Harvested algal biomass from Algal Turf Scrubber® systems can be processed into composted algae for potential use as a horticultural substrate, container-media component, compost, or soil amendment, depending on source-water quality, processing methods, and market requirements.
USDA Agricultural Research Service research evaluated composted algae as an alternative substrate for horticultural crop production. This work was conducted in response to growing interest in alternative container-media components due to the availability, cost, and environmental considerations associated with traditional materials such as peat and pine bark.
In controlled horticultural trials, composted algae outperformed peat-based media in the measured plant-growth responses, including plant vigor, leaf greenness, and flower development. The primary technical limitation identified was bulk density, which affects handling, shipping, and container-media formulation. Subsequent blending with peat-based or other lighter substrate components may provide a pathway for improving physical properties while retaining the nutrient and plant-growth benefits of composted algae.
CA = composted algae; PB = peat-based substrate; Fert = fertilized; DI = no fertilizer added.
USDA ARS trials evaluated composted algae as a horticultural substrate by comparing marigold growth in composted algae (CA) and peat-based (PB) media, with and without fertilizer. Results showed that composted algae supported strong plant growth and demonstrated potential as a higher-value container media component.
This distinction is important because container media and specialty horticultural substrates can command substantially higher market value than bulk compost. For ATS projects, harvested biomass should therefore be viewed not only as a residual requiring disposal, but as a recoverable biological material with potential value in horticulture, soil amendment, and related beneficial-use markets.
The suitability of algal compost for container media or soil amendment depends on the characteristics of the source water, biomass quality, composting process, regulatory requirements, and local market conditions. Where these factors are favorable, composted algae may provide a beneficial-use pathway that supports nutrient recovery, reduces residuals, and improves the economics of managed aquatic plant treatment systems.