AD Plants: why you should NEVER use digestate on top of silage

7/8/2020
Silage Clamps

You may be tempted to use digestate to cover silage stored in clamps to be fed to AD plants – it seems a quicker and cheaper option than covering silage clamps with silage sheets.

But there are some key points that should be considered:

Digestate is not airtight and causes significant silage clamp waste. What depth of silage below the digestate are you losing when you empty the clamps? Often this is impossible to tell as the silage clamp waste and the digestate are almost identical.

Research carried out in the UK identified a clamp with 754m² of floor space filled 6m high holding roughly 3,400t maize silage (without walls) 30cm of digestate was used to cover the silage.

As this clamp was fed out samples were taken to be professionally analysed. Results showed that using digestate meant a total financial loss of £48,169 in silage dry matter loss + gas yield loss (please ask us for more info on this research).

The cost of sheeting this clamp would have been roughly £2.77 per m² or £2,088.00 for the whole clamp including the silage sheets netting and bags which have a 10 year + lifespan.

Using some assumptions on labour, for example, if it takes 3 minutes of labour to apply the silage sheets over 1m² of clamp and labour costs £17 an hour, the total cost of sheeting the clamps would be around £650 – £700.

Materials £2,088 + labour £700 = £2,788 total sheeting cost.

Even if sheeting the clamp only halved the waste (£48,169/2 = £24,084)  and even if the sheeting costs were double (£2,788.00 x 2= £5,576.00) the AD plant owner would see a financial benefit of over £18,000.00 per annum using silage sheets.

Practical points:

Will the loading weight of your clamp walls allow for the extra density/ weight of the digestate? Especially over winter when it absorbs rain water for months on end – is your silage clamp built for this?

What happens when the loading exceeds the design of the wall  and what will be the long term costs?

How much more leachate will your clamps produce as the silage and digestate deteriorates and what is the cost of managing this?

If the increase in leachate isn’t managed properly it might increase the risk of pollution due to a potential leak.

It’s important to take all of the above into consideration if you are thinking of using digestate instead of silage sheets. It might seem a quicker and cheaper alternative to using silage film but it will cost you more in the long run.

We supply an all-in-one o2 barrier silage film called OXY SEAL™ – no cling film is needed.

OXY SEAL™ is much quicker and easier to use compared with traditional methods of sheeting clamps.

For further info CLICK HERE. For prices please call us on 01787 220560 or fill out the form below.

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