Influence of Multiple Parameters on Groundwater Iron Removal in the Presence of Ammonium Nitrogen

This paper studies the effect of the initial iron (2.1–6.9
mg/L) and ammonium nitrogen (2.5–6.0 mg/L) concentrations and
aeration parameters on the efficiency of two-stage purification of
complex groundwater. The experimental setup utilized two stages of
filters with air-to-water ratios of up to 5:1 and 1.5:1, respectively.
It was found that secondary aeration reduced residual iron to the
standard 0.3 mg/L, while the ammonium nitrogen concentration dropped
below 1.5 mg/L in most modes. The maximum efficiency of ammonium removal
was observed with optimal second-stage aeration: in the absence of
aeration, the purification efficiency was only 39.5%, while with optimal
parameters, the efficiency reached 75–80%. Correlation analysis
revealed the key role of the initial concentrations and aeration parameters:
for iron, the critical factor was Fe2+ and its interaction
with N-NH4+, and for ammonium nitrogen, it was
the intensity of second-stage aeration. Machine learning models (CatBoost
and GPR) showed R2 determination coefficients
of up to 1.000, confirming the high accuracy of forecasting. Practical
implementation of the second stage of purification at the station
made it possible to reduce residual iron concentrations by an additional
35–45% and reduce energy costs by 15–20% due to aeration
optimization, ensuring stable compliance with Fe and N-NH4+ standards.