Hello! We did a small biodigester at home, it had two units: a recipient with 0.25L and a another variable volume recipient for gas storage. The biodigester starts up with 1.5kg of food waste, 1 kg of cow manure and 5L of water. The system seems to be good during adaptation time (we planned 15d for this and then to operate it in semicontinuous mode), pH measurements every three days was nearly to 7. Neverthless, 9 days after the start up we have to burn the biogas the because the storage recipient was too small, but... it didn't burnt.
We have an hypothesis about what was bad in our design: the (inoculum/substrate ratio) was to small (0.6 aprox.) and for food waste the recommended ISR must be over 2 for preventing the inhibition (food waste are easily biodegradable matter)
We are not sure about adaptation time or if we can burnt the biogas daily, but in this case the pressure maybe won´t be for flow through the tube. Maybe we must change the design or we are doing something bad during the start up?
Rowayda is very useful your appreciation.
Now, I undertstand that our gas chamber was too small because in 9 days it was full and probably it was mainly CO2 due to anaerobic digestion stages.
We are going to try again and be more patient.
Thanks!
Good morning, Lenis, I have just seen your question. Your assertion was correct, in my opinion. However, for start-up and acclimatisation at the same time, even an inoculum/substrate ratio of 2 would be far too high. For example, just to carry out biomethane potential tests using already acclimatised biomass we use a ratio >6 to minimise potential stress. Now, we operate full-scale food waste AD plants in the UK. We have done it for over 10 years now and the volumetric loading to our 16000m3 plant is around 300m3/day => 50 days HRT. I see that your are probably starting in semi-batch mode, but at that initial loading I am surprised the pH has not dropped further. If it was me, I would start at an inoculum/substrate >25 and monitor biogas composition more regularly, if possible. It CH4>50% increase OLR gradually. I normally control start-up on the basis of biogas CH4 content and flow. Since you are looking at start-up and acclimatisation (i.e., you are not using an inoculum from a food waste digester), I would expect start-up to take a long time, as Rowayda indicated (or longer!). Can you not get some UASB solids to start-up. I hope this is useful.
Thank you, Edgar.
I never think to use an ISR so far, over 25 is surprisingly to my.
In your opinion, could I use this sludge like food waste adapted inoculum for a next experiment or it will be bound to fail? and how much time is necessary for increase the ORL in your case?
Now I am seeking a device or mechanism for H2S filtering. I haven't one yet because my scale is too small: daily biogas production rate is between 0.01 - 0.06 m3. If you have any recommendation, it will be valuable.
Regards!
Good morning, Lenis. To control H2S, I would recommend you consider dosing ferric, or ferrose chloride (liquid) in the digesters, only very small amounts required. Alternatively, Fe+3 hydroxide powder would work well as well. There is an added advantage to using Fe, it is a macronutrient and it normally has as contaminants small amounts of Ni that can be in short supply in some digesters. By dosing Fe in the digester you also control the reduced S. Reduced sulphur reacts with micronutrients, making them less bio-available so, dosing Fe in the digesters can have the additional benefit of improving the availability of the trace elements present in the feed. The suggestion is to start at a low loading and then increase it gradually on the basis of evolution of biogas composition (Say >50% CH4 and pH >7.3 for loading to be increased when working with mixed food waste). The steady state pH depends on the feedstock you use and how stabilised you want the digestate to be (look for "PAS110 protocol UK pdf" in google for a digestate stability protocol. I hope this is useful. I might go to Bucaramanga for a couple of days in October/November. Good luck
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