BIOTECHNOLOGY - V. H. Herasymenko - 2006

Part II. Special Biotechnologies

Chapter 22. BIOTECHNOLOGIES FOR WASTE UTILIZATION AND BIOCONVERSION IN THE AGRO-INDUSTRIAL COMPLEX

22.3. NON-TRADITIONAL METHODS. BIOTECHNOLOGY OF BIOGAS PRODUCTION VIA ANAEROBIC WASTE DIGESTION

22.3.3. Technical and Technological Aspects of Biogas Production

22.3.3.3. Classification of Biogas Plants by Operating Principle

According to their operating principle, all biogas plants can be divided into three main types:

Continuous-flow or flow-through biogas plants. In these systems, manure is fed continuously or at short intervals into a constantly filled Reactor, where optimal conditions for anaerobic decomposition are maintained through mechanical stirring and heating. Fresh material enters the upper part of the chamber and is discharged from the lower part (above the chamber floor). With each loading, the volume of fresh manure must correspond to the volume of digested manure being unloaded. This technological scheme ensures the highest productivity of the biogas plant and is used by the majority of domestic and foreign units currently in operation. This technology requires the smallest Fermentation chambers, which can be installed horizontally or vertically.

However, they have certain drawbacks. In flow-through installations, an increased flow rate of the incoming manure through the reactor causes the washout of methanogenic microorganism colonies, which in turn leads to a decrease in biogas yield. To eliminate this drawback in flow-through systems, it is necessary to use automatic process control systems capable of detecting deviations in the technological process, correcting them, and maintaining optimal parameters for biomethanogenesis.

Biogas plants with a batch or cyclic system of methane tank operation. Manure Processing in these plants is carried out in series-connected methane tanks (two or more) that are alternately filled with fresh manure biomass. The more reactors there are, the shorter the intervals between biogas production cycles.

A specific feature of operating these units is the incomplete removal of sludge from the reactor, which serves as an inoculum. Due to this, methanogenesis begins just a few days after the fermentation chamber is filled with fresh manure.

The utilization of the fermentation chamber volume is less efficient in this system. The periodicity in reactor filling necessitates maintaining a sufficient supply of manure, which requires the construction of manure storage facilities. In addition, to prevent air from entering the reactor during sludge unloading—meaning to prevent loss of reactor airtightness—it must be refilled with biogas from additional, specially designated vessels (gas holders).

Biogas plants with a storage system. In these systems, the same reservoir acts simultaneously as both a reactor and a sludge storage tank until it is hauled out to the fields. This system is also known as an accumulative or basin system. It is rarely used for biogas production.