A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Environmental Engineering and Management

Thesis (M. Sc.) - Asian Institute of Technology, 2026

Excessive discharge of nitrogen (N) and phosphorus (P) from inadequately treated domestic wastewater drives eutrophication across freshwater and coastal ecosystems in developing countries. In Thailand, centralized facilities treat only ~22% of wastewater generated, with influent TN (35{u2013}60 mg L⁻¹) and TP (4{u2013}8 mg L⁻¹) routinely exceeding Pollution Control Department (PCD) discharge standards of TN < 20 mg L⁻¹ and TP < 4 mg L⁻¹. Municipal sewage sludge and rice husk two abundant waste streams are largely landfilled or openly burned, compounding environmental burdens. This study addresses both challenges by developing a co-pyrolyzed sewage sludge{u2013}rice husk biochar composite (SSRH) as a low cost adsorbent for simultaneous ammonium (NH₄⁺{u²⁰¹³}N) and phosphate (PO₄³⁻{u²⁰¹³}P) removal.Three biochar materials sewage sludge biochar (SSB), rice husk biochar (RHB), and a 1:1 co-pyrolyzed composite (SSRH) were synthesized at 500 °C under oxygen-limited conditions. Materials were characterized by BET, BJH, pore analysis, and SEM. Adsorption performance was evaluated through batch kinetic and isotherm experiments using PFO, PSO, Langmuir, and Freundlich models, followed by validation in real domestic wastewater against PCD standards.Despite its lowest BET surface area (91.73 m² g⁻¹), SSRH exhibited hierarchical pore architecture (DFT pore volume: 0.054 cm³ g⁻¹) and a dual-domain morphology integrating porous carbon with reactive mineral phases (Fe/Al/Ca{u2013}OH). At 180 min, SSRH achieved 70.20% NH₄⁺{u²⁰¹³}N and 58.00% PO₄³⁻{u²⁰¹³}P removal, outperforming SSB and RHB at p < 0.001. PSO kinetics (R² = 0.995) and Langmuir isotherms (R² = 0.991) best described adsorption behavior, yielding q_max of 32.80 and 5.86 mg g⁻¹ for NH₄⁺{u²⁰¹³}N and PO₄³⁻{u²⁰¹³}P, respectively. In real wastewater (TN = 44.2 mg L⁻¹; TP = 5.5 mg L⁻¹), SSRH alone achieved simultaneous PCD compliance, reducing TN to 18.4 mg L⁻¹ and TP to 2.5 mg L⁻¹. Langmuir predictions matched experimental values within ±0.9 percentage points.Co-pyrolysis of sewage sludge and rice husk yields a multifunctional adsorbent meeting regulatory standards through synergistic porosity and mineral reactivity, offering a scalable circular-economy solution for decentralized wastewater treatment across South and Southeast Asia.