A viable and sustainable system might be on top of your list if you’re planning to venture into Aquaponics for commercial use. Several Aquaponics systems exist, but DWC (Deep Water Culture) is the preferred layout for large-scale and commercial food production. So, what’s DWC, and what does it entail?
DWC is an Aquaponics system involving the circulation of nutrient-rich water through long canals and perforated floating raft boards. In this layout, plants grow in raft board holes and are supported by net pots. Hence, their roots dangle in the water, absorbing nutrients and oxygen.
The rest of this article will discuss the DWC system in great detail. So read up to equip yourself with sufficient knowledge before embarking on this food production venture.
What Comprises the DWC Unit?
The DWC unit, also called the Float System, comprises a fish tank, filters, canals, and floating rafts. DWC is an integrated food production system where plants grow on floating rafts, obtaining nutrients from the water inside the fish tank.
In DWC tanks, the water is in continuous circulation, from the fish tank, through filters, to the canals, raft boards, and back.
DWC is common among farmers who venture into large-scale and commercial food production. Like the Nutrient Film Technique (NFT), this method entails suspending plant roots in water. However, in NFT, a small water volume flows through the channels, while in DWC, more water is pumped in deeper canals.
DWC is primarily applicable when there’s a high fish stocking density. There should be external filters (mechanical and biological) to sieve the fish wastes in such a system. Moreover, such a unit requires a high input, including purchasing enough feed to nourish the fish.
However, some farmers prefer a low stocking density to save on costs. In such a system, additional external filtration is unnecessary, and the space between the plant roots and the canals host the nitrifying bacteria (biofilter). Still, such a unit may have a lower food production unless the owner supplements the plants’ nutrients.
Now, let’s have a closer look at the components of DWC:
Grow Canals
Canals feed water to the floating beds. Though you can use various materials to construct them, always ensure that they’re sturdy, inert, and hold large water volumes. So, preferable materials include IBC plastic, fiberglass, and wood.
The grow canals can have varying lengths depending on the available space. However, they should be wide enough to hold plenty of water.
As far as the canal depth is concerned, 30 cm (11.81 in) is recommended. That’s because the canals should have a 1-4 hours retention time. So, this size will enable optimum mineral uptake by the roots to facilitate a fast plant growth rate.
Fish Tank
DWC is an integrated farming method involving a combination of aquaculture and hydroponics. Therefore, a fish tank is a fundamental component of a DWC unit. After feeding, the fish produce nitrogenous wastes that plants need for growth (after conversion into the appropriate form).
Moreover, a large tank is preferable to accommodate a large stock density in this system. However, in some cases, a low fish density is applicable, and in such a case, you’ll have to adjust your design. Therefore, you can use the feed rate ratio to determine how much feed enters the system, depending on the number of plants grown in the beds.
Floating Rafts
The floating rafts are flat boards that float on top of the canals. These rafts are also where you grow your plants. So, they should be made from lightweight materials, such as styrofoam or polystyrene. The floating rafts are also perforated to allow the plant roots to reach down into the nutrient-rich fish water.
You can use net pots to support the plants as you place them in the holes of the raft boards. These supporting pots will keep the roots growing downward while ensuring that the entire plant doesn’t fall into the water.
Mechanical Filters
A DWC lacks a medium. Hence, a dedication filtration component is essential in this system. Therefore, the water leaving the fish tank goes through a mechanical filter before entering the grow canals.
The physical filter sieves put solid wastes, including uneaten fish food and plant debris. Now, you can either have one or two filters, but a double filtration option is preferable. So, you can have a swirl filter to sieve particulate waste and a mesh sieve to filter the remaining debris.
Biofilter
Biofiltration is crucial in every Aquaponics system. Apart from filtration, a biofilter comprises a bacterial colony that breaks down nitrogenous wastes from the fish tank. As I mentioned earlier, there’s no medium (substrate) in the DWC system, and a separate biofilter is paramount.
A biofilter consists of air stones that provide oxygen to the system, apart from the bacteria. These airstones oxygenate the water, keeping the fish and bacteria happy and healthy.
