Together with population growth and industrialization, wastewater treatment became an international issue with enormous scope. Aquatic life conservation in lakes and rivers depends on the accurate treatment of wastewater.
Mathematical modelling is a method by it’s own that is capable to determine and keep wastewater quality standards at optimal levels while minimizing pollution. Benefits of activated sludge process Modeling include:
• Optimize existing plant processes
• Evaluate future plant design changes
• Perform detailed sensitivity studies
• Compare seasonal variations in plant operating conditions
• Boost staff training capabilities
• Enhance intuitive decision making
Modeling software allows engineers and operators to experience a broad range of system conditions, monitor the consequences of altering plant processes and perform sensitivity studies on operating conditions and influent characteristics.
Plant simulations are an invaluable aid for process evaluation and sensitivity studies, enabling the study of processes, design changes, contingencies and seasonal variations more quickly, economically and thoroughly than is possible in a real plant.
By increasing the base of experience and enhancing intuitive decision making, modeling facilities can play an essential role in assisting municipal wastewater plants to comply with the increasing quality and regulatory requirements of today’s environment.
1-Wastewater Treatment Plant Components:
1.1 Introduction:
Wastewater is the flow of used water from our community. It is 99.97% water by mass. The remaining 0.03% is organic and inorganic material which is either dissolved or suspended in the water. The concentrations of these materials are very small and are measured in milligrams per liter of water.
Wastewater treatment is a series of processes which remove the pollutant materials from the wastewater, such as solids, oil and greases, detergents, nutrients, heavy metals and bacteria. These processes are carried out at Wastewater Treatment Plants (WWTPs). The end products of the treatment are treated wastewater and biosolids. A by-product of processing the sludge is biogas, which in turn can be used as an energy source.
1.2 Wastewater Treatment Processes:
Wastewater treatment consists of many unit processes which are either physical, biological or chemical processes. These are traditionally referred to as primary, secondary and tertiary treatment respectively:
–Preliminary Treatment:
Preliminary treatment to screen out, grind up, or separate debris is the first step in wastewater treatment. Sticks, rags, sand, gravel, toys, etc., are removed at this stage to protect the pumping and other equipment in the treatment plant. Treatment equipments such as bar screens, comminutors and grit chambers are used as the wastewater first enters a treatment plant. The collected debris is usually disposed of in a landfill.
– Primary Treatment:
Primary treatment is the second step in treatment as shown in Fig (1), and separates suspended solids and greases from wastewater. Wastewater is held in a quiet tank for several hours allowing the particles to settle to the bottom and the greases to float to the top. The solids drawn off the bottom and skimmed off the top receive further treatment as sludge. The clarified wastewater flows on to the next stage of wastewater treatment. Clarifiers and septic tanks are usually used to provide primary treatment.
– Secondary Treatment:
Secondary treatment consists of biological processes to oxidize carbonaceous matter using micro-organisms in an aerobic (oxygen rich) environment. There are many technical variations of this process such as ponds, trickling filters and activated sludge processes. The process can also be used to reduce the level of nutrients such as nitrogen and phosphorus.
– Final Treatment :
Final treatment focuses on removal of disease-causing organisms from wastewater. Treated wastewater can be disinfected by adding chlorine or by using ultraviolet light. High levels of chlorine may be harmful to aquatic life in receiving streams. Treatment systems often add a chlorine-neutralizing chemical to the treated wastewater before stream discharge.
– Advanced Treatment:
Advanced treatment is necessary in some treatment systems to remove nutrients from wastewater. Chemicals are sometimes added during the treatment process to help settle out or strip out phosphorus or nitrogen. Some examples of nutrient removal systems include coagulant addition for phosphorus removal and air stripping for ammonia removal.
– Sludge Treatment:
Sludge is generated through the sewage treatment process. Primary sludge, material that settles out during primary treatment, often has a strong odor and require treatment prior to disposal. Secondary sludge is the extra microorganisms from the biological treatment. The goals of sludge treatment are to stabilize the sludge and reduce odors, remove some of the water and reduce volume, decompose some of the organic matter and reduce volume, kill disease causing organisms and disinfect the sludge. Table (1) Shows classifications of wastewater treatment processes.
