Evaluation of Biochar and Iron as Alternative Materials to Improve Performance of Septic Systems—Part 1. Material Selection and Batch Tests

The benefits of incorporating biochar and iron as alternative materials to improve septic effluent quality were assessed and compared to C33 sand, a traditional material used to construct septic system soil treatment areas. This study used sequential batch tests to investigate pollution reduction performance of C33 sand, eight types of biochar, and three types of iron with various dosages to identify and optimize operational parameters. Pseudo-first-order and pseudo-second-order kinetics models were used to simulate temporal performance of wastewater treatment and identify likely mechanisms driving improvements in septic effluent quality. Softwood pine (SP) biochar was most effective at reducing biological oxygen demand (BOD), total nitrogen (TN), and fecal coliform (FC) in septic effluent, while treatment with iron-enhanced-sand (IES) produced the highest removal efficiency for total suspended solids (TSS) (> 80%) and total phosphorus (TP) (> 95%) among substrates tested. Experimentation revealed dosages that achieved optimal pollutant removal from 50-mL septic effluent were 5-g C33 sand, 1-g SP, or 2-g IES. Kinetics study showed that the pseudo-second-order model generally described the adsorption performance better than the pseudo-first-order model regardless of materials (average R² value > 0.95). Furthermore, the pseudo-second-order model simulated adsorption capability (mg g⁻¹) at equilibrium status with a lower percent error when compared to the pseudo-first-order model results. Based on these results, incorporation of SP and IES as alternative materials can achieve higher contaminant removal efficiency and produce cleaner septic effluent, thereby benefiting the environment.