Alkalinity ratios to identify process imbalances in anaerobic digesters treating source-sorted organic fraction of municipal wastes

Early warning indicators for monitoring the process failure of anaerobic digestion system of food waste

“…Certainly there may be other unknown factors that improve the early warning performance of BA/TA in Reactor A. In addition, it is worth mentioning that IA/PA was used to replace VFA/BA in this paper, since these two were almost equivalent (Martín-González et al, 2013), and the threshold of IA/PA was lower than that of VFA/BA, so the warning effect of IA/PA is considered theoretically better than that of VFA/BA.…”

“…However, previous researches on early warning parameters always focused on a specific parameter, verified its effectiveness and defined its threshold value (Martín-González et al, 2013;Wang et al, 2009); or studied the responses of multiple parameters under a specific condition, and suggested the optimal parameters for this operating conditions (Nielsen et al, 2007;Kleyböcker et al, 2012;Ahring et al, 1995). Thus, though lots of researches on early warning parameters have been conducted, the proposed early warning indicators are only effective when applied to these specific operating conditions, while less effective in systems with different operation conditions.…”

“…S1-S3; and Table 2 summarized the specific early warning information of various parameters. Among then the dates of the process imbalance for IA/PA, VFA/TA and BA/TA were, respectively defined as the date when the ratios exceeded their critical value of 0.3, 0.35 and 0.8 (Martín-González et al, 2013;Méndez-Acosta et al, 2010). The selected thresholds are valid in all three reactors, and seem more suitable than any other thresholds to indicate the process imbalance of FW digesters.…”

“…Thus, though lots of researches on early warning parameters have been conducted, the proposed early warning indicators are only effective when applied to these specific operating conditions, while less effective in systems with different operation conditions. For example, the ratio of intermediate alkalinity to partial alkalinity (IA/PA) of 0.9 was suggested in order to maintain stable operation in thermophilic reactors treating sewage sludge; however IA/PA of 0.4 was proposed to assure a stable reactor performance when a potato-starch wastewater was treated; and IA/PA below 0.3 was recommended to maintain a stable operation when municipal solid waste was treated (Martín-González et al, 2013). In contrast, Hill et al (1987) suggested that the ratio of propionate to acetate (Pr À /Ac À ) higher than 1.4 indicated impending digester failure, but Weiland (2008) held that the Pr À /Ac À shall be lower than 1.0 in a stable system; and Ahring et al (1995) suggested that Pr À /Ac À was useless in determining process imbalance.…”

Protocol for Start-Up and Operation of CSTR Biogas Processes

“…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]. A value between 0.3 and 0.8 indicates, on the other hand, a risk of instability and a value above 0.8 suggests instability [49].…”