Effluent or Water Treatment Plant (WTP/ETP)

Effluent or Water Treatment Processes (WTP/ETP)

Criteria of Water: Criteria are requirements that a water source must satisfy in order to be used for a particular purpose. In other terms, criteria are specifications indicating the minimum quality level that the water must have to support a predefined use. Criteria are important in defining the characteristics of inlet water streams.

    

Different criteria exist for different water uses:

Water Use                              Water Quality Criteria

Drinking Water           : Microbial count, pH, color, turbidity,Organic content, pH, toxic compounds,dissolved oxygen, Temperature, Salt, Metals, etc.

Industrial                  : pH, suspended solids, temperature, dissolved oxygen.

Swimming, fishing       : Similar to drinking water criteria but not as stringent.
Cooling, navigation     : Floating solids, suspended solids and pH.

Standards of Water:   Standards are the characteristics that the waste water must satisfy to be lawfully discharged to a receiving body of water or to a POTW. In other terms standards refer to the quality of the outlet water, after its intended use.

Criteria vs. Standards of water: 

Types of Discharges of Industrial Wastewaters:

1. Direct industrial discharges to freshwater or saltwater streams.

2. Industrial discharges to a Publicly Owned Treatment Works (POTW).

Classification of Wastewater Treatments Processes:

 

Pretreatment: Pretreatment usually refers to any treatment the wastewater is subjected to before entering a conventional wastewater treatment plant, such as a POTW.  Pretreatment typically involves operations connected to separation of very coarse or easily separable materials and/or water conditioning before discharging to a treatment plant (e.g., equalization).

Pretreatment of industrial wastewaters commonly refers to any treatment required to make the water acceptable for discharge to a POTW.

It is common practice to classify wastewater treatment processes in three categories:

i) Primary treatment: Primary treatment pertains to the removal of easily separable materials such as oils, floating solids, or quickly settling solids, and the preparation of the wastewater (e.g., pH adjustment) for subsequent treatments. Primary treatment involves operations such as equalization, neutralization, sedimentation, oil separation, and floatation.

ii) Secondary treatment: Secondary treatment is typically the most important part of the process, and is used primarily to remove the bulk of the suspended solids, organic materials (both hazardous and non-hazardous), and other soluble materials. Biological treatment constitutes the process of choice during secondary treatment of wastewater.

iii) Tertiary treatment: Tertiary treatment, involving processes such as sand filtration,   reverse   osmosis,   adsorption,   and electro dialysis, is used (if necessary) to remove any residual contaminants not eliminated during the previous treatment processes.

Sludge treatment and disposal: Sludge treatment and disposal includes all the operations connected with the concentration, stabilization, and final disposal of the semi-solid sludge produced during the primary, secondary and tertiary treatments. Sludge treatment and disposal includes operations such as gravity thickening, air flotation, aerobic and anaerobic digestion, chemical or heat stabilization, centrifugation, drying, filtration, incineration, wet oxidation, and disposal in landfill or on soil.

Typical Activated Sludge Treatment Plant: 


 

Unit Operations in Wastewater Treatment:

Industrial wastewaters typically contain a number of heavy metals, halogenated organic compounds, and other priority pollutants. Therefore, industrial facilities must process their wastewaters before discharging to either a body of water (under NPDES permit) or a POTW.

Typically, these pollutants are removed from the wastewater using a variety of pretreatment processes, especially physical and chemical processes.

Examples include coagulation, flocculation precipitation, sedimentation, filtration, ion exchange, air stripping, membrane separation activated carbon adsorption, wet oxidation and photochemical oxidation.

