13 June 2016

28 September 2014

Aquaponics Dissolved Oxygen (D.O.)

Oxygen - Sizing your Aquaponic Air System
credit to: nwestwood
link: http://www.urbanaquaponics.com/content.php?129-Oxygen-Sizing-your-Aquaponic-Air-System

The success of an aquaponic or aquaculture venture depends on providing as near an optimum environment for the rapid growth of the fish as possible. Of all the environmental factors, water quality and in particular, dissolved oxygen (DO) is the most important and critical. 

Although the air we breathe usually contains about 21% oxygen, oxygen is only slightly soluble in water. As a result, aquatic species must spend a great deal of energy to remove what little dissolved oxygen there is. Temperature, barometric pressure, salinity, and altitude all directly affect oxygen concentrations in both air and water.

In addition, each species has varying tolerances to low levels of dissolved oxygen. Salmonids (trout), as a group, require 6.0 to 8.0 mg/L of dissolved oxygen. For catfish and tilapia allowable minimum levels can be as low as 2.0 or 3.0 mg/L although the recommended levels are 5.0 to 6.0 mg/L.

Cold water will hold more dissolved oxygen than warm water. Likewise, it is easier to reach a level of saturation at lower elevations than at higher elevations.

General Aeration for General Systems - The Easy Answer

Most aquatic suppliers provide data sheets that can help you quickly determine your general air flow needs. For example, AquaticEco's chart for their air diffusers here shows the number of pounds of fish a given diffuser will support. (In the column under the blue AES logo.) The AS15L 6" medium pore diffuser will support 14lbs of fish. This is a general guideline and was calculated for adult Tilapia at sea level and 72-78 degree water temperature with a healthy saftey margin. 

If our system is at sea level and we plan on having 125lbs of fish at harvest time, we would need (125/14=8.928) or 9 diffusers. At the suggested rate, each diffuser needs an input flow of 0.5 cfm of air, so we would need a pump that puts out 4.5 cfm (9 x 0.5) at a 3' depth in our tank. For each 1000 feet of elevation above sea level, the air requirement increases by an additional 4%. For example, if our system is located in Denver, Colorado at 5,000 feet, we would need 20% more air diffusers to get the desired result (8.928 x 1.2 = 10.7 or 11 diffusers). In our experience this general guideline contains a wide safety margin. If you want to more precisely calculate your specific system, read on.

How Big of an Air Pump do I Need?

In designing an aquaponic system we ask ourselves:
1. How big of a fish tank can I afford and fit into the space I have?
2. Which kind of fish will I raise and how many can I safely fit in my tank at harvest size?
3. How many grow beds and/or floating raft tanks do I need to process the bio-load from the fish?
4. How big of a water pump do I need to turn over the fish tank water at least once per hour?
5. Finally, How big of an air pump and how many air stones do I need to maintain safe levels of Oxygen? (generally 6.0 mg/L or above).

Key Aquaculture Oxygen Design Parameters:
1. Oxygen (O2) Consumption by the fish and bacteria(1)

A. 0.025kg of O2 needed per kg of feed fed to the fish for the fish.
B. 0.012kg of 02 needed per kg of feed fed for the nitrifying bacteria.
C. 0.13kg O2 needed per kg of feed fed for the heterotrophic bacteria (can be as high as .5)

Total = 0.5kg of O2 needed per kg of feed fed, or 1/2lb of O2 per pound of feed fed.

The author of Recirculating Aquaculture states: "In a pure recirculating aquaculture system (RAS) the ratio of 1.0 kg of oxygen per 1.0 kg of feed fed is the safe recommended design value"(1). However, in our experience the 0.5kg of O2 per kg of feed is adequate in traditional home aquaponic systems.

Next we look at how aeration transfers the oxygen into the water. In Urban Aquaponics we use air diffusers (air stones). There are many other methods aeration, most are more efficient, but more expensive. We will limit our discussion to 6" air diffusers and you can easily adapt the example to other methods.
2. Oxygen Production and Distribution.
A. There is 21% oxygen in normal air.
B. There is 0.075 lbs of air in a cubic foot.
C. By weight, 23% of a cubic foot of air is oxygen (oxygen is heavier than many of the other gases in air).
D. Standard Oxygen Transfer Efficiency rate (SOTE) or rate at which oxygen will transfer to water under "standard" conditions per 1 foot of depth. For a 6" medium pore diffuser it is .01 lbs per foot of depth.
E. Field Transfer Efficiency (FTE) - The actual tested transfer efficiency based upon the existing oxygen content of the water (the higher it is, the less will transfer), temperature and salinity. We assume the input water is at 68-78 degrees and 4.0-5.0 mg/L DO which gives an FTE of approximately .5 (2)

Note: Oxygen is transferred into water by having a density differential (low oxygen water to high oxygen air), exposing the greatest surface area of oxygen to the water and by keeping the oxygen in contact over time. The smaller the bubbles, the greater the surface area, but small bubbles require higher pressure. Medium pore air diffusers are recommended as the most cost effective. The deeper the diffusers, then the longer the time the air bubbles are exposed to the water, increasing diffusion. 

