The Role of Sulfur-Driven Autotrophic Denitrification in Sustainable Wastewater Treatment

Jiabao Wendy Qi1, Marc Russenberger1, Kaur Divraj1, Andrina Stiles1, Titania Huang1, Arthur Wang1, Yi-Lu Sun2, Ajit Sarmah1, Louise Weaver3, Alvin Setiawan4, Wei-Qin Zhuang1

1 Department of Civil and Environmental Engineering, Univerisity of Auckland 1142, New Zealand

2 Key Laboratory of Environmental Biotechnology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing, 100085, PR China.

3 Institute of Environmental Science and Research, Christchurch, 8041, New Zealand

4 National Institute of Water & Atmospheric Research Ltd (NIWA), Ruakākā, 0171, New Zealand

Sulfur-driven autotrophic denitrification (SdAD) utilizes reduced sulfur compounds as electron donors for nitrate reduction. Compared to conventional heterotrophic denitrification, SdAD can treat wastewater with low organic carbon to nitrogen ratios, such as dairy factory cleaning wastewater and post-anoxic municipal wastewater. Using sulfur compounds as electron donors avoids the need for external carbon sources for denitrification and reduces the overall carbon footprint of the denitrification process. In addition, previous studies have reported that SdAD produced less N2O emissions than the conventional heterotrophic denitrification processes. N2O is a potent greenhouse gas (GHG) with a global warming potential 295 times greater than carbon dioxide. The low GHG-emissions highlights that SdAD can be a more sustainable and environmentally friendly approach for the wastewater treatment industry.

However, one of the major challenges of SdAD is the generation of a large quantity of protons, which can consume alkalinity, reduce pH, and inhibit denitrification. To address this challenge, this study evaluated insoluble pH buffering materials—FeCO3 and sustainable CaCO3 materials (e.g., mussel shells)—for their capabilities to provide alkalinity in the SdAD process. Batch cultures with elemental sulfur powder as the sole electron donor were set up. The control experiments contained baseline alkalinity using NaHCO3. FeCO3 (1.74 g/L) and ground green-lipped muscle shell (GLS) (2.13 g/L) were added to different batch cultures, respectively. The nitrate concentrations, pH, sulfate, and phosphorus concentrations were monitored during a time-course experiment. The results showed that New Zealand green-lip mussel shells, among other tested materials, can act as an efficient pH buffer.

This study also investigated the prevalence of sulfur-utilizing denitrifiers in New Zealand Wastewater Treatment Plants (WWTPs). Return activated sludge samples were collected from three WWTPs in Auckland and used as seed sludge for batch experiments. Sodium nitrate and elemental sulfur powder were used as the sole electron acceptor and donor. The results showed that sulfur-utilizing denitrifies were ubiquitous in these WWTPs.

In conclusion, sulfur-driven autotrophic denitrification is a promising technology for sustainable wastewater treatment. This technology has the potential to significantly reduce the carbon footprint of the treatment process and provide a more cost-effective and sustainable alternative to conventional denitrification processes. Further research and development are needed to optimize and scale up the process for full-scale applications.