In Environmental Research, Wolfram Buss et al., explored methods to enhance phosphorus availabilityPhosphorus is another essential nutrient for plant growth, but it can sometimes be locked up in the soil and unavailable to plants. Biochar can help release phosphorus from the soil and make it more accessible to plants, reducing the need for chemical fertilizers.   More in sewage sludge biocharBiochar is a carbon-rich material created from biomass decomposition in low-oxygen conditions. It has important applications in environmental remediation, soil improvement, agriculture, carbon sequestration, energy storage, and sustainable materials, promoting efficiency and reducing waste in various contexts while addressing climate change challenges. More. The study revealed that using wood ashAsh is the non-combustible inorganic residue that remains after organic matter, like wood or biomass, is completely burned. It consists mainly of minerals and is different from biochar, which is produced through incomplete combustion.   Ash Ash is the residue that remains after the complete More extract to treat sewage sludge before pyrolysisPyrolysis is a thermochemical process that converts waste biomass into bio-char, bio-oil, and pyro-gas. It offers significant advantages in waste valorization, turning low-value materials into economically valuable resources. Its versatility allows for tailored products based on operational conditions, presenting itself as a cost-effective and efficient More can significantly increase phosphorus availability in the resulting biochar, improving its potential as a fertiliser.  

Sewage sludge, a byproduct of wastewater treatment, contains phosphorus, a valuable but finite resource. Pyrolysis, a thermal decomposition process, can transform sewage sludge into biochar, a stable carbon-rich material. However, this process often reduces the phosphorus’s availability to plants. The researchers investigated doping calcium-rich sewage sludge with potassium acetate, combustion wood ash, and wood ash extract to improve phosphorus release.  

The addition of potassium acetate increased water-extractable phosphorus in biochar produced at 500°C, but not at 700°C. The high calcium content in the sewage sludge limited the effectiveness of potassium doping. In a wheat pot trial, biochar treated with potassium acetate at 500°C still resulted in increased stem biomassBiomass is a complex biological organic or non-organic solid product derived from living or recently living organism and available naturally. Various types of wastes such as animal manure, waste paper, sludge and many industrial wastes are also treated as biomass because like natural biomass these More and grain phosphorus uptake compared to untreated biochar.  

While combustion wood ash did not enhance phosphorus availability, wood ash extract doubled the water-extractable phosphorus content in 500°C biochar. This highlights the potential of using waste-derived wood ash extract to enhance phosphorus availability in sewage sludge biochar. This innovative approach offers a circular economy solution, converting two waste materials into an effective fertiliser, reducing landfill waste and emissions.  

Source: Buss, W., Cooper, C., Rahbari, A., Khanna, N., & Bryant, B. (2025). Novel technique to enhance phosphorus availability in sewage sludge biochar using wood ash extract to produce an effective circular economy product. Environmental Research, 275, 121382.