A new and improved aquaponics system model for food production patterns for urban architecture

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With the rapid speed of urbanization… Many experts confirm that 85% of the world’s population is expected to live in cities by 2050.

Yong Zhang ab, Yu-kun Zhang a, Zhe Li aaSchool of Architecture, Tianjin University, Tianjin, ChinabCollege of Landscape Architecture and Art, Northwest A&F University, Xi’an, China

Received 6 September 2021, Revised 5 January 2022, Accepted 7 February 2022, Available online 10 February 2022, Version of Record 21 February 2022. What do these dates mean?

Handling Editor: Cecilia Maria Villas Bôas de Almeida

Source: https://www.sciencedirect.com/science/article/abs/pii/S0959652622005054

Abstract

Productive cities are one of the most important ways to achieve urban sustainable development. In the comprehensive production function, food production is the most basic function and should be defined as a priority. Considering the characteristics of buildings and the limitations of the urban environment, aquaponics is a safe and healthy green technology that protects the ecological environment and that has high potential to combine urban buildings and plant cultivation technology. Research on aquaponic systems has become increasingly mature, but some new problems that cannot be ignored, such as low nitrogen utilization efficiency, high aeration cost and noise problems, and unreliable water quality. In this study, a new aquaponics system model (photosynthesis reoxygenation aquaponics, PRO-AP) was proposed, and it was expected that the structure of the system can be adjusted by adding macroalgae to improve the existing problems in aquaponics. An experiment was conducted to preliminarily explore the feasibility of the proposed mode of operation. Spirogyra was added to the aquaponics system, and the DO, pH, TDS, EC, ammonia nitrogen and removal of the key nutrients from the systems were monitored during the operation. The results showed that the dissolved oxygen content in the system increased markedly and that the pH drop caused by nitrifying bacteria could be balanced when Spirogyra was irradiated with effective light. In addition, Spirogyra played a certain role in biofiltration in the aquaponic system, which reduced the values of TDS and EC, the contents of NH4+, NO3− and PO43− also decreased, and the nitrite content first increased and then decreased after a period of time. Finally, under the ratio of fish and vegetables in this experiment, the existence of Spirogyra did not create a negative image of the yield and root system of vegetables in aquaponics systems. The results showed that the aquaponic system with macroalgae has a stronger self-regulation ability. PRO-AP is an effective method in urban food production and is a very promising mode of production in the sustainable development of productive cities.

Introduction

With the rapid speed of urbanization, an increasing majority of the world’s population (more than 50%) lives in cities (Hatuka et al., 2018; Zarco-Perinan et al., 2021). In addition, many experts confirm that 85% of the world’s population is expected to live in cities by 2050 (Ramirez-Moreno et al., 2021). As a high population concentration area, cities are exposed to various problems or disasters, such as food shortages, energy shortages, clean water shortages, land loss, and traffic congestion (Kabir et al., 2018). Among these potential problems, FEW (food, energy and water) shortages are still potentially dangerous to becoming a social crisis (Yuan et al., 2021). However, a growing group of cities are considering urban agriculture as a promising avenue for improving both the sustainability and resilience of the city-region food system (Morgan, 2015). Moreover, agriculture has even become a focus of planning for urban regeneration in the United States (Vitiello and Wolf-Powers, 2014). With the development of urban agriculture (UA), producing food inside cities with UA increases agricultural performance and contributes to food safety for vulnerable people with fewer resources, among others. A growing group of cities considers urban agriculture a promising avenue for improving both the sustainability and resilience of the city-region food system, and increasing a building’s energy performance has proven to be very helpful in alleviating the pressure of energy shortages. However, the pursuit of urban agriculture is often a challenge, particularly within compact cities. When compared with green roofs, green walls have a larger potential surface area for greening because in tall buildings, the area of the walls is always greater than the area of the roof. Therefore, green walls can play an important role in urban rehabilitation, and they can contribute to the insertion of vegetation in the urban context without occupying any space at the street level. Applying double skin façades is not a new concept; however, it has not been approved as a productive space and light environment regulation system for buildings. To achieve this purpose, a constructing mode of the “Productive Architectural Surface System” (PASS) was proposed.

