Sewage Or Wastewater Treatment Process.
Sewage Or WasteWater treatment processes are primarily designed to purify industrial wastewater, household wastewater, and sewage water so that all of this water can be reused and does not harm our environment, its contain physical, biological, and chemical process.
Types of sewage water or wastewater treatment processes are;
In-fluent: Untreated Industrial Wastewater.
Effluent: treated Industrial Wastewater.
Sludge: Solid part separated from Waste Water.
Objectives of wastewater treatment plant:
Reduction of organic contains which are recalcitrant to biodegradation and may be toxic or carcinogenic.
Removal/reduction of nutrients (N, P) to reduce pollution of receiving surface waters or groundwater, if the effluents are applied onto land.
Removal/reduction of inorganic matters.
Removal of inactive pathogenic microorganisms and parasites.
Classes Of Wastewater Contaminate:
Suspended solids, biodegradable organics, refractory Organics, pathogens, nutrients, heavy metal, dissolved inorganics.
Tertiary (or advanced).
Physical: Screening, sedimentation, filtration, skimming, Equalization, etc.
Chemical: Coagulation, chlorination, adsorption, ion exchange, etc.
Biological: Activated sludge process, Trickling Filters, MBBR, etc.
=> Preliminary Treatment Level:-
Physical separation of big size impurities like cloth, Plastics, wood logs, papers, etc.
Common Physical Unit Operations At Preliminary Treatment Level Are:-
A screen with openings of uniform size is used. To remove coarse solids and other large materials often found in raw Wastewater. Removal of these materials is necessary to enhance the operations and maintenance of subsequent treatment units. Generally, a maximum of 10 mm is used.
Physical water treatment process using gravity to remove suspended solids from water.
The effluents do not have similar concentration at all the time, the pH will vary time to time.
Effluents are stored from 8 to 12 hours in the equalization tank resulting in a homogeneous mixing of affluence and helping in neutralization.
It eliminates shock loading on the subsequent treatment system.
Continuous mixing also eliminates the setting of solids within the equalization Tank.
Reduces SS, TSS.
=> Primary Treatment Level:-
Removal of floating and settleable materials such as suspended solids and organic matter.
Both physical and chemical methods are used at this treatment level.
Chemical Unit Process:
Chemical processes use the addition of chemicals to the Wastewater to bring about changes in its quality.
pH control, coagulation, chemical precipitation and oxidation,
To adjust the pH in the treatment process to make Wastewater pH neutral.
For acidic wastes (low pH):
Sodium hydroxide(NaOH), Sodium carbonate (Na2CO3), Calcium hydroxide (Ca(OH)2) or CaCO3, etc.
For alkali wastes (High pH):
Sulfuric acid (H2SO4), Hydrochloric acid (HCL), etc.
Chemical Coagulation And Flocculation:-
Coagulation refers to collecting minute solid particles dispersed in a liquid into a larger Mass.
Chemical coagulants like Al2(SO4)2 (also called alum) or Fe2(SO4)2 are added to wastewater to improve the attraction among fine particles so that they come together and form large particles called Flocs.
A chemical flocculant (usually a polyelectrolyte) enhances the flocculation process by bringing together particles to form larger flocks which settle out more quickly.
Flocculation is added by gentle mixing which causes the particles to collide.
The solid particles settle down and collected separately and dried this reduced SS, TSS.
Flocculation provides slow mixing that leads to the formation of macro flocs, which then settle out in the clarifier zone.
The settled solids’ primary sludge is pumped into sludge drying beds.
=> Secondary Treatment Level:-
Biological and chemical processes are involved in this level.
The aerobic treatment process takes place in the presence of air (Oxigen). Utilizes those microorganisms (aerobes), which use oxygen to assimilate Organic impurities convert them into carbon dioxide, water, and biomass.
Anaerobic treatment processes take place in the absence of air (oxygen). Utilizes microorganisms (anaerobes), which do not require air ( molecular/free oxygen) to assimilate organic impurities. The final products are methane and biomass.
Common Biological Processes:-
Trickling filter or bio-filter and
Activated sludge processes,
Rotating biological contractors (RBC),
Moving Bed Biofilm Reactor (MBBR).
01. Activated Sludge Process:-
Activated Sludge is defined as a suspension of microorganisms, both living and dead, in wastewater. The microorganisms activated by the input of air (oxygen). This process consists essentially of anaerobic treatment that oxidizes organic matter to CO2, H2O, Nh3 new cell biomass. Air is provided by diffused or mechanical aeration. The microbial cells form flocks that are allowed to settle in a clarification tank.
02. Trickling Filters:-
The trickling filter process consists of four components-
A circular or rectangular tank,
Waste Water distributor,
An underdrain system,
A finals clarifier.
In this process microorganisms introduced to grow on the filter media (Rocks, Plastics, or other coarse material). The row Waste trickling down over the filter media while air is blown up through the filter. After passing through the trickling filter, the wastewater then passes through a clarifier where sludge settles out. Like the activated sludge process, nutrients are added to accelerate organism growth.
03. Moving Bed Biofilm Reactor (MBBR).
The MBBR system consists of an aeration tank (similar to an activated sludge tank) with special plastics carriers that provide a surface where a biofilm can grow. The carriers are made of material With a density close to the density of water (01gm/cm3). An example is a high-density polyethylene (HDPE) which has a density close to (0.95 gm/cm3). The carrier will be mixed in the tank by the aeration system and thus will have good contact between the substrate in the influent wastewater and the biomass on the carriers. MBBR systems don’t need recycling of the sludge, which is the case with activated sludge systems.
Some other advantages compared to activated sludge systems are:
Higher effective sludge retention time (SRT) is favorable for nitrification.
Responds to load fluctuation without operator intervention.
Lower sludge production.
Less area required.
Process performance independent of secondary clarifier (due to the fact that there is no sludge return line).
04. Rotating Biological Contactor (RBC):
Biological growth is attached to the surface of the disk and forms a slime layer. The discs contact the wastewater with the atmosphere for oxidation as it rotates. The rotation helps to slough excess solids. The disc system can be staged in series to obtain nearly any detention time or degree of removal required. Since the systems are staged the culture of the later Stages can be acclimated to the slowly degraded materials.
=> Tertiary / Advanced Treatment Level:-
In Sewage Or Wastewater Treatment Process, Tertiary or advanced wastewater treatment is employed when specific Wastewater constituents which cannot be removed by secondary treatment must be removed. Individual treatment processes are necessary to remove nitrogen, phosphorus, additional suspended solids, refectory organics heavy metals, and dissolved solids. However advanced treatment processes are sometimes combined with primary or secondary treatment ( chemical addition to primary clarifier or aeration basins to remove phosphorus).
Air stripping step:-
Remove Ammonia, Nitrogen, or Other Gases.
Converts Ammonia to Nitrate.
NH4+ ⇒ Nitrosomonas Bacteria/Oxidation ⇒ NO2- ⇒ Nitro Bacteria/Oxidation ⇒ NO3-
DO Must >2.0 ∼ 5.0 mg/l,
pH = 6.5 ∼ 9.0,
Temp = 15 to 35°C,
SV (%) =30% to 40%
NO3- ⇒ ⇒ Enterobacter (NO3-)/Alcaligenes bacteria(NO2-) ⇒ ⇒ N2 + H2O.
Destroy pathogens and other diseases causing organisms.
Remove free and combined chlorine by adding sodium bisulfate just before its discharge.
Removal of heavy metals.
Reverse osmosis and ion exchange process:-
Remove dissolved inorganic materials.
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