Methanogenesis Inhibition in Anaerobic Granular Sludge for the Generation of Volatile Fatty Acids from CO2 and Zero Valent Iron

Abstract

A new approach for CO 2 utilization (as a sole carbon source) to acetic acid and other VFAs under ambient conditions using zero valent iron and anaerobic granular sludge was examined by methanogens inhibition. Zero Valent Iron when is anaerobically oxidized generates H 2 that can be utilized along with CO 2 by homoacetogens in the anaerobic granular sludge for the production of acetic acid or other VFAs. However, methanogens in anaerobic sludge act antagonistically with homoacetogens and therefore the main goal of this study is to examine strategies to inhibit methanogenesis and to enrich homoacetogens. Based on this, several strategies were investigated such as the exposure of (a) anaerobic granular sludge to low pH, (b) the short exposure of anaerobic granular sludge to heat, (c) addition of bromoethanesulfonate under various concentrations and (d) exposure of anaerobic granular sludge to salinity 30-90 g NaCl/L. The highest performance (2,020 mg/L of acetic acid) was found when anaerobic granular sludge was exposed to 50 mM of bromoethanesulfonate at 100 g/L (ZVI), pH 6-6.5, after 12 days whereas, the short exposure of anaerobic granular sludge to heat at 100 g/L ZVI at pH 6-6.5 resulted in 1,290 mg/L of acetic acid. The operation of this system in pH 5-6 generated less VFAs compared to operation at pH 6-6-5. The daily regulation of pH to 3 was not practical as the pH was increased to 6.5 due to abiotic anaerobic oxidation of ZVI and this resulted in CH 4 production and propionic acid generation. The exposure of anaerobic granular sludge to ZVI and 30 g NaCl/L as well as to seawater resulted in production of CH 4 (around 28% of the headspace) and mainly production of acetic acid (550-850 mg/L). The increased in salinity to 60 and 90 g NaCl/L resulted in reduction of CH 4 and VFAs however, a more diverse range of VFAs was produced. Exposure of anaerobic granular sludge to heat and then to CO 2 and ZVI resulted in an increase of Clostridium sensu stricto to 65.9% and the same genus was increased when anaerobic sludge was exposed to bromoethanesulfonate and ZVI.

Bioethanol Production From H2/CO2 by Solventogenesis Using Anaerobic Granular Sludge: Effect of Process Parameters

“… Chakraborty et al (2020) demonstrated enhanced ethanol production from C 1 gas by granular sludge and Clostridium autoethanogenum was successfully enriched at 33°C. Similarly, Samanides et al (2020) reported an increased relative abundance of Clostridium of 65.9% in anaerobic granular sludge for acetic acid production, when first exposed to heat (95°C for 30 min) and incubated with 100% CO 2 and 100 g/L zero valent iron at 33°C.…”

Initial pH Conditions Shape the Microbial Community Structure of Sewage Sludge in Batch Fermentations for the Improvement of Volatile Fatty Acid Production

“…Thus, the analysis of prokaryotic community structures shaped by pH conditions revealed the positive and negative selection of VFA producers and consumers, respectively, as well as the in silico prediction of metabolic functions—based on prokaryotic community structures—suggest that the development of fermentation conditions inhibiting methanogenesis and/or stimulating carbohydrate utilization can be a further practicable strategy to improve the production of VFA [ 49 , 50 ].…”

Improving Biological Treatment of Real Bilge Wastewater With Zero Valent Iron and Activated Charcoal Addition

“…For all anaerobic experiments, sealed glass serum bottles were used and were incubated at 37 • C. Anaerobic granular sludge was used at a concentration of 4% w/v, collected from a mesophilic upflow anaerobic sludge blanket reactor (UASB) that was treating dairy wastewater (Charalambides Christis Ltd, Limassol, Cyprus), operated at pH 6.8-7.3 (as reported by Samanides et al, 2020). Raw bilge wastewater was used, collected by a company treating this wastewater type (Ecofuel Ltd, Zygi, Cyprus), the wastewater characteristics are described in detail in a previous study by Vyrides et al (2018b).…”