BSEN Wastewater Final Report. Aquaponics Design. Group leader: Olivia Elliott. Group members: Elizabeth Bankston, Ann Nunnelley, Eric Vogt

Transcription

1 BSEN 5230 Wastewater Final Report Aquaponics Design Group leader: Olivia Elliott Group members: Elizabeth Bankston, Ann Nunnelley, Eric Vogt Date submitted: April 27, 2016

2 Table of Contents: Introduction 3 Project Goal 4 Design Constraints and Objectives 4 Safety, Health and Environmental Concerns 4 Methods 5 Cost analysis 10 Conclusion 12 References 13 2

3 Introduction: Aquaculture operations create wastewater containing toxic pollutants such as ammonia (NH3) which require remediation. In many cases these operations use moving-bed bioreactors (MBBR) to remove ammonia using nitrifying bacteria to convert the NH3 into nitrate (NO3 - ), which is less harmful to fish. However, the NO3 - should still remain under 10 mg/l (Colt, 2006). As the nitrification process is carried out, NO3 - can continue to increase unless there is denitrification or another form of filtration used to remove the NO3 -. Denitrification requires an anaerobic zone to cultivate denitrifying bacteria. This can be difficult to achieve in these operations because the process is slow and could be overloaded depending on the operation, which, in turn, could limit space of the operation. Another way of converting this NO3 - is through an aquaponics operation. Aquaponics systems utilize nutrients in fisheries wastewater to fertilize crops. This allows for food production in the operation, which increases the reuse potential of the water for aquaculture. Allowing the water to cycle from the fish, through a MBBR, to the plants, and back to the fish decreases the fish death because of the healthier water. It also stimulates the production of the crops because they receive nutrients at a higher concentration without the commonly problematic risk of polluting waterways from runoff. Since aquaculture is water intensive, the reuse of water in these systems is very important in reducing the municipal water requirement. An increase in the reuse of water helps minimize the cost of operation for the aquaponics system allowing for a greater profit margin. Additionally, while aquaponics systems 3

4 have a larger capital investment than standard aquaculture operations, they allow for an increase in long-term profitability because of the ability to sell the feedstock as well as the crop. Project Goal: The purpose of this project is to design an aquaponics system to maximize water reuse in the fisheries and expand the purpose for water to a food production operation. Design Constraints and Objectives: Design an aquaponics operation using tilapia as the feedstock and cucumber as the crop Develop a cost analysis to determine the feasibility and sustainability of the operation Using data from the wastewater obtained at the Auburn Fisheries Unit, the water will be characterized to assist in the design of the aquaponics system. The design will focus on a onetank system that is able to produce 1000 lbs of tilapia. This will be used to determine the number of cucumber plants that are able to be produced in this system. The project will be given a theoretical budget of $20,000 to design the aquaponics system and fill the operation with the feedstock and crop. Safety, health, and environmental concerns: This project consists of many different experiments to characterize wastewater that can pose chemical and biological hazards. Personal protective equipment (PPE) including eyewear, gloves, 4

5 closed-toed shoes, and long pants must be worn to ensure the safety of the lab participants during these experiments. Methods: It is necessary to determine the size of the tanks, the dimensions of the plant beds, the capacity of the MBBR, the pump size, and the amount of return flow to the fish tank during watering. The size of the fish tanks and MBBR were determined using the weight of fish for the system and data from the experiments performed on the Auburn Fisheries Unit wastewater. The ph, solids, chemical oxygen demand (COD), total nitrogen (TN) and total phosphorus (TP) were determined for the Auburn Fisheries Unit wastewater. These are necessary in the design of the aquaponics systems to ensure the health of the livestock and crop and proper flow of the system. A sand filter is required as an intermediate step between the fish tanks and the MBBR to remove solids from the wastewater so the drip irrigation system does not get clogged. It is necessary to monitor the ph and nutrients in the wastewater to ensure the health of the fish and the cucumber. Tilapia are a popular fish to raise in aquaponics systems because of their hardiness, however, they do have ranges for optimum growth, such as a ph between The dissolved oxygen (DO) needs to be maintained above 5 mg/l while taking in consideration the measured COD of mg/l, and aeration from a diffuser rope will be used to ensure the DO parameter is met. The ammonia levels for healthy fish should be less than 0.02 mg/l in the unionized form. Using a MBBR and aquaponics to recirculate the water will ensure proper conditions of the rearing space for the tilapia. 5

