Addressing nitrogen pollution and greenhouse gas emissions in advanced wastewater treatment processes using rope-type biofilm reactors
Abstract
This research addresses the dual challenge of nitrogen pollution and greenhouse gas (GHG) emissions from wastewater treatment systems. It encompasses studies to evaluate and enhance total nitrogen (TN) removal efficiency and reduce GHG emissions in simultaneous nitrification and denitrification (SND) and partial denitrification (PDN) processes through biofilm technology. The first study introduced a novel approach to achieve SND under dynamic load conditions using rope-type biofilm technology beneficial for remote and decentralized communities. The process used a carbon management strategy with constant timer-based intermittent aeration control versus online sensor dynamic control strategies. The most optimal nitrification and total inorganic nitrogen (TIN) removal efficiencies were 89% and 72%, respectively. Additionally, the study employs multivariate approaches to delineate key operational factors affecting SND process and a comprehensive microbial community analysis revealed complex interactions among various bacteria under different aeration conditions that further deepens the understanding of the system.
Furthermore, the study explored the PDN pathway to generate stable nitrite accumulation benefiting the anammox process pathway for TIN removal. The process viability, biofilm community evolution, and functional enzyme formation in rope-type biofilm reactors using primary effluent (PE) and anaerobically pretreated wastewater carbon sources were studied for the first time. The internal carbons resulted in thinner biofilms; nevertheless, modest nitrite accumulation (0.24 g N/m2/d) occurred with elevated pH. The highest accumulation (0.79 g N/m2/d) was exhibited in the biofilm thickness-controlled acetate-fed reactor, featuring porous biofilms dominated by denitrifier Thauera (10.24%) and imbalance between Nar, Nap, and Nir reductases. Lastly, the research extended to monitor and mitigate nitrous oxide (N2O) emissions in the PDN process. This research is the first to evaluate N2O emissions within the co-diffusion biofilm PDN process, reporting 0.0008 to 0.053 g N2O-N/m2/d N2O emissions, representing 0.1% to 18% of the removed nitrate, which was further mitigated by manipulating the COD/N ratio.
Overall, this research provided a holistic understanding of fixed biofilm technology in wastewater treatment. By advancing SND and PDN processes with a focus on operational development, microbial community analysis, and environmental impact, the study presented a significant step forward in developing efficient and sustainable treatment methodologies.