SEWAGE TREATMENT PLANT TECHNOLOGIES

SEWAGE TREATMENT PLANT TECHNOLOGIES

The process of removing contaminants from wastewater and household sewage, both runoff (effluents) and domestic. It includes physical, chemical, and biological processes to remove  the respective contaminants.

Why is it required?

•      It is important that wastewater must be properly treated before release to the environment.

•      Pollution caused by untreated water can have a damaging ecological impact.

•      In extreme cases especially release of pollutant  at catchment areas whereby supply of water is collected for human and household consumption, this could cause toxic accumulation and health impact in the long run.

Need of the hour  

•      Making the treatment more cost effective    

•      Reduction of cost will encourage a more economical and systematic approach

•      Critical due to diminishing water resources

Wastewater treatment plant basically has two stage of separation:-

             -Mechanical separation(solid wastes and oil removal)

             -Chemical separation(aerobic and anaerobic waste removal)

  Preliminary Wastewater Treatment. 

Removal of heavy settle able inorganic solids or the floating materials.

- This treatment reduces the BOD of the wastewater,

 by about 15 to 30%.

Primary Wastewater Treatment

The suspended solids and organic matter is removed from the wastewater.

-The liquid effluent from primary treatment, often contains a large amount of

suspended organic materials, and has a high BOD (about 60% of original).

-This removal is usually accomplished by physical operations such as sedimentation

in Settling Basins.

Secondary Wastewater Treatment

The removal of biodegradable organics and suspended solids.

-Through biological decomposition bacteria decomposes the fine organic matter into a clearer effluent .

The organic matter is decomposed (oxidized) by aerobic bacteria in,

       Aerobic biological units

-Filters (intermittent sand filters as well as trickling filters),

-Aeration tanks, with the feed of recycled activated sludge

  -Oxidation ponds and aerated lagoons.

The organic matter is destroyed and stabilized by anaerobic bacteria in,

         - Anaerobic biological units

                          -Anaerobic lagoons,

                          -Septic tanks,

                          -Imhoff tanks,

-The effluent contain a little BOD (5 to 10% of the original).

-The organic solids/ sludge separated out is disposed off by stabilizing under

anaerobic conditions in a Sludge digestion tank.

Tertiary/ Advanced Wastewater Treatment and Wastewater Reclamation:  

To remove constituents including nutrients, toxic compounds, organic material, suspended solids and particularly to kill the pathogenic bacteria.

     -This is carried out, while using the river stream for collecting water for re-use or for water supplies for purposes like industrial cooling and groundwater recharge.

Nutrient Removal or Control:-  

The nutrients of principal concern are nitrogen and phosphorus ,removed by biological, chemical, or a combination of processes.

     

This is important for several  reasons:

  -To confined bodies of water, cause or accelerate the process of eutrophication.

  -Wastewater discharges to flowing streams tax oxygen resources for the removal               of Nitrogenous BOD thereby depleting the aquatic life.

  -for groundwater recharging if its used indirectly could cause health problems.

Toxic Waste Treatment / Specific Contaminant Removal

-chemical coagulation, flocculation, sedimentation, and filtration reduces many toxic substances  such as heavy metals.

     -Wastewaters containing volatile organic constituents may be treated by air stripping or by carbon adsorption other small containments can be removed by ion exchange.

New Directions  

Instrumentation and Control in Waste Water Treatment Facilities

•      Typical process disturbances include process inputs and conditions such as variable flow rates, chemical and biological composition, temperature and density.

•      Instrumentation and automatic control allow continuous monitoring of process variables, rapid transfer of data to the operator or manager, and immediate automatic execution of corrective measures when needed.

•      The use of instrumentation and automatic control is growing nowadays, owing to the multitude of benefits that they confer in terms of process improvement, equipment performance, and convenience to personnel.  

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Artificial Intelligence  

·         New technological advances have made it feasible to use artificial intelligence for the monitoring and control of operations in a waste-water treatment plant.

·         Systems have been developed for that purpose, Like, expert systems and fuzzy control systems.

Application in the waste water treatment plant  

·         Many factors determine the need for instrumentation and control elements in waste-water systems viz., size of the facility, hours of manned operation, complexity of the process, reliability requirements, and availability of instrumentation maintenance personnel.

•      Most of the resultant decisions are made on an economic basis.

•      The decision to use instrumentation, automation, and control in waste-water treatment systems should be made early in the conceptual design phase of a facility, as it influences the design of the entire system; the size and configuration of existing vessels, tanks, channels, pipes and mechanical equipment.

•      There is a wide range of variables that can be monitored within each treatment unit used at the facility.  

Alternative options

Onsite Sanitation Options

The Conventional off-site excreta disposal and treatment method of water borne sewerage is an expensive option which is not affordable by low income communities and rural people. Hence, other onsite sanitation technologies were developed, practiced and popularized in due course of time. The most important among the two pit pour flush toilet technology developed and popularized by

Sulabh International Social Service Organisation.

Important on-site sanitation techniques are listed below:

1)  Septic tank

2)  Two pit pour flush toilets

3) Trench latrine

4)  Bore hole latrine

5) Dug well latrine

6) Aqua privy

7)  Ventilated improved pit latrine (VIP)  

SULABH EFFLUENT TREATMENT (SET) SYSTEM

•      Sulabh maintains over 5500 public toilet complexes spread all over the country, out of which 104 are linked with biogas plants.

•      The organisation developed a new and convenient technology by which effluent of human excreta based biogas plant turns into a colourless, odourless and pathogen-free liquid manure.

•      The technology is based on filtration of effluent through activated charcoal followed by ultraviolet (UV) rays.

•      The filtration unit makes it colourless, odourless and free from organic particles and UV eliminates bacteria. It reduces BOD, COD of the waste water drastically.

Biogas from human excreta is being used for cooking, lighting, electricity generation and body warming. Besides, the liquid effluent can be used as fertilizer, as it contains good percentage of nitrogen, potassium and phosphate.

ADVANTAGES OF DECENTRALISED SYSTEM OF BIOGAS PLANT WITH SET TECHNOLOGY:

•      Costson collection of sewage and operation and maintenance of the system are very

  low.

•No manual handling of human excreta is required.

•Socially accepted.

•Biogas is used for different purposes.

•Treated effluent is safe to reuse for agriculture, gardening, or discharged into any            water body.

•In draught prone areas treated effluent can be used for cleaning of floor of public toilets.

•If discharged into sewer, pollution load on STP will be much lowered     

DUCKWEED- BASED WASTE WATER TREATMENT 

Duckweed– a small free-floating and fast growth aquatic plant-has great ability to reduce the BOD, COD, suspended solids, bacterial and other pathogens from waste water. It is a complete feed for fish and due to the high content of proteins and vitamins A and C, it is also a highly nutritious feed for poultry and domestic animals.

Sulabh has successfully developed demonstration projects on duckweed-based cost-effective waste water treatment in rural and urban areas with direct economic return from pisciculture. Although duckweed is found in ponds and ditches, due to almost complete absence of any know-how of this technology in the country, the potential of duckweed for the waste water treatment, its nutrient value and economic benefits have not been fully exploited.