What is an attached membrane anaerobic digester?

The outstanding feature of the attached membrane anaerobic digester is that the microorganisms are fixed on the inert medium placed in the digester, and the microorganisms are fixed while allowing liquids and solids in the raw materials to pass through. in the digestive tract. The most widely used or studied attached membrane reactors include anaerobic filter (AF), fluidized bed (FBR) and expanded bed (EBR).

(1) Anaerobic filter (AF)

The anaerobic filter (Figure 8-13) is equipped with inert media (also called filler). In the past, stones and coke were mostly used , cinder or honeycomb plastic products, now mostly use synthetic fiber fillers. Biogas fermentation bacteria, especially methanogens, have the habit of attaching to solid surfaces. They adhere to inert media in a film-like form, and adhere to each other in the gaps between the media to form granules or flocs and remain. When sewage flows from the bottom When flowing upward or from top to bottom through the biofilm, organic matter is utilized by bacteria to generate biogas.

Figure 8-13 Schematic diagram of anaerobic filter

(2) Fluidized bed and expanded bed

Both fluidized bed and expanded bed belong to attached growth organisms Membrane reactor, the inside of the reactor is filled with inert (such as fine sand) or active (such as activated carbon) particles of the same size as sand (0.2 to 0.5 mm) for microorganisms to adhere to, such as coke powder, diatomaceous earth, and pulverized coal Ash or synthetic materials, etc., when the organic sewage flows through the fine particle layer from bottom to top, the air flow of the sewage and the produced gas causes the medium particles to expand or flow. The surface of each media particle is covered by biofilm, with a surface area of ??up to 300 m2/m3, which can support more microorganisms to adhere, resulting in a microbial retention period longer than the hydraulic retention time, thus making the digester have a higher efficiency.

Both reactors can be used with relatively short hydraulic retention times, allowing liquid and small amounts of solids in the feed to pass through. It is suitable for the treatment of organic wastewater with low solid content that is easy to digest. The advantage of these two systems is that they can provide a larger surface area for microbial attachment, and some granular solids can pass through the support medium; the disadvantage is that in order to expand or fluidize the medium particles, 0.5 to 10 times of feed liquid recirculation is required, which This increases the energy consumption of the operating process. Therefore, there are more studies on these two processes but less practical applications.