BERT 600m3 digester; positive feedback letter from South Africa

Dear reader,

Our Bert 600 Digester has been installed on of our 2800 breeding sow units and is running 5 years now. Due to bio-security precautions, grow out units and weaner housing are based on separate farms.

Regarding feeding the digester

Slurry from our farrowing unit forms the bulk of this waste a with further 3 cubes of slurry being brought in per day from one of our grow out units near by. Additional high energy feed also forms a major part of the AD’s diet. We are always on the look out for additional feedstock and feed almost anything organic that can decompose quickly ,we currently feed products such as: spoilt feed, grain/animal feed sweepings, whey powder, reject dairy products, chocolate, wafer, waste sugar products, expired palm oil, waste meat/fat from carcasses. Realy anything organic that will decompose. However! Space inside our digester is at a premium, so food must have a high energy value to warrant inclusion.

We faced 4 challenges:

  • Keeping the retention time to around 17 to 18 days.
  • Maintaining digester temperature when feeding high volumes mixed water.
  • Gas quality, because our feeding is not consistent, our gas quality tends to spike up and down, constantly resulting in a higher labour input.
  • Gas production spikes when high sugar is fed.

How we adapted to these challenges:

  1. Retention time- Nothing we could do here unless we build a second digester. This was not an option here. Fortunately for us, I believe the double chamber assisted by keeping most of the newly fed waste in the outside chamber and away from the overflow positioned in the middle chamber.
  2. A 10K plastic tank was installed with a very simple home made heater vessel (old air compressor tank) Hot water was plumbed from the TGL lines trough this to heat up the 10K of water which was in turn used to transport additional feed into the digester.
  3. Gas quality remains a challenge, the trick is to try and feed the same volumes of certain feeds as well as balance the energy content. Almost like mixing a well balance feed. Space out high energy feeds over days or even weeks if necessary. Bacteria take time to adapt.
  4. Spikes in gas production, this was learnt the hard way, after feeding a very high sugar content feed our gas production suddenly spiked (within an hour) the gas bag on top of digester was already full at the time when the “Sweep Swop” triggered, this resulted in so much gas being released it burst the gas bag. To prevent this from happening again a 240 cubic meter gas bag was manufactured and secured on the ground next to the AD plant.

Please note here: This is far from the usual gas production and a learning curve for us.

Power Production

  • On average we produced 63 451 kW/h per month in 2018.
  • Slightly lower amount of 60.836 kW/h per month in 2019.
  • Our best month recorded for 2019 so far was 80.870 kW/h 

I am amazed at what gas volumes can be produced from this relatively small bio-digester (Bert 600). Our kW/h performance is the result of teamwork, special care and attention not only given to the BIG things but just as much to the smaller things that contribute to the overall success of the plant.

If I may give one piece of advise to biogas owners and operators it would be this.

You are more than likely a Farmer / Stockman – don’t  try and be a chemical engineer! Stop looking at the plant as a machine-It is NOT- It contains billions of living creatures by far the largest herd of animals you have ever owned or taken care of. Treat them with respect, give them the proper housingsas you would any of your animals, supply them with a CONSISTANT supply of feed, suitable temperature and/or environment just as you would for any livestock that formed part of your income. This “digester” should be seen as an animals gut, a very large animals gut! Look after the animals gut health and it will supply you with a good feed conversion and produce. It is really that SIMPLE!

We are happy to share this information and our experience with you and are pleased to hear that we are the best in the league Bert 600 m³.

In closing:

  • Biogas plants can work for us!
  • Just make sure you align yourself with the correct people in the industry.
  • Make sure all the relevant tests are done to ensure suitability of your waste & farm site.
  • Ask for references and contact 3 or 4 of them, if possible visit one.

Best regards,

Michael van Zeeland, Number Two Piggeries

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