Data from: High-density cultivation of microalgae continuously fed with unfiltered water from a recirculating aquaculture system

Water from recirculating aquaculture systems (RAS) has been shown to be a suitable growth medium for microalgae and their cultivation can, therefore, be used to reduce RAS emissions. However, while efficient wastewater treatment is possible, the nutrient content of RAS water limits attainable microalgae biomass densities to 1–2 g l−1 at best, which requires frequent harvesting of microalgae. We have taken advantage of the constant evaporation of water from an open thin-layer photobioreactor (200 l volume, 18 m2 illuminated surface, artificial supply of CO2) to continuously add water from RAS to a microalgae culture and thereby provide nutrients for continued growth while evaporating all water. To test for a possible inhibitory effect of RAS water on microalgae growth, components of mineral medium were omitted stepwise in subsequent cultivations and replaced by RAS water as the only source of nutrients. This approach showed that microalgae can be grown successfully for up to three weeks in RAS water without additional nutrients and that high (20 g l−1) biomass densities can be attained. While growth in wastewater did not reach productivities measured in mineral medium, analysis of growth data suggested that this reduction was not due to an inhibitory effect of the RAS water but due to an insufficient supply rate of nutrients, even though RAS water contained up to 158 mg l−1 NO3-N. It is, therefore, concluded that this method can be used to fully treat the wastewater discharge of a RAS. Furthermore, because both water evaporation from and microalgae growth in the photobioreactor correlated positively with each other due to their shared dependency on solar radiation, supply of nutrients continuously adjusts to changes in demand. It is estimated that the area of a photobioreactor required to treat all emissions of a RAS requires approximately 6.5 times the area of the latter.

循环水养殖系统（recirculating aquaculture systems, RAS）产出的水体已被证实可作为微藻（microalgae）适宜的生长培养基，因此利用微藻养殖可有效削减RAS的排放。尽管该体系可实现高效的废水处理，但RAS水体的营养盐含量上限仅能将微藻生物质密度维持在1~2 g·l⁻¹左右，这意味着需要频繁采收微藻。本研究利用开放式薄层光生物反应器（photobioreactor，容积200 L、光照表面积18 m²、人工补给CO₂）持续蒸发水分的特性，将RAS水体连续通入微藻培养体系，在为微藻持续生长提供营养盐的同时实现水体完全蒸发。为验证RAS水体是否会对微藻生长产生抑制作用，我们在后续培养实验中逐步省略矿物培养基的组分，仅以RAS水体作为唯一营养盐来源开展培养。结果显示，微藻可在无需额外添加营养盐的RAS水体中成功培养长达三周，且可获得高达20 g·l⁻¹的生物质密度。尽管废水中的微藻生长速率未达到矿物培养基中的水平，但生长数据分析表明，该差异并非源于RAS水体的抑制作用，而是由于营养盐供应速率不足——即便RAS水体中硝态氮（NO3-N）含量可达158 mg·l⁻¹。据此可得出结论：该方法可实现RAS废水排放的全量处理。此外，由于光生物反应器的水分蒸发与微藻生长均依赖太阳辐射，二者呈正相关关系，因此营养盐供应可随生长需求的变化自动调整。据估算，用于处理一套RAS全部排放所需的光生物反应器面积约为该RAS系统自身面积的6.5倍。