Although the principle of productive cities is well accepted, further study of the concept and assessment methodology for the food production mode is absent. Food production within buildings in cities can take many forms, and three main integrated modes for combining productive space with existing buildings have been proposed. Rooftop greenhouses (RTGs), indoor vertical farming, green façades and living wall systems (LWS) (Manríquez-Altamirano et al., 2020; Sanyé-Mengual et al., 2018). The choice of food production of the UA method will vary due to the circumstances of different communities and their preferences, but the benefits of UA can be generalized. UA has the potential to increase access to healthy and nutritious food, strengthen local economies (Zhong et al., 2020), and promote a sense of community (Kingsley et al., 2021).

Among the different food production systems mentioned above. As a specific production mode of the system, aquaponics have received considerable attention from scientists and governments in recent years due to their potential for sustainable food production (Greenfeld et al., 2021). Aquaponics is an integrated system that links hydroponic plant production with recirculating aquaculture systems (RASs) (Farrant et al., 2021). Aquaponics is the process of growing aquatic organisms and plants symbiotically, in which the effluent of aquaculture undergoes microbial transformations to be used as a source of nutrients for plant growth, while nutrient absorption from plants remediates water for aquaculture (Yep and Zheng, 2019). Very few production factors are needed, and aquaponics systems use resources and energy more efficiently than single production systems. Additionally, there is no need for soil in the production process. Therefore, it is a facilitating sustainable and environmentally friendly food production system for urban buildings.

Aquaponics systems can be set up almost everywhere and have the potential to urbanize food production. This could bring important socioenvironmental benefits. Implementation Aquaponics farming plants could in old industrial neglected buildings with the advantages of re-establishing sustainable activity without increasing urbanization pressure on land (Goddek et al., 2015). However, there is a lack of quantitative research to support the development of suitable aquaponics systems for urban buildings. Three main problems are a priority and should be addressed. A model organically combining architecture with aquaponic systems should be constructed. Then, the key element of excellent combination between existing buildings and aquaponics systems must to be determined. Finally, the key performances and stability of new aquaponics systems need to be systematically validated.

Compared with green roofs, green walls have a larger potential surface area for greening because the area of the walls is always greater than the area of the roof in tall buildings. Thus, green walls can play an important role in urban rehabilitation and contribute to the insertion of vegetation in the urban context without occupying any space at the street level. Given these constraints, this research proposed new integrated modes for combining the productive space with the existing buildings—productive double-skin facades (PDSFs)—as shown in Fig. 1.

Aquaponics is a modern agricultural production mode that integrates planting and breeding and is considered to have great potential for innovation and sustainable development (Greenfeld et al., 2019; Silva and Van Passel, 2020). Research shows that among many ecological compound-farming models, aquaponics have a complex community structure, high self-purification ability and stable ecological environment; the same land could be simultaneously and profitably utilized to produce different crops and livestock enterprises so that the productivity of the land is increased (Kloas et al., 2015; Samuel and Mathew, 2014). It has been proposed as a sustainable solution to solve the current food production challenge because it recovers more than 98% of aquaculture wastewater (Wongkiew et al., 2017).

Compared with the general aquaponics system, there are several basic design criteria for aquaponics integrated with existing buildings. First, the aquaponic system must be highly modulated and organic integrated. Second, the system should have an efficient self-purification function and higher stability. Third, the system should meet the acoustic requirements of domestic architecture; in other words, the system cannot make too much noise. The system must be as quiet as possible. The new type of aquaponics should satisfy the criteria mentioned above.

Research on aquaponic systems has become increasingly mature, but there are still some problems that cannot be ignored, such as low nitrogen utilization efficiency (Paudel, 2020; Wongkiew et al., 2017), high aeration cost (Tokunaga et al., 2015), unreliable water quality (Fang et al., 2017) and accumulation of nitrate-nitrogen (N03–-N) in aquaculture water, which limits the popularization and development of aquaponic systems. Although many optimization measures have been taken to improve the sustainability and reliability of hydroponic technology, such as adjusting key operating parameters and changing technical strategies (Fang et al., 2017; Pinho et al., 2017), the improvements of these measures are limited. All of the issues mentioned above indicate that dissolved oxygen (DO) is the most important indicator of water quality in aquaculture ponds (Qin Ren et al., 2018). Insufficient or excessive oxygen will adversely affect the living environment of fish.

