Blue biomass composting technology

Summary

This report presents the methods and results from preliminary trials with composting marine residual raw materials under the auspices of MARIGREEN, a project funded by the ERA-NET BlueBio cofund program. The main goal of MARIGREEN is to upgrade poorly utilized residual raw materials from blue value chains (fish, shells, algae) for use as fertilizer and biostimulants in organic farming. The project is led by UPB (Romania) and is in collaboration with USAMV (Romania), AUTh (Greece), DTU (Denmark), UCPH (Denmark), NORCE (Norway), and the industrial partners Alumichem AS (Denmark), Norgeskjell AS (Norway), Sigurd Folland AS (Norway), Fjordlaks AS (Norway), and Algea AS (Norway). The compost experiments were carried out at three different levels: small-scale (2 litres) in so-called Dewar flasks; medium-scale (140 liters) with a Jordakompost® insulated compost drum; and large-scale (approx. 7 m3) with windrow composting. The first experiments in the Dewar flasks were based on known raw materials such as horse dung, sawdust, and straw and were intended to familiarize ourselves with the equipment and the method, which is called a self-heating test. This test is usually used to estimate the maturity and stability of finished compost, but here we wanted to look at heat development in fresh material. The trials with the familiar raw materials were followed by trials with the marine residual raw materials, tangle kelp, two types of algae fiber from processing rockweed (brown seaweed), ground fish bones from hydrolyzed cod heads, and dried fish meal from fish in the cod family. These materials have, to our knowledge, not yet been tested in Dewar flasks. As an alternative bulking material in the Dewar bottles and in the compost drum, we experimented with expanded clay aggregates (Leca®). The experiment with horse dung confirmed that the Dewar flasks can be used to estimate the potential for heat generation in fresh material. The marine residual raw materials also developed heat, in several cases above 45 °C (which is the lower limit for being thermophilic) and in some cases up to 60 °C, including algae fiber alone with Leca®. The mixture with algae fiber and Leca® was used to make compost in the compost drum, but on this scale, the temperature never exceeded 30 °C. This may be due to the fact that the room was cold at the start (below 5 °C), that the drum gave off too much heat, that there was too little easily available nitrogen or carbon, or that the ratio between algae fiber and Leca® was incorrect. On a large-scale level, we built a compost windrow with a mixture of algae fiber, bedding from cattle, wood chips from conifers, and sediment from acidified, ground-up residues from codfish, which contained substantial bones. This mixture gave rise to temperatures above 60 °C for short periods. Many useful experiences came out of these initial experiments, which are being used to plan further experiments with marine residues. The Dewar flasks are suitable for estimating the potential compostability of fresh materials, but they have their limitations. The dynamics of a compost mixture change when the volume is increased from 2 liters to several cubic meters. And the bottles cannot be used to produce "finished" compost, which depends on being in contact with a variety of organisms over a long period of time. The experiments confirm that marine residues are suitable as raw materials in compost, both in combination with familiar materials such as horse dung and wood chips, but also alone (with Leca®). The Leca® aggregates, which do not contain carbon or nitrogen, work well as a structural material.