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The activated sludge process produces about 70–100 grams per cubic metre (1.9–2.7 oz/cu yd) of waste activated sludge (that is grams of dry solids produced per cubic metre of wastewater treated). 80 grams per cubic metre (2.2 oz/cu yd) is regarded as being typical. [6]
Sludge Volume Index (SVI) is a process control parameter used to describe the settling characteristics of sludge in the aeration tank of an activated sludge process. [1] It was introduced by Mohlman in 1934 and has become one of the standard measures of the physical characteristics of activated sludge processes.
Aerobic digestion is a process in sewage treatment designed to reduce the volume of sewage sludge and make it suitable [1] for subsequent use. [2] More recently, technology has been developed that allows the treatment and reduction of other [3] organic waste, such as food, cardboard and horticultural waste. It is a bacterial process occurring ...
The sludge age may be too low to enable nitrification. The typical control band for the concentration of MLSS is 2 to 4 g/L for conventional activated sludge, or up to 15 g/L for membrane bioreactors. One of the easiest control procedures for activated sludge systems is the Constant Mixed Liquor Suspended Solids method.
Extended aeration agitates all incoming waste in the sludge from a single clarifier. The combined sludge starts with a higher concentration of inert solids than typical secondary sludge and the longer mixing time required for digestion of primary solids in addition to dissolved organics produces aged sludge requiring greater mixing energy input per unit of waste oxidized.
Sludge treatment is focused on reducing sludge weight and volume to reduce transportation and disposal costs, and on reducing potential health risks of disposal options. Water removal is the primary means of weight and volume reduction, while pathogen destruction is frequently accomplished through heating during thermophilic digestion ...
Thermal processes can greatly reduce the volume of the sludge, as well as achieve remediation of all or some of the biological concerns. Direct waste-to-energy incineration and complete combustion systems (such as the Gate 5 Energy System) will require multi-step cleaning of the exhaust gas, to ensure no hazardous substances are released.
One type of system that combines secondary treatment and settlement is the cyclic activated sludge (CASSBR), or sequencing batch reactor (SBR). Typically, activated sludge is mixed with raw incoming sewage, and then mixed and aerated. The settled sludge is run off and re-aerated before a proportion is returned to the headworks.