Indian researchers have proposed a groundbreaking method for treating wastewater sustainably by utilizing a microalgae-bacterial consortium. This innovative approach, highlighted in a recent study, offers a cost-effective and eco-friendly alternative to traditional ammonium removal techniques, which rely heavily on energy-intensive oxygenation processes.

The Problem of Ammonium in Wastewater

Ammonium, a toxic nitrogen compound derived from gaseous ammonia, is a significant pollutant in wastewater. It poses severe risks to aquatic life, animals, and human health by altering water pH and contributing to eutrophication—where excess nutrients fuel harmful algal blooms. Professor Kannan Pakshirajan from the Indian Institute of Technology Guwahati explains, “Ammonia can harm mammalian cells and human health due to its potential to alter water pH. Drinking water is typically slightly alkaline, and if its pH becomes acidic, it becomes unfit for consumption.”

India faces a critical wastewater management challenge. A 2022 Niti Aayog report reveals that urban areas generate approximately 72,368 million liters per day (MLD) of wastewater, while rural regions produce 39,604 MLD. Sources include agricultural runoff, industrial effluents, and sewage, all containing harmful chemicals, with ammonium being particularly concerning.

Traditional Methods and Their Drawbacks

Conventional ammonium removal processes involve oxygenation through mechanical or aeration systems, accounting for up to 90% of a treatment plant’s energy consumption. These methods are not only costly but also generate waste-activated sludge, which presents disposal challenges. “The major cost involved in wastewater treatment comes from aeration, where oxygen is supplied by pumping or mechanical operations,” Pakshirajan explains.

Chemical methods, while faster, require additional energy and are less environmentally friendly. As such, biological approaches, such as anaerobic digestion using microorganisms, have gained preference due to their sustainability and lower energy demands.

The Role of Microalgae-Bacterial Consortia

The study introduces a photo-sequencing batch reactor (PSBR) that uses a combination of microalgae and bacteria for ammonium removal. This biological process involves:

1. Ammonia oxidation: The microalgae produce oxygen via photosynthesis to support this step.
2. Nitrate conversion: In anoxic conditions, nitrate is reduced to nitrogen, the least harmful form of nitrogen.

By alternating light and dark cycles, researchers regulate the oxygen levels necessary for each stage. During light exposure, algae produce oxygen, aiding ammonia oxidation. In the absence of light, algae consume residual oxygen, creating conditions conducive to nitrate conversion.

“This process, known as the photo-activated sludge process, mimics natural ammonium absorption mechanisms while reducing reliance on external energy sources,” Pakshirajan notes.

Advantages of the New Approach

The PSBR system leverages photosynthesis to cut energy consumption by 50–90% compared to traditional aeration methods. Additionally, the absorption of ammonia by bacteria leads to increased biomass, which enhances oxygen production under light, creating a self-sustaining cycle.

“This is a nature-based solution that reduces costs associated with aeration, oxygen supply, and pumping while utilizing entirely natural substances,” Pakshirajan highlights.

Limitations and Future Directions

While the approach shows great promise, some limitations remain. High ammonia concentrations can hinder the efficiency of ammonia-oxidizing bacteria. However, typical ammonium levels in wastewater are within tolerable ranges, minimizing this concern.

T.V. Ramachandra from the Indian Institute of Science Bengaluru commends the theoretical modelling but suggests that incorporating more field samples could strengthen the results. He also points out that similar consortia are already used in lake rejuvenation projects, particularly in Bengaluru.