You are correct that septic systems require special considerations when considering the discharge from school science areas. We are not aware of any resource that specifically addresses this situation. However, we can provide some links to general resources and waste minimisation strategies.
Septic systems work using anerobic microbes and physical settling process to clarify the waste water. The addition of excessive water or very acid or alkaline solutions can dilute or destroy the microbes. Many laboratory chemicals are hazardous to the environment. Anything chemical that is toxic or hazardous to the environment such as those classified as a Dangerous Goods class 6 or 9, should definitely not be disposed down the sink.
Science ASSIST recommends that no chemical waste should be disposed of into a septic system as it has the potential to disrupt the bacterial processes within the system and harm the environment. It would be acceptable for the rinsing of glassware of most water-soluble chemicals to be disposed in the septic system as it would involve only trace amounts of chemicals. Very small quantities of acids/bases could be diluted and neutralised, but the total volume of liquid should not be excessive. It would be wise to place caution notices advising of this above the sinks in the laboratories.
The best approach is to minimise the amount of waste produced and arrange for all hazardous waste to be disposed by a chemical waste contractor. As far as practicable, we suggest conducting activities on a microscale where possible to reduce the quantity of chemical waste produced,
General information regarding septic tanks
The following documents are generally written to address requirement for households and may contain state specific requirements. They explain how septic systems work and may have some general comments regarding waste that is unsuitable for septic systems that could be applied to schools.
- Government of Western Australia Department of Health. 2011. Understanding Septic Tank Systems, Shire of Esperance website, https://www.esperance.wa.gov.au/sites/default/files/publication/files/un...
- Government of Western Australia Water and Rivers Commission. 2000. Water quality protection guidelines no 8 Mining and mineral processing laboratory waste discharge. Government of Western Australia Department of Water and Environmental Regulation website, https://www.water.wa.gov.au/__data/assets/pdf_file/0012/4224/10141.pdf
- SA Department of Health. 2008. Maintenance of septic tank systems. Wastewater fact sheet, SA Health website, http://www.sahealth.sa.gov.au/wps/wcm/connect/91200f04-89a8-4aaa-87d9-55...
- ‘Septic Tank Regulations’, A&A Worm Farm website, https://www.wormfarm.com.au/septic-tank-regulations/ (Accessed 26 October 2018)
- NSW Department of Local Government. 2000. The Easy Septic Guide, NSW Office of Local Government website, https://www.olg.nsw.gov.au/wp-content/uploads/Easy-septic-guide.pdf (Link updated May 2020)
Waste Minimisation strategies
These documents contain ways of minimising and handling hazardous waste in school science laboratories:
- American Chemical Society. 2002. Less is Better: Guide to minimizing waste in laboratories. American Chemical Society website, https://www.acs.org/content/dam/acsorg/about/governance/committees/chemi...
- Flinn Scientific. 2017. Reducing Chemical Waste. Flinn Scientific website, https://www.flinnsci.ca/api/library/Download/92969b10341a4a75a893ea32fc2...
- Morrison, Kendra A. 2006. Hazardous Waste Management for School Laboratories and Classrooms. US EPA website, https://nepis.epa.gov/Exe/ZyPDF.cgi/P100JR1S.PDF?Dockey=P100JR1S.PDF
- National Research Council (US) Committee on Prudent Practices in the Laboratory. Prudent Practices in the Laboratory: Handling and Management of Chemical Hazards: Updated Version. Washington (DC): National Academies Press (US); 2011. 8, Management of Waste. Available from: https://www.ncbi.nlm.nih.gov/books/NBK55885/
- Science ASSIST. 2015. Q&A: Hazardous waste. Science ASSIST website, https://assist.asta.edu.au/question/3243/hazardous-waste
- Science ASSIST. 2016. Q&A: Laboratory Chemicals and Waste Management/Setup. Science ASSIST website, https://assist.asta.edu.au/question/3903/laboratory-chemicals-and-waste-...
- Washington State Department of Ecology. 2003. Step-by-Step Guide to Better Laboratory Management Practices. Montana Tech website, https://www.mtech.edu/env_health_safety/chem_lab/docs/Step_by_step_guide...