Plants in the system may also require or produce some oxygen (algae produces during the day, consumes at night). Additionally, in a RAS system, there may be other components that require oxygen. For the purpose of this article we will work the calculations as if there were no other demands. We want to produce enough oxygen to maintain 6.0 mg/L of oxygen in the fish tank if the water pumps were to fail, assuming 0.5lbs of Oxygen per 1lb of feed fed. (Again, in our experience this is more than adequate for a typical aquaponic setup, including the plants and other components.)

Lets work through an example system using this 0.5:1 ratio and see how this all goes together.

Let’s assume we have a fish tank in our system that is 250 gallons (946 liters). And we are raising Rainbow Trout and that final stocking density is 1/4 lb per gallon (25-30grams per liter).

Also assume that the fish consume 2% of their body mass at harvest (species vary) or 1.25lbs (567 g) of feed per day. (250 gallons x 0.25 = 62.5lbs x 0.02 = 1.25lbs of feed per day). 

Figuring at the 1lb of Oxygen to 1lb of feed, that means we need 1.25lbs (567g) of Oxygen every 24 hours or 0.052lbs (24g) per hour. Or, using the 0.5 to 1 oxygen to feed ratio, 0.625lbs (284g)/24 hours, 0.026lbs (12g) per hour.

The formula for oxygen injection is as follows:

CFM (ft3/min) of device X lbs of air/ft3 X lbs of oxygen/lb of air X (SOTE X Depth) X FTE X Time = lbs of O2 per Time transferred.

To break this down:
CFM (ft3/min) of device = 0.5 cfm (Using our 6" medium pore diffusers from Aquaticeco).
Lbs of air/ft3 = 0.075 (The weight of a cubic foot of air)
Lbs of Oxygen per lb/air = 0.23 (The weight of the Oxygen in a pound of air)
SOTE = 0.01 
Depth = 3' (assuming a standard IBC tote or typical circular fish tank).
FTE = 0.5
Time = 60 (minutes per hour to get to O2 per Hour)


0.5 x 0.075 x 0.23 x (0.01 x 3) x 0.5 x 60 = lbs of O2 per hour per 6" stone = 0.0077625 lbs of O2/hr

You can calculate 3" air stones or calculate different depths by substituting the correct values.

Then we divide the oxygen needs of the example system by the O2 produced by each air stone to find out how many air stones are needed.

0.02604167 / 0.0077625 = 3.35 air stones at sea level.

I'm at 5000 feet so with a 4% loss per thousand feet, I need an extra 20%. I need 3.35 air stones x 1.20 = 4.026 air stones.

If I go with 4 air stones (5 would be safer), and each air stone uses 0.5 cfm, then we need a pump that produces a minimum of 2.0 cfm at 3' depth. (0.5 x 4 = 2.0).

In my own system I have enough fish to reach a density of 1/2lb per gallon (not recommended). I started with an air pump that produced 2.5 CFM at 3' and as the fish grew, the Dissolved Oxygen levels declined to 5.6 mg/L and I had fish that were not eating as well and showing signs of stress and sickness. I added a second air pump (same as the first) and several more air stones (equivalant of 10) and the Dissolved Oxygen level went back up to 6.4 mg/L.

Much higher densities are supported in pure RAS systems through the use of pure oxygen and more efficient aeration methods. These are not generally employed or needed in a properly designed and sized aquaponics system.

23 September 2014

Aquaponics Top 10 Requirements

credit to: Fresh with Edge 
link: http://freshwithedge.com/2012/10/top-10-requirements-for-successful-aquaponics/

Saturday morning of the Aquaponics Association Conference was kicked off by featured speaker Dr. Wilson Lennard. Dr Lennard kicked off the festivities with a very fitting speech about the Top 10 Requirements for Successful Aquaponics. Showing off his years of research into this field, I would challenge anyone to come up with a better top 10 list than what we have here. You may be able to modify this list to fit your specific region or situation, but this is a solid base for anyone.

So without further delay, here’s the top 10:

Good quality information is always valuable no matter what stage of the process you are in. Find information with numbers behind it to back it up and trust the science that has been proven. Too many people in this young industry try to completely reinvent the wheel from scratch as soon as they begin their adventure. If you stat with a solid base, decide what works and what could be changed for your situation you will be years ahead of a new custom design making the same set of mistakes as your predecessors.

Correct Design
Knowing what is correct will only come from time. Only time will lead to the ability to say you know what you are doing. Anyone can design a system and show you have wonderful it’s working after 8 months. When that same system is working beautifully 5 years from now, then you have something to impress anyone. In addition to that, the only way that you can prove that something works before running each individual system is to build up your assumptions with Math. Math is what has to be the answer to proper design.

Use Correct Ratios
FACT: The amount of plants that can be grown is directly related to the amount of fish fed per day. This is referred to as the Feeding Rate Ratio. This is the base for any successful ratio. Beyond that you can tweak it to run more fish or more plants, but the base will always be the same.