Dissolved oxygen in an aquaponic system is significantly influenced by water quality, which is affected by many environmental factors (Q. Ren et al., 2018a, Ren et al., 2018b). However, oxygen production by algae photosynthesis is the main source of increasing dissolved oxygen content in water, and 76.9% of dissolved oxygen content in water comes from algae photosynthesis (Dalla Santa and Vinatea, 2007). In this context, algae are able to convert a large amount of CO2 into biomass, releasing even more oxygen through photosynthesis (Chew et al., 2021). Previous studies have shown that dissolved oxygen in water can be as high as two times saturation in the case of abundant algae (Li et al., 2021).

Algae composition has been proven to play a positive role in aquaponic systems. They are able to produce chemical energy that has much higher photosynthetic efficiency, 4.0–8.0% for microalgae and 10.0% for macroalgae, than terrestrial biomass, which is approximately within 0.5–2.2% (Chew et al., 2021). Some studies at home and abroad have analyzed the application of microalgae in the internal circulation of aquaponic systems. Microalgae can help the system balance the pH value, increase dissolved oxygen in water, control ammonia in the system and improve the ammonia utilization rate (Addy et al., 2017; Askari-Khorasgani and Pessarakli, 2020; Fang et al., 2018). Although algae are very important elements for aquaponics, they have not been proposed as an element of normal aquaponics, and their influence on the performance of the whole production cycle of aquaponics has not been discussed in depth. Therefore, it is necessary to find algae species with large morphology, strong decontamination ability and no need for fixation and to explore their application value in aquaponic systems. Therefore, a sustainable aquaponics system mode, photosynthesis reoxygenation aquaponics (PRO-AP), was constructed in this study, which can improve the stability of ecosystems, increase species diversity (Loreau, 2000) and utilize special physiological functions of algae (Liu et al., 2020).

By comparing the different illumination conditions of algae, the effects of different illumination conditions on the DO concentration and pH level of aquaponics system were clarified, and the more suitable illumination methods of PRO-AP were determined. The supplementary effect of algae on dissolved oxygen in aquaponics system was discussed. Compared with AP, the changes of dissolved oxygen and pH of PRO-AP in a plant growth cycle were measured. The aim of this study was to verify the feasibility of integrated macroalgae and aquaponics and provide a new approach for clean and green PRO-AP.

Section snippets

New aquaponics construction design

With the multiple criteria of the combination of aquaponic systems and existing buildings, the PDSF model was established, as shown in Fig. 1. It may become an innovative architectural envelope that can provide stable environments for both people and plants. The mode of the PRO-AP proposed in this paper was different from AP in that it had an algae culture unit at its end. In principle, the sustainable aquaponics system mode was the symbiosis of fish, microorganisms, vegetables (plants), and

Dissolved oxygen in PRO-AP

Dissolved oxygen (DO) is an important indicator in aquaculture (Ren et al., 2020; Zhu et al., 2019). Nitrifying bacteria need enough dissolved oxygen at any time, and the root system of plants needs oxygen for respiration and growth. Therefore, dissolved oxygen in aquaponic systems is also a key indicator. In the experiment conducted in this study, all three experimental conditions were conducted on sunny days.

ModeⅠ: Only water circulation between the algae culture tank and aquaculture was

Conclusion

Based on the classic aquaponics system (AP), the new urban food production system PRO-AP within PDSF was constructed. All key elements (fish, vegetables, bacteria, algae) were organically integrated. In this chapter, not only are the conditions of algae in the system compared and selected, but the ability and rate of DO supplementation of Spirogyra are also explored, and the following conclusions are drawn:

  • (1)The new aquaponic system PRO-AP based on effective photosynthesis of Spirogyra can

CRediT authorship contribution statement

Yong Zhang: Writing – original draft, Conceptualization, Methodology, Software, Supervision, Conceptualization, Methodology. Zhe Li: Supervision, Methodology, Writing-review & correcting, Provide project support.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

This work was supported by the National Natural Science Foundation of China (51878439, 51878437, 51908179) and the Project of Key Laboratory of Ministry of Culture and Tourism (20180508). This work was also supported by the Youth Foundation for Humanities and Social Sciences of the Ministry of Education (17YJCZH095).

References (50)

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