Remediation and valorization of process streams in ragworm culture
In the Province of Zeeland ragworms (Nereis virens) are farmed on large scale (6 ha) in open rectangular (flow through systems) ponds. In April the ponds are stocked with ragworm larvae from the hatchery. From a certain size/ age on the juveniles bury themselves in the sediment layer in the pond and are fed with feed pellets. Dependent on the market (bait for fishing or maturation feed for shrimp farming) market size ragworms are harvested after 7 – 20 months.
The waste water which is produced by ragworm farming has great potential for growing micro-algae and subsequently bivalves. However, little is known about the composition in terms of dissolved nutrients and particles of the waste streams, under different conditions (density of ragworms, seasonal variations, amount and type of feeding, etc.).
During the winterperiod however, ragworms are not fed, so no experiments in the actual farm were possible. Therefore labscale experiments were set up in Spring 2017 to determine the effect of feeding regime and ragworm density on the amount of nutrients in the waste water, sediment, and ragworms themselves. Also the potential for production of the micro algae Skeleletonema costatum was investigated in controlled small scale experiments. Having done these studies on labscale, the question arose of how compatible these results are with reality. Therefore experiments need to be designed to investigate the nutrient compositions in the actual ragworm farm and the way to optimize this for micro algae production.