In this study, the optimization of nitrate removal from wastewater with a low C/N ratio using solid-phase denitrification was investigated. Biodegradable polymer, an attractive alternative to liquid carbon sources for biological denitrification, was used as a carbon source and biofilm support for nitrate removal. An experiment was conducted based on a central composite design (CCD) with response surface methodology (RSM). A secondary polynomial regression with nitrate removal efficiency as response value was developed. Based on statistical analysis, the nitrate removal model was highly significant with very low probability values (<0.0001). At the optimal conditions for nitrate removal (hydraulic retention time (HRT), 3.5 h; influent NO3 (-)-N concentration, 14.73 mg/L; and influent CODCr concentration, 15.00 mg/L), the nitrate removal efficiency was 99.23 %. The results of an ANOVA and response surface analysis showed that HRT, influent NO3 (-)-N concentration, influent CODCr concentration, and the interaction between the HRT and influent CODCr concentration significantly affected the nitrate removal efficiency (P < 0.05). In solid-phase denitrification process, electron donor for denitrification could be obtained by biological degradation of biodegradable polymer. Therefore, the influent CODCr concentration has no major effect on nitrate removal efficiency compared with that of HRT and influent NO3 (-)-N concentration.
Keywords: Low C/N ratio; Optimization of operation parameters; Polycaprolactone (PCL); Response surface methodology (RSM); Solid-phase denitrification process.