Phosphorous recovery potential from sewage sludge by struvite precipitation: remodelling policy framework in Rajasthan, India

The manufacturing of fossil-based fertilizers by extraction of rock phosphate has contributed to carbon emissions and depleted the non-renewable phosphorous reserves. Sewage sludge, which is a waste product from sewage treatment plants (STPs), is rich in phosphorous. The existing techniques for sludge management contribute to carbon emissions and ecological footprint. Struvite (raw fertilizer) and biochar recovery from sludge have emerged as viable methods to reduce carbon emissions and ensure the economic sustainability of STPs. In this work, the potential for phosphorous recovery and revenue generation is discussed for Rajasthan state in India. The fate of phosphorous and heavy metals in STPs is evaluated which indicates that about 70% of the phosphorous and trace amounts of metals end up in sewage sludge. Further, the power consumption is high in STPs due to industrial wastewater ingress. There is a need to bridge the gap between sewage treatment and generation in Rajasthan and improve STP performance before resource recovery inclusion at policy-level and scale-up. Mixing struvite with biochar can lead to the safe application of struvite as raw fertilizer as heavy metals are sequestered by biochar. A business framework is developed to serve as a blueprint and potential model for linking technical and market viability.