Maintain Good Water Quality
This is one of my favorite points that he brought up. So many people come to aquaponics from the hydroponics world and only care about the nutrients available to their plants. It’s an easy thing to do, especially when you’re raising something like a tilapia. Tilapia can handle extremely low water quality standards. Their ability to adapt to major variances in tempurature, pH and general water quality is one of the large draws for most people using them for aquaponics. Dr. Lennard brings up the point though, that tilapia deserve good water quality too, toughness should not mean lower standards.In addition to that he pointed out that trout, who are notorious for their necessity for cold, high DO level, and high water quality requirements can actually handle a much higher temperature than what is considered mandatory for a trout as long as the water quality is managed vigorously.

Water Flow Rate
A knowledge of flow rates is important for the design of an aquaponic system. You need to know what the design flow rate is when you create a new system. This leads to the point that your system should be designed from mathematical calculations. Not on what will fill out your greenhouse best or what sizes you can get down at the local hardware store. If you are serious about creating a successful system, you should be creating your system using calculations based on stocking density, water volume and planting/harvest rates.Rule of thumb: Be able to replace the entire fish tank volume in one hour

Proper D.O
This isn’t extremely complex in implementation, being that there isn’t any way (without using liquified oxygen) that you can overdo your DO inputs. So most people will just go a little overboard with it and call it good. One thing that you may want to pay attention to is the fact that you also want to keep proper DO levels available for your root system. In slower moving DWC systems you may need to add air stones to your trough to allow for proper oxygen availability to your plants.

Water Temp
This is something that you think of most with your fish, but it is important to all three. Being that your fish are cold blooded creatures, their entire system temperature depends on the water temperature surrounding them. If water temperature swings in either direction too quickly for a fish the bacteria in the gut of a fish will start to work out of control on any available fish food. This is why it’s important to refrain from feeding your fish in a temperature swing.For your plants the root systems will prefer a certain temperature range depending on the time of season that they grow in with a normal garden/field condition. In addition to that, the efficiency of your nitrifying bacteria will take large hits when temperature starts to drop too far. This will cause water quality issues and possible, depending on your margins for error, can lead to inadequate nutrient availability.

PH Level & Testing
Always know the level of your pH. Your pH level should be a constantly moving target. The level of your pH should be in a constant free-fall (lowering, acidifying) due to the nitrification process causing a drop of hydrogen particles from the amonia.

Because of all this occurring with your pH level changes, you should constantly be checking your levels and adding a buffering agent such as calcium hydroxide & potassium carbonate. This should be done on a daily basis to keep from large swings in pH levels.

Quality Fish Feed
Last but not least you need to make sure you are using a high quality fish feed. Keep in mind that using a high quality fish food will lead to high quality fish waste which will eventually become your high quality nutrients for your plants.

These are the top 10 requirements for successful aquaponics that Dr Lennard listed out for everyone. I think this makes up a fairly comprehensive list from what I know so far. Do you have any you would add or anything that you would add to the list that you find mandatory for your aquaponics system?

18 September 2014

Aquaponics Fish Food Maker

Aquaponics Small Pellet Mill

credit to: GEMCO Energy
link: http://www.pellet-press.com/Products/Home-Use-Pellet-Mills.html


The home-use pellet mills also named flat die pellet mill, which was first invented in the early 20th century, is mainly for home use. Due to its lower cost and simple construction, this type has become the most widespread at residences and farms internationally. Thanks to our ISO 9000-certified factories, our well-trained engineers’ hard work, and our staff’s efficiency, we are able to provide some of the best design and installation services for wood pellet mills. Through years of experience in this industry we have acquired advanced technology for wood pelletization. The conditioning of raw materials is one of the most important steps in making wood pellets. Taking into account that wood waste is more difficult to compress than feedstuff, our machinery is able to adjust the material's moisture and size to make the finest biomass pellets. 

Key Parts of Home-use Pellet Mill:

Flat Die Flat die and Press Rollers Flat Die and Press Roller Installation

Scope of Application:

Our pellet mills are appropriate for compressing a variety of fibrous biomass material: corn (maize) husks, peanut shells, rice husks, corncobs, cotton seed hulls, wheat biproducts, sunflower seed shells, sawdust, cotton stalks, weeds, house refuse, waste plastic and similar types of factory waste. It is also suitable for raw materials which are otherwise difficult to pelletize owing to low bonding ratios. All of organic bacterial manure, organic fertilizer and compound fertilizer can be also pelletized by our machines at low temperatures.

Advantages of Home-use Pellet Mill:

1. Reliable, versatile and efficient
2. ISO and CE certified
3. Potential for 24 hour continuous running
4. Competitive price with excellent quality
5. Low energy consumption and less manpower
6. Durable spare parts
7. Simple, automated operation
8. Easy maintenance
9. Advanced technological design requiring less labor
10. Stable and durable functionality

Technical Data of the Electric Motor:
Homemade-Pellet-Mill-with-Electric-Motor-1.jpg Homemade-Pellet-Mill-with-Electric-Motor-2.jpg Wood-Pellet-Machine-with-Electric-Motor-3.jpg
Output (kg/h)
Measurements (mm)
N.W/G.W (kg)
ZLSP 230B11300-4001050*480*930290/320