![]() Even though the contact time found for the studied process is similar to that for a filter column, the required area for the proposed process combination of dosing and UF would still be significantly smaller. Technical rules in Germany for granular CaCO 3 filters specify a theoretical EBCT of 15–17 min for the given water quality at a temperature of 10 ☌ ( DVGW-Arbeitsblatt W 214-2 (A) 2019). It is to be expected that the target can be achieved, despite the reduction of the contact time, if a higher concentration (40 g/L) is used. The experiments revealed that with this lower intermediate tank volume, the target pH was just met at the same dosing concentration of 20 g/L (JP). Considering that effective air-enhanced backwash and acidic chemical cleanings will be implemented in large-scale applications, the investigated process combination promises to be an appropriate treatment technology for turbid and soft acidic waters.Ĭonsidering the importance of the contact time for a complete deacidification to take place, the intermediate tank volume was further reduced from 75 to 30 L, corresponding to a shortening of the contact time from around 35 to 14 min. At a higher flux, a CaCO 3-fouling layer was formed, which decreased the membrane's permeability by 20% over 5 h. Stepping-flux experiments revealed the presence of fouling only at high-dosing concentrations, resulting in a critical flux of 55 L m −2 h −1. Critical flux was determined in a laboratory scale to evaluate the potential impact of CaCO 3 particles on the UF operation. No significant increase in transmembrane pressure was observed during the operation of a pilot-scale UF module at low flux (34 L m −2 h −1). The deacidification followed the same kinetics as for limestone filtration and yielded similar filtrate characteristics with dosing concentrations of 20 and 40 g/L CaCO 3. In order to reach the targeted pH value (≥7.8), dosing concentration, type of material and retention time were evaluated in pilot-scale experiments. The present study investigated the process parameters of a relatively new process combination in which powdered calcium carbonate (CaCO 3) was added prior to an ultrafiltration (UF). ![]() Soft acidic waters are often treated for drinking water purposes by using limestone filters to attain chemical equilibrium.
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