In recent decades, one of the most important innovations and trends in tilapia culture has been towards a circular bioeconomy, as characterized in this review by several recirculation systems, such as biofloc technology (BFT), recirculation aquaculture systems (RASs), bio-RAS, partitioned aquaculture systems (PASs with split ponds, SPs, and in pond recirculation systems, IPRS) and integrated multitrophic aquaculture (IMTA).
Resource flow in a circular economy can help reduce the use of increasingly scarce resources, reduce waste production and limit energy consumption. In a world with a growing demand for clean water and healthy food, the economy in a linear model is no longer adequate, since modern societies cannot build a future under a ‘take-do-discard’ model.
The movement towards environmentally sustainable systems are necessary through circular and life cycle thinking to preserve our finite natural resources. Water, in particular as a valuable resource, must be treated with respect and managed with methods to reuse and conserve it, putting it into action the concepts of circular bioeconomy.
Circular Bioeconomy without Effluents
The circular economy can be defined as a production strategy that aims to reduce inputs, as well as waste production, close economic and ecological resource flows or links, decentralize production systems (local production and consumption) and question tools for measuring economic performance and the role of money and finance in building natural and social economic capital.
The analysis of physical resources flows are of two main types:
(1) linear, where biological wastes (nutrients) are expected to be reintroduced into the biosphere, and
(2) circular, with biological wastes (nutrients) being recirculated and used again in the production system, not returning to the biosphere.
Traditional aquaculture generates wastes that are deposited directly into nature, providing high levels of nitrogen and phosphorus to the natural environment. These represent a threat to human health, the welfare of fish and shrimp and the overall environment.
“The frequent diseases that occur in aquaculture and the growing demand of the population for clean, sustainable aquafarming that is environmentally friendly are leading to the development of alternative production models with greater and more efficient controls, increase in predictability and repeatability of activities.”
These include a series of structural changes in aquaculture activity that consider the treatment of water and waste through closed landbased recirculation aquaculture systems (RASs) and the reuse of waste as nutrients.
The partial or total reuse of water from aquatic crops has generated a series of land based RAS, undoubtedly the most important innovation in aquaculture in recent decades when integrated with complementary systems forming a donor and receiver system.
Recirculation is based on the movement of water through various compartments, tanks or ponds of different sizes. The water passes from one compartment to another and is partially or totally reused, depending on the intensity of the culture, ranging from more extensive/semiintensive ponds to intensive/superintensive tanks.
The more intensive systems make use of sophisticated biofilters, compartments with biofilters, mechanical filters, geo-membranes/liners and various treatment methods, using any species grown in conventional aquaculture such as fish, crustaceans, molluscs, algae, and so on.
“Recirculation technology is widely used today in tropical fish farms, primarily for biosecurity reasons. RAS is showing enormous growth in marine shrimp, bivalve and seaweed farming, especially in the initial phases (hatchery and nursery).”
There is also enormous investment in recirculating water in salmon farming, but at low temperatures filter microorganisms are not very efficient, which greatly increases the costs of biofilters and additional structures.
Low water demand systems, either in isolated or recirculating compartments with intense aeration and a high load of omnivorous tilapia or shrimp (more than 8 units/m3 for fish and 100 units/m3 for shrimp) end up spontaneously generating bioflocs.
In a single compartment, for example, a pond or tank, bioflocs are known as BFT (from biofloc technology). By recirculating the water in more compartments, this system can be called bio-RAS, a combination of the BFTs and the RAS. The primary objective is to improve the biosecurity of crops in places where water is scarce and/or land is expensive since the minimum exchange of water reduces the incidence of diseases.
The recirculation and reuse of water is the most classic application of the circular economy in aquaculture.
These techniques are deployed in several aquaculture systems with possibilities of ‘zero effluents’ (Figure 1), whose focus is to maintain stable water quality and levels through the recycling of nitrogenous and carbon components, carried out mainly by specific bacteria, which are stimulated by the balance/ratio of carbon and nitrogen (C:N) in the water.
Recirculation Aquaculture Systems
The main objectives of a more extensive recirculation aquaculture system (RAS) in ponds is to conserve water and generate less effluent that could damage the surrounding environment. To achieve this, an increased technology level is needed, which by default increases productivity.
Despite the productive and environmental advantages, the reuse and maintenance of water quality, especially in more intensive RAS, will depend on a series of structures and equipment that are still relatively expensive, such as: settlers, mechanical filters, biological filters, ultraviolet lamps (disinfection), water pumps, air blowers, power generators, emergency aeration, ozone generation, and so on (Figure 2).
