Some of the typical implementations of large-scale anaerobic digestion systems are described below.

(a) Sewage Sludge

Sewage sludge is a waste biomass which is discharged in large quantities from sewage treatment facilities. For a long time, anaerobic digestion has been one of the treatments on sewage sludge to stabilize the sludge and reduce its volume. The reactor design usually applied to sewage sludge digestion is a completely mixed reactor design (Fig. 8.2.2). A contemporary anaerobic digester for sewage sludge is as large as 10,000 m3 in the effective volume. Typical design parameters include the operational temperatures of ambient (ca. 20 degC) to mesophilic (ca. 35 degC) range, and the relatively long retention time of 20 to 30 days.

(b) Industrial organic wastewater

Industrial wastewater containing readily biodegradable organic matters, but little solids, such as the wastewater discharge from a beer brewery, the UASB (up-flow, anaerobic sludge blanket) reactor design, which was originally developed in the Netherlands, is usually selected. The UASB reactor design maintains a high density of anaerobic microorganisms in the form of self-aggregated microbial "granules" that enables a high rate of anaerobic digestion.

(c) Organic wastes from food industries

Anaerobic digester designs which allow a high rate anaerobic digestion on readily biodegradable biomass containing high concentrations of organic solids are being developed, and some have already been in actual operation in recent years. An example of such a new design is the DAPR (down-flow anaerobic packed-bed reactor) design. Many high-rate anaerobic digestion facilities for food wastes and distillery wastes, incorporating the DAPR design, have been implemented in Japan. The largest facility as of writing has the design capacity of 400 tons/day (Fig. 8.2.3).

Further information

R. E.Speece: Anaerobic Biotechnology, Archae Press, pp.127, Tennessee (1996)

Japan Sewage Works Association: Sewage Facilities planning, policy and explanation (second part) 2001, pp.384, Japan (2001)

J. B.Lier: Current Trends in Anaerobic Digestion; Diversifying from waste(water) treatment to re-source oriented conversion techniques, 11th IWA World Congress on Anaerobic Digestion, 23-27 September

2007, Brisbane, Australia (2007)

Hisatomo Fukui and Motonobu Okabe: Distilled spirit processing waste recycling plant using thermophilic dawn-flow packed-bed reactor, Gas fuel manufacture from biomass and its energy utilization, NTS, pp.265-275, Japan (2007)