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BSEN 5230

Wastewater Final Report

Aquaponics Design

Group leader: Olivia Elliott

Group members: Elizabeth Bankston, Ann Nunnelley, Eric Vogt

Date submitted: April 27, 2016

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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

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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

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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 one-

tank 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,

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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 6.5-8. The dissolved oxygen (DO)

needs to be maintained above 5 mg/L while taking in consideration the measured COD of 697.75

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.

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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 11.40 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/ft3 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

𝑓𝑡3) (1)

The MBBR capacity was determined using an ammonia removal rate of 0.05 g/ft2/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 = 𝑎𝑚𝑚𝑜𝑛𝑖𝑎 𝑝𝑟𝑜𝑑𝑢𝑐𝑡𝑖𝑜𝑛 (

𝑔

𝑑𝑎𝑦)

𝑎𝑚𝑚𝑜𝑛𝑖𝑎 𝑟𝑒𝑚𝑜𝑣𝑎𝑙 (𝑔

𝑓𝑡2−𝑑𝑎𝑦) (2)

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𝑀𝐵𝐵𝑅 𝑉𝑜𝑙𝑢𝑚𝑒 = 𝑆𝐴 𝑜𝑓 𝑏𝑖𝑜𝑟𝑒𝑎𝑐𝑡𝑜𝑟 (𝑓𝑡2)

𝑆𝑆𝐴 𝑜𝑓 𝑀𝑒𝑑𝑖𝑎 (𝑓𝑡2

𝑓𝑡3) (3)

The specific surface area (SSA) of the biofilm carrier media chosen for the MBBR is 338 ft2/ft3.

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

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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 ft2/plant, the total area of the cucumber beds will be 840 ft2. This gives a total

soil requirement of 1680 ft3, however, assuming settling will occur once the system is in place,

2100 ft3 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.

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

Figure 1. Side view schematic of aquaponics system with arrows indicating water flow direction

(not to scale)

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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 0.436 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)

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pressure, the pressure entering each drip line needs to be at least 10.436 psi (pressure loss in the

main line is negligible). Over all six beds this results in a pressure requirement of 62.21 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

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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 $2,393.05 (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.

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Item Qty Price

1500 gallon fish tank 1 $ 1,233.75

1500 gallon tank 1 $ 620.00

70 gallon bioreactor 1 $ 1,037.80

drip irrigation emitters 210 $ 115.08

PE piping (500 ft) 1 $ 117.50

0.5 hp pump 1 $ 243.74

valves 3 $ 9.57

sand filter 1 $ 184.99

hog wire (420 ft) 1 $ 1,391.00

posts 420 $ 1,260.00

soil ($2/ft3) 2100 $ 4,200.00

plant beds 6 $ 3,000.00

bell siphons 105 $ 525.00

cucumber seeds (20 seeds/pack) 10 $ 210.00

fish (hatchlings) 120 $ 300.00

fish feed (18 lb) 84 $ 4,555.32

Media ($1.6/gal) 45 $ 216.00

TOTAL - $ 19,219.75

Fish, seeds, feed (/cycle) - $ 5,065.32

Conclusion:

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.

Table 1. Cost per cycle for food production of aquaponics system.

Table 2. Materials list for the 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

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3

4

2,393.05$ $300 $7,120 25,603.26$

2,393.05$ $300 $7,120 38,404.89$

$7,120 (1,352.80)$

2,393.05$ $300 $7,120 12,801.63$

2,393.05$ $3001

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References:

Almanac Staff. (2012). Cucumbers. Retrieved April 21, 2016 from

https://www.almanac.com/plant/cucumbers

Bonnie Plants. (2012). Growing Cucumbers – Bonnie Plants. Retrieved April 21, 2016, from

https://bonnieplants.com/growing/growing-cucumbers/

Burpee. (n.d.). How to Grow Cucumbers – Vegetable Seeds and Plants, Gardening Tips and

Advice at Burpee.com. Retrieved April 24, 2016, from

https://www.burpee.com/gardenadvicecenter/vegetables/cucumbers/all-about-

cucumbers/article10230.html

Ingestad, T. (1973). Mineral nutrient Requirements of Cucumber Seedlings. Plant Physiology,

52(4), 332-338. doi:10.1104/pp.52.4.332

Rakocy, J.E., (1989). Tank Culture of Tilapia. SRAC, No.282.