Biomethanization from sulfate‐containing municipal solid waste: effect of molybdate on microbial consortium

Abstract

BACKGROUND: The effect of molybdate on a microbial consortium of dry thermophilic anaerobic digestion (AD) from sulfate-containing municipal solid waste was studied. RESULTS:The study showed molybdate inhibition affecting hydrolysis, acidogenesis, and methanogenesis, but the main microbial populations in AD can sustain the molybdate load over a short period of time. Molybdate was not a bactericide for all members of the principal groups, only a few of them are affected. Although all the microbial populations decreased, the weakest groups were sulfate reducing bacteria (SRBs) and butyrate-utilising acetogens (BUAs) and the most resistant group was propionate-utilising acetogens (PUAs). Prior to using molybdate, the relative percentages were: Eubacteria:Archaea 80:20; acetogens 25% (BUAs 11% and PUAs 14%) and SRBs 17%. After molybdate addition the relative percentages were: Eubacteria:Archaea were 83:17, acetogens remained over 28% (BUAs 8% and PUAs 20%) and SRBs around 11%. The relation between acetate-utilising methanogens (AUMs) and hydrogen-utilising methanogens (HUMs) changed slightly from 55:45 to 53:47. CONCLUSION: All biochemical reactions in AD were inhibited and an increase in food:microorganism(F:M) ratio was observed. The microorganism's removal rates and growth inhibition rates are indicators of inhibitory effect in all analysed populations by inhibitor addition.

Assessment of free nitrous acid pre-treatment on a mixture of primary sludge and waste activated sludge: Effect of exposure time and concentration

“…The pH level reached a constant value of 7.8 ± 0.4 in all BMP tests. This has been identified as the optimal pH for enhanced acetogenic and methanogenic activity (De la Rubia et al, 2009;Zahedi et al, 2014bZahedi et al, , 2016. At the end of the assay, VFA concentrations were lower than 0.2 g/g VS and no propionic acid was detected under any pre-treatment tested.…”

Enhancing sludge biodegradability through free nitrous acid pre-treatment at low exposure time

“…TS, VS, soluble Kjeldahl nitrogen (SKN) and SCOD were determined according to standard methods [22] and Zahedi et al [23,24]. NH 4 + was analyzed via ion chromatography (ICS5000, DIONEX).…”

Changes in microbial community during hydrogen and methane production in two-stage thermophilic anaerobic co-digestion process from biowaste

“…The cellular concentration and percentages of Eubacteria, Archaea, Firmicutes, Clostridium and different groups of methanogens, described below, were obtained by epifluorescence method (FISH). These analyses were performed according to Montero et al (2009) and Zahedi et al (2013aZahedi et al ( , 2013bZahedi et al ( , 2014aZahedi et al ( , 2014b. The 16S rRNA-targeted oligonucleotides employed in this study are showed in the Table 2.…”

“…About two-stage AD process, most of researchers have been focused on the optimization of gas production (GP), removal organic matter and process optimization but very few reports discussed in detail the microbial population dynamics involved during different stages of the thermophilic anaerobic co-digestion of WAS and OFMSW for hydrogen production. Molecular tools like the fluorescence in situ hybridization (FISH), based on sequence comparison of small-subunit ribosomal RNA (rRNA) molecules, can detect specific whole cells/organisms in biological samples (Crocetti et al, 2006;Ariesyady et al, 2007;Montero et al, 2009;Zahedi et al, 2013aZahedi et al, , 2013bZahedi et al, , 2014aZahedi et al, , 2014b.…”