FLOCponics: The integration of biofloc technology with plant production

Author(s)

Sara M. Pinho

• Document type: Doctoral Thesis
• Press: Jaboticabal. 2022-05-11.
• Institution: Universidade Estadual Paulista (Unesp). Faculdade de Ciências Agrárias e Veterinárias. Jaboticabal
• Defense date: 2022-02-22
• Advisor: Maria Célia Portella

Abstract

Aquaculture has been responsible for providing healthy food for the growing population. Aquaculture contribution to the global food production scenario is expected to continuously grow through intensive and sustainable production methods, such as biofloc-based culture and aquaponics (integration of fish-plant production). This thesis explored a new aquatic-based food production method, i.e., the integration of biofloc-based aquaculture with soilless plant (hydroponics) production in so-called FLOCponics systems. FLOCponics is a special case of integrated agri-aquaculture, where nutrients from a biofloc-based culture are used to nourish and irrigate plants in a hydroponics subsystem. FLOCponics is quite a new research field, and little is known about fish and plant productivity, resource use efficiency, and sustainability of this integrated system. Developing a better understanding of FLOCponics may bring advantages to food producers and society. In this context, the overall aim of this thesis was to investigate and discuss the technical feasibility, efficiency and sustainability of on-demand coupled FLOCponics for tilapia juveniles and lettuce production. For that, the following specific objectives were formulated: (1) To identify the status quo of FLOCponics, highlight current FLOCponics challenges and give directions for further research. (2) To determine the technical feasibility of producing tilapia juveniles and lettuce in on-demand coupled FLOCponics compared to traditional (RAS-based) on-demand coupled aquaponics, hydroponics and biofloc-based monoculture systems. (3) To determine how the reduction of protein content in the fish diet affects fish and plant growth, dietary nutrient use by fish and water quality in on-demand coupled FLOCponics system. (4) To investigate the efficiency of on-demand coupled FLOCponics system in terms of resource use and amount of food produced and discuss the overall advantages and disadvantages of FLOCponics compared to biofloc-based fish culture. (5) To assess and discuss the sustainability of biofloc-based fish culture with and without integrating with hydroponic plant production and provide insights on how to improve the sustainable character of food production in such systems. (6) To identify suitable fish species for aquaponics and discuss their applicability to diversify FLOCponics’ products. To achieve the research objectives, the thesis comprises seven chapters. Chapter 1 presents a general introduction containing a brief background on the topics that guide this thesis, including biofloc-based aquaculture, aquaponics, and the methods to measure the systems’ efficiency and sustainability. Chapter 2 critically reviews and analyses the FLOCponics research regarding the system setups, water quality and nutrient recycling, and the productive results of plants and fish. In this chapter, we also identified economic and environmental aspects and discussed the gaps, opportunities, and challenges of FLOCponics systems. In general, FLOCponics systems seem to be applicable in the short-term by farmers who already operate biofloc-based fish culture and seek to improve the system efficiency. An important contribution of this chapter was the identification of current FLOCponics drawbacks that are essentially related to systems’ design and operation and proper destination of solid wastes. The review paper presented in Chapter 2 served as a theoretical basis for the following chapters. An experiment was conducted to investigate and evaluate the production of tilapia juveniles and lettuce in an on-demand FLOCponics system to explore the technical feasibility of it compared to other production systems (objective 2) and to what degree is it possible to take advantage of the nutritional benefits of biofloc for tilapia production in such system (objective 3). For that, tilapia juveniles and lettuce were cultured in on-demand coupled FLOCponics, traditional aquaponics using recirculating aquaculture system (RAS), biofloc-based monoculture, and/or hydroponics systems, and four fish diets were formulated, produced, and tested in FLOCponics systems. The findings of this experimental trial are reported in Chapter 3. We found similar lettuce yields in on-demand coupled FLOCponics, RAS-based aquaponics and hydroponics systems. With respect to fish production, FLOCponics outperforms fish yield of RAS-based aquaponics by 24%. In addition, benefits of bioflocs for fish nutrition were also seen in on-demand coupled FLOCponics systems, leading to 8% reduction in the fish dietary crude protein compared to RAS-based aquaponics. These results indicated that on-demand coupled FLOCponics systems are technically feasible and allow a reduction in the crude protein content in fish diets and thus can be used as an alternative feeding strategy in an integrated system. Chapter 4 follows a dynamic modelling approach to investigate the efficiency of FLOCponics system compared to stand-alone biofloc-based system. The results showed that, in general, FLOCponics was more efficient in using resources than the biofloc system. The water and nutrient use efficiencies were higher in FLOCponics than in biofloc system by 10 and 27%, respectively. The volume of solids discharged in FLOCponics was 10% lower than in biofloc-based fish monoculture. When performing scenario simulations, the FLOCponics system was even more efficient by expanding the planting area up to 3.2 times in relation to the nominal case. The findings presented in this model-based study support the hypothesis that integrating with hydroponics makes biofloc-based fish culture more efficient in terms of resource use and wastes avoidance. Assessing the sustainability of food production systems in their early stage of development is essential to identify unsustainable practices and guide further research to avoid them. In Chapter 5, we applied emergy synthesis to compare the sustainability of stand-alone biofloc and hydroponics systems with their integration in a FLOCponics system, based on the previews experimental results. The emergy indicators indicated that FLOCponics is as sustainable as the stand-alone biofloc and hydroponics systems. Additionally, we found that the unit emergy value (UEV) in FLOCponics was 104 times lower than in hydroponics system, indicating higher efficiency. On the other hand, FLOCponics was less efficient in converting energy to outputs than biofloc system, as the UEV of FLOCponics was 78% higher. The emergy synthesis of the FLOCponics system pointed out that further improvements must be made to increase the efficiency of the system and explore its full potential for sustainable food provision. Chapter 6 reviews fish species suitable for aquaponics as a mean to improve the diversification of integrated agri-aquaculture systems. This chapter presented the characteristics that make a fish species sustainable for each system layout (permanently or on-demand coupled). In permanently coupled RAS-based aquaponics, the choice of fish species depends on the crop grown. In on-demand coupled RAS-based aquaponics, the choice of the fish species is directly dependent on the fish market acceptance, production costs and growth rate. In general, fish suitable for RAS production are also suitable for RAS-based aquaponics. The implications of the findings of Chapter 6 on FLOCponics is discussed in Chapter 7. The diversification of FLOCponics can be increased by producing alternative fish species suitable for the biofloc-based systems, as tambaqui, pacu or jundia. Lastly, Chapter 7 discusses the main findings of the thesis, highlighting the advances in the FLOCponics research field and their social impacts. From a broad perspective, FLOCponics can bring the production of a mix of fresh and healthy food close to the consumer. That is because FLOCponics seems suitable for implementation in regions usually not destined for food production, contributing to increasing food security and fair food distribution. As a final remark, developing FLOCponics to be a representative activity for food supply guarantees more efficient use of resources and contributes to sustainable aquaculture development. (AU)

• FAPESP's process: 18/13235-0 - Technological innovations for the use of biofloc systems in decoupled aquaponics
• Grantee: Sara M Pinho
• Support Opportunities: Scholarships in Brazil - Doctorate