6 Cucumbers require specific conditions to have an optimum growth rate. The soil should be a loamy soil to allow for optimal temperature and proper aeration. The ph of the soil needs to be between 6-6.8, and the cucumbers require a TN source of 400 mg/l and 40 mg/l of TP to grow at optimum rates. From ph titration and nutrient analysis, the ph was determined to be 6.2, TN was 20 mg/l, and TP was mg/l meaning the wastewater from the fish would allow for healthy growth of the cucumber plants. Measuring solids in the wastewater determined that a sand filtration system with a capacity of 216 mg/l/day or greater is required. The size of the tank needed to house the 1000 lbs of tilapia was determined to be 1500 gallons. Using methods outlined by Rakocy (1989) where a rearing space of 5 lbs/ft 3 is needed to grow the fish. Therefore, the tank size is determined from Equation 1. Tank size = Weight of Fish Raised (lbs) Rearing Space ( lbs ft 3) (1) The MBBR capacity was determined using an ammonia removal rate of 0.05 g/ft 2 /day and an ammonia production rate of 100 g/day for 1000 lbs of tilapia. This number is an estimation supported by the wastewater analysis performed by the 3D printed bioreactor media team, since the TN analysis laboratory was inconclusive. Using Equation 2 and Equation 3 the size of the MBBR was calculated. Surface Area of Bioreactor = g ammonia production ( day ) g (2) ammonia removal ( ft 2 day ) 6

7 MBBR Volume = SA of bioreactor (ft2 ) SSA of Media ( ft2 ft 3) (3) The specific surface area (SSA) of the biofilm carrier media chosen for the MBBR is 338 ft 2 /ft 3. This media was developed by the 3D printed bioreactor media senior design team. This allowed for a minimum reactor size of 45 gal, so a reactor of 70 gal will be purchased to allow for increased ammonia removal from the water when necessary. Cucumbers are irrigated using drip irrigation and are an ideal crop to be grown using aquaponics. To save space, the cucumbers will be grown using trellises made of hog-wire and garden posts. Using the trellises, the cucumbers will be spaced 1 ft apart to allow for optimal growth. The cucumber will be grown in a 50/50 mix of sand and organic matter that is assumed to have the same properties of a sandy loam soil. This soil will be 2 ft deep to allow the cucumber to have enough depth for its taproot to grow without impedance. As seedlings, cucumbers require a minimum of 1 in of water per week, which is about 0.5 gal/plant/week. As the plants mature and begin to produce fruit, this irrigation increases to at least 1 gal/plant/week (Almanac Staff 2012). To ensure adequate water supply, an irrigation interval will be implemented to be for 10 minutes twice daily. Valves are necessary for the operation to allow for controlled flow in the system. The valve that recirculates the water from the MBBR to the fish will be shut, and the valve to the plant bed will be open to start the irrigation. These irrigation requirements served as the basis for determining the number of cucumber plant that could be grown given a flow of 7 gpm from the MBBR. This flow rate, which yields a hydraulic 7

8 retention time of 6.5 min, was chosen to allow the water to remain in the bioreactor for long enough to sufficiently reduce ammonia levels. The drip irrigation system will operate using a single 2 gph emitter per 4 cucumber plants. Since 7 gpm gives 420 gph, the system is large enough to handle 210 emitters and 840 plants. Given the spacing of 1 ft 2 /plant, the total area of the cucumber beds will be 840 ft 2. This gives a total soil requirement of 1680 ft 3, however, assuming settling will occur once the system is in place, 2100 ft 3 of soil will be purchased and laid in the beds. It is difficult for the operators to physically walk on the soil because of the trellises, therefore, it was decided that six beds of 2 ft by 70 ft will be used for accessibility. The entire layout of the system can be seen in Figure 1 below. Figure 1. Side view schematic of aquaponics system with arrows indicating water flow direction (not to scale) Bell siphons are used to improve drainage efficiency and allow for soil saturation. These drainage ways also improve the aeration of the soil which enhances the growth environment for the 8

9 cucumber. These can be easily built using simple PVC components and bulk heads. As well as being easily manufactured, they are easily installed into the plant bed. Since this aquaponics operation is not entirely gravity fed, a pump is required to move water from the MBBR through the drip irrigation system. To size this pump, the worst case emitter was analyzed (Fig. 2). The minimum pressure for proper emitter operation is 10 psi, therefore, the worst case emitter must at least receive this water pressure from the pump. The drip tape used for these purposes is a Hardie 16mm PE pipe with 35 emitters per line. Each of the six beds will have one line running down the middle of the bed that operates at 70 gph. A friction loss table constructed using the Darcy Weisbach equation determined that for this particular drip line at 70 gph, the water pressure loss per 100 ft of pipe would be only 1.78 psi. Given only 70 ft of drip line and assuming equal flow out of all emitters, this value can be multiplied by 0.7 and 0.35 to give a final pressure loss of psi per line. Since the worst case emitter requires 10 psi of water Figure 2. Plan view schematic of aquaponics system indicating the worst case emitter (not to scale) 9

