Investigation into the use of inorganic binders for upgrading anaerobic digestion streams

  • Haili Chen

Student thesis: Doctoral ThesisDoctor of Philosophy


For the sustainable growth of Northern Ireland, renewable energy sources like anaerobic digestion streams could become one of the most attractive substitutes to generate energy in the near future, and the developments on treatment and conversion technologies for energy production may encourage the industrial development of this potential. This research focused on the granulation of the waste digestate from AD plants using drum granulation and inorganic binder (silicate- based). Both the engineering and chemical parameters that would affect the properties of the final agglomerated granules were investigated, and the pyrolysis and combustion of the granules produced were also studied. Commercial compost was selected as a model bio-waste substrate to make granules to generate the initial granulation results, then digestate from different AD plants was used to make granules for different applications.

Using a laboratory-scale drum granulator (300 g/batch), spherical compost granules within the targeted size range (3.35 - 14 mm) could be produced with a good compressive strength in good to excellent yields. The effects of compost moisture content, process parameters (drum speed, granulation time) and binder parameters (binder concentration, binder to compost ratio and binder gelation time) on the properties of the resulting granules (size distribution, bulk density, compressive strength, water resistance, gross calorific value, ash content) were investigated. The optimal conditions for producing granules as a solid biofuel with competitive properties when compared with woody biomass fuels were achieved by applying a drum rotational speed of 32 - 37 rpm, granulation time of 15 min, sodium silicate solution 1 - 3 wt% and binder to solid ratio 0.77 - 0.90. Adding acetic acid to sodium silicate solution could result in the granules produced with slightly higher water resistance ability, though the results are not statistically significant.

The full-scale demonstration trials also showed that it was possible to manufacture granules using sodium silicate solution through drum agglomeration process, though more future work would be considered.
Date of AwardDec 2019
Original languageEnglish
Awarding Institution
  • Queen's University Belfast
SponsorsCentre for Advanced Sustainable Energy-CASE
SupervisorDavid Rooney (Supervisor) & Mark Muldoon (Supervisor)

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