In addition to the high investments in building structures and equipment, there are high operating costs such as electricity, maintenance and depreciation. This is in part compensated for by the flexibility to locate production facilities near large markets, complete and convenient harvesting, and quick and efficient disease control.
RAS have been widely used for hatcheries and nurseries for both freshwater and marine aquaculture. In recent years, large scale production with RAS for grow-out to harvest size has come into commercial success.
Unfortunately, there were significant number of failures in RAS commercial operations before the more recent successes.
The bioflocs are composed of assemblages of heterotrophic, nitrifying and cyano-bacteria as well as various algae and fungi. Therefore, compared with the more intensive RAS, it does not require filtration structures and can simply consist of tanks and aerators/pumps (Figure 3).
The bioflocs in a single compartment (BFT) can be inserted into a recirculation system (optional), with a settler (optional) to control excess solids, a drainage system (optional), a blower and/or water pump and power generators.
The structural and operational advantages of a BFT allows cultivation with high loads of suspended solids in the water, characteristics that affect different species produced in the RAS, but do not impact omnivorous filter-feeding species such as tilapia and marine shrimp, two of the most used species in BFTs around the world.
The ability to work with a relatively high solids load makes the BFT less dependent on mechanical filters. It also abolishes the need for either partial water exchange or a secondary denitrification system typical of a highly intensive RAS.
Bio-RAS is the combination of RAS with BFT (a recirculation system with bioflocs in more than one compartment). The advantages of BFT over classical RAS became apparent three decades ago, when different systems based on bioflocs were developed.
Currently, there is a trend to merge these two low water demand systems to optimize crops with a reduction in production costs (especially food and electricity). The bio-RAS strategy uses the best and most efficient of each of the previous technologies, with cost reduction combined with the maximization of technological, zootechnical and animal welfare efficiency and the sustainability of the crops.
Bio-RAS has been used in the last decade in a number of low-cost aquaculture projects (Figure 4). In bio-RAS and bioflocs can form in part in one or more compartments, or in the entire circulating water.
Partitioned Aquaculture Systems
The objective of a partitioned aquaculture system (PAS) is to produce zero effluents, where fish are confined in high densities in concrete tanks (raceways) or smaller channels/ponds, around 5% of the total area for the tank and 95% of the pond or lake for recirculation and reuse of water.
The fish residues from its catabolism circulate and recycle through the water body where there are high concentrations of algae (fertilized by these residues), similar to a domestic wastewater treatment, which increases or even doubles the support capacity of the system.
“By doubling the rate of photosynthesis of algae in these generally isolated baffles and ponds, the rate of removal of nitrogenous, phosphorous and other waste products double, thus doubling the potential maximum feeding rate and the consequent carrying capacity to sustain the system and the fish and shrimp production.”
PAS represents a high degree of intensification of previously extensive ponds and reservoirs where phytoplankton predominate. In its various forms, productions in the range of 10–50 tons of tilapia per hectare of surface or 10,000 m3 of total volume are attainable.
Its two main variations are increasingly common around the world:
(a) IPRS for in pond raceway system with a pond/reservoir/lake holding cages, raceways or containers and
(b) SPs for split ponds (Figure 5).
IPRS confines omnivorous fish at high densities in cages or raceways (channels with high water flow) installed along the inside periphery of an existing lake or pond. The water recirculates through the large bodies of water that assimilates the waste from the small, cultivated areas, facilitating the feeding, sampling, protection and harvest of the fish.
Although IPRS was originally designed for channel catfish aquaculture in the southern United States, its use expanded and became more popular in the farming of carp, tilapia and other omnivorous fish in China, India, Brazil, Colombia, Thailand and several other countries.
Integrated Multitrophic Aquaculture (Aquaponics and Ferti-irrigation)
In an integrated multitrophic aquaculture system (IMTA), two or more complementary species with different trophic levels or niches are farmed.
For example, tilapia with shrimp and seaweed in brackish water. Another example would be tilapia, silver carp and water lotus in freshwater. In some cases, fish and terrestrial animals and/ or hydroponics (vegetables) could be in the same production system as recirculation with single or multiple loops.
“The integration between aquatic and terrestrial species (such as plants, pigs, poultry, among others) is maintained with multiple relationships between resources (such as space, water, food or nutrients). Generally, these are shared between different species, thus offering greater potential in terms of technical and economic efficiency and redundancy.”
