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This system is a project of the National Council for Agricultural Education, Alexadria, Yirginia with a grant from
United States Department of Agriculture

This system with the recognition that the system may not be operated by experienced personnel. With this in mind, the system should be designed to be "forgiving" of operator error. To realize this in a design, each system component should be over-designed for its function. This does not mean that the system needs to be complicated or automated. On the contrary, the students are involved in the curriculum to gain experience in AQUACULTURE, thus the manual operation and care of the system is desirable.

In many cases, the system will need to operate as a "stand alone" unit with little support available from the existing physical plant, Additionally, the system should operate in setting with a minimum of room modification and distractions (i.e. it should operate quietly).
With these requirements in mind, the recycling system described here was designed as a model for getting educational programs "off the ground" with a minimum of trial and error. We hope that as you build and operate the system, you will be both creative and innovative in its design and operation. Please share these innovations with us and your colleagues so that we may improve our systems.

OVERALL SYSTEM LAYOUT
The Model AQUACULTURE Recycling System (MARS) was designed to handle the feed requirements for up to 200 pounds of fish ( if you are going to harvest the fish at 1 pound then you would stock 200 fingerlings ) in any number or configuration of culture tanks. The waste treatment system and other life support components take into account all of the considerations described in previous sections. The MARS unit has four major components.
1.A solids removal basin.
2.A nitrification basin.
3. Two fish culture tanks
In addition, the system has a low-pressure air pump and delivery system, a 1/5-hp submersible water pump and delivery line, a wastewater drainage line, and an alarm system. In all, the MARS unit takes up 130 square feet of floor space and cost approximately $3509.00 to build.

The Solids Removal Basin
Wastewater from the bottom of the fish culture tanks is delivered by gravity through a 1-1/2" PVC pipe to one end of the Solids Removal Basin. The basin measures 36" wide by 48" long by 42" high and has a sloped bottom (approx. 240 angle) from the back to the front of the basin.
Upon entering the solids removal basin, the solids laden water encounter a "top" baffle and is forced to travel up through a tube assisted settling area constructed of two blocks (1' x 1' x 3') of commercially available settling media (Part #LS68, Aquatic Ecosystems, Inc.). As the water passes up through the settling media, heavy solids such as uneaten feeds and fecal matter settle to the basin bottom or on the media itself. The sloped bottom of the basin causes the solids to collect in the front of the solids removal basin where they can be siphoned from the system. The clarified water then overflows into two troughs (fashioned by cutting a top and flows through a dividing wall in the tank to two vertical filters. The water first flows through a coarse polyester fiber filter (Part #PF2, Aquatic Ecosystems, Inc.) placed perpendicular to the flow.
The water then finally passes through a fine polyester fiber (Part #PF2, Aquatic Ecosystems, Inc.), where the remaining fine suspended solids are trapped. The polyester fiber filter material in both vertical filters is given rigidity by sandwiching the filter material between two sheets of plastic mesh
(Part #N1170, Aquatic Ecosystems, Inc.). The filters are held in the vertical position by tracks along the sides of the basin fabricated from 1" x 1" wood stock or by using commercially available fiberglass U-channel. The water then exits the solids removal basin through a bulkhead fitting on the end of the basin and is delivered by gravity to the Nitrification Basin.

Nitrification Basin
The Nitrification Basin receives clarified water that still contains high levels of ammonia nitrogen.
The function of this basin is to reduce the level of the ammonia and nitrite-nitrogen prior to returning the water to the fish culture tanks. The dimensions and construction details of this basin are identical to the solids removal basin, except it doesn't require baffles. The sloped bottom, while not required, assists in concentrating biological solids that are shed from the biological filter. A rotating biological filter (RBC) was selected as the primary vitrifying filter for the system. A Floating RBC design, developed by the Rodale AQUACULTURE Project was selected because of its simplicity of construction and operation. Either water or air can power the RBC. In this design, a small (2 g. p. m.) flow-stream of water from the submersible pump was used as the primary source of rotational power due to the limited air volume output of the air pump selected. While the RBC unit was purchased fully assembled (Part #RBC440, Aquatic Ecosystems Inc.), the construction details for the unit are included in Appendix A of this module ????. The treated water is pumped from the nitrification basin (17-21 g. p. m.) by a 1/5 hp submersible pump (VP1650 Big Versa Pump, 222 Watts.) via a 1 1/2" diameter PVC delivery line to the fish culture tanks.

