https://sciencing.com/dispose-methanol-8699726.html

If you have the expertise neutralize it. Wastewater Treatment Plants can use it. Methanol can be incinerated easily.

All depends what is the other 80%. If it is water, WWTP, but not via the drain.

Methanol is not hazardous to WWTP microorganisms. The wastewater reaching WWTP is often depleted of C-compounds and for heterotrophic denitrification, methanol is added as an easily consumable carbon source: NO3 − + 1.08 CH3OH + H+ → 0.065 C5H7NO2 + 0.467 N2 + 0.76 CO2 + 2.44 H2O. Thus for small quantities dilution of methanol to be less than 1% and pouring down the sink is a better option than leaving it under fume hood to evaporate.

Yes Anne Menert mam is right. methanol is as such required as a supplemental carbon source for denitrification- activated sludge and denitrification filter process. The dosing has to be based on low BOD : N or Low COD : N It is used in moving bed bio film reactor MBBR process.

If required lab studies may be conducted to examine as to 20% methanol and 80% water- mixture is consumed by bacteria or not. If the activated sludge is acclimatized, methanol is likely to be consumed in Activated sludge process

Prof Dr K N Sheth, Gujarat Technological University

If this is laboratory waste it needs to be stored and labeled properly according to hazardous waste laws and regulations in you country, city, state, institution. You should ask your health and safety officer how to store and properly dispose of hazardous waste in your lab.

20% methanol has a flash point of 40C, this is considered a hazardous waste and is potentially dangerous. Make sure you label it properly indicating the hazard it poses to other lab employees, and to first responders should there be an emergency on site. In US it is illegal to dilute and dump hazardous waste of any kind any where.

Prior to generating hazardous waste, you should have a plan in place on how to deal with the by products of your experiments.

Here, you would need to pour into a properly labeled satellite container, which would indicate that it is flammable and toxic.

For WB 10% ethanol in western blot transfer buffer works well and 100% ethanol for wetting the membrane.

Also dry or seminary transfer work well reducing waste.