Adding worms during composting of organic waste with red mud and fly ash reduces CO2 emissions and increases plant available nutrient contents

Higher CO2 emissions were observed during vermicomposting compared to composting. These emissions were decreased by red mud addition, while fly ash had no effect. Nitrate (NO3-N) content of the end-products were more affected by worms than by alkaline materials, while higher ammonium (NH4-N) contents were recorded for composts than vermicomposts. Red mud vermicompost showed higher soluble P proportion than red mud compost, suggesting that worm presence can counterbalance P adsorption to the inorganic matrix. Final composts produced with red mud showed no harmful heavy metal concentrations. Adding worms during composting thus improved the product nutrient availability and did not increase metal toxicity. From a practical point of view, this study suggests that for carbon stabilisation and end-product quality, the addition of red mud during composting should be accompanied by worm addition to counterbalance negative effects on nutrient availability.