Mentor:

  • Denys Villa Gomez

Team Members:

  • Tzia Yeung Lai
  • Joon Wai Ng (Gavin)

Background

Anaerobic digestion is considered a cost-efficient technology for waste treatment since it produces bioenergy from the biogas produced. Biogas can be produced from available organic raw materials and recycled waste. Biogas projects involve the conversion of waste into valuable products (bioenergy and nutrients) and waste reduction. Key benefits include

Cost reduction in:

  • Electricity
  • Heating
  • Waste treatment
  • Waste disposal

Revenue from:

  • Carbon Credits
  • Excess power sale
  • Recovered nutrient sales

Environmental benefits from reduction in:

  • Greenhouse gas emissions
  • Harmful pollutants
  • Odours

Project Brief

The decision of using these residues for bioenergy production is influenced by economic and environmental factors. Therefore, this project aims to evaluate the opportunities for biogas production from key residues generated in the inner Brisbane region through a cost-effective analysis carried out with information obtained from literature review and a set of lab experiments. Economic factors to be analysed include seasonal and annual changes in substrate amounts, costs of possible substrate pre-treatments, and biogas yield per substrate (lab experiments), while environmental factors include greenhouse gas emission reductions.

The work flow will be the following:

  • Selection of a case study and waste
  • Biogas potential test experiments
  • Digester design, flow plan and mass balance
  • Cost-effective analysis

Project Completion Report

The project commenced with research on potential wastes in the Queensland region to be used for bioenergy production. The bioenergy focussed on was biogas production. Options that looked promising include banana tree waste and used coffee grounds. However, coffee waste was selected to be pursued further seeing that coffee consumption is generally high in Australia, which enables a wider scope for application.

Consequently, the team initiated preliminary tests to determine the biogas potential of coffee grounds. It was determined that biogas can be produced from the coffee without any prior pre-treatment. Hence, the coffee grounds only need to be added with water, and once the volatile components dissolve, the solids are filtered out. The solution is then added with the inoculum and sealed, which will assist the anaerobic decomposition and biogas production.

Experimentation was conducted with two manipulated variables, namely temperature and solution concentration. Temperature was set at ambient temperature (24oC) and 35oC, while the concentrations tested were 10g/L and 20g/L respectively. Interestingly, it was ascertained that higher concentrations of coffee were shown to have inhibition effects on biogas production. Results also exhibited higher yield of biogas at higher temperatures.

Overall, the project was a success as biogas was successfully generated in the tests conducted. It demonstrated the viability of utilising spent coffee grounds as a bioenergy feedstock. Methane and carbon dioxide were the two main gases generated during the experiment. This is economically favourable as the coffee grounds, which were initially disposed of, can now produce energy by means of using the biogas as a fuel.

dissolved components from coffee grounds in water
Figure 1: Dissolved components from coffee grounds in water (unfiltered)
Solution filtration (removal of coffee ground solids)
Figure 2: Solution filtration (removal of coffee ground solids)
Seed sludge (inoculum) deposition into the test bottles
Figure 3: Seed sludge (inoculum) deposition into the test bottles