Eco-Friendly Hybrid Cellulosic Adsorbents for Simultaneous Nitrate and Phosphate Removal from Wastewater and Further Use as Controlled-Release Fertilizer for Plant Growth

The worldwide rise in population and fast arable land decrease caused pressure on agricultural productivity. Overuse of conventional fertilizer causes leaching, denitrification, volatilization, and runoff. Nitrogen and phosphate contamination in natural streams harms ecosystems and causes eutrophication. Extracting trace amounts of nitrate and phosphate from treated wastewater is challenging due to competing ions. Despite this, if nitrate and phosphate could be sustainably collected or repurposed in agriculture, substantial savings in fertilizer expenditures may be achieved. Agricultural waste, although poses challenges, has substantial cellulose that has notable potential as a biodegradable material. This study synthesized an adsorbent utilizing cellulose nanofibers (CNF) derived from agricultural waste and carboxymethyl cellulose (CMC), impregnated with metal nanoparticles to eliminate phosphate. It was also modified with an amine functional group to remove nitrate from secondary treated wastewater selectively. The adsorbent HNSC exhibited a nitrate and phosphate adsorption capacity of 10 mg/g and 4 mg/g, respectively. The adsorbent exhibited biodegradability, with almost 61% of its mass decomposed by soil microbes within three months, indicating commendable biodegradability in soil environments. These results prompted us to use the nitrate and phosphate-enriched exhausted HNSC adsorbent for the provision of plant nutrients. The findings indicated that the nitrate and phosphate-enriched HNSC may significantly improve seed germination and plant growth. It also facilitated enhanced plant development relative to urea, single super-phosphate, and control samples owing to the gradual release of nutrients. The results show that the slow-release, eco-friendly nitrate and phosphate-loaded HNSC have significant promise for use in agriculture.