Each year, Australia produces approximately 360,000 tons of biosolids from sewerage systems. Biosolid disposal and nutrient recovery is challenging for all waste water treatment plants. Traditional high temperature pyrolytic (degradation by heat) furnaces yield relatively simple chemicals and use significant energy. Microwave-assisted pyrolysis has many advantages such as:
- operation at relatively low temperatures (200 – 500 °C), which leads to a more energy efficient process;
- yielding more complex higher value chemicals, fertilisers, and fuels; and
- producing a by-product (bio-char) that can capture carbon and improve soil properties.
However, microwave-assisted pyrolysis of biosolids has received little attention. This project by the University of Melbourne will test the applicability of microwave energy for pyrolytic breakdown and chemical and nutrient recovery from biosolids and food processing waste streams.
- Study the existing literature about pyrolysis, microwave heating, and microwave-assisted extraction and pyrolysis, with a particular focus on pyrolysis of organic sludges or biosolids (Milestone 1)
- Study dielectric properties of biosolid materials sourced from Melbourne Water, Goulburn Valley Water, and Mackay Regional Council (Milestone 2)
- Study electromagnetic behaviour of various design options for a prototype pyrolytic chamber and subsequently use these evaluations to complete an engineering design for the final chamber. The microwave pyrolysis system will also be fabricated and tested (Milestone 3)
- A fully replicated pyrolysis experiment using biosolids from at least 3 sources will be conducted. The products from this experiment will be examined for their chemical composition and where appropriate their influence over the growth of crop plants and soil properties (Milestone 4)
- Based on the experience gained during the first experiment, conduct a second fully replicated, statistically valid experimental study of microwave-assisted pyrolysis of biosolids and determine the chemical composition and soil amelioration properties of the pyrolytic products and understand what seasonal influences may affect the final pyrolysis processes and products, especially from sources with high organic loads from agricultural produce processing (Milestone 5 – End)
The Anticipated Outcome
This study has a significant “blue sky” element to it because microwave-assisted pyrolysis of biosolids has not previously been studied. Microwave assisted pyrolysis of wet sewerage sludge (greater than 70 per cent water content by weight) has recovered up to 70 different chemical compounds in its oil based fraction. These chemicals range in value between $1,200 per tonne and $250,000 per tonne. Although wet sewerage sludge is very different from biosolids, there is potential to recover a similar range of chemicals from biosolids. Therefore assuming that microwave-assisted pyrolysis of biosolids could be implemented throughout Australia; the value of the oil recovered from the annual production of biosolids around the country could be approximately $27 million per year.
If your interested in this area, there is an interesting paper in ScienceDirect from 2019 – Microwave-assisted pyrolysis of sewage sludge: A review