Water Delivery Lines and Hydraulic Gradients
Water flows from the fish culture tanks to the treatment basins by gravity. When the submersible pump in the nitrification basin is off, the water in both the tanks and treatment basins reach a 'static level". It is important that the top of the treatment basins be equal to or higher than the maximum "static" water level within the system. The inside diameter of the wastewater drainage lines should be between 1 1/2" and 2". Using larger diameter pipe may result in the settling of waste solids within the lines, while smaller diameter pipe will result in a reduced flow rate to the treatment basins, causing the water levels to fall below an operational minimum (where the RBC hits the bottom of the basin). The "dynamic water" level (the water level with the pump running) in the fish culture tanks should be 4' to 6" higher than the treatment basins, It is important to note the construction details of the drainage lines within the model system. All right angle turns are made with "tee" fittings with end plug clean-outs instead of 90° elbows. This was done to ease the cleaning of the pipes within the drainage system. The pipes should be cleaned whenever the dynamic water level difference (head loss) between the fish culture tanks and basins becomes greater than 8-9". For cleaning procedures, see the maintenance section to follow.

Fish Culture Tanks
The fish culture tanks within the system can be of any configuration and number within reason.
In order to insure adequate dissolved oxygen levels, the density of fish in each tank should not exceed 1/4 pound of fish per gallon of water. This MARS unit is configured using two 440 gallon polyethylene tanks (Part #TP440, Aquatic Ecosystems, Inc.) having a diameter of 5' and an overall depth of 36". The tanks are elevated by one layer of concrete blocks and rest on a 1/2" plywood base to bring their tops even with the top of the basins, Drains at the bottoms of the tanks are 1 1/2" diameter bulkhead fittings located in the center. No standpipes are required in this system.
However the center drains should screened to prevent blockages in the drains by large objects.

Recalculated water is provided to each tank via a 1 1/2'' diameter PVC delivery nitrification basin. The flow-rate in each tank is regulated with a 1" ball valve.

Temperature Control System
The water temperature of the system will depend upon the requirements of the species being cultured. For most warm water species, a temperature range of 75-90°F is ideal. Keep in mind that in aquatic biological systems, the higher the water temperature, the faster disaster can strike! If the air temperature of the room in which the system is housed is within this range, then no additional heat source is required. However, if the room temperature is below the desired operational temperature, simple aquarium heaters will suffice as a controllable heat source.

The model recycling system is equipped with three 300-watt aquarium heaters located within the solids removal basin. Each heater (Model #VT300, aquatic Ecosystem, Inc.) in the system has an adjustable thermostat. The thermostat is set at the lowest water temperature you would desire the system to be maintained at. If the room air temperature is below 70° F, your system may require more heaters to maintain an appropriate temperature.
In culturing cold water species, a water temperature of 70° far less is desirable. Unless the room can be maintained at 65°F or less, a water cooling unit will be required. Water cooling units are generally expensive and will significantly increase the cost of your system ($1000 - $1600 ).

Aeration System
Aeration is provided via eight 4" long air-stones (Part #AA4, Aquatic Ecosystems) in each tank.
The air-stone diffusers are located at a depth of 24" below the surface of the water. Air is supplied from a linear air pump (Part #L29, Aquatic Ecosystems, Inc.) mounted above the water level (to prevent back siphoning when turned off) near the basins. A Linear air pump was selected (vs. A regenerative blower) due to the quiet operating characteristics of this unit. While the entire system could be operated with a larger regenerative air blower and air-life pumps, the submersible pump and linear air blower were selected to provide quiet operation for classroom (lab) use. The air delivery line is 1" diameter PVC pipe and fittings with 1/4" diameter flexible clear tubing (Part #TV40, Aquatic Ecosystems, Inc.) connecting the PVC pipe air delivery system (via tubing adapters, Part #62014, Aquatic Ecosystems, Inc.) with the air-stone diffusers.

Fine and Dissolved Solids Removal
Fine solids and dissolved solids are removed with a simple airlift type of foam fractionator (Part
#FMS4, Aquatic Ecosystems, Inc.). The foam fractionator is mounted within one of the fish tanks
and discharges solids laden foam to an external container. Because the water to both fish tanks is mixed in the treatment basins, one foam fractionator should serve to control the buildup of fine and dissolved solids within the entire MARS unit.

Feed Delivery System
Feed should be delivered to the tanks evenly over a period of time to minimize "spikes" in ammonia-nitrogen or depletions in the dissolved oxygen content. Fortunately this process is easily accomplished using automatic feeders (belt feeders) that were developed for the fingerling production industry, Each tank in this MARS unit has a spring driven 12 hour belt feeder (#Part  BF24, Aquatic Ecosystems, Inc.) suspended 12" - 18" over the water. The appropriate amount of feed (see section on fish production management) for the day is spread evenly over each belt to be delivered during the working day.

