Treatment Methods and WWTP Sample Design

There are three types of treatment processes to treat wastewater, including physical treatment, chemical treatment, and biological treatment. Wastewater treatment plants (WWTP) usually combine at least two types, depending on the composition of the wastewater. For most contaminants, there is more than one treatment option, and the different methods in question will differ in effectiveness, as well as investment and operation cost involved.

If the WWTP is designed properly and based on an analysis of the wastewater flow and characteristics, the WWTP will effectively reduce contaminant levels to be legally compliant, and thereby reduce river contamination. Effects of wastewater quality and quantity fluctuations are considered highly influential in the selection of the WWTP.

Physical treatment methods

Physical methods are used to remove large objects and non-degradable materials from wastewater. This can prevent pumps and equipment from damage. Processes like screening (Bar screen) sedimentation and skimming (Grit chamber) are used to remove the solids.

One of the main techniques of physical wastewater treatment includes sedimentation, which is a process of suspending the insoluble/heavy particles from the wastewater. Once the insoluble material settles down at the bottom, the pure water can be separated.

Another effective physical water treatment technique includes aeration. This process consists of circulating air through the water to provide oxygen to it. Filtration, the third method, is used for filtering out all the contaminants. Special types of filters can be used to pass the wastewater and separate the contaminants and insoluble particles present in it. The sand filter is the most commonly used filter. The grease found on the surface of some wastewater can also be removed easily through this method.

Source: Bar Screen, India Mart

Chemical treatment methods

Source: Grit Chamber, India Mart

The chemical coagulation process involves destabilizing wastewater particles so that they aggregate during chemical flocculation. This treatment involves the use of chemicals in water. Chemical precipitation is the most common method for removing dissolved metals from a wastewater solution containing toxic metals. To convert the dissolved metals into solid particle form, a precipitation reagent is added to the mixture. A chemical reaction, triggered by the reagent, causes the dissolved metals to form solid particles. However, it can be difficult to create hydroxides from dissolved metal particles in wastewater because many wastewater solutions contain mixed metals. Fine solid particles dispersed in wastewater carry negative electric surface charges (in their normal stable state), which prevent them from forming larger groups and settling.

After larger particle groups are formed, sedimentation can be used to remove the particles from the mixture.

With the introduction of an oxidizing agent during chemical oxidation, electrons move from the oxidant to the pollutants in wastewater. The pollutants then undergo structural modification and become less destructive compounds. Alkaline chlorination uses chlorine as an oxidant against cyanide.


Biological treatment method

Biological treatment processes are used to break down the organic matter present in wastewater, such as soap, human waste, oils, and food. Microorganisms metabolize organic matter in the wastewater in biological treatment. In ad­di­tion, bio­lo­gical treat­ment meth­ods prove to be the best solu­tion for the pulp-and-pa­per in­dustry, laun­dry fa­cil­it­ies, tex­tile pro­duc­tion, the food in­dustry, and ag­ri­cul­ture. Bio­lo­gical wastewa­ter treat­ment sys­tems provide solu­tions for the re­moval of or­ganic wastewa­ter con­tents, am­monium, and ni­trate con­tam­in­a­tions. It can be divided into mainly two categories:

Aerobic processes: Bacteria decomposes the organic matter and converts it into carbon dioxide that can be used by plants. Oxygen is used in this process. Wastewater from the primary treatment phase enter an aeration tank, where it is aerated in the presence of suspended (freely floating) aerobic microorganisms. The organic material is broken down and consumed, forming biological solids which flocculate into larger clumps or flocs.

The suspended flocs enter a settling tank and are removed from the wastewater by sedimentation. Activated sludge treatment systems typically have larger space requirements and generate large amounts of sludge with associated disposal costs, but capital and maintenance costs are relatively low compared to other options.

In Anaerobic processes, fermentation is used for fermenting the waste at a specific temperature. Us­ing mi­croor­gan­isms in a spe­cial re­actor ab­sent of at­mo­spheric oxy­gen, the pol­lut­ants are chemic­ally trans­formed into bio­gas. Bio­gas is a gaseous mix­ture that primar­ily con­tains meth­ane and car­bon di­ox­ide. It can be used as an en­ergy source in pro­duc­tion, typ­ic­ally in a co­gen­er­a­tion unit, to gen­er­ate power and heat. This par­tic­u­lar ver­sion of a bio­gas plant can be used for the treat­ment of wastewa­ter in the food-and-bever­age in­dustry.

Wastewater Treatment Plant- Sample Designs

Here is WWTP sample designs for Dairy,Vermicelli, Bakery, Vinegar & Sauce, and Preservative fruits processing, which were developed by Tha Bar Wa project supports.

Based on the experimental studies by a design project team, the effluent from Dairy Processing and Vermicelli processing can be treated by either chemical or biological treatment method. However, chemical treatment is not feasible for Vinegar & Sauce processing and Preservative fruits processing. For Bakery processing, there needs to be a combination of chemical and biological treatment methods.

For Dairy Processing (Discharge Volume – 10 m3/day, Maximun COD – 3000 mg/l)

WWTP Design by Chemical method 

WWTP Design by Biological method

For Vermicelli Processing (Discharge Volume – 7.6 m3/day, Maximun COD – 2700 mg/l)

 WWTP Design by Chemical method

            WWTP Design by Biological method

For Vinegar & Chili Sauce Processing (Discharge Volume – 5.4 m3/day, COD – 3000 mg/l)

 WWTP Design by Biological method

For Bakery (Discharge Volume – 15 m3/day, Maximun COD – 4000 mg/l)

 WWTP Design by Chemical & Biological method

For Preserved Fruit Processing (Discharge Volume – 25 m3/day, Maximun COD – 7000 mg/l)

 WWTP Design by Biological method

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