Brief Technology Description
Processing of water-rich, cellulosic industrial and municipal waste streams employing in-tandem fermentation and anaerobic digestion. Opportunity is offered to generate energy (ethanol, methane) with integrated wastewater reclamation.
Next Steps Required
Design for a mobile fermentation plant in a standard shipping container completed. Designs for mobile anaerobic digester using low-cost materials are underway. Pilot scale digestate dryer is in-hand and available for operation. Construction of mobile units in 2017/2018. Deployment at demonstration scale to follow.
Postgraduate student in chemical engineering (research project opportunities)
Postdoctoral fellow/Research engineer
The facility will be operated under the auspices of Stellenbosch University (SU), one of the oldest universities in South Africa with world-wide recognition and research and innovation leader. Personnel and students are resident at the Dept. Process Engineering at SU, also recognised as a leader in training world-class chemical engineers.
Detailed Technology Description
This project targets the so-called “valley of death” where perceived risk in technology investment outweighs the benefits of novel approaches. Hence, most technologies remain at bench scale or industries follows the beaten path. Demonstration scale equipment is under design that will be housed in standard 12 m shipping containers, where such containers can be employed in tandem. The first container will house two 1 200 litre reactors and a distillation column, whereas the second container will house a 60 m3 digester made of rugged canvas, rendering the design rugged yet light and easy to operate and maintain. A third container (in-hand) is a digestate dryer where the product can be used as fertiliser. Fermenters are designed to operate in batch, fed-batch and continuous mode, where the two reactors can be operated in series or in parallel.
Waste streams for processing include;
- paper waste sludge emanating from paper mills.
- spent sulphite liquor from Kraft processing during wood pulping
- brewers’ spent grains (BSG), a by-product of the brewing industry
- residues from furfural production from lignocellulose
- municipal waste including food waste and non-recycled paper waste
- fruit waste, such as pomace, waste fruit and grape skins from grape pressing.
Four products will be produced, namely reclaimed water, ethanol, methane and fertiliser. The system will allow waste water to be diverted from landfill, thus decreasing ground water contamination and GHG emissions, and offering a water reclamation solution with integrated energy production.
Fermentation performance will depend on the nature of the substrate treated. Paper waste sludge, for example, can be treated in continuous mode at a solids loading of 12 weight% (wet weight) and a residence time of 8 h, which implies a throughput of approx. 10 kg/h or 7.5 ton material treated/month. Such volumes would allow accurate estimates of a full commercial plant where substrate flow rates are in excess of 30 tons/day, but were inconsistencies in the feedstock and are seldom accounted for at laboratory scale. The extended operation would allow accurate estimation of ethanol, gas and water yields, given the variation in feedstock composition and consistency. Real-time and accurate estimates of process performance would support building a bankable business case for infrastructure investment by the relevant industry.
Testing and Demonstration Results
Construction of the mobile plants will commence 2018 with commissioning, testing and demonstration thereafter.
Papers and Publications
Scientific outputs will be forthcoming from students training on and operating the demonstration plant under real industrial conditions. Unique opportunities for students to acquire such experience during academic studies are extremely rare and would serve to broaden the student training value proposition of Stellenbosch University as research leader and school for engineers.
The plant is designed to be multipurpose in nature, which means that it can be used to demonstrate any biological production process. Substantial opportunity exists for generating patentable data during future biomass and biological processing applications.
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