Extracellular polymeric substances (EPS) play an important role in wastewater sludge structure and stability, yet measured EPS concentrations depend strongly on the extraction method. This study compared three established protocols (thermal sodium carbonate, thermal sodium chloride, and chemical formamide–NaOH extraction) across activated sludge (AS), aerobic granular sludge (AGS), algal–bacterial granular sludge (ABGS), and an AGS–membrane bioreactor (AGS-MBR). Proteins (PN) and polysaccharides (PS) were quantified in soluble, loosely bound, and tightly bound EPS fractions, with total EPS defined as PN + PS. Sodium carbonate consistently produced the highest apparent PN, PS, and total EPS recoveries across the sludge matrices, while sodium chloride and chemical extraction generally produced lower and comparable recoveries. Because the protocols differed in reagent chemistry, temperature, incubation time, and centrifugation conditions, these differences cannot be attributed to a single extraction parameter. A complementary Escherichia coli experiment showed that adding intact cells to an autoclaved-sludge background altered subsequent polymer recovery during sodium carbonate extraction, suggesting a potential contribution of cellular-associated material; however, PN and PS measurements cannot directly demonstrate cell lysis. Overall, extraction-method selection should consider both recovery performance and potential extraction-induced cellular contributions when interpreting and comparing EPS measurements.

Phosphorus recovery from wastewater can improve resource circularity while reducing eutrophication risks. This study directly compared calcium- and magnesium-modified commercial biochar for phosphate capture from a controlled synthetic solution and real anaerobic digestion centrate. Biochar was modified with Ca and Mg salts at biochar:salt mass ratios of 1:1–1:20 and characterized by Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM-EDS) before and after adsorption. In synthetic solution, 24-h experimental adsorption capacities reached 55.8 and 24.6 mg P gBC⁻¹ for Ca- and Mg-modified biochar, respectively. In centrate, the selected 1:5 Ca-BC and Mg-BC conditions achieved 83.6 and 54.5 mg P gBC⁻¹, corresponding to calculated phosphate-P removals of 69.6% and 45.4%, respectively. Ca-modified biochar showed stronger phosphate-associated surface changes and higher measured phosphate uptake under the tested conditions, while FTIR, SEM-EDS, pH behavior, and kinetic modeling were interpreted as supporting evidence of adsorption behavior rather than definitive identification of specific mineral phases or molecular-scale mechanisms. The 1:5 biochar:salt ratio was selected because higher modifier loadings did not provide proportional gains in phosphate capture. Phosphate-loaded Ca- and Mg-modified biochars achieved 100% germination for wheat and lettuce, with no evidence of early phytotoxicity. Overall, Ca-modified biochar showed higher phosphate-capture performance, while both phosphate-loaded materials demonstrated preliminary germination compatibility; phosphorus release, leaching, and plant phosphorus uptake were not evaluated.