Example of Physical-Chemical Wastewater Treatment Process:

 

Typical Physical-Chemical Treatment Plant:

Physical Separation Processes:  

 Activated carbon adsorption 

 Distillation

 Electrolytic recovery

 Hydrolysis

 Ion exchange

 Solvent extraction

 Membrane separation technologies

 Air stripping and steam stripping

 Thin film evaporation

 Freeze-crystallization

Operations Involved in the Removal of Suspended Solid in Wastewaters:

 Screening and comminution

 Grit removal

 Sedimentation

 Floatation

 Filtration and centrifugation

 Coagulation/sedimentation

Operations Involved in the Removal of Biodegradable Material in Wastewaters:

 Activated sludge treatment

 Trickling filters

 Rotating biological contactors (RBC)

 Aerated lagoons

 Anaerobic lagoons

 Facultative lagoons

 Anaerobic treatment

Operations Involved in the Removal of VOCs in Wastewaters:

 Adsorption

 Absorption

 Air stripping

 Condensation

 Freezing

 Incineration

 Combustion

Operations Involved in the Removal of Nitrogen in Wastewaters:

 Biological nitrogen utilization in activated sludge process

 Biological nitrification and denitrification

 Air stripping of ammonia

 Chlorination

 Adsorption

Operations Involved in the Removal of Phosphorus in Wastewaters:

 Biological phosphorus utilization in activated sludge process

 Chemical additions (metal salts or polymers)

 Lime addition

 Biological/chemical treatment

Operations Involved in the Removal of Organic Priority Pollutants in Wastewaters:

 Aerobic biological treatment

 Anaerobic biological treatment

 Biological treatment/activated carbon adsorption (PACT)

 Adsorption

 Chemical oxidation

Operations Involved in the Removal of Heavy Metals and Dissolved Inorganic Solids in Wastewaters:

 Chemical oxidation/reduction and precipitation

 Ion exchange

 Reverse osmosis

 Ultrafiltration

 Electrodialysis

Example of Heavy Metal Remova :    

Example of Organic Chemical Removal:

Classification of Hazardous Waste Treatment Processes:

 Physical

 Chemical

 Biological

 Thermal

 (Disposal)

Physical and Chemical Processes for Hazardous Waste Treatment:

 Filtration and separation

 Chemical precipitation

 Photolysis

 Chemical oxidation and reduction

 Dehalogenation

 Ozonation

 Evaporation

 Solidification and stabilization

Biological Processes for Hazardous Waste Treatment:

 Aerobic processes

 Anaerobic digestion

 Composting of industrial wastes

 Land treatment of industrial wastes

 Biodegradation of environmental pollutants

 Enzymatic systems

Thermal Processes for Hazardous Waste Treatment:

 Liquid injection incineration

 Rotary kilns

 Fluidized-bed thermal oxidation

 Hazardous wastes as fuel for burners

 Cement kilns

 Wet oxidation

 Pyrolisis processes

 Oceanic incineration

 Molten glass processes

 Deep shaft wet air oxidation

 Supercritical water extraction

 Plasma systems

 Mobile thermal treatment systems

 Catalytic incineration

 Infectious waste incineration

Land Storage and Disposal of Hazardous Wastes:

 Surface impoundment

 Disposal in mines and sand domes

 Aboveground disposal

 Hazardous waste landfilling

 Subsurface injection of liquid hazardous wastes

Additional Information and Examples on Wastewater and Waste Treatment Processes

References:

 Droste, R. L., 1997, Theory and Practice of Water and Wastewater

Treatment, John Wiley & Sons, New York, pp. 219-242.

 Eckenfelder, W. W., Jr., 1989, Industrial Water Pollution Control,

McGraw-Hill, New York, pp. 33 - 39.

 LaGrega, M. D., Buckingham, P. L., Evans, J. C., 1994, Hazardous

Waste Management, McGraw-Hill, New York, pp. 405 - 444.

 Metcalf & Eddy, 1991, Wastewater Engineering: Treatment, Disposal,

and Reuse, McGraw-Hill, New York, pp. 121 - 146.

 Sundstrom, D. W. and Klei, H. E., 1979, Wastewater Treatment,

Prentice Hall, Englewood Cliffs, NJ, pp. 28 - 40.

 Wentz, C. W., 1995, Hazardous Waste Management, 2nd edition, McGraw-Hill, New York, pp. 153 - 248.