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A novel alternative for digestate valorisation is under development in a demonstration plant in Granollers, Spain.

A Novel Alternative For Digestate Valorisation Is Under Development In A Demonstration Plant In Granollers, Spain.

Even in the current health crisis, the Autonomous University of Barcelona (UAB) and Aeris researchers have managed to keep on working on the development and demonstration of a pilot plant located in a centralised waste treatment facility operated by the Consorci per a la Gestió dels Residus del Vallès Oriental located in Granollers  at 20 Km from Barcelona.

During the mid-stage of the DECISIVE lifespan, UAB team devoted efforts into the definition and development of a process enabling biowaste digestate valorisation into marketable bioproducts. Researchers of the Composting Research Group (GICOM) screened the production of several bioproducts such as hydrolytic enzymes, biosurfactants, and biopesticides. Results showed that biopesticides derived from a commercially known strain “Bacillus thuringiensis” (Bt) were the most promising bioproducts obtained by solid-state fermentation (SSF). This anaerobic facultative bacterium is able to produce a biopesticide highly specific for the elimination of commonly found plague. Biopesticides currently have great market value; therefore, it is an asset for the DECISIVE consortium. However, the innovation of the process relies on the use of biowaste digestate as a source for attractive bioproducts using a sustainable technology as SSF. New ways to valorise biowaste digestate are intensively studied by several researchers and institutions, as it is a waste that can only be composted or landfilled.

UAB researchers developed an optimised biopesticide production process. The process development was performed at three different packed-bed reactor volumes (0.5, 1.6, and 22 L), obtaining a consistent operation strategy in terms of biological performance and biopesticide production yield. As biopesticide proteins are related to the sporulation process, spore concentration was the target product to monitor. Maximum production was achieved when a mixture of biowaste digestate and biowaste was used as a substrate, applying an aeration strategy, divided into two stages:  a first micro-aeration stage to promote Bt growth and a second full-aerated stage, to promote Bt sporulation and biopesticide proteins production. The technical achievements of the developed operational protocol were submitted for a European and UK patent. Also, a scientific publication entitled: “A novel two-stage aeration strategy for Bacillus thuringiensis biopesticide production from biowaste digestate through solid-state fermentation” is published on the Biochemical Engineering Journal.

After the development of the biopesticide production process, the next step was to validate the process at a demonstration scale, which is one of the main challenges tackled in this kind of processes. To achieve this goal, a 290 L SSF reactor was designed, built and currently operated by the DECISIVE partners UAB and Aeris SL. The demonstration plant was operative for 4 months prior the general cease of activities due to the lockdown caused by coronavirus pandemic. During the operation, the researchers were able to perform operational tests in order to validate the functionality of the reactor and five sets of experiments of biopesticide production. The main constraint found during this period is related to temperature control, as the system quickly increases its temperature higher than 45ºC, thus reducing the microorganism’s viability and biopesticide production yield. Initial attempts were made to reproduce the production process defined in an early stage of the project, as this is the main objective of Aeris in DECISIVE.

Then, additional experiments focusing on achieving similar or higher level of product concentration compared to the laboratory results will be performed once the lockdown is relaxed and external personnel is allowed to enter Granollers waste facility. More work is expected to finally obtain a profitable and successful operation.


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