A Teaching Reform Case for Water Quality Engineering Based on C@CaCO3 Enhanced Biological Nitrification of Low-Alkalinity Digestate Wastewater

Undergraduate Water Quality Engineering courses rely on verification experiments lacking real engineering scenarios, limiting undergraduate participants’ comprehensive problem-solving skills. To remedy this issue, this study constructs an inquiry-oriented experiment using carbon-coated nano-calcium carbonate (C@CaCO3) to enhance biological nitrification for digested wastewater with low alkalinity and high ammonia. It involves wastewater characterization, sequencing batch reactor (SBR) operation, quantification of chemical oxygen demand (COD), ammonium nitrogen (NH4+-N) removal, mechanism discussion on alkalinity slow release and microbial carrier role of C@CaCO3, and high-throughput analysis of microbial communities. Experimental results show that C@CaCO3 increases NH4+-N removal by 94.5 ± 4.8% in low-alkalinity water, while COD removal improves from 5.7 ± 3.0% to 29.5 ± 5.2%. These findings demonstrate that C@CaCO3 effectively mitigates alkalinity limitation, facilitates microbial attachment, and promotes functional microbe enrichment, offering a practical solution for sustainable nitrogen management in nutrient-rich waste streams. Pedagogically, the case links water-quality monitoring, reactor control, and solid-waste resource recovery, enabling undergraduate participants to trace the full engineering workflow problem identification through quantitative design, operation, and mechanistic interpretation. Post-laboratory surveys and performance assessments indicate significant gains in experimental competence, data-analysis skills, and engineering judgment. By embedding a real-world, low-alkalinity wastewater challenge within the curriculum, the module advances sustainable water-resource management education and provides a replicable model for reforming laboratory teaching in Water Quality Engineering and related environmental-engineering courses.