Kinetic analysis of biological degradation for tetramethylammonium hydroxide (TMAH) in the anaerobic activated sludge system at ambient temperature

• Evaluation of a non-heated anaerobic activated sludge process.
• High-rate decomposition (0.63 kgC/m3/d) of tetramethylammonium hydroxide (TMAH).
• A microorganism-based biochemical kinetic model including cryptic growth.
• Gene analysis to justify the model structure composed of 4 kinds of microorganisms.

With rapid development of thin-film transistor liquid crystal display industries, improvements of the wastewater treatments for spent developing fluid (Tetramethylammonium hydroxide (TMAH)) is essential. As an alternative to the conventional aerobic processes, an anaerobic process in ambient temperature composed of a suspended sludge reactor and subsequent two gravity thickeners with addition of flocculants was elaborated. Methylotrophic TMAH-degraders were enriched from an anaerobic digester at a municipal wastewater treatment plant, feeding TMAH as a sole substrate. In the system TMAH was converted to methane via methanol whilst trimethylamine, dimethylamine, monomethylamine and ammonium were sequentially produced with the biomass yield of 0.14 gCOD/gTMAH, maximum specific growth rate at 0.372 d−1 and specific decay rate at 0.017 d−1 under 23 °C. The system could remove TMAH at 0.37–1.2 kgTMAH/m3/d with 2000–6000 mg/L of sludge concentration in the reactor, and achieved low effluent dissolved organics at about 2–5 mgC/L. A kinetic model of TMAH degradation, including cryptic growth of ordinary acidogens, acetotrophic and hydrogenotrophic methanogens from the decayed TMAH-degraders was built, and validated using a quantitative PCR method. Since the calculated fractions of bacterial and archaeal biomass were consistent with those detected, the kinetic model based on the metabolic pathways could be used as a design platform to maximise the target species and reaction rates in the new system.

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