Root Aeration Devices
Since a DWC unit lacks a substrate, plant roots are submerged in water continuously. Hence, it’s crucial to have a sufficient supply of oxygen to prevent anaerobic conditions that are unfit for the plants and fish. The oxygen supply at the biofiltration stage isn’t enough for the DWC unit, and additional aeration devices are preferable.
DWC farmers use air stones for aeration in most cases, as it’s one of the simplest options. These root aeration devices provide oxygenated air at a rate of 4 liters (1.06 gal) per hour. However, you can also use other alternatives to supply oxygen, including pumping, the addition of Venturi siphons to water inflow pipers, or the Kratky method.
The Kratky Method removes the need for aeration devices as there’s a space between the plant roots and the water. So, if you have a 3 to 4 cm (1.18 to 1.57 in) gap, this will facilitate sufficient air circulation around the root region. Also, the spacing prevents some plant diseases around the collar zone.
How Does DWC Work?
Despite being ideal for large-scale and commercial use, a DWC system isn’t as complicated as you may presume.
Instead, it’s a straightforward technique that newbies or learners can set up. Moreover, its working mechanism is a no-brainer, as it’ll pick up quickly once you’ve assembled your unit appropriately.
DWC works by circulating water from a fish tank to the grow canals and back. The water flow is almost identical to the Nutrient Film Technique (NFT). However, in this case, the water volume is higher, and the canals are deeper.
So, let’s have a look at the water flow dynamics:
- The fish tank is the starting point of water circulation, and water flows by gravity to the mechanical filter for physical filtration.
- Water moves to the biofilter, which acts as the sump.
- Water is pumped through a ‘Y” connector and channels through the valves in two directions from the sump. Some water goes back to the fish tank, while the rest moves to a manifold.
- The manifold distributes water equally to the grow canals, where it flows by gravity to the floating boards.
- After passing through the plant-filled rafts where plants take in the nutrients, the water flows back through the canals to the biofilter (or sump).
- Water is pumped again to the fish tank and into the manifold from the sump.
- The water going back to the fish tank overflows via an exit pump and back to the mechanical filter. Hence the cycle is complete, and the circulation continues.
How To Set Up a DWC System
Having learned the components and the working mechanism of the DWC system, you’re probably wondering how to set up your unit. However, worry not. It’s not complicated.
A DWC’s simplicity will depend on its variation, space availability, and preferences, so you can make it as fancy or simplistic as you want.
Here’s a basic setup procedure for a generalized Deep Water Culture unit:
- Gather all your materials, including two IBC tanks (fish tank and sump), a water/air pump, grow channels, filters (mechanical and biological), raft boards, and net pots.
- Prepare the fish tank and raise it by about 15 in (38.1 cm) on concrete blocks (ensure it’s made from an inert material that can hold water).
- Build three DWC canals using wood or concrete and line them with an inert material (e.g., PVC liners) to hold water. Connect the DWC canals to the two IBC tanks.
- Connect the mechanical and biological filters to the fish tank (use a “Y” connector and valves). Add a submersible pump at the bottom of the biofilter barrel (sump). Then, connect the pump to a 1 m (3.28 ft) long polyethylene pipe using a 25 mm wide adaptor (0.98 in).
- Install an air pump at the highest position of the system (preferably on one side of the fish tank). Attach one end of the pump to the DWC canals using a pipe. Drill an 8 mm (0.31 in) wide hole in each tank and add air stones near the inlets to supply oxygen to the canals.
- Prepare three drainage pipes into the biofilter. This filter will require a 24 cm (9.45 in) PVC pipe, three barrel connectors, three PVC adaptors and elbows, two rubber washers, and a PVC T-connector. Find more information on how to connect these pipes here.
- Prepare the raft boards using polystyrene. The polystyrene sheets should be 3 cm (1.81 in) thick to withstand the plants’ weight. Then, mark the plant holes with diameters between 16 mm (0.63 in) and 30 mm (1.18 in). However, this will depend on what plant types you’ll grow and the available net pots.
