Imece2014‑39441
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Proceedings of the ASME 2014 International Mechanical Engineering Congress and Exposition IMECE2014 November 14-20, 2014, Montreal, Quebec, Canada IMECE2014-39441 AQUAPONICS: A SUSTAINABLE FOOD PRODUCTION SYSTEM Maryam Shafahi Daniel Woolston Mechanical Engineering Department Mechanical Engineering Department California State Polytechnic University California State Polytechnic University Pomona, CA, USA Pomona, CA, USA ABSTRACT re-circulating aquaculture, water discharge/replacement is 5% Aquaponics is an eco-friendly system for food production to 10 % of re-circulating water volume per day which makes utilizing aquaculture and hydroponics to cultivate fish and crop these systems subject to discharge restrictions due to concerns without soil. It is an inexpensive symbiotic cycle between the with environmental waste management [1]. Aquaponics does fish and plant. In an aquaponic system, fish waste (ammonia) is not have any of those problems since Nitrogen compounds are fed into the plant bed which acts as a bio-filter and takes the taken by plants providing clean water for the fish. The nitrate which is essential to grow vegetation. The fresh new development of modern aquaponics is often attributed to the water is then returned to the fish enclosure to restart the cycle. A various works of the New Alchemy Institute at the North unique advantage of an aquaponic system is conserving water Carolina State University where researchers developed the use more effectively compared to traditional irrigation systems. of deep water culture hydroponic grow beds in a large-scale Conservation of water is accomplished by recirculating water aquaponics system in the 70s [4]. between the plant bed and the fish habitat continuously. Organic fertilization of plants using dissolved fish waste is the other Although the word ‘aquaponics’ naturally implies the benefit of aquaponics. Utilizing plants as a natural alternative to freshwater systems, there is ongoing work in Israel and other filters, requires less monitoring of water quality. In our Australia on using saltwater in the production of saltwater algae project, an aquaponics system was designed and built in Lyle and seaweed as the plant elements, and sea finfish, sea Center for Regenerative Studies at California State Polytechnic crustaceans (shrimp), sea urchins and sea mollusks (shellfish University of Pomona. The future purpose of our project is such as abalone) as the animal elements [3]. finding an optimized situation for the aquaponics system to produce food and save water more efficiently and eco-friendly. Goodman [5] performed a cash flow analysis for an aquaponics system growing tilapia, perch and lettuce in Milwaukee, Wisconsin. She concluded that small scale 750 gallons systems INTRODUCTION are not profitable in temperate climates. Aquaponics consumes 10% of the amount of water used in traditional farming. It can Aquaponics is an integrated system that links hydroponic plant be safely mentioned as the most water efficient natural food production with re-circulating aquaculture. Hydroponics is a production system. term used to describe the plants production without soil. Plant roots grow in a nutrient solution with or without an artificial In our project we designed and built two aquaponics medium for mechanical support [1,2]. Aquaculture, also known systems in the Lyle Center of Regenerative Studies in Cal Poly, as aqua farming, is the farming of aquatic organisms which is Pomona. This article is on the design and manufacturing steps, the fastest growing sector of the world food economy, and important influencing factors of the systems. increasing by more than 10% per year [1]. One negative aspect of hydroponics is high demand for Nitrogen cycle expensive nutrients to feed the plants, and also periodic flushing of the systems which can lead to waste disposal issues. As for There are three stages of the nitrogen cycle as seen in figure 1: 1 Copyright © 2014 by ASME Calculations and Analysis Initial stage: The cycle begins when fish are introduced to the aquarium. Their feces, urine, as well as any uneaten food, are Sizing of the components in an aquaponics system is quickly broken down into either ionized or unionized ammonia. critical to ensure that the systems nutrient levels are properly The ionized form, Ammonium (NH4), is present if the pH is balanced and promote overall stability for the plants, bacteria below 7 which is not toxic to the fish. The unionized form, and fish. Since IBC totes and 55 gallon drums are selected for Ammonia (NH3), is present if the pH is 7 or above and is highly the construction of the project, these two components become toxic to the fish. Any amount of unionized Ammonia (NH3) is limiting factors for the design of system. By using optimum dangerous