The Latrobe Valley in Victoria, southeast Australia, is home to three large open-cast brown coal mines. Due to the nature of the mining operations, there is a lack of topsoil to cover the whole area that is to be progressively rehabilitated. This has led to the development of technosols, employing the ideas of the circular economy by using waste products from three industries located in the Latrobe Valley: mining and energy production (overburden, subsoil, topsoil, waste brown coal and fly ash from the powerplant), paper milling and recycling (effluent sewage recovery and recycling waste) and municipal green waste collection (compost). These waste products have been mixed at different ratios and tested in laboratory, greenhouse and field conditions to establish the best type of technosol that is safe for the environment and can turn into a productive soil in the long-term. If proven suitable, this new concept will not only aid in rehabilitation of large post-mining areas but also help in waste reduction. In a greenhouse study, we tested plant germination and growth in seven different mixtures. Although grass germination was highest in natural topsoil, both grass and clover biomass and leaf length were generally higher in technosols than in topsoil. Also, the plant tissue nutrient levels were similar or higher in technosols than in topsoil. Four out of seven technosols were then transferred into a field trial. Preliminary results from the trial have shown that plant biomass in three out of four technosols is greater than in natural topsoil. Further monitoring of soil properties is being undertaken to assess long-term performance of these soils.

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The Latrobe Valley region of eastern Victoria houses three major mines which burns lignite for power generation and is referred to as the power house of Victoria. These mines are looking for sustainable ways to manage their waste and achieve successful mine rehabilitation. One of the problems to be addressed for attaining successful mine rehabilitation is the scarcity of topsoils for vegetation cover. The possible solution for overcoming this problem is the use of artificial topsoils (ATS) developed using waste streams, i.e. overburden, interseam brown coal, ash from the onsite powerplant and nearby paper industry waste i.e. effluent sewage recovery (ESR). Field lysimeter experiments with ATS proved that there is no leachate toxicity but the plant available nutrients were relatively low. Hence, clear understanding of ATS as a substrate for vegetation should be examined before applying it in the field. In a recent study, we tested the growth of ryegrass, clover and ryegrass + clover mixture in ATS with and without addition of nitrogen-phosphorouspotassium fertilizer (NPK) in a greenhouse experiment compared to control, i.e. overburden, overburden + ash, natural topsoil. The results after 12 weeks indicate that the height of ryegrass in ATS with NPK is 2.7 cm higher than the height of ryegrass in natural topsoil and is 16 and 17 cm higher than the growth of ryegrass in overburden and overburden + ash mixture respectively. The height of clover in ATS with NPK is 1 cm higher than the clover grown in natural topsoil and around 5 cm more than the height of clover in overburden and overburden + ash mixture. The germination in ATS was slightly delayed as compared to natural topsoil due to higher exchangeable sodium percent in soil, but the presence of NPK in ATS later aided in survival and growth of grass and clover. The initial results from these experiments show that ATS with addition of NPK can be a potential solution in mine rehabilitation and can be used as a substrate for revegetation.

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