Alarm System
Due to the intensive nature of recycling systems, and the number of hours that the system will
be unattended on evenings and weekends, use of a simple alarm system is strongly recommended.
The MARS unit was developed, has a simple alarm system that incorporates an automated telephone dialer (Part #A2, Aquatic Ecosystems, Inc.). The system monitors the air delivery line pressure (Part #B601, Aquatic Ecosystems, Inc.), water level in the fish culture tanks (Part #ST7, Aquatic Ecosystems, Inc.), water temperature in the overall system (Part #A-3,??? Aquatic Ecosystems, Inc.), and flow status in the water delivery system (Part #6940-015????, Ryan Herco, Inc.). In the case of low air pressure, low water level, high or low water temperature, or no recycled water flow, the telephone dialer will dial and deliver an alarm message to four predetermined telephone numbers. The alarm message must be acknowledged by the recipient by a phone call back to the telephone dialer within 30 seconds of the call or the automatic dialer will call the next number in its memory. This process continues until the alarm is acknowledged.
While the inclusion of an alarm in the system is not absolutely necessary, the security and peace of mind knowing that the system is "on guard" 24 hours a day, 7 days a week is well worth the $400 dollars required to implement the system.

CONSTRUCTION DETAILS
The major work entailed in implementing this model AQUACULTURE recycling system was the fabrication of the wastewater treatment basins. Plywood and fiberglass was chosen as the materials for this model to facilitate the fabrication of these units in a high school wood shop. In fact, the models prototype basins at North Carolina State University were put together by the FFA class at Fuquay - Varina High School in North Carolina. It should be noted that the work required to build the basins can be reduced if prefabricated tanks of similar dimension can be located. While sloping bottoms are desirable for the basins, flat bottoms basins can be substituted. Flat bottom tanks used as settling basins require more effort in the cleaning of the settled solids. Remember, the basin material must be non-toxic to fish; no galvanized steel or copper pipes!

Basin Construction Details
The basic treatment basin construction details are described in plan. The basins were fabricated from good quality (A/B grade) 3/4" thick exterior grade plywood. The plywood sheets were cut into panels according to the layout. The wood panels were glued (with a water-proof wood glue) and screwed together. The sloped bottom of each basin were supported by four evenly spaced 2" x 2" stringers. Each inside seam and corner were sanded and rounded with a silicone sealer and fiberglass tape was applied to give the seams strength and make them water proof. The entire inside of each basin was given a coat of epoxy primer (Part #PT17, Aquatic Ecosystems Inc.) and a second finish coat of epoxy paint (Part #PT5, Aquatic Ecosystems Inc.).
The exterior of both basins were coated with a colored "exterior" wood paint. To reduce side bulging of the tank walls caused by the water pressure, a wood girdle was fabricated from four pieces of 2 x 4 and four bolts and placed mid-way up the tank sides (see figure 4). Holes in the ends of both basins are cut to fit a 1 1/2" bulkhead fitting. The holes should be located 20" (on center) from the bottom of the basins. The solids removal basin must be fitted with two additional baffles.
A short "top" baffle and a full baffle need to be installed as noted in Figures 3 and 4 and sealed (silicone alone will do). Two sets of tracks to hold the vertical polyester screen filters must also be fabricated from 1" x 1" wood stock or U-channel structural fiberglass can be used (1 1/4" x 1/4", Hulls Unlimited-East, Inc.)

Basin Support and Drain Set-Up
The tanks that were used in the model system were 36" high. To raise the tank tops level with the treatment basins and to facilitate bottom drain construction, the tanks were placed on 1/2" thick plywood set on common cement blocks (cinder blocks). The block placement and drain system components are outlined.

SYSTEM BUDGET
A budget for building the model system is found in Table 1. The reader should note that the budget does not include any labor cost for this project. It is assumed that the students wilt provide the labor in developing this system. The reader should also note that the costs listed are list prices.
In many cases, a discount can be obtained for many of the items. The model was built from premium materials which, in many cases, can be downgraded without a degradation of operational characteristics or reliability. An example can be found in the plywood used to build the treatment basins. While the model used A/B exterior grade ($37 each), a lower exterior grade such as A/C or
CDX ($15 -$20 each) could be substituted. Another example can be found in the cost of PVC pipe fittings. We have used the "list" catalogue price where in most cases state agencies and private contractors can buy PVC pipe and fittings at up to 70% off of these prices. Suffice it to say, your system should cost less than the models price tag of $2,878. See Appendix B for a list of AQUACULTURE equipment suppliers.

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