Nitrate removal from groundwater using an activated sludge as a source of bacteria

Abstract

In this study, the denitrification of nitrate-contaminated groundwater by the heterotrophic denitrification (HD) method was studied to produce drinking water. Preliminary tests were carried out in a denitrification reactor, consisting of an opaque PVC column filled with a plastic packing, and fed with a synthetic solution based on glycerol, in which activated sludge bacteria were added. The performance of the reactor was monitored by measuring physicochemical parameters such as pH, turbidity, nitrates, and nitrites. This monitoring was carried out for different tests within the same reactor to evaluate the adaptation possibilities of the denitrifying bacteria. At the end of each test when the substrate was exhausted, a new synthetic solution was added to the reactor under discontinuous aeration (aeration period = 1 h). The results obtained showed that the nitrate removal efficiency reached a value of 99.42% after 8 h of treatment depending on the adaptation of the denitrifying bacteria. This experiment also showed that the concentration of produced nitrite depends on the aeration mode and it reached a value below the detection limit in the sequential aeration mode after 12 h of treatment under discontinuous aeration (aeration period = 1 h). HIGHLIGHTS The biological denitrification using activated sludge is used to remove nitrate from groundwater.; The residual nitrate concentration depended on the bacteria adaptation.; The nitrate removal efficiency increased to 99.42% after 8 h under discontinuous aeration.; The mode of aeration influenced the nitrate removal and also the removal of accumulated nitrite.; The produced nitrite was removed after 12 h in discontinuous aeration.;

Keywords

• activated sludge
• denitrification
• groundwater
• nitrate