Household wastewater treatment

 Single dwelling units /Household wastewater treatment

 Used for small scale/domestic waste water treatment. Household wastes are treated in single units eg., Cesspools, Septic tank, lagoons

 Cesspool

•         Temporary arrangement where house sewage is discharged into a tank- in cases, where a well-defined sewage management system is absent

•         Cesspools are constructed underground- it has walls of cylindrical rings with pores with an opening near ground level

•         Wastewater enters through the opening/inlet- liquids escape into the surrounding soil and the solid matter retained in the tank

•         Bottom of the cesspool opens to the underground; suspended solid matter settles down and form sludge at the bottom

•         Water passes out through the pores in the walls to the surrounding soil

•         Organic materials are digested by primarily aerobic and then anaerobic bacteria

•      After a time, the crevices become filled with soil and other solid matter, and the leeching process is interfered with, so occasional cleaning to be done (with strong acids) 

Septic tank

• The septic system is a waste treatment facility on a small scale.
• In a septic tank, household sewage is digested by anaerobic bacteria, and solids settle to the bottom of the tank. The water seeps out  and enters the soil, where bacteria complete the breakdown processes.

  

• Septic tank is prepared under the ground- Small rectangular chambers just below ground level
• Sewage along with toilet content is placed into septic tank where heavier solid wastes settle down to from sludge whereas lighter solids including fats form layer on top of sewage called scum.

§  In septic tank organic compounds in sewage is anaerobically digested by anaerobic microorganisms such as methanogenic bacteria.

§  After anaerobic decomposition, the sludge become stable and inoffensive whereas liquids in sewage percolates into soil from septic tank. Liquid effluent is taken through pipes in distribution box and discarded underground

• Sedimentation as well as biodegradation of sedimented sludge

• Effective for small settings- however effluent should be further treated before disposal since there is no complete removal of pathogens
•  Drainage prevented from entering drinking water supply
• Should be located away from drinking water source
• Should be de-sludged at regular intervals

• Two compartment setup preferred now; more effective sedimentation

 Oxidation ponds

•         Useful if comparatively large area of land is available

•         small ponds/lagoons

•         Organic materials undergo aerobic digestion whereas sediments undergo anaerobic digestion

 Imhoff tank

•         Designed by Karl Imhoff – German Engineer

•         A chamber for receiving and processing of sewage

•    Clarification of sewage occurs by simple settling and sedimentation, followed by anaerobic digestion of the sludge

•         There is an upper chamber for sedimentation, collected solids slide down into a lower chamber and is digested

•         The two chambers are unconnected, with sewage flows in to the upper sedimentation chamber and no flow of sewage in the lower digestion chamber

•         Sludge is collected in the lower chamber where it undergoes anaerobic digestion

•     The lower chamber has separate biogas vents and pipes for the removal of digested sludge, typically after 6-9 months of digestion.

•         It is basically a two-story septic tank- retains the septic tank's simplicity while eliminating many of its drawbacks, such as mixing of fresh sewage and septic sludge in the same chamber.

•         Imhoff cone: used in drinking water treatment facilities