Examining the quality of a compost product derived from sargassum

Abstract

The free-floating algae known as sargassum (Sargassum fluitans and Sargassum natans) drifts onto coastlines throughout the Atlantic Ocean during spring and summer months. Beach communities seek to maintain tourist appeal and, therefore, remove or relocate the sargassum drifts once it collects on shore. Maintenance efforts have attempted to incorporate the sargassum into dunes and beach sand. However, not all communities have the resources to manage the bio-mass and must dispose of it in a landfill. The utility of the seaweed biomass as a fertilizer for plant growth has been renowned for centuries. The purpose of this project was to evaluate the appropriate proportion of sargassum for other compost ingredients used in a large-scale composting system to create a quality product for utilization in horticultural and/or agricultural products. This study used ≈32 yard3 of sargassum as part of 96 yard3 of compost material that also included food waste, fish waste, and wood chips. Four protocols were prepared and included either 25% or 41.5% sargassum and various proportions of food or fish waste and wood chips, which are ingredients that would be readily available in coastline communities, to determine the ideal ratios of materials to create a quality compost. Piles were turned regularly and monitored for pH, moisture, and temperatures according to compost industry standards and approximately every 5 to 7 days. Piles cured for 4 to 8 weeks and the entire composting process lasted 5 months. Samples of compost were collected and tested through the Agricultural Analytical Services Laboratory’s U.S. Composting Council’s Seal of Testing Approval Program at Pennsylvania State University. All final compost products and protocols had reasonable quality similar to those required by current compost standards. However, the protocol in-corporating equal parts sargassum (41.5%) and wood chips (41.5%), fish waste (4%), and food waste (13%) had the best results in terms of organic matter content and overall nutrient levels. Therefore, this study determined that waste management industries can use sargassum as a feedstock through a large-scale composting system to create a desirable compost product that could be used in the horticulture industries. Sargassum could also be composted and then returned to the shoreline, where it would help build soils and vegetation.