- Place the raft boards on the grow canals, mark the edge lines, and cut the outline of each channel. Then, drill the plant holes using a drill bit and cut a hole for the standpipe.
- Fill the fish tank, filters, and the DWC canals with water. Run the pump to check for any leaks in the system and fix them by tightening connections, securing valves, and checking all taps.
- Check the system’s flow rate and measure the water inflow using a stopwatch.
- Once your system is good to go, you can stock your fish tank and proceed with the planting process.
Note: You must determine the nutritional requirements of your plants and calculate the appropriate fish feeding ratio.
Now, let’s look at the planting procedure in a DWC unit.
How To Plant in a DWC System
Although you can plant your crops after setting up your system, it’s advisable to plant your seeds in a nursery a few weeks before completing your unit.
Hence, your seedlings will be ready for transplant once you’re ready to run your system. Also, you can choose to have a dedicated nursery on soil blocks or a soilless medium, depending on your space and preferences.
Transplanting seedlings should only occur when the seedlings are large enough to handle the system. The seeds’ maturity will depend on the plant breed and your nursery’s environmental conditions. So, once matured, transfer the seedlings into net pots and place them in the prepared holes on the raft boards.
At times, it may not be necessary to plant seeds first in a nursery bed. Hence, you can just plant them in a net pot and place them in the DWC unit. However, this will depend on several factors, including environmental conditions, availability of vegetable seeds, and plant species.
Once your plants have grown and are ready for harvesting, remove the whole plant (including dead leaves and roots). Pulling the lant from the raft will allow easy cleaning of the floating rafts for successive planting. However, don’t leave the rafts dry for a long time to avoid killing the bacteria colony.
Best Crops To Grow Under DWC
Selecting the best crops to plant in a DWC unit can be a nerve-cracking task. However, research will provide up-to-date information on the ideal plants to incorporate into your system and the best time to plant them.
First, here are factors to consider when choosing the right type of plants for a DWC unit:
Plant Breed
Not all plant species will do well in a DWC unit. For instance, drought-resistant crops such as rosemary herbs don’t need so much water and won’t thrive if their roots are always dangling in the water. So, select plant breeds that can do well in plenty of water, including basil, lettuce, collard greens, tomatoes, and kale.
Location
Plants have varying environmental requirements. Hence, your location’s parameters, including temperature, pH, and humidity, will determine the type of plants you can have in your DWC system. Moreover, if you want to combine two or more varieties, choose plant breeds with overlapping environmental needs.
If you’re in a warm climate, go for crops that can withstand high temperatures. For instance, okra is a warm-weather crop that does well in the southern region of the United States. It requires acidic conditions (a pH range of 5.8 to 7.0) and temperatures between 65°F (18.33°C) and 70°F (21.11°C).
Contrastingly, if you’re in a cold region, go for cold-weather crops such as lettuce. The plant thrives at lower temperatures at 45°F to 60°F (7.22°C to 15.56°C) and will turn bitter if exposed to higher temperatures. Lettuce also requires 10 to 18 hours of light and a pH range of 5.6 to 7.2.
Plant Weight
A DWC unit comprises lightweight floating rafts. So, you can only plant small-sized and lightweight crops. These crops should also have small root bases that don’t require media-based root anchorage.
Therefore, select top-light plants such as spinach, lettuce, basil, and kale. Contrastingly, avoid planting larger flowering crops in your DWC system. These crops have massive root bases that require sturdy root anchorage, apart from being too heavy.
Sustainability
Your DWC unit should be sustainable, both economically and environmentally. So, you don’t want to incorporate plants that will exhaust your resources. Therefore, the available space will determine the ideal crop amount to include.
Therefore, choose crops that require minimum spacing and can do well when densely planted if you have limited space. On the other hand, if space is a non-issue, go for crops with broad leaves that thrive better when sparsely spaced.
