Crushed Glass as a Filter Medium For On-site Wastewater Treatment

Q. Truong, M. Ramezanianpour (Ara Institute of Canterbury)

M. Jensen, I. Yuki (TM Consultants Ltd)

The on-site wastewater treatment system (OWTS) with a sand trench is an economical option for residents in rural areas or the countryside where a centralised sewer system is inaccessible. 2A sand achieves improved filtration, microbial activity and consistent long term performance when compared to gravel or scoria based trench systems. However, it is expensive and only readily available in a few areas across New Zealand. Additionally, it has a reputation for premature blockage when overloaded or compacted. The aim of this project 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 of the sand column in a discharge control trench. The treatment efficiency of three filters was recorded and compared in this study. Overall, the CG loaded at 25mm/day (CG25) and 50mm/day (CG50) provided an average of 13% and 6% more Total Nitrogen (TN) reduction than the sand filter respectively. The CG50 filter performed similarly at 50mm/day as the 2A sand filter in terms of Total Suspended Solids (TSS) and Biochemical Oxygen Demand (BOD5) removal, the CG25 exhibited low TSS and BOD5 removal rates at the start of the trial (likely due to residual liquid contamination from the bottles when crushed), improving over the sampling period and ultimately achieving similar results to the filters loaded at 50mm/day. Lifecycle 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 CO2 emissions than 2A sand. A 3-bedroom dwelling could save up to $500 and reduce 200kg of CO2 released to the environment annually when 2A sand is substituted for CG. Based on the findings of this paper, it is likely that the reduced installation cost, lessened environmental impact and theoretical availability will lead to CG systems becoming more common in New Zealand and abroad.


1 MB
03 Nov 2022

1400 Marc Jensen Crushed Glass WaterNZ Presentation 05 Oct 2022 MKJ.pptx

35 MB
09 Nov 2022