Treatment of Septic Tank Discharge Using Crushed Glass Filter Media

The onsite wastewater treatment system (OWTS) with a sand trench is an economical option for residents in rural areas or the countryside where a centralized sewer system is inaccessible. The 2A sand achieves improved filtration, microbial activity, and consistent long-term performance when compared with gravel- or scoria based-trench systems. Additionally, it has a reputation for premature blockage when overloaded or compacted. Although sand trenches overcome the failures reported on septic tank discharge, this could not be the only and the most sustainable solution. The aim of this research is to investigate and critically evaluate the performance of crushed glass (CG) with respect to 2A sand when treating primary treated effluent from a septic tank. A test rig was designed and constructed to simulate the real environment in a discharge control trench. The treatment efficiency was recorded and compared in this study. Overall, the CG loaded at $25\mathrm{mm}/\mathrm{day}$ (${\mathrm{CG}}_{25}$) and $50\mathrm{mm}/\mathrm{day}$ (${\mathrm{CG}}_{50}$) provided an average of 13% and 6% more total nitrogen (TN) reduction, respectively, than the sand filter. The ${\mathrm{CG}}_{50}$ media performed similarly as the 2A sand media in terms of total suspended solids (TSS) and biochemical oxygen demand (${\mathrm{BOD}}_5$) removal rate of 95% and 96%, respectively. The ${\mathrm{CG}}_{25}$ media exhibited low TSS and ${\mathrm{BOD}}_5$ removal rates of 92% and 91%, respectively. The rates have been improved over the sampling period and ultimately achieving similar results to the filters loaded at $50\mathrm{mm}/\mathrm{day}$. Life-cycle cost analyses and carbon balances were completed for the two media. It highlighted that the current price of CG is only half of 2A sand, yet it produces significantly less ${\mathrm{CO}}_2$ emissions than 2A sand. A three-bedroom dwelling could save up to $500 and reduce 200 kg of ${\mathrm{CO}}_2$ released to the environment annually when 2A sand is substituted for CG.