Optimization of Preparation Conditions for a Novel Composite Slow-Release Carbon Source and Its Denitrification Performance
To address the issues of insufficient carbon sources and low denitrification efficiency in rural domestic wastewater, this study developed and optimized a composite slow-release carbon source using corncob, rice husk, reed straw, polyvinyl alcohol (PVA), and sodium alginate (SA). The preparation conditions and raw material ratios were systematically optimized using Plackett-Burman (PB) design, response surface methodology (Box-Behnken design, BBD), and mixture-optimal design (MOD). The denitrification performance was evaluated through carbon release characteristics and denitrification experiments. The optimal preparation conditions were determined as PVA 8.64 g, SA 2.41 g, rice husk 3.82 g, corncob 4.47 g, reed straw 6.06 g, freezing time 19.11 h, and crosslinking time 12 h. The 7-day cumulative carbon release was (43.38 ± 1.3) mg·(g·h)−1. The release process followed first-order kinetics, Higuchi, Ritger-Peppas, and Weibull models, indicating that carbon release is controlled by multiple mechanisms including diffusion and skeleton erosion, ensuring stable slow-release characteristics. In denitrification experiments with influent NO3−-N concentration of 50 mg·L−1, the composite carbon source (RCR-PVA-SA) achieved a maximum NO3−-N removal rate of 90.8% after 10 days of operation, with a removal rate of 0.079 mg·(g·h)−1. Under dynamic conditions with hydraulic retention time (HRT) of 3 h, the average removal rate remained at 87.9%, demonstrating efficient and stable denitrification performance under both static and dynamic conditions. This research provides a reference for the preparation of natural slow-release carbon sources and the resource utilization of agricultural waste.