Dry anaerobic digestion: A sustainable, water-wise, waste-to-energy solution

Imagine an ideal world where cattle manure, crop waste and food scraps do not end up accumulating in landfills but are used to light up homes, cook meals, heat schools, and fertilise gardens.

- By Ashira Roopnarain and Haripriya Rama, ARC-Natural Resources and Engineering

This is not a far-fetched idea thanks to dry anaerobic digestion or AD, a clean, sustainable technology that is rapidly gaining recognition and momentum worldwide.

From rural villages in South Africa to high-tech farms in Japan, dry AD is proving to be a catalyst in the fight against waste accumulation, climate change, energy poverty, and reliance on fossil-fuel derived energy and chemical fertilisers.

Anaerobic digestion explained

Dry AD is a natural process that occurs in the absence of oxygen, whereby special microorganisms, including bacteria and archaea, break down organic matter such as animal manure, food waste, and crop residues. The products of this process are biogas and digestate. Biogas is a renewable energy source rich in methane that can be burned for cooking, heating, and even electricity generation. The semisolid material produced during the process is referred to as digestate, which is nutrient-rich and ideal for agricultural applications.

Anaerobic digestion is classified as wet or dry, based on the amount of solids in the system. Unlike traditional wet AD, dry AD works with waste that has a much higher solid content (15 to 45%). This means it requires substantially less water, thus providing a huge advantage in water-scarce regions.

Let's explore how dry AD may be adopted in South Africa, Mozambique, and Japan. These three very different countries are united by one common goal, namely turning waste into treasure in a water-wise manner.

South Africa: Empowering rural communities by tackling waste management and energy poverty