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Spent Hops antimicrobial effect in an "activated sludge" wastewater treatment plant

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  • Spent Hops antimicrobial effect in an "activated sludge" wastewater treatment plant


    At our brewery we are at the moment considering different methods of dry-hopping. The question about what to do with the spent hops has been raised.

    For the spent hops process we will spend about 800 kg of hop pellets per batch.
    We have the option to either flush the spent hops to the drain with water (a total of 12m3) or to remove most of the water with a decanter and then dispose of the spent hops for composting (will be quite expensive for us).

    We have a waste water plant at the brewery, it removes most of the solids and adjusts the pH to around 7. There is a settling tank in this plant whith a constant Level of 350 m3 Waste water.
    Our Waste water will then go from this settling tank to the municipal plant with a constant flow of 15 m3/hour.

    The issue is the municipal waste water plant which is a activated sludge treatment plant (
    This plant relies on a biological process to treat the water and therefore it is vital that our Waste water has a neutral pH and that it does not contain substances with an antimicrobial effect.

    I can't find research on the antimicrobial effect of spent hops and the technicians at the municipal plant don't know anything about hops.
    The active substances of the hops will be diluted. First 800 kg spent hops to 12m3 of water and then 12 m3 to 350 m3 of Waste water in our settling tank before leaving for the municipal plant.

    I would be grateful if anyone could point me in the right direction or if you have som experience with this you could share with me.

    Thank you!!

  • #2
    I worked at one brewery where we replaced the old hopbacks, which were actually being used as not very effective whirlpools with new properly designed whirlpools. As we couldn't add the hops back to the spent grains for a few months whilst building work was ongoing, we had to store the reslurried trub and tanker off site. The stench from this tank after a few days was horrific, due to infection. So I don't think there is any meaningful biocidal activity left after trub separation. Trub has an incredibly high COD & BOD. I can't find the details of the typical contents of trub solids(proteins, sugars, COD etc.) though I have got the details somewhere from the first mentioned brewery, and did stumble another set of data on the internet at some time. Your biggest problem will be the COD and suspended solids. Most large breweries send trub out with the spent grains as they put it back on top of the following brew in the lauter / mash tun / mash filter, but on one or perhaps two brews a day that isn't going to be practical.

    Other breweries returning trub to spent grains, the trub tank had to be fully CIP'd weekly along wiht the rest of the brewhouse


    • #3
      If you want more details on solid wastes, try this link