10 pressure, the pressure entering each drip line needs to be at least psi (pressure loss in the main line is negligible). Over all six beds this results in a pressure requirement of psi, thus, a 65 psi pump will be purchased for the irrigation system. During the irrigation, it is assumed that there will be a 15% water loss from the system due to plant up take and soil retention. This loss will require the system to have a resupply from a municipal source. During the two 10 minute irrigation intervals, a resupply of 1.05 gpm from a municipal source is required to adjust for the 15% water loss. This will ensure the tilapia have optimum water levels for growth. Cost Analysis: A cost analysis was performed for the required materials needed to start and operate the aquaponics system. It is assumed that the system will be housed in an existing greenhouse, so the cost of housing is not represented in the cost analysis. The analysis was performed for a four cycle operation where each growing cycle, for both fish and cucumber, is comprised of 6 months. The fish will be bought as hatchlings and raised until they have reached market size, which is around 9 lbs per fish. Once the fish have reached market size, a team of five workers will be tasked to capture and clean the fish for sale. This team will be given eight hours at the end of the cycle to complete their task. Each worker will be given an hourly pay rate of $10/hour. Cucumbers will be purchased and raised from seed. The growth of the cucumber takes approximately 2 months before they begin to fruit. Once fruiting begins, the harvest of the cucumber will last 12 weeks or 84 days. It is assumed that each cucumber plant will produce 2 lbs of fruit per week and will be sold at a market value of $2.25/lb. Two workers will be tasked 10

11 with harvesting the fruit for four hours a day throughout the harvest window. Each worker will be compensated at a rate of $10/hour. After harvesting, reseeding is required and will be completed during the last month of the cycle. Maintenance of the system will be required every month and is estimated to last two hours. Maintenance ensures proper operation of the aquaponics system, and this will include backwashing of the sand filter and general upkeep of the pumps and drip emitters. A skilled laborer will be responsible for the maintenance and will be compensated at $25/hour. Operation cost for the first cycle includes the start-up cost for the water needed to fill the system. After this is taken into account, normal replenishing of the water will remain at a constant rate. Since the aquaponics system is in a greenhouse, the only power consumed is by the pumps. The operation of the system for one cycle, including water and power, will cost $2, (Table 1). The system proposed will take approximately $19,000 to build and stock, which is under the budget of $20,000. From Table 1, it is seen that the net profit will be negative after the first initial cycle. Once this is complete, there will be a profit of approximately $13,000 per cycle. This yields a yearly profit of $26,000. Therefore, this system is extremely economical and pays for itself within the first year. The reason the negative profit is only in the first cycle is because of the fixed cost necessary to begin the operation. This capital cost can be seen in Table 2 which outlines the materials used to build the operation. The media chosen for the MBBR was a specifically designed media that is assumed to be approximately three times the expense of the current media the K1 Kaldnes. 11

12 Table 1. Cost per cycle for food production of aquaponics system. Cycle Item Selling Price Yield Gross Profit Operation Costs Maintenance Costs Labor Costs Net Profit tilapia $5/ lb 1000 lb/ cycle $5000/cycle cucumbers $2.25/lb 840 lb/wk $22680/cycle tilapia $5/ lb 1000 lb/ cycle $5000/cycle cucumbers $2.25/lb 840 lb/wk $22680/cycle tilapia $5/ lb 1000 lb/ cycle $5000/cycle cucumbers $2.25/lb 840 lb/wk $22680/cycle tilapia $5/ lb 1000 lb/ cycle $5000/cycle cucumbers $2.25/lb 840 lb/wk $22680/cycle $ 2, $300 $7,120 $ (1,352.80) $ 2, $300 $7,120 $ 12, $ 2, $300 $7,120 $ 25, $ 2, $300 $7,120 $ 38, Table 2. Materials list for the aquaponics system. Conclusion: Item Qty Price 1500 gallon fish tank 1 $ 1, gallon tank 1 $ gallon bioreactor 1 $ 1, drip irrigation emitters 210 $ PE piping (500 ft) 1 $ hp pump 1 $ valves 3 $ 9.57 sand filter 1 $ hog wire (420 ft) 1 $ 1, posts 420 $ 1, soil ($2/ft3) 2100 $ 4, plant beds 6 $ 3, bell siphons 105 $ cucumber seeds (20 seeds/pack) 10 $ fish (hatchlings) 120 $ fish feed (18 lb) 84 $ 4, Media ($1.6/gal) 45 $ TOTAL - $ 19, Fish, seeds, feed (/cycle) - $ 5, The aquaponics system designed will be economically feasible and efficient at removing excess pollutants from the water. Since the system is recirculating, the water will be at a sufficient nutrient levels for the fish and cucumbers to grow at a healthy and optimum rate. 12

13 References: Almanac Staff. (2012). Cucumbers. Retrieved April 21, 2016 from Bonnie Plants. (2012). Growing Cucumbers Bonnie Plants. Retrieved April 21, 2016, from Burpee. (n.d.). How to Grow Cucumbers Vegetable Seeds and Plants, Gardening Tips and Advice at Burpee.com. Retrieved April 24, 2016, from Ingestad, T. (1973). Mineral nutrient Requirements of Cucumber Seedlings. Plant Physiology, 52(4), doi: /pp Rakocy, J.E., (1989). Tank Culture of Tilapia. SRAC, No