Enhancement of the capability in wastewater treatment by adding biochar into a conical-shaped sequencing batch reactor

Abstract

The present study evaluates the manner in which reactor geometry and corn-cob biochar (CCBC) collectively enhance the performance of sequencing batch reactors (SBRs). Four bench-scale SBRs (1.5 L) were operated in parallel, initially in cylindrical vessels and subsequently in conical vessels, followed by CCBC addition (1.5 g and 3.0 g per reactor, with weekly replenishment). Water quality parameters (TOC, NH4+−N, NO2−−N, NO3−−N, TN), DO, and MLSS were monitored, and FE-SEM was used to confirm biofilm development on CCBC. In conditions of identical operating cycles, the conical SBR exhibited a higher TOC removal rate (95 ± 2%, effluent 6.7 mg-C/L) in comparison to the cylindrical SBR (90 ± 2%, 12.8 mg-C/L). This is indicative of an estimated effluent BOD of 26.3 mg/L as opposed to 49.9 mg/L. The effluent total nitrogen (TN) levels exhibited a decline from 21.0 mg-N/L (cylindrical, 3 cycles/day) to 9.6 mg-N/L (conical, 3 cycles/day) and 9.2 mg-N/L (conical, 4 cycles/day). Following the CCBC addition, a marked decrease in effluent TOC was observed (1.1 and 2.2 mg-C/L for 1.5 g and 3.0 g, respectively), which then stabilized at low levels (3.5 and 2.9 mg-C/L on average). Concurrently, there was a significant reduction in , NH4+−N, NO2−−N, NO3−−N,, and TN relative to the control groups. A TN mass balance indicated that adsorption contributed only marginally to long-term T-N removal (< 0.1%), with denitrification instead predominating. This was likely promoted by larger anoxic zones in the conical geometry and by CCBC-supported microhabitats. FE-SEM analysis confirmed progressive biofilm colonization on CCBC. This study demonstrated for the first time that synergistic functions are achieved by placing a high-performance carrier, which combines macro-pores suitable for microbial habitation with high organic matter adsorption capacity, into a conical reactor with excellent flow and sedimentation stabilization. This method is considered to be a highly cost-effective approach for the removal of nutrients and organic matter via SBR in decentralised wastewater treatment systems in small-scale facilities and local hospitals in developing countries.