Low cost waste treatment - Waste stabilization Pond

LOW COST WASTE TREATMENT
Low capital and low operating cost sewage treatment methods such as WASTE STABILIZATION PONDS (WSP) technology along with low operational cost sewage treatment method such as Upflow Anaerobic Sludge Blanket (UASB) reactor along with Polishing Pond (PP) are quite effective in BOD removal and fecal coliform removal. Overall efficiency of STPs based on these low cost technologies in terms of BOD removal and FC removal can be improved if effluent suspended solids are controlled by improvement of final outlet structures.

• Waste stabilization pond is a carefully designed structure constructed to contain and facilitate the operation and control of a complex process of treating or stabilizing wastewater. 
• In a waste stabilization pond, the components of in the wastewater are changed so that there is little no or additional change. 
• The purpose of stabilization tanks is to provide operation and control of complex process by stabilizing components under control along with minimizing hazards when discharged. 
• These ponds utilise the same process that occur in a natural pond or lake under controlled conditions.  These processes are carefully designed and constructed. 
• The process involves physical, chemical and biological processes. 
• The physical processes involved are
• evaporation
• seepage
• gas exchange
• sedimentation of solids and 
• U.V. Radiation. 

• Chemical processes involved are
• inorganic activity and
• formation of precipitates. 

• The wastewater treatment process is mostly biological in nature. 
• Bacteria used in treatment of waste are aerobic, anaerobic and facultative type.
• Similarly, the zones in the pond are aerobic, facultative and anaerobic depending on the maximum population of type of bacteria. 
• In the aerobic  zone, bacteria act on soluble organics. 
• During respiration, bacteria act on organic compounds in the presence of oxygen to produce carbondioxide and water. 
• In the facultative zone, organisms utilize dissolved oxygen and adapt to changing circumstances. 
• They continue decomposition during changing conditions. 
• Sufficient oxygen is necessary for efficient treatment and preventing odours.
• The sources of oxygen may be by way of absorption from atmosphere or photosynthesis of aquatic microflora or macroflora.
• The symbiotic cycle can be understood as sunlight from the sun is used by algae for photosynthesis liberates oxygen in the water which is used by bacteria for respiration. 
• The bacteria decomposes organic matter, uses oxygen for respiration and releases carbondioxide which is used by algae for photosynthesis. 
• In the anaerobic zone, the solids settle and the organic matter is stabilised to organic acids by anaerobic bacteria. 
• The organic acids are further metabolised by bacteria into carbondioxide, ammonia, hydrogen sulfide and methane.
• Not all of the settled solids are broken down. 
• The sludge layer increases slowly over the life of the lagoon.
• Presence of wind adds oxygen and increasing mixing. However, it must be controlled by minimizing accumulation of material on, in or around the lagoon.
• Light influences activity in waste stabilization ponds by photosysthesis and disinfection which must be controlled.
• Other factors that affect the treatment process in waste stabilization ponds are -
• The influence of temperature which in-turn is responsible for rate of biological activity
• Growth of algae and saturation of dissolved oxygen.
• Daily fluctuations in temperature, dissolved oxygen and pH also influence the activity in stabilization ponds. 
• Seasonal variations also influence the activity in these ponds.  

Advantages of this technique are -

• Economical to construct and operate,
• Low monitoring and control requirements,
• Rapid recovery from shock loads,
• Low energy and Chemical Usage,
• Low mechanical failure,
• Minimal sludge disposal, and
• long life. 

Disadvantages of this method are -

• Large requirement of land,
• Low control options,
• Operations are dependent on climate,
• Presence of high suspended solids, 
• Seasonal odours,
• Possible ground water contamination,
• Not very useful for high loading situations.

Good results can be achieved if -

• Process is in balance,
• Facility is properly designed, 
• Process is controlled and System is maintained. 

 A very important tool of design and operation is the ability and use of SERIES OR PARALLEL flow through the system. Series operation involves placing majority of the load on the first cell. Parallel operations involve dividing organic load between atleast two cells.


The term loading refers to the amount applied to the treatment process. It is related to the size of the system. It refers to the surface area of the system. Loading may be - Population loading, -Hydraulic loading and Organic loading. Population loading is the ratio of Population served to Area of the lagoon (ha). Hydraulic loading is the volume of wastewater to be treated. Detention time is the ratio of volume to influent rate