In airlift bioreactors, medium of vessel is divided into two interconnected zones by means of a baffle or draft tube. Air is pumped in one of two zones. The or zone that receives no gas is down comer.

Based on operation, reactors are classified as batch and continuous. Batch reactors follow non-continuous mode of reaction. While in a continuous flow reactor, continuous reaction takes place.

Grit chambers are of type horizontal flow, aerated, vortex. There’s no type such as vertical flow. These protect mechanical equipment from abrasion and reduces formation of heavy particles in pipes.

The term “biosolids” was introduced by Water Environment Federation in U.S. in 1998. However, some people argue that term is a form of “propaganda” with aim to hide fact that sewage sludge may also contain substances that could be harmful to environment when treated sludge is applied to land.

Aerobic-anaerobic ponds consist of three zones: a surface zone of algae and aerobic bacteria in a symbiotic association; an intermediate zone populated with facultative bacteria (aerobic or anaerobic); and an anaerobic bottom zone where settled organic solids are decomposed by anaerobic bacteria.

Filtration is to removal of fine particle sand dissolved solids where fine sand layer and coarse sand layer below serves as media to remove colloidal solids and water remains completely free of solids.

The percentage of dry solids for a primary sludge is assumed as 5-7% at outlet. In most cases, it is considered as 6%. In case of sludge is from flocculator or clarifier percentage of solids is considered as 2-4%.

Ultrafiltration is usually prior to reverse osmosis. This is to remove TSS present in sample. Reverse osmosis reduces total dissolved solids in water sample.

The clear space between bars for a mechanical screen would be in range 15-75mm. The clear space between bars for a hand screen would be 25-50mm. The slope from vertical for se screens would range from 0-30 degree.

Generally size of belt in belt filter press is 0.5-3.5 m. In most cases, a belt of width 2m is used. Sludge loading rate varies from 90-680 kg/mh depending on sludge type.