Upcycling pectin spent peel into high-value fatty acids via arrested anaerobic digestion

Overview

This technology upcycles spent peel from pectin production—a wet, acidic, and compositionally variable byproduct—into higher-value fatty acids, specifically butyric and caproic acids. The process uses arrested anaerobic digestion (AAD), which employs mixed microbial communities to hydrolyze complex organic matter and ferment the resulting substrates while deliberately preventing the conversion of fatty acids to methane. The result is a valuable chemical output instead of a waste stream.

The core value proposition is waste valorization: transforming a low-value, difficult-to-manage processing residue into market-relevant carboxylic acids that serve as chemical intermediates, feedstock precursors, and potential platform chemicals. Because the process handles wet feedstocks without drying and operates near pH 5, it aligns naturally with the acidic character of spent peel, potentially reducing pretreatment and pH-adjustment requirements.

Technical specifications

The platform builds on a low-pH AAD process operating at approximately pH 5, developed at Colorado State University. This process has been demonstrated on multiple complex wastes, including food waste, manure, grass, and paper/paperboard, at scales up to 10 liters.

Key features:

• Mixed microbial communities adapt to complex and changing substrate compositions, accommodating the variability of spent peel
• Low-pH operation (around pH 5) aligns with the naturally acidic feedstock, limiting pH-adjustment needs
• A 36-reactor, pH-controlled screening platform supports rapid validation and optimization
• Stage-gated workflow evaluates whether additional steps—such as D-limonene removal or hydrolysis-enhancing pretreatments—are needed, rather than assuming them
• Performance is guided by fatty acid titer, yield, and selectivity, with emphasis on butyric and caproic acids

Two potential barriers are addressed conditionally: D-limonene inhibition and slow hydrolysis of cellulose and hemicellulose. If they meaningfully impair performance and economics, established pretreatment technologies can be incorporated; otherwise they are avoided to minimize cost and process complexity.

Technology readiness level

The underlying AAD platform is at technology readiness level 5 (TRL-5), having been validated with multiple complex wastes at bench scale. The proposed work adapts this platform to pectin spent peel through a 12-month, stage-gated program covering validation, optimization, and scale-up demonstration. Bench-scale reactors will first confirm conversion performance; subsequent optimization will determine whether D-limonene removal or hydrolysis pretreatments are beneficial. Pending success, the process will be demonstrated at larger scale using existing AAD infrastructure to evaluate performance and stability under scale-up-relevant conditions.