CNash - A novel parameter predicting cake solids of dewatered digestates

Area of Science:

• Environmental Engineering
• Waste Management
• Biotechnology

Background:

• Efficient digestate dewatering is vital for reducing solid residue volume and transportation costs from anaerobic digestion (AD) plants.
• Existing predictive models for dewatered cake solids lack validation across diverse substrates, pre-treatments, and full-scale facilities.
• Variability in dewatered cake solids necessitates reliable predictive tools for AD plant design and operation.

Purpose of the Study:

• To validate thermogravimetric analysis (TGA) as a reliable method for predicting dewatered cake solids.
• To identify a novel physicochemical parameter for predicting digestate dewatered cake solids.
• To assess the influence of pre-AD thermal hydrolysis process (THP) and other factors on dewatered cake solids.

Main Methods:

• Thermogravimetric analysis (TGA) was employed to predict dewatered cake solids.
• A novel combined physicochemical parameter, C/N•ash (C/N ratio multiplied by ash content), was developed and tested.
• Samples from multiple full-scale wastewater, food waste, and co-waste AD plants were analyzed.

Main Results:

• TGA proved to be a reliable prediction model for dewatered cake solids across 15 commercial plants.
• The novel C/N•ash parameter demonstrated a linear relationship with predicted cake solids for digestates with and without pre-AD THP.
• Solids characteristics (C/N ratio and ash content) significantly influenced predicted cake solids more than pre-AD THP or dewatering device type.

Conclusions:

• The C/N•ash parameter is a robust predictor of dewatered cake solids, independent of dewatering device and sludge origin.
• Pre-AD THP enhances dewatered cake solids by increasing free water, but C/N•ash remains a more influential factor.
• This study provides a validated, simplified approach for predicting digestate dewatering performance in AD plants.