Valorization of wastewater-derived biopolymers for use as soil amendments in agriculture

Extracellular polymeric substances (EPS) recovered from aerobic granular sludge (AGS) produced in wastewater treatment plants (WWTP) offer valuable biomaterials with multiple applications, including in agriculture. This study evaluated the potential of EPS derived from AGS collected from two full-scale WWTP in Utrecht (EPS_U) and Faro (EPS_F) and one laboratory-scale reactor (EPS_R), as soil amendments. A 49-day greenhouse experiment assessed the effects of two wet EPS doses (0.5% and 1% w/w) on maize (Zea mays L.) growth, nutrient uptake and use efficiency, and soil enzymatic activities. EPS amendments were compared to vermicompost at equivalent doses and a non-amended control. Overall, EPS outperformed vermicompost amendments, although the source and dose greatly influenced their performance. Notably, applying 1% of EPS, regardless of the source, consistently increased maize chlorophyll content, with EPS_R_1% increasing it by 62% and 105% compared to 1% vermicompost and the control, respectively. The EPS doses applied had a marginal influence on biometric traits, but 1% of EPS_R significantly increased shoot fresh weight and thickness. Magnesium and potassium contents in shoots increased by 46% and 34% in EPS_R_1% and EPS_F_1% amendments, respectively, over the control. The soil enzyme activities differed across EPS amendments, with soils containing EPS_U_1% showing higher urease (+ 41%) and fluorescein diacetate hydrolysis (+ 31%) activities, whereas EPS_R_1% stimulated acid phosphatase (+ 35%) activity, demonstrating EPS contribution to microbial activity and nutrient cycling in the rhizosphere. EPS amendments have great agronomic potential, providing superior benefits to vermicompost while supporting waste sludge valorization and embracing sustainable agriculture practices.