Harvest Potential
Are you planning to make money from your DWC? If your answer is ‘Yes,’ go for a crop that’ll earn you some profits. A plant’s profitability will depend on its demand, maturity duration, and yield.
Now, prior market research will update you on what crops are ‘hot cakes’ in your locality. Also, knowing your crop’s maturity duration will help determine the best time to plant your crop.
Therefore, if your crop is high-yielding, combining the other two factors will give you a better chance of earning money from your produce.
Now, here are some of the most sought-after crops that do well in DWC systems:
- Lettuce – it’s the most common plant in DWC units due to its fast growth, few maintenance requirements, and high market demand. Lettuce grows well in cooler climates and acidic conditions.
- Collard greens – are popular vegetables worldwide comprising broccoli and cabbage. Since they have broad leaves, collard greens will require ample spacing. They’re fast-growing and will mature 7 to 8 weeks after seed germination.
- Swiss chard – though susceptible to temperature changes, Swiss is a popular and easy-to-grow vegetable. It does well in DWC but requires close monitoring due to an attack by powdery mildew.
- Okra – it’s a warm-weather crop that originates from Africa. Although it does well in hot climates, it also requires moisture. So, it’s ideal for the raft system. However, it can grow large, requiring a bit of caging or trellising.
- Kale – another common vegetable. Kale does well in cool climates and can be combined with lettuce to meet the high market demand. The crop also does well indoors and is ready for harvesting in 5 to 6 weeks.
- Basil – it’s a sought-after plant in salads and numerous delicacies. Although it grows well in DWC systems, basil is labor-intensive and has high-maintenance requirements. So, it’s not a perfect crop for newbies and learners.
- Sorrel – it’s a cold-weather crop that usually thrives during fall and winter. However, you can also plant it indoors all year round by adjusting your environment’s parameters. Although it’s not well-known in most households, sorrel is a great addition to the sauce- and cream-based dishes.
- Bok Choy/Tatsoi – are Chinese vegetables (cabbages) that do well in DWC. However, not all varieties are ideal for this system, as some can grow pretty heavy for the floating rafts. Hence, the preferable variants are Mustard Bok Choy, Napa cabbage, Tatsoi.
Pros and Cons of DWC
Deep Water Culture is a sought-after Aquaponics system among hobbyists, learning institutions, and large-scale farmers. It’s ideal for both learners and experts due to its simplicity and cost-effectiveness. Also, its versatility, flexibility, and reliability make it one of the most preferred techniques for commercial food production.
Like any other Aquaponics system, DWC has its share of drawbacks. For instance, although it’s the most preferred technique for large-scale and commercial use, it can become a mosquito breeding site due to the considerable water volume.
Now, let’s take a more in-depth look at the benefits and drawbacks of the DWC system:
Pros of a DWC System
- It’s easy to set up a DWC unit.
- Since the water flow is continuous and plants are submerged in nutrient-rich water, there’s a consistent supply of minerals.
- Due to the large water volume in circulation, plants aren’t susceptible to poor water quality or temperature fluctuations.
- It’s ideal for mass food production due to its scalability and nutrient adequacy.
- It’s cost-effective, as you can choose available building materials to construct grow canals and floating rafts. The rafts are also reusable and durable if built well.
- It has minimal cleaning and maintenance requirements.
Cons of a DWC System
- The system requires an extensive water reservoir for the large water volumes.
- DWC is unsuitable for flowering plants such as tomatoes, as they’re heavy and have massive root bases.
- Maintaining the optimum water temperatures can be expensive, especially during cold seasons or colder climates.
- It requires aeration devices, as the plants directly contact water.
- A DWC unit needs a separate biofilter since there’s no media for growing crops.
- The large water volume and a sub-standard layout may convert the unit into a mosquito breeding site.
- The system requires sturdy hydroponic structures that can withstand high plant volumes.
Conclusion
Deep Water Culture (DWC) is your go-to system if you’re looking into establishing an Aquaponics system for money. Although it’s complicated on a small-scale basis, the technique is most effective for mass food production. Hence, it works best in ample space and with a large fish stocking density.
