Valorization of waste aerobic granular sludge: Exploring the recovery of tyrosine, phenylalanine, and other high-value products

Abstract

The aerobic granular sludge (AGS) biotechnology has emerged as a compact, sustainable, resilient, and highly efficient technology for wastewater treatment. Beyond wastewater treatment, AGS provides significant potential for resource recovery, aligning with circular economy principles. This review explores the recovery of six key resources from AGS systems: phosphorus, alginate-like exopolysaccharides (ALE), tryptophan, tyrosine, phenylalanine, and biogas. Phosphorus recovery pathways include enhanced biological phosphorus removal, biologically induced precipitation as hydroxylapatite (Ca₅(PO₄)₃(OH)), and struvite (MgNH₄PO₄·6H₂O) formation. ALE extraction techniques and optimization strategies are examined for their industrial applications. Biogas production from waste granules can be improved through co-digestion and pre-treatment methods such as steam explosion. Tryptophan production in the aerobic granule matrix can be enhanced through optimized operational parameters, while extraction and quantification are achieved using high-performance liquid chromatography. Tyrosine and phenylalanine, recently identified in the aerobic granule matrix, have a wide range of industrial applications including feed and food supplement, production of medicines, in agriculture for postharvest preservation, and as a raw material for other chemical products. Their biosynthesis in the aerobic granule matrix can be enhanced via process optimization and approaches such as quorum sensing. Addressing current AGS challenges such as extended start-up times when using low-strength wastewater and operational issues with industrial wastewater is critical for maximizing AGS performance. AGS exemplifies innovative biotechnology for sustainable wastewater treatment and resource recovery, leading the way to attaining a circular economy in wastewater management.