Alkalines are necessary to be added to make pH neutral. The pH in se systems drops very low. Hence addition of such alkaline to increase pH becomes necessary.

There are two types of sludge present, primary and secondary sludge. Primary sludge includes settleable solids removed during primary treatment in primary clarifiers.

The unthickened sludge from extended aeration is around 0.5-1%. The thickened sludge is around 2-3%. In most cases, it is considered 2%.

The volumetric organic loading in Kg COD/ m³ day for an anaerobic sequence batch reactor digestion process is 1.2-2.4. This is loading rate obtained at 30 degree Celsius. This value holds good for suspended growth anaerobic digestion.

These are hydrolysis, acidogenesis, acetogenesis and methanogenesis. In this process, complex proteins and sugars are broken down to form more simple compounds such as water, carbon dioxide and methane.

Water removal is primary means of weight and volume reduction, while pathogen destruction is frequently accomplished through heating during rmophilic digestion, composting or incineration.

Process temperature affects rate of digestion and should be maintained in mesophilic range (95 to 105 degrees Fahrenheit) with an optimum of 100 degrees Fahrenheit.

Sludge treatment technologies that are used for thickening or dewatering of sludge have two products and those are thickened or dewatered sludge and a liquid fraction.

To remove 3% primary sludge usually a 65 sized mesh is used. After degritting, sludge is stored for not more than 4-5 hours. Then sludge is thickened using a centrifuge, gravity belt etc.

The COD level would be around 1500-2000 mg/L if it is subjected to anaerobic digestion. In case if it is around 1300 mg/L n aerobic digestion is carried out. In anaerobic digestion, methane is produced.