Titration methodologies for monitoring of anaerobic digestion in developing countries—a review

Abstract

An increase in volatile fatty acids (VFA) concentration (or the proportional decrease in carbonate alkalinity concentration) is the first practical measurable indication that an anaerobic treatment system is in a state of stress. If the system is not rectified at this early stage, failure is likely. Current methods for VFA measurement include distillation, colorimetry, gas chromatography and various titration techniques. In terms of simplicity, speed and cost-effectiveness it is generally accepted that titration methods are superior for the purpose of on-site routine monitoring and control, particularly in developing countries. This paper reviews the methods published in the last four decades concerning on-site titration measurement of VFA and carbonate alkalinity concentrations. The review encompasses the following: aquatic chemistry related to the theory on which most of the methods are based, and a detailed description of each of the principal methods published followed by critical and comparative evaluation.

Effects of feedstock carbon to nitrogen ratio and organic loading on foaming potential in mesophilic food waste anaerobic digestion

“…3a) during the same period. During this period, NH 3 -N, which is also known to act as a buffer against the acidic VFA effect (Lahav and Morgan 2004), also decreased slightly from 3 to 2.8 g/L (Fig. 2a).…”

“…Reduction in pH during digestion may result to poor methanogenic activities, which may lead gradually to inhibition (Izumi et al 2010;Griffin et al 1998). For proper performance of methanogenic bacteria, it has been reported that the pH of the digestion medium should be within the range of 6.8 to 7.8 (Zeshan and Karthikeyan 2012;Lahav and Morgan 2004). Although there was more rapid pH drop during the digestion of F1, however, the pH was still within neutral bounds of 6.5 to 7.2 during the first 10 days of digestion before decreasing below pH 6.…”

Protocol for Start-Up and Operation of CSTR Biogas Processes

“…the ability of a solution to neutralise acids, and can be expressed in different ways. The total alkalinity (TA) gives a measure of the combined effect of several different buffering systems [76] The partial alkalinity (PA) represents the buffering capacity of the carbonate system, and includes in addition the ammonium-ammonia system. The intermediate alkalinity (IA) is the difference between TA and PA and includes mainly the buffering capacity of the VFA [75,76].…”

“…The total alkalinity (TA) gives a measure of the combined effect of several different buffering systems [76] The partial alkalinity (PA) represents the buffering capacity of the carbonate system, and includes in addition the ammonium-ammonia system. The intermediate alkalinity (IA) is the difference between TA and PA and includes mainly the buffering capacity of the VFA [75,76]. The stability of the process can be evaluated by calculating the IA/PA ratio where a ratio of 0.3 or less indicates a stable process [75,77].…”

Examining a Pretty Simple and Low Cost Method for Modeling of Biogas Production from Biodegradable Solids

“…Dry matter (DM) and volatile matter (VM) content of substrates and inocula were measured according to Mayland [11] and Standard Methods [12]. Total alkalinity and total volatile fatty acids (TVFA) were measured by titration according to Lahav & Morgan [13]. 29.6±2.85 1947±63 4878±49 1856±270 * total alkalinity as mg-CaCO3 ** total volatile fatty acids as mg-CH3COOH 1) stabilized sludge from a swine farm biogas digester 2) mature digestate from a pilot reactor…”