Using Recuperative Thickening Technology to Boost Biogas Production

Wastewater treatment is complex, expensive, and uses a lot of energy. High performance technologies, such as recuperative thickening techniques, can help wastewater treatment facilities reduce their energy consumption on-site by generating biogas, a renewable energy source.

McMaster Researcher


Cobbledick, J., Aubry, N., Zhang, V., Rollings-Scattergood, S., & Latulippe, D. R. (2016). Lab-scale demonstration of recuperative thickening technology for enhanced biogas production and dewaterability in anaerobic digestion processes. Water Research,95, 39-47. doi:10.1016/j.watres.2016.02.051

Funded by


Anaergia Inc.

What is this research about?

Biogas is an important renewable energy source derived from digestion of organic waste materials (e.g. manure, sewage, garbage) by bacteria in the absence of oxygen. This study examines the use of recuperative thickening, a high-performance wastewater treatment process that involves recycling a portion of the digested materials back into the treatment process. The produced biogas can then be converted into electricity, which can be used on-site at wastewater treatment facilities or distributed to the local electricity grid. If the produced electricity is used on-site, treatment facilities will be better able to balance their energy needs and reduce excess consumption.
Previous studies on recuperative thickening have occurred in large pilot plant or full-scale trials, which makes it difficult to optimize the process.  In this study, the researchers developed a small scale version and demonstrated its usefulness in examining a complex process.  Lab-scale studies allow researchers to more easily manipulate specific aspects of the treatment process, such as pre-treatment of the feed material or using a blend of different feeds.

What did the researchers do?

A thorough lab-scale study of recuperative thickening was conducted, involving the operation of two digesters at the same time, with one using recuperative thickening (RT digester), and the other acting as the control. The feed for this project was obtained from the wastewater treatment plant in Dundas, Ontario. To achieve recuperative thickening, a polymer flocculant was added to the digester effluent to isolate the solids from the liquid fraction. The solids were then recycled back into the treatment process.
The digester operation schedule involved five days of feeding and two days of starvation. For the first 12 weeks both digesters underwent a ‘pre-test’ step every weekday to make sure there was no difference in the contents of the digesters when starting the test cycle. Both digesters were monitored during the 5-day feeding cycles with the following quality measurements:

  • Total chemical oxygen demand and soluble chemical oxygen demand
  • Biogas production rate
  • Biogas composition
  • Digestate dewaterability (via capillary suction time measurements)

What did the researchers find?

Test cycles and subsequent measurements resulted in the following conclusions:

  • The biogas produced by the two digesters was of the same quality, however the biogas productivity of the RT digester was over two times higher than the control digester.
  • Recycling the polymer flocculant back into the RT digester improved the dewaterability  performance relative to the control.
  • Overall consumption of polymer flocculants can be decreased by carefully adjusting the dose of polymer in RT processes.

How can you use this research?

This research demonstrates the effectiveness of using small-scale studies to examine complex wastewater treatment processes. This study is particularly relevant for researchers interested in recuperative thickening and its potential for improving the energy efficiency of wastewater treatment processes.

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Research Impacts

The Mac Engineer - fall 2015

October 25, 2016

Eight departments in McMaster's faculty of engineering conduct innovative and transformative research as they contribute to building smart cities of the future. This work is featured in the fall 2015 issue of the Mac Engineer.

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