Treated Effluent Disposal
Natural Evaporation
Groundwater Recharge
Irrigation
Recreational Lakes
Aquaculture
Municipal Uses
Industrial Uses
Discharge into Natural Waters
Treated Effluent Disposal
The proper disposal of treatment plant effluent or reuse requirements is an essential part of planning and designing wastewater treatment facilities. Different methods of ultimate disposal of secondary effluents are discussed as follows.
Natural Evaporation
The process involves large impoundments with no discharge. Depending on the climatic conditions large impoundments may be necessary if precipitation exceeds evaporation. Therefore, considerations must be given to net evaporation, storage requirements, and possible percolation and groundwater pollution. This method is particularly beneficial where recovery of residues is desirable such as for disposal of brines.
Groundwater Recharge
Methods for groundwater recharge include rapid infiltration by effluent application or impoundment, intermittent percolation, and direct injection. In all cases risks for groundwater pollution exists. Furthermore, direct injection implies high costs of treating effluent and injection facilities.
Irrigation
Irrigation has been practiced primarily as a substitute for scarce natural waters or sparse rainfall in arid areas. In most cases food chain crops (i.e. crops consumed by humans and those animals whose products are consumed by humans) may not be irrigated by effluent. However, field crops such as cotton, sugar beets, and crops for seed production are grown with wastewater effluent.
Wastewater effluent has been used for watering parks, golf courses and highway medians.
The effluent from the secondary treatment facility is stored in a lagoon for approximately 30 days. The effluent from the lagoon is chlorinated and then percolated through an area of sand and gravel, through which it travels for approximately 0.5 km and is collected in an interceptor trench. It is discharged into a series of lakes used for swimming, boating and fishing.
Aquaculture
Aquaculture, or the production of aquatic organisms (both flora and fauna), has been practiced for centuries primarily for production of food, fiber and fertilizer. Lagoons are used for aquaculture, although artificial and natural wetlands are also being considered. However, the uncontrolled spread of water hyacinths is itself a great concern because the flora can clog waterways and ruin water bodies.
Technology is now available to treat wastewater to the extent that it will meet drinking water quality standards. However, direct reuse of treated wastewater is practicable only on an emergency basis. Many natural bodies of water that are used for municipal water supply are also used for effluent disposal which is done to supplement the natural water resources by reusing the effluent many times before it finally flows to the sea.
Effluent has been successfully used as a cooling water or boiler feed water. Deciding factors for effluent reuse by the industry include (1) availability of natural water, (2) quality and quantity of effluent, and cost of processing, (3) pumping and transport cost of effluent, and (4) industrial process water that does not involve public health considerations.
Discharge into Natural Waters
Discharge into natural waters is the most common disposal practice. The self-purification or assimilative capacity of natural waters is thus utilized to provide the remaining treatment.
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