Anaerobic digestion vs dehydration of food waste

Do it well, do it good. Comparing dehydrated food waste with the digestate (fertilizer) produced by an on-site biodigester, like a Waste Transformer, reveals key differences in nutrient composition, microbial benefits, and soil health impacts. Let’s have a deeper look how to use food waste to reach the highest environmental positive impact:

Nutrient composition and soil enrichment

• Dehydrated food waste: fast dehydraters remove water content from food waste by mechanically heating the food waste, but do not fully break down the complex organic molecules and nutrients. As a result, dehydrated food waste lacks stabilized forms of nutrients like nitrogen, phosphorus, and potassium in forms easily accessible to plants. Research indicates that fast-dried waste lacks humus, which is essential for long-term soil fertility and carbon sequestration.
• Biodigester digestate: in contrast, digestate (fertilizer) from anaerobic biodigesters, contains bioavailable forms of nitrogen, potassium, and phosphorus. Studies have shown that anaerobic digestion breaks down organic compounds to simpler, readily absorbable nutrients, enhancing their immediate availability to plants. Digestate has a balanced nutrient profile suitable for crops and can replace chemical fertilizers, reducing environmental impacts.

Microbial activity and soil ecology

• Dehydrated food waste: dehydration removes water but doesn’t create an ideal medium for microbial life, as the rapid heating processes by fossil energy kill off both pathogenic and beneficial organisms. This lack of microbial diversity in dehydrated food waste does little to stimulate soil microbial communities once applied to fields, leading to slower organic matter turnover and reduced soil fertility over time.
• Digestate from biodigesters: digestate, however, undergoes microbial fermentation in anaerobic conditions, preserving beneficial microbes that continue breaking down organic matter in the soil, thus supporting soil microbiota and nutrient cycling. Studies indicate that soils treated with digestate see increased microbial activity, which boosts organic matter decomposition and enhances soil structure. 

Pathogens

• Dehydrated food waste: the rapid processing of food waste in fast composters doesn’t allow sufficient time for pathogens or harmful compounds to break down completely. Without the sustained high temperatures or microbial activity found in traditional composting or anaerobic digestion, pathogens may survive, potentially impacting soil health and food safety.
• Digestate from biodigesters: Each Waste Transformer biodigester has a standard process of pasteurizing digestate on 7- degrees Celcius for 1 hour. A requirement by law to reduce pathogen levels, thereby producing a safer soil amendment. Digesters also decompose toxic compounds, and pesticides more effectively than dehydration due to the prolonged microbial and biochemical activity in anaerobic digestion.

Environmental benefits and waste management:

• Dehydrated food waste: Dehydration reduces waste volume, but the process itself often requires energy input, which contributes to greenhouse gas emissions if powered by non-renewable energy sources. Furthermore, dehydration does not offer by-products beneficial to the environment, such as clean energy and fertilizers.

• Biodigester digestate: on-site biodigesters like those from The Waste Transformers generate clean biogas as a by-product, which can be used as a renewable energy source for the facility, reducing reliance on fossil fuels. Research indicates that on-site anaerobic digestion not only decreases food waste volume but also reduces methane emissions from landfills and contributes to circular economy goals by returning nutrients to the soil to restore soil health. Studies show that digestate-amended soils improve plant-available water retention, promote better root growth, and increase crop yields . Moreover, digestate’s composition as a nutrient-dense, liquid fertilizer allow distribution and absorption in various soil types, making it adaptable for widespread agricultural use.

Scientific comparisons show that biodigester digestate offers numerous benefits over dehydrated food waste for soil health, crop productivity, and environmental sustainability. While dehydration reduces waste volume and shift the problem to the sewage companies, it provides limited soil benefits and lacks the balanced nutrients, microbial richness, and pathogen safety offered by biodigester outputs. On-site biodigesters like a Waste Transformer support a circular economy by creating a safe, nutrient-rich, and environmentally friendly soil amendment while also producing renewable energy.

About The Waste Transformers: The Waste Transformers is a Dutch cleantech pioneer, providing on-site innovative technologies to transform unavoidable food waste into sustainable energy and natural fertilisers, enabling local positive change.

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