Optimization and performance improvement of Anaerobic Membrance Biocreactor (AnMBR) for volatile fatty acid and biohydrogen production

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Anaerobic Membrane Bioreactors (AnMBRs) have been widely used for source recovery from municipal and industrial wastewater treatment. Most of the research initiatives are inclined to optimize the production of methane-containing biogas from the anaerobic process. Volatile Fatty Acids (VFAs) and biohydrogen are two major intermediate products of AnMBR that can be recovered to improve the energy efficiency and product revenue from AnMBR. Research studies have investigated the technical feasibility of the production of VFA and biohydrogen using anaerobic digestion. The optimisation of VFA and biohydrogen production has been carried out through reducing their consumption by methanogens. This research study aims the optimisation of VFA and biohydrogen production through process optimisation so that the findings can be applied in a generic AnMBR model producing multiple products. Production of VFA has been investigated by reducing the Hydraulic Retention Time (HRT) and increase Organic Loading Rate (OLR) of the AnMBR. The solvent extraction method was used for VFA extraction and individual concentrations were measured using Gas Chromatogram-Mass Spectrometry. At 8 hrs HRT the concentration of major VFA components were maximum whereas at 550 mg/L COD feed showed the optimum nutrient and COD removal efficiency of AnMBR. Selective production of major VFA components has been investigated by altering the pH of the bioreactor. At pH 7.0 the percentage of acetic acid was highest indicating acetate type fermentation was predominant at that condition. However, a major alteration in the percentage of VFA components were observed at pH 12.0 indicating isobutyric acid as the major VFA components. The result implies that butyrate type fermentation was predominant at pH 12.0. Production of VFA and biohydrogen both were investigated during a stepwise reduction of HRT. Without inhibiting methanogenic activity, the highest VFA and hydrogen yields were 37.08g VFA / 100 g COD feed, and 24.6 mL H₂/ g COD feed, observed at 8 and 6 hr HRT respectively. Optimization AnMBR operating pH was carried out to maximize the production of biohydrogen. The highest yield and production rate were observed to be 122.21 ± 39.05 mL H₂ / L. d and 65.38 ± 3.2 mL H₂ /g COD added respectively and at pH 5.0 at an HRT of 6 hrs.
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