Large-scale Cultivation Of Chlorella Sp. In Floating Photobioreactor For Green Water Generating In Mariculture

The mariculture industry is developing rapidly due to the increasingly demand for aquatic products and the reduction of traditional aquaculture resources,but it is featured with serious environment problems,so it is imperative to control the aquaculture environment.As a primary producer in aquaculture environment,microalgae has an irreplaceable role in green water.Despite the increasing demand of microalgae in green water,the use of green water microalgae in aquaculture is still in its early stage.In mariculture system,there are few species of microalgae that used in green water,and backward in large scale cultivation of microalgae and the application of system.In order to solve these problems,the main contributions are as follows:In this study,a marine microalgae strain was isolated and purified from the cultuvations of Isochrysis Zhangjiangensis in Lingshui Bay in Dalian,and it was further identified as a Chlorella sp.by the morphological and molecular biology identification.The effect of bicarbonate concentration on the growth of Chlorella sp.was investigated,the results showed that the highest dry cell weight?DCW?and biomass productivity of cultivation were achieved in the medium with 7.0 g/L sodium bicarbonate,which were 1.20±0.0 g/L and 0.47 g/L/d,respectively.This culture also produced the highest recovery efficiency of 98.9±0.0%at the harvesting time of 24 h.And Chlorella sp.grew well in the medium supplemented with 0.4 g/L sodium nitrate.Additionally,the culture supernatant after microalgae flocculation could be used to absorb CO₂ for the recycling cultivation of Chlorella sp.The results showed that recycling cultures produced a better cultivation performance than the fresh medium cultures.In order to obtain a large number of green water microalgae,the effect of different culture depths on the growth of Chlorella sp.was investigated in floating PBR,firstly.The results showed that the highest cell density was obtained at the culture depth of 7.5 cm,which was0.743±0.0 g/L.Secondly,the growth of Chlorella sp.in open pond,flat panel and floating PBR was evaluated and compared.The biomass concentration in floating PBR was significantly higher than that of the other two systems?p<0.05?,where its highest biomass concentration was 0.532±0.0 g/L.Additionally,the cultures drawn from the floating PBR were used for investigating the stability of the flocculation in the outdoor cultures.The results indicated that the recovery efficiency was over 99%,indicating this flocculation method can be stable for large-scale outdoor cultures that had high pH values.In order to realize the controllable cultivation of green water microalgae,the growth model of Chlorella sp.was constructed.The initial parameters of each factor were determined by single factor experiment,and the parameters of growth model were obtained by parameter identification with least square method.The results showed that the established growth model had a good predictability for the growth of Chlorella sp.According to the results,a marine microalgae Chlorella sp.used for green water of mariculture was identified,and it was efficiently cultivated in the floating PBR,and the produced biomass showed the higher recovery efficiency.Compared with other cultivation systems,the floating PBR provides a better combination between microalgae cultivation and green water,since the fresh cells of Chlorella sp.can be produced in floating PBRs on site,and the green water inoculated with these cells in large-area mariculture water bodies can significantly increase success ratio of water quality improvement and supplying natural feed for aquaculture animals.More importantly,the growth model of green water microalgae not only provides the prediction and guidance for the inoculation and nutrient addition in the practice of green water,but also provides a theoretical foundation for the application of green water.