Laboratory‐Scale Comparison of Anaerobic‐Digestion Alternatives

Abstract

Laboratory‐scale digesters were used to perform side‐byside evaluations of alternative digestion systems including thermophilic– mesophilic‐phased digestion (TPAD), acid/methane‐phased digestion, mesophilic digestion, and the performance of the thermophilic stage of TPAD alone. Total detention times in the systems evaluated varied from 8 to 20 days. Temperatures in the mesophilic stage of TPAD were varied from 35 to 43.3°C and temperatures in the thermophilic stage were varied from 55 to 58.9°C. The purpose of the study was to evaluate volatile solids (VS) reduction and thickening properties of the different systems. Parameters evaluated included solids, volatile acids, gas production and quality, various chemical constituents of the sludge, and thickening properties using polymer and ferric chloride plus polymer. The TPAD systems were found capable of higher VS destruction at total detention times of 10 and 12.5 days compared to single‐stage mesophilic or thermophilic digestion at 15 to 20 days. A laboratory‐scale thickening test was performed to evaluate thickening properties. Based on obtaining 95% capture in the test, the polymer demand of mesophilic and acid–methane‐phased digestion was the lowest. The TPAD system required approximately 180% of the dosage of the mesophilic sludge and thermophilic sludge required approximately 310% of the dosage. Temperatures of 40.5 and 43.3 8 C in the mesophilic stage of TPAD were found to increase the polymer requirement and decrease the VS reduction of the TPAD system. Higher temperatures (above 56.1°C) and lower detention times (less than 15 days) in the thermophilic digesters seemed to result in problems with degradation of volatile acids, particularly propionic acid. Water Environ. Res., 76, 360 (2004).

High pressure homogenization and temperature phased anaerobic digestion for enhanced biogas conversion from municipal waste sludge

“…Whereas, at 14 d SRT, relative improvements were in the range of 24 to 26% and 10.6 to 11.1% for mesophilic and thermophilic digesters, respectively. Reusser and Zelinka (2004) also obtained an increase of about 11% in VS removal for a thermophilicmesophilic TPAD system at 20 d SRT. Digestion at 7 d SRT also demonstrated the superiority of pretreated digesters over the controls.…”

Anaerobic Digestion

“…There are several benefits to the utilisation of thermophilic conditions, for example increased reaction rates and thus organic breakdown as well as a greater pathogenic kill. In addition, there is evidence to suggest that the thermophilic bacteria enhance the seeding for the subsequent mesophilic stage [16]. It has been cited by several authors that start-up of thermophilic reactors can often be problematic due to the sensitivity of thermophilic bacteria to organic loading rate, influent characteristics and other operational factors [16,17].…”

“…There are two common designs of AD plant (single and multiphase). Single-phase systems contain all of the microbial population in one vessel whereas multi-phase AD is carried out in several separate vessels (see Figure 2 operation often has the advantage of allowing optimisation of conditions for the specific bacteria required in each phase [16]. There is also evidence to suggest that multi-phase systems which split the hydrolysis/acidogenic phase and the methanogenic phase require less residence time than single phase systems.…”

The effect of upper mesophilic temperature and feed-to-seed ratio on batch anaerobic digestion systems

“…[17,18] Since anaerobic digestion is a vitally important component in municipal wastewater treatment with respect to fostering a sustainable approach to biosolids management, [19,20] further knowledge on process behavior in the upper mesophihic range could enhance performance potential and subsequently minimize operational costs. [21] Therefore, the main objective of this study was to explore the effect of temperature (within the 37 to 49 • C range) on the anaerobic digestion process using batch bench-scale reactors.…”