Wheat Straw can be used as biofilter media / Aquacultural Engineering (2007) 37, 222-233

Soares and Abeliovich (1998) and Aslan and Turkman(2003) indicate that wheat straw can be used as biofilter media and as a carbon source for the denitrification of drinking water. Lowengart et al. (1993) also used wheat straw to denitrify turbid and nitrogen-rich irrigation water. Similarly, Blowes et al. (1994) have demonstrated that wood chips can be used to as a biofilter media to treat runoff and irrigation water. Kim et al.(2003) investigated the use of both wood chips and wheat straw for nitrate removal in a bioretention study. Robertson et al. (2000) have evaluated sawdust, leafcompost, unprocessed grain seeds and wood mulch as reactive barriers to the flow of nitrate-laden waters. More recently, Robertson et al. (2005) reported on a commercially available wood-based biofilter media (marketed as NitrexTM) to remove nitrate–nitrogen froma pretreated residential septic tank effluent. Volokitaet al. (1996) studied shredded newspaper as a biofilter media in denitrification columns.

Study evaluated wood chips and wheat straw as inexpensive and readily available alternatives to more expensive plasticmedia for denitrification processes in treating aquaculture wastewaters or other high nitrate waters. Nine 3.8-L laboratory scale reactors (40 cm packed height  10 cm diameter) were used to compare the performance of wood chips, wheat straw, and Kaldnes plastic media in the removal of nitrate from synthetic aquaculture wastewater. These upflow bioreactors were loaded at a constant flow rate and three influent NO3–N concentrations of 50, 120, and 200 mg/L each for at least 4 weeks, in sequence. These experiments showed that both wood chips and wheat straw produced comparable denitrification rates to the Kaldnes plastic media. As much as 99% of nitrate was removed from the wastewater of 200 mg NO3–N/L influent concentration. Pseudo-steady state denitrification rates for 200 mg NO3–N/L influent concentrations averaged (1360 Æ 40) g N/(m3 d) for wood chips,(1360 Æ 80) g N/(m3 d) for wheat straw, and (1330 Æ 70) g N/(m3 d) for Kaldnes media. These values were not the maximumpotential of the reactors as nitrate profiles up through the reactors indicated that nitrate reductions in the lower half of the reactors were more than double the averages for the whole reactor. COD consumption per unit of NO3–N removed was highest with the Kaldnes media (3.41–3.95) compared to wood chips (3.34–3.64) and wheat straw (3.26–3.46). Effluent ammonia concentrations were near zero while nitrites were around 2.0 mg NO2–N/L for all reactor types and loading rates. During the denitrification process, alkalinity and pH increased while the oxidation–reduction potential decreased with nitrate removal. Wood chips and wheat straw lost 16.2% and 37.7% of their masses, respectively, during the 140-day experiment. There were signs of physical degradation that included discoloration and structural transformation. The carbon to nitrogen ratio of the mediaalso decreased. Both wood chips and wheat straw can be used as filter media for biological denitrification, but time limitations forthe life of both materials must be considered.

CENT RAS on going operation by farmers

Kg Bukit Keluang, Besut, Terengganu

Kg. Kuala Semerak, Pasir Puteh, Kelantan

Kg. Bukit, Keluang, Besut, Terengganu

Kg. Limau Nipis, Setiu, Terengganu

Kg. Air Tawar, Besut, Terengganu

Kg. Gong Medang, Besut, Terengganu

Kg Bukit Keluang, Besut, Terengganu

Kg. Mangkuk, Setiu, Terengganu

DIY own zeolite filter (Low cost - material PVC)

You can make yours simple zeolite filteration on Cents-Ras. The cost of filter system is less than RM70 per unit. The material that you need is list below ;
1. PVC pipe 2 inch - 100 cm
2. PVC pipe 1 inch - 50 cm
3. Valve 1 inch - 5 unit
4. Tee pvc 3 to 2 inch - 1 unit
5. Tee pvc 2 to 1 inch - 1 unit
6. Elbow 3 inch- 1 unit
7. Cap 2 inch - 1 unit
8. Reducer 3 to 2 inch - 1 unit
9. PVC Pipe 3 inch - 80 cm
10. Pvc pipe 3/4 inch - 100 cm
11. Elbow 3/4 inch - 4 unit

You can fabricate yours Zeolite filter based on picture above

Calculating Ammonia Loading:

The amount of ammonia excreted into a tank depends on a number of variables including the species, sizes, and densities of fish stocked and environmental conditions (temperature, pH). Ammonia loading can be roughly estimated from the biomass (weight) of fish in the tank or it can be based on the weight of feed fed each day. On the average about 25 mg (milligrams) of ammonia per day is produced for every 100 grams of fish in the tank. Therefore, in a tank containing 1,000 seabass fingerlings each weighing 75 g (75,000 g total fish weight), the daily ammonia load produced by all the fish would be 18,750 mg (18.8 g). To remedy excessively high
ammonia levels, add freshwater, eliminate feeding or reduce the density of fish in the tank.

