Dynamics of the anaerobic process: Effects of volatile fatty acids

Abstract

A complex and fast dynamic response of the anaerobic biogas system was observed when the system was subjected to pulses of volatile fatty acids (VFAs). It was shown that a pulse of specific VFAs into a well-functioning continuous stirred tank reactor (CSTR) system operating on cow manure affected both CH(4) yield, pH, and gas production and that a unique reaction pattern was seen for the higher VFAs as a result of these pulses. In this study, two thermophilic laboratory reactors were equipped with a novel VFA-sensor for monitoring specific VFAs online. Pulses of VFAs were shown to have a positive effect on process yield and the levels of all VFA were shown to stabilize at a lower level after the biomass had been subjected to several pulses. The response to pulses of propionate or acetate was different from the response to butyrate, iso-butyrate, valerate, or iso-valerate. High concentrations of propionate affected the degradation of all VFAs, while a pulse of acetate affected primarily the degradation of iso-valerate or 2-methylbutyrate. Pulses of n-butyrate, iso-butyrate, and iso-valerate yielded only acetate, while degradation of n-valerate gave both propionate and acetate. Product sensitivity or inhibition was shown for the degradation of all VFAs tested. Based on the results, it was concluded that measurements of all specific VFAs are important for control purposes and increase and decrease in a specific VFA should always be evaluated in close relationship to the conversion of other VFAs and the history of the reactor process. It should be pointed out that the observed dynamics of VFA responses were based on hourly measurements, meaning that the response duration was much lower than the hydraulic retention time, which exceeds several days in anaerobic CSTR systems.

Demand-driven biogas production in anaerobic filters

“…This is in contrast to the ndings of Pind et al (2003) who observed an increase in CH 4 concentration as well as in pH after injecting VFAs. The reason for the converse reactions may be attributed to the neutralization with NaOH of the VFAs by Pind et al (2003).…”

Effects of heavy metals as stress factors on anaerobic digestion processes and biogas production from biomass

“…Cow manure Temperature: thermophilic conditions Addition of VFA affected CH 4 yield, pH, and gas production Pind et al (2003) be a consequence of industrial activities that eliminate residues in the soil and aqueous media that in long term promote their accumulation (Glick 2003) with a majority of the sources being anthropogenic (Zhang et al 2005). For Cd, Pb, Cu and Zn, their toxicity increases as follows: Pb \ Zn \ Cu \ Cd (Bååth 1989), depending on numerous abiotic and biotic factors.…”

High rate anaerobic treatment of Sago wastewater using HUASB with PUF as carrier

“…VFA started building up in the wastewater as the digestion proceeded and the maximum concentration of 2650 mg/ L was recorded at an OLR of 24.7 kg COD/m 3 .day. VFA has been recognized as one of the important intermediates during the anaerobic digestion (Wang et al, 1999;Ahring Angelidaki 1997) and is considered a central parameter for anaerobic treatment (Ahring and Angelidaki, 1995;Pind et al, 1999;2002). The impact of VFA accumulation was reflected in the marked decrease of COD removal from 86 to 68% when the OLR was increased to 24.7 kg COD/m 3 .day.…”