Encapsulation technology to improve biological resource recovery: recent advancements and research opportunities†
Encapsulation technology has been extensively investigated for various microbiological applications for decades. Combined with biological processes, encapsulated bacteria have great potential to efficiently and cost-effectively recover resources (e.g., hydrogen, methane, metals) from various waste streams, such as wastewater, metal wastes, and sludge. This review focuses on recent advances in four areas: encapsulation of specific bacteria or biocatalysts, effectiveness in separating the solids retention time from the hydraulic retention time, control of the encapsulant internal environment, and improved reusability and storability of encapsulated bacteria. In most cases, encapsulation technology enhanced biological resource recovery by facilitating stable high-rate operation; nevertheless, challenges remain that limit application. Consequently, this review points to three major research opportunities that, if addressed, could enable broader application of encapsulated bacteria for resource recovery: (1) encapsulant impacts on bacterial growth, leakage, and community changes with time, (2) use of encapsulant chemistry to control the encapsulant internal environment, and (3) modifications of the encapsulant matrix to improve the reusability and storage of bacteria. With the better control and predictability that should result, the use of encapsulation technology in biological processes could be further advanced as a reliable and efficient option for resource recovery.