Effect of different pH-values on process parameters in two-phase anaerobic digestion of high-solid substrates

Abstract

In many publications, primary fermentation is described as a limiting step in the anaerobic digestion of fibre-rich biomass [Eastman JA, Ferguson JF. Solubilization of particulacte carbon during the anaerobic digeston. J WPCF. 1981;53:352-366; Noike T, Endo G, Chang J, Yaguchi J, Matsumoto J. Characteristics of carbohydrate degradation and the rate-limiting step in anaerobic digestion. Biotechnol Bioeng. 1985;27:1482-1489; Arntz HJ, Stoppok E, Buchholz K. Anaerobic hydroysis of beet pulp-discontiniuous experiments. Biotechnol Lett. 1985;7:113-118]. The microorganisms of the primary fermentation process differ widely from the methanogenic microorganisms [Pohland FG, Ghosh S. Developments in anaerobic stabilization of organic wastes-the two-phase concept. Environ Lett. 1971;1:255-266]. To optimize the biogas process, a separation in two phases is suggested by many authors [Fox P, Pohland GK. Anaerobic treatment applications and fundamentals: substrate specificity during phase separation. Water Environ Res. 1994;66:716-724; Cohen A, Zoetemeyer RJ, van Deursen A, van Andel JG. Anaerobic digestion of glucose with separated acid production and methane formation. Water Res. 1979;13:571-580]. To carry out the examination, a two-phase laboratory-scale biogas plant was established, with a physical phase separation. In previous studies, the regulation of the pH-value during the acid formation was usually carried out by the addition of sodium hydroxide [Cohen A, Zoetemeyer RJ, van Deursen A, van Andel JG. Anaerobic digestion of glucose with separated acid production and methane formation. Water Res. 1979;13:571-580; Ueno Y, Tatara M, Fukui H, Makiuchi T, Goto M, Sode K. Production of hydrogen and methane from organic solid wastes by phase separation of anaerobic process. Bioresour Technol. 2007;98:1861-1865; Zoetemeyer RJ, van den Heuvel JC, Cohen A. pH influence on acidogenic dissimilation of glucose in an anaerobic digestor. Water Res. 1982;16:303-311]. A new technology without the use of additives was developed in which the pH-regulation is executed by the pH-dependent recycling of effluent from the anaerobic filter into the acidification reactor. During this investigation, the influence of the different target pH-values (5.5, 6.0, 7.0 and 7.5) on the degradation rate, the gas composition and the methane yield of the substrate maize silage was determined. With an increase in the target pH-value from 5.5 to 7.5, the acetic acid equivalent decreased by 88.1% and the chemical oxygen demand-concentration by 18.3% in the hydrolysate. In response, there was a 58% increase in the specific methane yield of the overall system. Contrary to earlier studies, a marked increase in biogas production and in substrate degradation was determined with increasing pH-values. However, these led to a successive approximation of a single-phase process. Based on these results, pH-values above 7.0 seem to be favourable for the digestion of fibre-rich substrates.

A review of anaerobic digestion systems for biodegradable waste: Configurations, operating parameters, and current trends

“…Deublein and Steinhauser [35] showed that pH > 10 caused an irreversible loss of the activity of the microorganisms. The pH values between 5.5 and 6.5 were often reported as an optimal range and the best pH values was 6.0 [54,[82][83][84]. These results are reasonable for each condition of hydrolysis and acidogenesis as presented in section 2.1.…”

The impact of Ni, Co and Mo supplementation on methane yield from anaerobic mono-digestion of maize silage

“…Furthermore, it must also be taken into account that, in an agricultural biogas digester fed with renewable biomass, along with proper supplementation of macro-and micronutrients (trace metals), optimization of process variables, such as pretreatment techniques applied to the biomass, temperature, pH and mixture ratios (if the biogas plant is operated in co-digestion mode), is also of paramount importance. [35][36][37][38][39] …”

Electrical Conductivity for Monitoring the Expansion of the Support Material in an Anaerobic Biofilm Reactor

“…This condition corresponds to HR effluent and MR influent with pH adjusted to 7 with the purpose of emulate the neutral conditions of the methanogenic stage of the two-stage AD process. pH values in a range of 7.0-7.5 favor the methanogenic stage of the anaerobic digestion process since this factor increases biogas production and the specific CH 4 yield [28]. Under these conditions, the bed expanded faster than in tests with the S1 substrate.…”