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Managing anaerobic digestion digestate in sludge treatment

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AD digestate 204198697

Managing AD digestate

The digestate is the residual slurry, containing up to 20% solids, generated from the anaerobic digestion (AD) process. It is usually rich in nutrients such as ammonia and phosphates as well as micronutrient metals. Its primary use is as a soil conditioner, subject to its meeting regulatory standards regarding toxic metals content.

Integration of anaerobic digestion with downstream processes for resource recovery Credit: Judd Water & Wastewater Consultants
Integration of anaerobic digestion with downstream processes for resource recovery
Flowsheet showing how anaerobic integrates with downstream processes of dewatering and hydrothermal treatment of the digestate stream, along with combined heat and power (CHP) for the biogas, for resource recoveryCredit: Judd Water & Wastewater Consultants

If the digestate metals content is too high to allow it to be applied to soil then further treatment is required, or else alternative end disposal options, such as landfilling, explored. If landfilling is the intended disposal route then concentration of the solids by thickening and/or dewatering is usually carried out to reduce the sludge volume, and thus the disposal cost. The water-soluble nutrients may then be recovered from the liquid stream from these solid−liquid separation processes.

Other processing options have been explored for recovering resources from digestate, including hydrothermal treatment. These processes recover the latent energy from the digestate, related to its carbon content.

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About this page

'Managing anaerobic digestion digestate in sludge treatment' was written by Simon Judd

This page was last updated on 19 September 2020

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