Effect of Nitrite and Nitrate-N Accumulation and Removal on the Suspended Solids in the Aeration Tank of Opal’s Secondary Water Treatment Plant

Abstract

- High concentrations of Total Suspended Solids (TSS) in the aeration tank of the Secondary Water Treatment Plant (SWTP) were found to be related to the increased levels of nitrate and nitrite-N because of the nitrification and denitrification processes under the reduced oxygen conditions at mesophilic temperature. This issue was triggered in the aeration tank due to the transfer of residual ammoniacal-N from the Extended Granular Sludge Bed (EGSB) reactor through the effluent water. Under the low oxygen nitrification conditions, more oxygen supply facilitated nitrification, thus converting nitrite into nitrate by Nitrobacter. Almost 90 % reduction in TSS was found in the disposal water @ 36-37 ᵒC in the field conditions. However, in the case of high NO 3 -N, low levels of Dissolved Oxygen (DO) are recommended to enhance denitrification in the presence of Nitrosomonas in such a manner that NO 2 -N can squeeze O 2 from NO 3 -N. Similarly, in the case of high NO 2 -N, increased oxygen supply helped to reduce TSS. These strategies reduced TSS-laden N 2 liberation towards the surface of clarifiers. Total Suspended Solids (TSS) in the aeration tank were reduced to almost 90% compared to the initial solids in the aeration tank of the SWTP due to the nitrogen removal. Increased levels of DO (82 %) help to resolve the NO 2 -N accumulation issue in the aeration tank. Sludge volume in the aeration tank was reduced by 62% compared to the initial volume. Similarly, a 50% reduction in SVI30 was observed after 40 days of samples under field conditions, thus showing the removal of nitrogen from the system, which reduced the floatation of TSS.