Enhancing sludge conditioning and dewatering characteristics by active surfaces modified with fast recombining immobilized nanoparticles

Abstract

Nichrome is a composite of nickel chromium alloys and commonly used as resistance wire for heating equipment. In this study, ability of multilayered heterojunctions between Cr⁺³-TiO₂ and Ni²⁺-TiO₂ nanoparticles to disintegrate acidified slurry sludge was investigated experimentally. Recombination and photoactivity of the Cr³⁺ and Ni²⁺ nanoparticles were optimized alternating their atomic mass fractions in the nanocomposites by their heating ability, using a central composite statistical design approach. Effects of the applied method on sludge conditioning, stabilization, and drying behaviors were systematically investigated. Temperature increase (ΔT) at the highest volatile suspended solids (VSS) oxidation level in the treated sludge samples were 2 ± 1 °C, 5 ± 1 °C, and 20 ± 1 °C for “UV C + H₂O₂-no catalyst,” pure and Cr-Ni-TiO₂ thin films (TFs), respectively. Obtained results also indicated that the modified TiO₂ nanoparticles were able to decrease sludge bound water content by 45 ± 1% efficiency. Cr³⁺ and Ni⁺² co-doped TF functioned to decrease the unit drying energy from 236 ± 10 kJ kg⁻¹ H₂O_evaporated to 140 ± 10 kJ kg⁻¹ H₂O_evaporated. Drying profiles of raw and treated the sludge samples were fitted to Henderson and Pabis Model. Drying constants (k) for raw and treated sludge samples by pure TiO₂ and Cr-Ni-TiO₂ TFs were found to be 0.11 ± 0.01 min⁻¹, 0.12 ± 0.01 min⁻¹, and 0.19 ± 0.01 min⁻¹, respectively. VSS degradation followed pseudo-first-order reaction kinetics in the all assayed conditions and pseudo-first-order reaction rates (k_obs) for pure and the modified TFs were determined as 6 × 10⁻⁴ min⁻¹ and 4 × 10⁻³ min⁻¹, respectively. 2,2′,5-Trichlorobphennyl, 2,2′,5,5′-Tetrachlorobiphenyl, 2,3′,4,4′,5-Pentachlorobiphenyl, and 2,2′,3,4,4,5,5′-Heptachlorobiphenyl were detected in raw sludge and after the photocatalytic oxidation through Cr³⁺ and Ni²⁺ co-doped TiO₂ TF reactor, their total concentration was reduced from 4.36 mg kg⁻¹ to 9.76 × 10⁻³mg kg⁻¹.

Graphical Abstract

Keywords:

• Sludge disintegration
• conditioning
• dewatering
• photocatalysis
• stabilization
• PCBs

Disclosure statement

The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.

Additional information

Funding

This work is founded by The Scientific and Technological Research Council of Turkey TÜBİTAK (Project 111Y209) and Çerkezköy Organized Industrial Zone Management.