Samenvatting

In the Province of Zeeland, ragworms (Alitta virens) are farmed on large scale in open rectangular (flow through systems) ponds. In April these ponds are stocked with ragworm larvae from a hatchery. 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 process water produced by ragworm farming has great potential for growing microalgae and subsequently shellfish. This research amis to model the reuse to process water from ragworm culture.
In this research, Topsy Baits and Delta Farm are the chosen companies to investigate, by means of model which has been setup. Firstly, the composition of waste water in ragworm ponds is analyzed and then nutrients (nitrogen and phosphorus) balance equation is built based on the different parameters. Secondly, it is assumed that only N and P limitation for the microalge prodcution. A link between nutrients and algae dry weight is established based on literature study. Thirdly, a model for the relation between microalgae and shellfish production was used based on the food conversion rate.
The model was calibrated by means of comparing field data with model data. Waste water composition vary between the two ragworm production locations and between ponds and different months at the same production location. Therefor a more intensive monitoring at production locations is needed. The results of the calibration show that the model results are in the same order of magnitude as some field measurements. . However model formulations and parameter settings in it can be improved and optimized, especially calculated P concentrations seems to be under estimated in the model.
Based on the model calculations, the algae production in dry weight can achieve about 27.9 tons and shellfish production in wet weight can achieve about 61.9 tons with reuse of all waste water at Delta Farm.