Hi,
I do apologise for not posting, I haven't been on here or VOD for a few days now as it's all been a bit manic here. I have barely had a spare waking moment for various reasons.
Anyway, I am back now.
I can vouch for this method working really well. I have done three batches in this way now, with different feedstocks and have had perfect results every time.
I do the two stage no titration method with methylate to get a perfect 5/45 test. Then drain the second stage glycerol.
To titrate the bio I made up a titration fluid of 1ml of 96% sulphuric acid in 1 litre of water. The titration itself is carried out with 50ml of IPA with enough drops of Bromophenol blue in it to make it a visible blue colour.
I then drop in 1ml of the bio which, being alkaline, keeps the solution blue
Then, using a 0.5ml syringe, I drip in the 0.1% acid solution and keep stirring until the solution turns greenish yellow.
At that point it is really easy to calculate how much acid is needed.
If the titration took 0.75 ml of acid solution then the bio will need 0.75ml per litre to neutralise.
On a 100 litre batch that would be 75 ml of acid.
Clearly, adding 75ml of concentrated sulphuric acid would carbonise the bio it touched so firstly I mix the acid with the 7% batch volume of water as Paul suggests above.
*** Safety warning - ALWAYS add the acid to the water. NEVER add water to concentrated sulphuric acid as the exothermic reaction will cause the water to instantly boil and throw acid out of the mixing vessel ***
Then mix, stop and allow the water to settle.
The water that comes out is dirty and, with suplhuric acid at least, smelly.
After this, I do another wash with 20% batch volume of clear water. Only needs 10 to 20 mins of mixing then a short time to settle.
The water coming out is then almost crystal clear. I take a sample before switching off the pump so I can see it settle in a jar.
If the water is not crystal clear, I do another wash. So far I have not had to do more than two 20 minute washes to have sparkling clear water coming out.
Then it is just a case of drying, which I also do in the processor with a bubble ring and koi air pump. After that, the bio is ready to use.
Doing one of Nigel's soap tests shows 0 ppm of soap too.