The synthesis of medium chain carboxylic acids (MCCAs) from syngas provides a promising route for converting coal/organic waste/natural gas into high value-added chemicals. However, neither purely chemical synthesis methods nor purely biological approaches seem poised to realize the potential of syngas-to-MCCAs. Hereby, we developed a hybrid approach and created an alternative pathway for C1 chain elongation to C6, where we combined the efficient carbon fixation of heterogeneous catalysts with the high specificity, low cost, and self-adaptation of anaerobic microbiomes. In the hybrid system, inorganic carbon fixation into organic carbon (adsorbed pyruvic acid) was accomplished by the heterogeneous Pt/Fe2O3 catalysts, and the adsorbed pyruvic acid was subsequently metabolized by the anaerobic microbiome. This hybrid system significantly improved CO conversion and n-caproic acid production (6600 mg COD/L), which was 50–190% higher than that observed in previous studies. The interactions were revealed by macro-omics and in situ diffuse reflectance infrared Fourier transform spectroscopy, demonstrating a manipulated inorganic carbon-to-chemical fixation route.

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In order to optimize the operating conditions for a combined polyaluminum chloride (PACl) coagulation/flocculation and ultrafiltration process for treating potable water, the main, second order and interaction effects of PACl dose and flocculation retention time (FRT) on permeate turbidity, UV 254 and membrane permeability were investigated using a 100 kDa hollow fiber membrane operated in the dead-end mode. A multilevel factorial design was used to determine the relevant ranges of the two factors for optimization. A 2 2 central composite design (CCD) was then used to develop mathematical correlation models for the optimum operating conditions. The main effect of PACl dose was the most significant factor on all the responses. For permeability, both the main effect of FRT and FRT -PACl dose interactions were found to be insignificant. The optimum PACl dose and FRT for the feed water were 20 mg/L and 14 min respectively. Corresponding permeate turbidity, UV 254 and permeability were 0.15 ± 0.01 NTU, 0.003 ± 0.001 cm À1 and 62.0 ± 9.52 Lm À2 h À1 bar À1respectively. Experimental validation runs confirmed the reliability of the predicted optimal conditions thus implying that CCD models can be used to predict/optimize the quality and quantity of permeate from hybrid coagulation-ultrafiltration systems for potable water treatment.

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