Agenda

31 Dec 2025 00:00

Interview with Prof. Joan Dosta - Resource Recovery with Purple Phototrophic Bacteria

During his visiting period at DAIS, Prof. Joan Dosta (University of Barcelona) collaborated with researchers from Ca’ Foscari on an innovative project integrating Purple Phototrophic Bacteria (PPB) with membrane bioreactor (MBR) technology for resource recovery from wastewater and agro-industrial by-products. We asked him to summarise the key points of this research.

What motivated this project and which challenges does it address?
The University of Barcelona and DAIS have a long-standing scientific collaboration. This project aimed to combine a photobioreactor with an ultrafiltration membrane to improve biomass retention and selectivity. This configuration allows full decoupling of hydraulic and solids retention times, with potential benefits for bioproducts generation and treated-water quality. More broadly, the complementary expertise of both institutions supports the development of sustainable biorefineries.

Why are PPB promising for resource recovery?
PPB are metabolically versatile anoxygenic phototrophs able to absorb infrared light and use diverse organic and inorganic substrates. They can grow in extreme environments, making them extraordinarily useful for wastewater treatment. Beyond removing organic matter and nutrients, PPB can produce valuable bioproducts such as biohydrogen, polyhydroxyalkanoates (PHA) and microbial proteins. With up to 60% crude protein, PPB biomass can represent a potential animal feed ingredient without requiring arable land. Agro-industrial by-products are particularly interesting feedstocks for high-quality microbial protein production.

What is the advantage of integrating PPB with an MBR system?
Conventional suspended-biomass systems rely on PPB settleability, which is often limited. The implementation of ultrafiltration membranes ensure efficient solid–liquid separation, improving PPB retention and resource recovery. Although membrane units increase operational costs, these may be counterbalanced if bioproduct yields significantly improve. For this reason, its implementation should be assessed on a case-by-case basis.

How does the project address salinity stress?
Some PPB species tolerate saline environments and can even increase protein or pigment production under salinity stress. In this context, integrating PPB with an MBR for treating saline effluents could enhance bioproduct generation while maintaining treatment efficiency.

Which bioproducts can be obtained and what are their applications?
PPB could lead to a wide variety of valuable applications, including the production of bioplastics, microbial proteins, biohydrogen or biofertilizers, together with wastewater treatment and nutrient recovery. The PPB-MBR configuration offers the same outputs while providing enriched biomass and higher-quality treated effluents or even reclaimed water, enhancing the overall value chain.

What is the most innovative aspect of this research?
The cultivation of PPB in MBR systems has not received high attention and is still underexplored, although it could be very useful especially when wastewater characteristics could limit PPB abundance or diversity, such as high salinity or high-strength effluents. Combining PPB and membrane filtration could help select resilient microbial communities while improving valuable bioproduct formation.

What are the next research steps?
In my opinion, future work should investigate how operating conditions - salinity, light availability, organic loading - affect PPB metabolic pathways and bioproduct yields. Selectively inhibiting competing pathways could favour targeted bioproducts. Developing mechanistic models that capture PPB metabolic versatility and their behaviour will also be essential to provide useful tools for technology development and control.

Organized by

DESC Progetto di Eccellenza DAIS [DESC-DAIS]

Link

https://www.unive.it/desc

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