Dolomite reactor
The dolomite reactor is a process for the improved supply of a biological sewage treatment plant with calcium and magnesium .
It has been used as a cleaning process (neutralization) since 2005 in small to medium-sized sewage treatment plants (3000 - 200,000 PE ). Especially in areas with very soft water, the dolomite reactor increases the water hardness ( acid capacity ).
In the past, wastewater treatment plants with a weak buffer were rather the exception, today plants with sufficient acid capacity have become rare. This has changed with the introduction of more extensive nitrogen elimination. The cause is the increased formation of carbon dioxide (CO 2 ) and the greater consumption of acid capacity by nitrification (formation of H + ions). The consequences are dramatic, because the lime-dissolving free carbon dioxide (CO 2 ) attacks concrete and the flake structure. Concrete corrosion, bulking and floating sludge burden the plant operation and weaken the substance of the plant.
With the help of the process, the total hardness , i.e. calcium hydrogen carbonate Ca (HCO 3 ) 2 and magnesium hydrogen carbonate Mg (HCO 3 ) 2 as well as calcium carbonate CaCO 3, of the activated sludge flake is increased in a targeted manner and thus the structure is stabilized, while the content of free carbonic acid in the system decreases. In addition, other functions are favorably influenced, such as the settling behavior in the secondary clarifier, the hydraulics of the sewage treatment plant, the outgassing of carbonic acid in the digester and the biological breakdown of nitrogen and phosphate.
Working principle
Activated sludge (around 10% of the dry weather feed) from the end of the denitrification stage is fed into the reactor from below via a partial flow. The activated sludge reacts with the filling material. The outlet then takes place in the inlet of the nitrification stage.
The dolomite reactor is filled with half to fully calcined dolomite in different grain sizes. Dolomite is a naturally occurring, homogeneous mixture of calcium and magnesium carbonate ( chemical formula CaMg (CO 3 ) 2 (CaCO 3 · MgCO 3 )) and can therefore be "half" burned, ie. H. to MgO and CaCO 3 . This half-fire is on the one hand still solid rock (does not generate dust), on the other hand the magnesium oxide MgO is water-soluble and leaves a calcium carbonate CaCO 3 with very large surfaces in the dolomite reactor . Similar to activated carbon , the large surfaces enable reactions that are not possible with normal mixtures in a comparable time.
Due to the grain size and the degree of fire, the effect can be individually adapted to the needs of the sewage treatment plant. All levels of calcium and magnesium supply are possible, from a simple increase in the acid capacity to setting the lime-carbonic acid balance or correcting the pH value to adjusting the Ca / Na ratio.
The filling material is consumed without residue. When there is less need, such as increasing the acid capacity or adjusting the lime-carbonic acid balance, the free carbon dioxide available controls consumption and is therefore self-regulating. If larger quantities are required, a pH probe in the outlet of the dolomite reactor controls the charging of overcalcined dolomite.
Different designs of the reactor enable permanently installed submerged variants or dry-installed tanks, with which sewage treatment plants can also be retrofitted.