Effluent treatment anaerobic filter

Anaerobic reactor configurations that have found application in the treatment of pulp and paper mill effluent include anaerobic contact, UASB, anaerobic filter, UASB/AF hybrid, and fluidized bed reactors. Specific features of these reactors are described in the following sections. 

Anaerobic Filter. An anaerobic filter consists of packed support media that traps biomass as well as facilitates attached growth of biomass as a biofilm (Fig. 8). Such a reactor configuration helps in the retention of suspended biomass as well as gas-liquid-solid separation. The flow of liquid can be upward or downward, and treatment occurs due to attached and suspended biomass. Treated effluent is collected at the bottom or top of the reactor for discharge and recycling. Gas produced in the media is collected underneath the bioreactor cover and transported for storage or use. Volumetric loading rates vary from 5 to 20 kg COD/m day with HRT values of 0.5-4 days. 

Arora H C, Chattopadhyda S N 1980 Anaerobic contact filter process a suitable method for the treatment of vegetable tanning effluents. Water Pollut Control (Maidstone Engl) 79 501-506... 

Primarily, activated sludge processes and, less often, trickling filter processes are employed for aerobic biological treatment. In North America and Northern Europe, effluent purification is frequently carried out in aerated oxidation ponds. Recently, anaerobic treatment has become established, especially in paper mills processing recovered paper. 

The sludge that is produced from the clarifiers goes into a treatment train typically consisting of an anaerobic digester (AD) having a HRT of 15 to 20 days or more. The liquid effluent from the AD is recycled back to the head of the plant. The gas produced, containing primarily methane and carbon dioxide, can be used for electricity production in gas turbines with the waste heat used to heat the ADs. In some plants the gas is used to heat the digester directly with the excess methane burned (flared). The solids from this process are filter pressed to remove more water, and composted. These treated and stabilized solids, called biosolids, are now suitable for safe land application and often times can be used as a source of fertilizer. 

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