable for their current and future biosolids production and is able to accept feedstock with toxic metals.
Carry out a basic financial analysis considering the value of the biosolid disposal service and the value of the biofuel product. This includes an estimation of the rough capital and operating costs of a HTP plant as a first assessment of financial viability for such a process.
Undertake research, design and development work including pilot-scale trials to evaluate possible processing and re-use pathways for stockpiled biosolids. This particular study considered two different biosolids treatment processes: Fluidised Bed Gasification (FBG) and Hydrothermal Processing (HTP).