Digested sludge is an end product of anaerobic decomposition processes that take place in special reactors such as digestion towers or biogas plants. During these processes, microorganisms decompose organic substances in the absence of oxygen and convert them into biogas (mainly methane and carbon dioxide) and stabilized solids.
Composition
Digested sludge consists of organic residues, minerals, water and small amounts of trace elements. It is highly concentrated and often has a viscous to pasty consistency. Typical components are cellulose, proteins and lipids, which have been largely broken down by anaerobic treatment.
Photo: ALMA BHU GMR biogas plant for the sugar industry
Technical background to digestion
Digestion takes place in several stages:
- Hydrolysis: Complex organic substances such as carbohydrates and proteins are broken down into smaller units.
- Acidogenesis: The resulting monomers are broken down into organic acids, hydrogen and carbon dioxide.
- Acetogenesis: Organic acids are converted to acetic acid.
- Methanogenesis: Acetic acid and hydrogen serve methanogenic microorganisms as a substrate for biogas production.
The process temperature has a significant influence on the efficiency of the digestion process:
- Mesophilic digestion (30-40 °C) is less energy-intensive.
- Thermophilic digestion (50-60 °C) offers a higher degradation rate and shorter retention times.
Areas of application
Digested sludge is mainly produced in municipal and industrial wastewater treatment, e.g. in the treatment of wastewater from the food industry, paper and pulp production and chemical processes.
Photo: ALMA BHU GMR biogas plant with post-treatment and biomass recirculation
Drainage and disposal
After digestion, the digested sludge is dewatered to reduce the volume. Processes such as chamber filter presses, decanters or belt filter presses are used for this. The dewatered sludge can then be landfilled, incinerated or used as fertilizer in agriculture.
Advantages of digestion
- Biogas production: renewable energy source.
- Reduced sludge volume: Reduction in disposal costs.
- Stabilization: minimization of odour emissions and hygienization.
Conclusion
Digested sludge plays a central role in wastewater treatment and the generation of renewable energy. ALMAWATECH offers comprehensive solutions for the treatment and dewatering of digested sludge that are individually tailored to the requirements of the industry.
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