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DFM Denitrification Filter Media

The autotrophic bacterial denitrification of water   involves the conversion of nitrate into sulphate by the action of bacteria. The process requires a sulphur source and a means of buffering the water against acidic conditions. This is accomplished by use of two types of filtration media, DFM & MagPhlow.

          1. DFM sulphur based pellets view price
          2. Magphlow media composed of magnesium oxide buy or view price

When 1 g of Nitrate is removed by the bacteria 2.5 g of sulphate are produced, the sulphate will then continue to increase in the water, however sulphate is already present in marine systems at a very high concentration ( click here for seawater analysis). Approx 1 g of DNF (sulphur) media and 1.9 grams of MagPhlow media will be consumed per gram of nitrate and 0.7 grams of bacteria cell biomass will be produced.

The Bulk bed density of DFM = 1.2kg per litre, Bulk Bed density of Magphlow = 1.8kg per litre

The DFM media and MagpHlow media can be used in a DIN specification pressure filter or a purpose designed denitrification systems

Equipment

Denitrification system

The purpose designed denitrification system uses two columns, one for the DFM media through which the water first passes, and then on to the MagpHlow media to correct the pH. For system details click here

Denitrification system using pressure filters

Our DIN specification pressure filters or your own pressure sand filter may be suitable as a denitrification systems, click here for details

Technical issues

Autotrophic bacteria such as Thiobacillus denitrificans and Thiomicrospira denitrificans are capable of reducing nitrate to nitrogen gas. The energy source of autotrophic denitrifying microorganisms is derived from oxidation-reduction reactions with elements such as hydrogen or sulphur as the electron donor. Autotrophic denitrifiers utilise inorganic carbon compounds (such as CO2, HCO3-) as their carbon source. The system therefore requires a buffer and Magphlow Media is ideal for this application. In contrast, no organic carbon is needed as in heterotrophic denitrification. Another advantage of autotrophic denitrificans is that reproduction rate is low resulting in less sludge production which minimises the handling processes. Autotrophic denitrification has been divided into hydrogen-based and sulphur-based processes. Autotrophic organisms such as Micrococcus denitrificans are capable of reducing nitrate to nitrogen while oxidising hydrogen to water. The bacteria are aerobic but can also function under anerobic conditions by using the oxygen released from the reduction of nitrate and utilisation of carbonates and water.

55S + 50NO3^2- + 38H₂O + 20CO₂ + 4NH⁺⁴ ----> 4C₅H₇O₂N + 25N₂ + 55SO₄^-2+ 64H⁺

Based on this equation, for each gram of NO₃-N removed approximately 0.64 g cells and 2.5 g of SO₄^2- are generated the following buffering capacity will be consumed.

1.89 g of MagpHlow ( magnesium oxide) media

It is therefore important to sufficient buffering in the system, and a 1 : 2 ratio of DFM and MagPhlow works well for the application. The actual relationship is as follows;

1 g of Nitrate requires 1 g of DNF (sulphur) media and approx 2 grams of MagPhlow media, and will produce 0.7 grams of bacteria cell biomass.

Phosphate is also consumed in the process and will limit the rate of denitrification, so additional phosphate may be required. This can be dosed into the water either continuously or as a batch process. However in most cases in marine aquaculture or public aquaria there will be a surplus of phosphate.

DFM filter media 2 - 4mm

Denitrification column

pressure filters used for sand or AFM as well as for denitrification