Thermochemical processes

Thermochemical methods are employed for either significantly reducing the sludge solids content, or pre-treating sludge upstream of anaerobic digestion (AD) to increase the biodegradability of the organic carbon. When operated at elevated temperatures, i.e. for solids destruction rather than for AD pre-treatment, they provide energy recoverable either as heat (for oxidative processes) or a combustible gas or liquid (non-oxidative processes).

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Sludge thermochemical treatment

An introduction to sludge thermochemical treatment methods

Hierarchy of thermochemical methods for sludge treatment, showing the oxidative processes of incineration, wet (or wet air) oxidation and supercritical water oxidation along with the non-oxidative processes of pyrolysis, gasification and hydrothermal treatment.

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Sludge thermochemical treatment − an overview

Thermochemical methods are used for either degrading the sludge solids or pre-treating sludge upstream of anaerobic digestion

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Sludge thermochemical reactor design configurations

Various reactor configurations exist for sludge thermochemical treatment which vary in design, operation and application

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Oxidative thermochemical treatment

An introduction to oxidative sludge thermochemical treatment methods

Waste incinerator against a blue sky with clouds

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Incineration of sludge

Incineration is the most well established and widely implemented of the sludge thermochemical treatment processes

Wet air oxidation (WAO) process showing reactor tank, gas-liquid separator, solid-liquid separator, and heat exchangers.

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Wet (air) oxidation of sludge

Wet/wet air oxidation of sludge is the thermal degradation, hydrolysis and oxidation of organics at high temperatures

States of water as a function of temperature and pressure, showing the critical point and the supercritical region

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Supercritical water oxidation (SCWO) of sludge

Supercritical water oxidation refers to the oxidation of organics in water in the so-called supercritical phase of water

Hydrothermal processes and approximate regions of operation with reference to the pressure:temperature water phase diagram.
(HTC: Hydrothermal carbonisation, HTL: Hydrothermal liquefaction, HTG/SCWG: Hydrothermal gasification/supercritical water gasification.)

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Non-oxidative thermochemical treatment

An introduction to non-oxidative sludge thermochemical treatment methods

Thin cylinders of sludge (pelleted, pyrolysed sewage sludge)

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Sludge treatment − pyrolysis

Pyrolysis refers to the decomposition of organic matter at elevated temperatures in the absence of oxygen and water

Counter-current gasifier reactor, showing four regions/steps of organics conversion to the syngas product. The four regions, from the reactor inlet to its outlet, are oxidation, reduction, pyrolysis and drying.

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Sludge treatment − gasification

Gasification is an extension of the pyrolysis process for thermochemical treatment of sludge

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Sludge treatment − hydrothermal processes

Hydrothermal sludge treatment employs elevated temperatures and pressures in wet conditions and in the absence of oxygen

Thermochemical processes related videos

Example of pyrolysis process for sewage sludge: the Eisenmann Pyrobuster® Source: Eisenmann SE / YouTube

Example of pyrolysis process for sewage sludge: the Eisenmann Pyrobuster®

An example of the pyrolysis process for sewage sludge: the Eisenmann Pyrobuster® for the thermal treatment of sewage sludge.

Thermochemical processes features and blogs

Feature

Co-processing of sewage digestate by hydrothermal carbonisation

Hydrothermal carbonisation (HTC) can be used to co-process anaerobic digestion (AD) digestate and lignocellulosic (or plant-based) feedstocks to improve the the hydrochar product quality. This AD waste co-processing route has been studied at bench scale. Read article