Ammonia loading also can be estimated based on the total amount of feed fed. For manufactured fish feed with standard protein levels of 30 to 40 percent, simply multiply the total weight of the feed (in grams) times 25. For example, if the fingerling seabass are fed 454 grams of pelleted feed per day, the amount of ammonia produced per tank would be about 11,350 mg per day.

Zeolite, ammonia and fish health

Zeolites are an ideal means of managing ammonia levels in the short-term until full filter active is restored or achieved. Even modest levels of ammonia are a threat to fish health. This is particularly a problem in new ponds and aquaria where we have to let ammonia levels rise a little to encourage the establishment of nitrifying bacteria in the filter. Elevated ammonia can occasionally be a problem in established set-ups.

What are zeolites?
These are naturally occurring types of minerals, although because of their usefulness as molecular sieves they can now be artificially produced. In their natural form they are aluminosilicates, which are normal silicate minerals containing aluminium. The structure is such that these minerals can loosely bind positive charged ions, usually sodium.
They act as ion-exchangers and 'swap' their sodium ions, for other positively charged ions, for example calcium or ammonium. So they are often used for water softening to remove hardness-forming calcium ions. Fish keepers can make use of this unusual characteristic and employ them to remove ammonia (or more strictly ammonium - NH4+) from the water.

Using zeolite
The required amount is simply placed in the filter just before the water is returned to the pond or tank. Don't place it before the biological section otherwise there may not be enough ammonia left to encourage the growth of nitrifying bacteria.
Depending on the current ammonia levels, the zeolite is removed when it is 'full' and left overnight to soak in a very strong salt solution, during which the collected ammonium is "swapped" for sodium (you will recall that salt is actually sodium chloride). After a good rinse in clean water it is ready for use again

How much and how often?
For aquaria use, zeolite and other ion-exchanger products usually come in pre-prepared pouches with instructions. For pond use it is best to have at least two 10 kg sacks - one in use, the other being recharged.

Initially it will probably need to be changed daily, until such times that ammonia test kit readings show that levels are stabilising. Once this happens the period between cleans can be extended

To clean it use 2-3 oz salt per gallon of water. The actual amount is not critical as long as it is good and salty. It should only be used to manage an existing problem and not used on a long-term 'just in case' basis. First, if used permanently there is always the risk that it will 'dump' its ammonium collection. Secondly, it also acts as a water-softener and will remove calcium from the water.

Initially, even with zeolite it may still be necessary to do partial water changes to keep ammonia at an acceptable level. Zeolite cannot be used in ponds or aquaria where the water is salted

How Biological Filtration can works????

A biological filter is quite simply the heart of the RAS system. It's purpose is to convert the waste matter produced by the fish from harmful ammonia into less toxic waste. It is less important to remove solids particles from water than it is to process nitrogen, so if there is to be a compromise between mechanical and biological, err on the side of biological.

In other words, it is much better to allow particles below a certain size to escape back into the pond,while converting a great deal of ammonia to nitrate, than it is to catch every little thing down to a micron or less which in the process would slow the water down to the point where the bacteria have a hard time living (because they're not getting enough oxygen).

The bacteria that convert ammonia to nitrate for us are among a class of bacteria that you may have heard of before. They are the so-called, “nitrogen fixing” bacteria. This means that they take nitrogen that is unavailable to plants in its ammoniacal form, and make it available to plants in an oxidized form.

There are 2 types of bacterial species that colonise the biological filter media. Nitrosomonas sp.bacteria which oxidize ammonia to nitrite, and Nitrobacter bacteria convert nitrite to nitrate.