and it will be fatal for the fish once the concentration design ratios from existing works, it is possible to determine the reaches 2 ppm. Ammonia usually begins rising by the third day overall sizing of the remaining system components. after introducing fish to the system. A few assumptions must be made before completing the calculations. Firstly, since the fish rearing tanks are harvested Second stage: During this stage, Nitrosomonas bacteria oxidize and stocked in a staggered manner, the total density of both fish the ammonia and change it to nitrite, which is also highly toxic rearing tanks will never both be near the maximum 0.5 lb/gallon to the fish. Nitrites levels as low as 1 mg/l can be lethal to some recommendation. A conservative value of 0.3 lbs/gal will be fish. Nitrite usually begins rising by the end of the first week used instead. Additionally the hydraulic loading rate will be after introducing fish to the system. assumed at a value in the recommended range that allows for proper water retention time in the clarifier component of the Third stage: In the last stage of the cycle, Nitrobacter bacteria filtration of approximately 20 minutes. Lastly a feed to growing convert the nitrites into nitrates. Nitrates are not highly toxic to area was selected near the high value range, 0.33 oz. /ft^2, to the fish, in low to moderate levels. Established tanks should be reduce construction costs of the system and allow for board tested for nitrates every few months to ensure that levels are not lengths of readily available 16 feet lumber. becoming extremely high. Pump Requirements With the nitrogen process established, plants will consume nitrates and provide the system with clean water. In order to Pump requirements are based on frictional losses and maintain this dynamic system, the growing environment for height increases. To maintain a low cost and minimize pipe both fish and plant must be balanced. To ensure this, temperate, losses PVC piping was used. The pump that was chosen was a pH, and chemical components of the system must be monitored. basic pond pump, because it can handle the required loads at If the pH levels become too acidic, nitrifying bacteria will the required flow rates. suffer. Conversely, if the water becomes too basic, nutrient uptake of many micronutrients in the plants will be stopped. An ideal pH value of 7 is required to ensure a proper growing Major Losses environment for the plants, fish and nitrifying bacteria. Additionally the fish are going to need to be fed regularly and The major losses are dependent on fluid properties, the plants may need to be monitored against harmful pests. pipe properties, and flow properties. The water used has nutrients and chemicals that enrich the plants and fish. These nutrients are measured in parts per million and their effect on the fluid properties is negligible. The temperature ranges from 50 degrees Fahrenheit to 80 degrees Fahrenheit, based on the fishes required environment. The pipes are made of polyvinylchloride, or PVC. PVC piping is considered smooth. Pump Power To calculate the pump power, we obtain Reynolds number from equation 1 and based on the flow regime, head losses will be Figure 1.Aquaponics Nitrogen cycle calculated. VD (1) Re 2 Copyright © 2014 by ASME LV2 (2) Table 4. Total head losses Hfl, major A B Dg2 Total Head Loss (Cold) 0.06 0.21 V 2 (3) Total Head Loss (Warm) 0.06 0.08 HK l,min or 2g Average Head Loss 0.0592 0.1436 Table 5. Total amount of oxygen needed per kg of feed Oxygen Need per kg of (4) HHHpump l,m ajor l,min or Organism Feed Fish 0.025 kg The pump head will be calculated as follows: Nitrifying Bacteria 0.012 kg Heterotrophic Bacteria 0.13 kg (5) Total 0.5 kg Total pump power is a function of mass flow rate, height, and efficiency Stress Analysis (6) HQp P pump The plant bed frame will be a rectangular frame without a base. The ground will support a significant portion of the weight, but where Q is the volumetric flow rate, is the specific the framework still needs to be strong enough to contain the weight, and is the pump efficiency. water pressure. According to the previous calculations the plant The flow rate is variable, but must be maintained between 2.8 bed will be two beds of 4’x16’, but calculations still need to be gallons per minute and 5.6 gallons per minute to make sure the performed to determine the thickness of the wood and if pants can absorb the nutrients. supports are required to span the length to prevent bowing. In order to determine the values for the plant bed a finite element Table 1. Water properties analysis was completed using FEMAP and NEI-Nastran to find Density 1.94 slugs/ft3 the maximum stresses and deflections. To reduce the number of nodes, only the long length of the plant bed is modeled using Specific Weight 62.42 lb/ft3 fixed end support conditions.