Investigation of Iron- and Organic-Rich Waterworks Sludge for Fertilizer Application

Massive amounts of waterworks sludge produced globally have generated increasingly urgent environmental concerns. To ensure the sustainability of drinking water treatment, valorization of waterworks sludge for specific applications depends on actual sludge characteristics, which are determined by multiple factors, such as raw water sources and treatment steps. One unique type of waterworks sludge with high iron content and natural organic matter (NOM) was valorized to fertilize spinach growth. Instead of spreading the sludge for soil conditioning without fertilizer capability, this Fe-NOM sludge with different post-treatments was dispersed in half-strength Hoagland solution in preparation for a nutrient solution for plant growth studies. The fertilizer performance is benchmarked with that of synthetic fertilizer FeEDTA, which acts as a ligand/carrier for Fe micronutrients. The results show that Fe-NOM sludge can be utilized for plant growth with minimal concern for heavy metal contents. By clearly elucidating the beneficial and synergistic roles of Fe and NOM in enhancing nutrient delivery and photosynthesis, this work underlines the suitability of Fe-NOM sludge to fertilize plant growth.