Value added product recovery and carbon dioxide sequestration from biogas using microbial electrosynthesis

470-478Issues like global warming and the associated climate change demand alternative green biofuel in place of the fossil fuel. Biogas, which mainly contains carbon dioxide and methane, is produced by anaerobic degradation of organic matter. Microbial electrosynthesis (MES), a novel type of bioelectrochemical systems (BES), can be used to improve the calorific value of biogas, and also to reduce the CO2 content in the biogas, and thus increase the percentage of methane present in the biogas. In this study, MES has been used to sequester carbon dioxide present in biogas to produce electro-biocommodities like acetate, isobutyrate, etc. The biogas generated from an up-flow anaerobic sludge blanket (UASB) reactor treating sewage was fed into the cathodic chamber of MES cell, which consisted of carbon felt as a biocathode poised at –0.9 V vs. SHE. The abiotic anode was also made up of carbon felt and phosphate buffer solution was used as anolyte. The electrotrophic microbiome present on the cathode produced acetate (52.4 mM m-2 d-1), isobutyrate (36.2 mM m-2 d-1), propionate (41.6 mM m-2 d-1), 2-piperidinone (26.7 mM m-2 d-1) and traces of methyl derivatives of these compounds. Thus, it demonstrated successful CO2 sequestration from the biogas and synthesized multi-carbon organic compounds and in turn produced biogas with higher methane content in it

Characteristics of sludge developed under different loading conditions during UASB reactor start-up and granulation

Sludge characteristics available inside the reactor are of vital importance to maximize advantages of UASB reactor. The organic loading rate and sludge loading rate applied during start-up are among the important parameters to govern the sludge characteristics. Effects of these loading rates on the characteristics of the sludge developed are evaluated in six laboratory scale UASB reactors. The sludge characteristics considered are VSS/SS ratio of the sludge, sludge volume index, specific gravity, settling velocity and metal contents of the sludge developed under different loading rates. The experimental results indicate that, for developing good characteristics sludge, during primary start-up from flocculent inoculum sludge, organic loading rate and sludge loading rate should be in the range of 2.0-4.5 kg COD/m(3) d and 0.1-0.25 kg COD/kg VSS d, respectively (chemical oxygen demand, COD). Proper sludge granulation and higher COD removal efficiency will be achieved by these loading rates. (c) 200

Experience with UASB reactor start-up under different operating conditions

Four laboratory upflow anaerobic sludge blanket (UASB) reactors were operated at different operating parameters viz., hydraulic retention time (HRT), upflow velocity, organic concentration, and Ca2+ concentration in the wastewater. These operating parameters gave different values of organic loading rates (OLRs) and sludge loading rates (SLRs). The reactor performance during start-up was evaluated at different values of the above listed parameters. Also, the effects of these parameters on the granule characteristics were investigated. It was observed that COD removal efficiency at steady state was profoundly influenced by SLR. The reactor started with SLR of 0.6 kgCOD/kgVSS.d could result in about 50% COD removal at steady state. The reactor performance could not improve even after three months of operation. Up to 0.3 kgCOD/kgVSS.d the reactor performance was good with more than 90% COD removal at steady state. The OLR and SLR also determine time required for the reactor to achieve steady state. Different operating conditions also have the bearing on the strength of the granules cultivated. The methanogenic activity measured on acetate for each reactor was observed between 0.259 and 0.909 kg CH4 COD/kgVSS.d. The sludge production in all the reactors was between 0.087 and 0.13 kgVSS/kgCOD(in). The mathematical model was developed in order to predict sludge production. Copyright (C) 1996 IAWQ