Groundwater can look clear and still carry metals that damage pipes, spoil taste, and threaten health. This study found that changing one small part of an air-powered treatment device made a major difference. Groundwater can be contaminated by natural sources and human activity.

Soils and rocks, industrial wastewater, and excessive groundwater extraction can contribute to iron and manganese in groundwater. These metals can give water an unpleasant metallic taste and odor, damage water distribution systems, and pose health risks. When they change form, they can also create reddish-brown deposits that clog pipes and reduce water pressure.

Venturi aeration can improve oxygen transfer and remove dissolved metals, but previous studies mostly focused on airflow, device shape, or discharge rate. The relationship between the air-hole arrangement, oxygen movement, and the behavior of iron and manganese in groundwater remained insufficiently understood.

Real-time monitoring of oxygen, flow, and metal changes was also insufficiently explored. The challenge is especially serious for manganese, whose oxidation is radically slower than iron oxidation under identical flow conditions. The study therefore evaluated how different air-hole arrangements affect oxygen transfer and metal oxidation, with the goal of supporting low-cost and energy-efficient groundwater treatment systems.

The treatment device moved water through a narrowed passage, where air was drawn in and bubbles formed in the aeration tank. The device used one, two, or three air holes. The bubbles generated by the device were very small, typically ranging from ten to three hundred micrometers across.

Manual measurements showed that increasing the arrangement from one hole to three raised the rate of oxygen transfer into the water. The sensor confirmed the same pattern: three holes transferred oxygen more effectively than one, with the measured kLa value increasing as more holes were added.

In everyday terms, the change worked like opening more windows in a stuffy room: more openings gave air more routes into the water. Both aeration time and the number of air holes affected metal removal. After the treatment period, the three-hole arrangement produced the largest decreases in both iron and manganese.

The three-hole arrangement removed 98.77 percent of the iron and 67.01 percent of the manganese. Greater oxygen availability speeds the oxidation of these dissolved metals into insoluble hydroxide and oxide species, including predicted precipitated products.

The picture makes the timing clear: iron removal rises sharply toward the end, while manganese changes more gradually, especially with fewer openings. Iron was removed more successfully than manganese. The lower manganese removal reflects its slower oxidation, meaning manganese needs stricter conditions and longer reaction times than iron.

The exact crystal structures of the resulting solids were not directly confirmed, although their formation was considered the most likely pathway under the measured water conditions. Changing the number of air holes significantly altered five water-quality measures, including physical properties of the water.

Water temperature decreased as the arrangement changed from one hole to two and then three holes, with the three-hole arrangement forming a separate statistical group from the other two. Overall, the number of air holes controlled airflow distribution, bubble formation, oxygen transfer, and the later oxidation of iron and manganese.

The three-hole arrangement produced the highest oxygen level and the strongest removal results. Manganese still lagged behind iron because it oxidizes more slowly and needs more oxygen. The results indicate that oxygen availability, rather than the amount of dissolved metal, was the main factor controlling oxidation.

For people relying on groundwater, a carefully arranged air-treatment device can improve treatment: the three-hole setup reached nearly nine milligrams per liter of dissolved oxygen and removed both iron and manganese. Manganese oxidizes more slowly and demands more oxygen, so achieving its removal may require a higher level of oxygen availability than iron removal.

Adding more air openings gave oxygen more ways into the water, helping remove nearly all the iron and much of the manganese without chemical oxidants. For households and communities, that points toward simpler groundwater treatment.