Date

Spring 2025

Document Type

Master's Thesis (Open Access)

Degree Name

Master of Science (M.S.)

Department

Moss Landing Marine Laboratories

Abstract

This feasibility study investigates the potential of anaerobic fermentation of Ulva spp., a locally sourced macroalga, using Clostridium acetobutylicum to produce biofertilizer and biohydrogen. It further examines the viability of Ulva as fermentation biomass by identifying seasonal trends in nutrient concentrations of biofertilizer and gas production while determining the impact of the preservation method on gas yield. The biofertilizer used for nutrient analysis was produced from fresh Ulva harvested within 24 hours prior to fermentation. Orthophosphate (PO4-P), nitrite (NO2-N), nitrate (NO3-N), and ammonia (NH3-N) concentrations were analyzed post-fermentation using spectrophotometric flow injection analysis (FIA). Potassium (K+) concentrations were measured using a K+ ion- selective electrode. PO₄ -P concentrations declined after summer, while NO₃ -N increased into winter and spring; NO2-N and NH3-N did not show significant fluctuations correlated with the season. Nutrient concentrations were used to establish biofertilizer N-P-K ratios and were compared against commercial fertilizers. The composite biofertilizer sample had an N- P-K of 10-7-65, aligning with commercial potash-focused fertilizers (0-0-60) used for heavy- fruiting crops. Biogas production volume and composition were compared across three preservation treatments: fresh, dried, and frozen. Results indicated no statistically significant differences in gas yield between treatments, though high variability was observed within them. Gas volume was measured using water displacement. Gas composition was determined using a GC-TCD, which varied across samples; some achieved 85–95% hydrogen by volume, while others were as low as 19.5%. There was no obvious seasonal trend in gas volume between or within treatments. Despite some limitations in data consistency, the study demonstrates the technical feasibility of producing nutrient-rich biofertilizers and carbon- neutral biohydrogen from Ulva-based fermentation. Removal of Ulva and subsequent recycling of nutrients through biofertilizer application may reduce the impacts of coastal eutrophication. The successful biohydrogen production validates the method and could lessen reliance on fossil fuels. However, sampling technique and method refinement is needed to reduce variability between treatments and fully optimize end products.

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