3.1.2. Hydraulic shock
The hydraulic shock lasted for 12 h or half of the feeding period of intermittent operation. This consisted in decreasing the average HRT from 11.3 h to 6.1 h in the intermittent systems, and from 12.0 to 6.1 h in the continuous systems. During the hydraulic shock the COD of the feed was halved in order to maintain a constant OLR throughout the experiment: 10.9 g COD/L/day and 11.3 g COD/L/day for the intermittent and continuous systems respectively. The hydraulic shock was severe for both continuous and intermittent systems. Methane production (Fig. 5) in the intermittent systems diminished from an average of 0.89 L/h to an average of 0.26 L/h, equivalent to a 70% decrease. In the continuous systems the effect was even more severe, with methane production decreasing by 76%, from an average of 0.50 L/h to an average of 0.12 L/h. The slightly higher resilience of methane production in the intermittent system may be attributed to the presence of microorganisms from the Syntrophomonadaceae group (Fig. 8) and to a lower biomass washout (Fig. 5c). The heavy TSS washout observed in the continuous system was attributed to the combined effect of the high upflow velocity and the presence of accumulated substrates on the biomass surface, a typical result of continuous operation of UASB reactors [55]. As in the intermittent reactors the biomass flocs were not so heavily surrounded by adsorbed fatty substrates, the effects of high upflow velocity were not so severe. The clean biomass resulting from the intermittent operation also results in a higher capacity for adsorption of the wastewater substrates, thus explaining the higher COD removal efficiencies (Fig. 5b). It is worth noting that the effluent COD for the continuous system decreased slightly after the hydraulic shock as compared to baseline. This is probably due to the effect of the shear forces of the ascending liquid, resulting in the liberation of adsorbed substrates and consequent higher availability of adsorption sites for substrate removal. The effect of higher upflow velocity upon mass transfer [35] is also to be considered.
3.1.2 การไฮดรอลิกช็อกThe hydraulic shock lasted for 12 h or half of the feeding period of intermittent operation. This consisted in decreasing the average HRT from 11.3 h to 6.1 h in the intermittent systems, and from 12.0 to 6.1 h in the continuous systems. During the hydraulic shock the COD of the feed was halved in order to maintain a constant OLR throughout the experiment: 10.9 g COD/L/day and 11.3 g COD/L/day for the intermittent and continuous systems respectively. The hydraulic shock was severe for both continuous and intermittent systems. Methane production (Fig. 5) in the intermittent systems diminished from an average of 0.89 L/h to an average of 0.26 L/h, equivalent to a 70% decrease. In the continuous systems the effect was even more severe, with methane production decreasing by 76%, from an average of 0.50 L/h to an average of 0.12 L/h. The slightly higher resilience of methane production in the intermittent system may be attributed to the presence of microorganisms from the Syntrophomonadaceae group (Fig. 8) and to a lower biomass washout (Fig. 5c). The heavy TSS washout observed in the continuous system was attributed to the combined effect of the high upflow velocity and the presence of accumulated substrates on the biomass surface, a typical result of continuous operation of UASB reactors [55]. As in the intermittent reactors the biomass flocs were not so heavily surrounded by adsorbed fatty substrates, the effects of high upflow velocity were not so severe. The clean biomass resulting from the intermittent operation also results in a higher capacity for adsorption of the wastewater substrates, thus explaining the higher COD removal efficiencies (Fig. 5b). It is worth noting that the effluent COD for the continuous system decreased slightly after the hydraulic shock as compared to baseline. This is probably due to the effect of the shear forces of the ascending liquid, resulting in the liberation of adsorbed substrates and consequent higher availability of adsorption sites for substrate removal. The effect of higher upflow velocity upon mass transfer [35] is also to be considered.
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