Disposal of used agar plates

[elaruu]

I think I'd better not use the microwave, as the Science staff use it for food. (it's in my prep room but they heat their lunch in it). The pressure cooker purchase has been rejected, and I have been told to do it in bleach. I will do it in a big tub in an out of bounds area where it can be left overnight.

Thanks all!

[RosalieL]

I think I'd better not use the microwave, as the Science staff use it for food. (it's in my prep room but they heat their lunch in it). The pressure cooker purchase has been rejected, and I have been told to do it in bleach. I will do it in a big tub in an out of bounds area where it can be left overnight.

Thanks all!

I'd be sticking a biohazard warning on the microwave and using that! Surely the teachers have another microwave they can use? If they want to argue the point then they can fight for their own microwave. That's what it would have been put in the prep room for initially (science use, not staff convenience). No point putting your own health on the line when the item has already been purchased for the purpose. That's my tired and cranky Monday-itis talking...

[Labbie]

Fully agree with you Rosaliel, Get there own

[bigmack]

I used our Microwave ( which was the HTs old one from home ) to make Agar plates after learning about it from another Labbie at a Collegial meeting .

It certainly boils agar very well and if you aren’t quick on the button , it sure does make one hell of a mess .

I have do doubt it would work as a steriliser ….. but yup…. I’d double bag it for sure .

My guess is if they won’t buy you a pressure cooker , chances are , the budget is also screwed for buying the teachers a staffroom Microwave .

Pull the WH&S card . There is always budget at the admin level fir WHS even when Science Budget is gone .

[elaruu]

Thanks for that bigmack. I have used a microwave for melting agar (premade) in a previous life (research lab), and yes, you do have to be careful!

The issue with the pressure cooker was not budget-related. This school generally spends money like nothing else! It was that the person in charge of signing off once used one at home and it blew her electrics somehow, and she was worried that our electrical system wouldn't stand up to it. Bit odd, but oh well. Maybe we will revisit it in the future. The other staff members also thought the reasoning was weird. I'm leaving the school in a week anyway , as I have taken a job elsewhere.

There are other microwaves in the staff lunchroom. They just prefer to use the one in here.

All good. The bleach set up went ok yesterday and it was left out overnight. Now to dispose of somehow without bleaching my clothes .

[Wayne]

Taken from Science Assist,

Microwave ovens
Microwave ovens are not a suitable alternative to an autoclave or laboratory pressure cooker as they do not
provide moist heat in the form of steam under pressure and therefore, will not sterilise.

Microwaves penetrate unevenly and there can be ‘hot spots’ caused by wave interference. The whole heating
process is different because you are ‘exciting atoms’ rather than ‘conducting heat’.3 The heat and pressure
required to effectively sterilise agar is not produced and many microorganisms will not be killed.



I've also been told this at various PD's over the years

[Wayne]

Also from Science Assist,

Laboratory pressure cookers must contain a pressure gauge, a control and pressure relief valve and be
able to reach a pressure of 15psi (103kPa) and a temperature of 121°C.

These sterilisers can be purchased from biological suppliers however costs vary and schools need to source
one that is suitable for their use and budgetary requirements. Laboratory pressure cookers are generally
cheaper than autoclaves.

Note that most domestic pressure cookers are not suitable as they do not meet these requirements.

[RosalieL]

Taken from Science Assist,

Microwave ovens
Microwave ovens are not a suitable alternative to an autoclave or laboratory pressure cooker as they do not
provide moist heat in the form of steam under pressure and therefore, will not sterilise.

Microwaves penetrate unevenly and there can be ‘hot spots’ caused by wave interference. The whole heating
process is different because you are ‘exciting atoms’ rather than ‘conducting heat’.3 The heat and pressure
required to effectively sterilise agar is not produced and many microorganisms will not be killed.



I've also been told this at various PD's over the years

Thanks Wayne! Good info and it makes sense. I always forget about Science Assist. It is such a good resource! I need to make better use of it.

[elaruu]

I read that about domestic pressure cookers too (on Science Assist). But then I googled the pressure of domestic pressure cookers and it said that they did reach this pressure. Who knows? I also looked briefly online for a laboratory pressure cooker and couldn't find one.

[Wayne]

Southern Biological sell them (they have them named as autoclaves).

[Marama T]

Wow! Even the cheap ones are $1200.

[RosalieL]

So the time has come for me to pressure cook the life out of the agar plates... I haven't done it since being at this school and it's been more than 10 years since I left my previous school... I had an old pressure cooker I used on the hotplate there and would just have it cooking away for a very long time (I now know this wasn't the best way but at the time it was all I knew to do). It definitely was pressurised for more than 15 min each time!

My problem is that this school has an electric pressure cooker and I can't find a manual for it in the prep room or anywhere online... Do I just put some water in it, put the plates in an oven bag and set it for 15 min? Will the oven bag let enough steam in? Or do I leave it unsealed and seal it after it has cooled down before I put in the bin? I have autoclave tape to stick on it. Should I stick it to the inside of the bag to be sure it's sterilised?

[Merilyn1]

Google the brand name. Most companies have their user manuals on line. Or, share the brand name here and someone else may have the same one.

[RosalieL]

It's lumina which is an Aldi brand. I have worked out they've changed the brand name and some of the specs but managed to find a manual for a more recent model. It does not go up to the recommended psi but there's not much I can do about that! The first batch has just finished so when it has cooled down enough to open I will see what the tape says... 15psi (recommended by Science ASSIST) is about 104kPa and the info I can find regarding the Aldi pressure cookers is that they run at about 60kPa so... if it doesn't make the tape change then I'll look at getting one that meets requirements. Not sure how I'll go with that as this year I got a new dishwasher, my fridge and freezer are both on their last legs and I'm hoping to get new ones next year and I don't know that I can add an autoclave/pressure cooker to the list!

Edit to Update: It didn't even melt the plates. The agar was melted though. The tape was slightly discoloured on the indicator strips so I guess it was getting close! I've put it back on for a 35 minute cook instead of the 20min I started with... I'll see what happens at the end of that. Maybe I've added too much water? On the plus side, I haven't blown anything up (yet)!!