IMTA combines the cultivation of fed species (e.g., tilapia + shrimp) with extractive (species, grazers and filter feeders) feeding on organic matter (echinoderms, molluscs, especially bivalves, micro-crustaceans and worms, other herbivorous fish) and inorganic extracting species (such as phytoplankton and marine macroalgae or hydroponic vegetables).
The goal is to match in the right proportions to create balanced systems that generate environmental and economic sustainability and social acceptability. In addition, the sludge from RAS and bio-RAS systems can be reused as predigested ingredients (highly digestible) in rations for aquatic and terrestrial animals (Figure 6).
Aquaponics is one of the classic examples of IMTA, an interaction between hydroponics and aquaculture, where one crop benefits from the by-products of another, making the respective ecological ‘bottlenecks’ of both systems become strengths, considerably reducing the need for inputs, nutrients and effluent production, unlike when the same systems are run individually (Figure 7).
Comparing the Systems
In 2021, the Brazilian Ministry of Agriculture published a booklet with the main characteristics and production costs of several tilapia intensive rearing systems, such as BFT, bio-RAS, ponds and cages from the States of Sao Paulo and Paraná (subtropical climate).
The authors stressed that the comparison between technologies should go beyond the observation of the production costs per ton of tilapia.
“It is very important to evaluate the Capital Expenditure/Operational Expenditure (CAPEX/OPEX), and especially the increasing land costs (not considered in the study, thus favoring the more extensive systems such as IPRS and SP), as well as water volumes and the annual production potential of each technology.”
This last feature altered the financial result and may favor one or another technology. This is the case of BFT and bio-RAS, which could perform 2.6–3.0 cycles per year, with the financial differential of low water requirement production technologies, where management efficiency should reach high levels for the systems to be viable, as well as the appeal of being environmentally sound.
This study was later published in more detail with a short economic analysis, and it is summarized together with other references characterizing the systems in Table 1.
Tilapia culture will evolve along with the trends in food production that are increasingly urban, ‘on the roofs of supermarkets’ and in urban industry facilities, where aquaponics and water saving/ recirculation systems will be the producers of these new forms of Circular Economy.
During the COVID-19 years and more recently the war in Ukraine, it is clear that the increasing disruptions of the centralized extractive industries that today sustain the global economy in the five main sectors (materials, energy, information, transport and food/ health), are evolving into a more local model.
It is suggested that production and process costs could decrease by an order of magnitude of 10 times by 2030, that is, we will use 90% less natural resources and produce 10 times less waste.
“Modern tilapia culture systems with resources flowing in a circular economy will reduce the use of increasingly scarce resources such as water, energy, labor and especially feed ingredients, minimizing waste production. Novel pre-digested doughlike feeds (FermentAqua®), produced from inexpensive by-products or diet ingredients are replacing traditional diets with low costs and improvements in productivity.”
The convergence of precision fermentation and water circularity is enabling rapidly falling costs. The recirculation systems characterized in this review include: BFT, RAS, bio-RAS, PAS with SPs and IPRS and IMTA.
Each system has different characteristics in terms of production costs, carrying capacities, FCR, cycles per year, CAPEX/OPEX, financial characteristics, water requirements, production technologies and can be chosen based on specific situations such as land prices, market demands/ distance, water availability and several other parameters.
This article is sponsored by: REEF INDUSTRIES INC.
This is a summarized version developed by the editorial team of Aquaculture Magazine based on the review article titled “THE FUTURE OF INTENSIVE TILAPIA PRODUCTION AND THE CIRCULAR BIOECONOMY WITHOUT EFFLUENTS: BIOFLOC TECHNOLOGY, RECIRCULATION AQUACULTURE SYSTEMS, BIO-RAS, PARTITIONED AQUACULTURE SYSTEMS AND INTEGRATED MULTITROPHIC AQUACULTURE.” developed by: Sergio Zimmermann – R&D, Zimmermann Aqua Solutions, Sunndalsøra, Norway; Anders Kiessling – Department of Animal Nutrition and Management, Swedish University of Agricultural Sciences and Jiasong Zhang- South China Sea Fisheries Research Institute, Chinese Academy of Fishery Sciences.
The original article, including tables and figures, was published on SEPTEMBER, 2022 through REVIEWS IN AQUACULTURE.
The full version can be accessed online through this link: DOI: 10.1111/raq.12744