NH3 + CO2 + 1.5 O2 + Nitrosomonas → NO2- + H2O + H+NO2- + CO2 + 0.5 O2 + Nitrobacter → NO3-

The conversion of ammonia to nitrates is performed primarily by bacteria and other nitrifying bacteria. The primary stage of nitrification, the oxidation of ammonia (NH3) is performed by bacteria such as the Nitrosomonas species, which converts ammonia to nitrites (NO2-). Other bacterial species, such as the Nitrobacter, are responsible for the oxidation of the nitrites into nitrates (NO3-).It is important for the nitrites to be converted to nitrates because accumulated nitrites are toxic to plant life

Denitrification

Denitrification is the reduction of nitrites back into the largely inert nitrogen gas (N2), completing the nitrogen cycle. This process is performed by bacterial species such as Pseudomonas and Clostridium in anaerobic conditions. They use the nitrate as an electron acceptor in the place of oxygen during respiration. These facultatively anaerobic bacteria can also live in aerobic conditions.

Ammonia

Ammonia (NH3) is produced by fish as part of their normal metabolic function and is excreted from the gills. The amount of ammonia produced is directly related to the amount of food they eat. Approximately 3-4% of normal 30-40% protein level food will be excreted as ammonia, i.e. for every 100grams of food 3-4grams (3000-4000mg) of ammonia is produced. Fish exposed to unacceptable levels of ammonia risk damage to gills, eyes, fins and skin which can result in them being susceptible to secondary bacterial infection. Using standard drop type tests kits any ammonia reading is considered unacceptable and remedial action should be taken.NitriteAmmonia is oxidized by the Nitrosomonas sp. bacteria in the filter to produce nitrite (NO2). Whilst it is not considered as dangerous as ammonia it can still do serious damage to your fish. High levels of nitrite are likely to stress your fish leaving them susceptible to secondary infection. As with ammonia, target levelsshould be that nitrite is undetectable. Before the fish pond filter can efficiently remove ammonia and nitrite from the fish pond water, it must first become fully colonized with nitrifying bacteria. This can take some time and is a process known as fish pond filter "maturation". Each time a fish is put in the fish pond it will add to the total amount of ammonia being produced. The ammonia level in the fish pond will therefore increase slightly. Because there is more ammonia for the bacteria to utilize, they start to multiply until there are enough to use all of theammonia being produced inside the fish pond. The ammonia level in your fish pond will then fall back to zero.NitrateAs the ammonia level falls, the amount of nitrite produced by the bacteria in the fish pond filter will start to increase. Therefore, the level of nitrite in the fish pond will rise. The increasing nitrite level means that the bacteria that break it down can start to multiply in the fish pond filter until, as with the ammonia, there are enough to use up all the nitrite that is being produced. The nitrite level within the fish pond can then fall to zero. As this occurs, the nitrate level increases.

Conversion of nitrite to nitrate (NO3) is the final stage of the nitrification process.

There is debate as to the possible problems that elevated levels of nitrate may cause.Nitrate and it causes no problem at all. High nitrate may also attribute to green water(phytoplankton). The green water problem can get worst when you clean the biofilter and make water change outs, due to the reduction in bacteria.The bacteria also produces a certain phytoplankton-killing enzyme. As algae starts to grow in the biofilter,or on the walls of the pond, the bacteria loves to feed on this algae, and as it does so it releases the enzyme into the water. Green water is a pain for many reasons. Ultra Violet Clarifier lights will kill single cell phytoplankton algaethat cause green water, and when dead they clump together and can be removed by the filter. However there is sometimes a concern expressed that passing water through the UVC also kills beneficial bacteria.

Cost efficient RAS technology for nursery (Article in Aquaculture Asia Pasific Magazine- March/April 2009 Vol. 5 Number 2)

The team led by Ahmad Daud Om at the Marine Fish Production and Research Centre has developed a low cost and easy to manage recirculation aquaculture system suitable for small hatcheries. They have named this CENTS – Cheap Efficient Nursery Tank System. The system is ideal for nursing the highly carnivorous tiger grouper from 2-3cm to 7.5 - 10 cm total length in seawater of 15ppt. There are two partitioned concrete biological filters, two water pumps, one air blower and 20 concrete tanks holding 180 litres of water. Each of these can hold 2,000 2-3 cm juveniles. The investment cost is MYR 20,000. A unique feature is a waste trap which reduces the load on the biological filters. This is merely lifted for cleaning twice a day. Waterin the tanks and biological filters are topped up by 10-15% daily. Fish is graded every two weeks and stocking density is reduced by transferring fish to nursery tanks. In a one month operation, the yield is 14,000 juveniles. Fish are fed to satiation 4-6 times daily. Pre operation procedures include preparation of probiotic bacteria for tanks and biological filters. The benefits of this system include improvement in survival at 80-90% as compared to juveniles reared in open systems such as cages and ponds. The system has been commercialised and it now used by 20 farmers for nursing of various species of marine fish fry.