Hydrogen and NH3 from organics

The value of waste

Value recovery from biosolids can play a vital role in closing the loop for nutrients, water and energy used in our food and agriculture sector. CSIRO is currently investigating a biological pathway to produce hydrogen that could deliver a triple bottom line benefit to agriculture, food and wastewater treatment industries. Leveraging CSIRO expertise in dark fermentation and applied industrial heat research, the multidisciplinary team is beginning trials using a selection of microbial strains and organic wastes to investigate an integrated approach to improve dark fermentation for hydrogen and ammonia production.

Bugs and heat

  • Dark fermentation is microbially catalysed fermentative conversion of organic substrates to hydrogen in the absence of light and electron acceptors. It can be facilitated by a large range of microorganisms that differ in their optimal growth conditions.
  • The laboratory experiments will evaluate whether thermal hydrolysis will improve biological hydrogen generation rates and yields from selected organic waste materials. It is expected that thermal hydrolysis will increase the bioavailability of the organic substrates for dark fermentation. Moreover, the hydrolysis is expected to eliminate hydrogen consuming microbes from the waste, and thereby potentially increase hydrogen yields.
  • The diagram below shows the use of concentrated solar thermal heat for the thermal requirements of the process. This stage of the project is focused on investigating the potential benefits of thermal hydrolysis as a pre-treatment. Through dark fermentation experiments, CSIRO will establish if thermal hydrolysis improves hydrogen yield and if so a further integration with anaerobic digestion plus solar-reforming of biogas will be explored to ascertain the thermal efficiency of the entire system.

Which wastes?

Waste to energy projects typically rely on cost effective access to waste residues (feedstocks) that are transported to a processing plant of sufficient scale to ensure economic feasibility. The integrated process also requires access to technically feasible and economically sourced heat with concentrated solar thermal energy a good option for regional areas. Given these conditions Mackay in Queensland with an average yearly direct normal irradiance (DNI) of approximately 20 MWh/m2 has been chosen as a case study site. Apart from having a moderate source of solar irradiance, the site also has a reasonable size of population (> 80,000 people) that generates large quantities of municipal sewage sludge. This municipal waste stream, together with other biosolid waste streams such as bagasse, sorghum and abattoir wastewater generated from the surrounding agriculture and food industry will be considered as the waste feedstocks in this project.

 

Left: Abattoir paunch biosolid sample after autoclaving; Right: Abattoir save-all biosolid sample after autoclaving.

Sample of sorghum from silage being used in dark fermentation trials.

Source: Global Solar Atlas 2.0, Solargis database version: 2.1, Map issue date: 2020-04-03

Progress to date

  • Bagasse and sorghum have been sourced and pre-treated with thermal hydrolysis.
  • The pre-treated and untreated materials have been characterised.
  • PhD student has been secured to explore dark fermentation and the student has completed 6 months research proposal milestone.
  • Known hydrogen producing microbes have been sourced from a culture collection, cultivated in various growth media and stored for later use.
  • Analytical equipment and instruments have been purchased and methods developed for analysing gaseous and soluble microbial metabolites.
  • The effect of thermal hydrolysis on the release of sugars and organic acids from bagasse and sorghum has been evaluated.
  • An automated biogas potential test system has been purchased and tested with selected microbial cultures with glucose as a model substrate to check the ability of the cultures to produce hydrogen.
  • Early modelling of the integrated heat + dark fermentation process indicates that an energy balance can be achieved for particular biosolid characteristics and temperature settings.

Left: pure cultures of hydrogen producers established in anaerobic test tubes; Right: phase-contrast microscopic image of a selected hydrogen producing culture.

Gas chromatography set-up in CSIRO laboratory for analysis of microbial metabolites from dark fermentation trials.

What’s coming up…

  • Upscaling active H2– producing microbial strains to a quantity required for use in fermentation experiments.
  • Setting up batch fermentation experiments to compare the abilities of various microbial strains to generate H2 using the hydrolysed and unhydrolysed organic feedstock materials available (sorghum and bagasse). The results will be used to guide the selection of the most promising pre-treatment condition and cultures for further experiments.
  • Sourcing abattoir waste and biosolids from municipal wastewater treatment plant for thermal hydrolysis and subsequent dark fermentation experiments.
  • Evaluate potential for ammonia recovery from selected waste streams.

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