VARIOUS WASTE WATER TREATMENT SYSTEMS
Physical Treatment Systems
Screening
Screening is to remove solids through a series of bars or net. The sizes of solids removed are dependent on the size of opening employed. Screening is normally used at the beginning stage of the waste water treatment plant to remove large sizes of solids that could cause problem to the waste water treatment plant and its equipment.
Sedimentation
Sedimentation or settling is one of the methods used in clarification. Clarification is a process of separating suspended solids from the waste water. Sedimentation allows the suspended solids to sink and settle at the bottom, thus producing clear supernatural.
Floatation
Floatation is another method normally used in clarification. Floatation allows the suspended solids to float at the surface, thus producing clear supernatant. Floatation is normally mechanically-aided. One of the many floatation systems that are widely used is Dissolved Air Floatation.
Pressurize Filtration
Pressurize filtration are designed as tertiary treatment or polishing for pre-treated water or wastewater. Medium will feed through media filling under pressurized condition and achieve contaminants removal base on types of medias filled. The media configuration consists of mono-media anthracite or sand, dual media anthracite and sand, granular activated carbon and sand, or tri-media for applications with demanding effluent quality requirements.
Membrane Filtration
Membrane filtration uses membrane as the filtration media. Membrane filtration can produce better quality of water compare to sand filtration. Membrane filtration can be divided into ultra-filtration, nano-filtration and reverse osmosis filtration.
Evaporation
Evaporation is a process of converting the water component in the waste water into water vapor and then converting the water vapor back to water, therefore leaving behind the solid impurities.
Chemical Treatment Systems
Chemical Oxidation
Chemical oxidation is a process of oxidising the pollutants by chemical addition, therefore reducing the BOD and COD. Chemical oxidation is more effective in BOD and COD removal that the biological treatment but has higher operation cost.
Chemical Precipitation
Chemical precipitation is a process of converting dissolved solids into suspended solids and bonding the solids together to form bigger particles that can be easily removed by chemical addition. Chemical precipitation is normally used to remove heavy metals as well as suspended solids in the waste water.
Activated Carbon Adsorption
Activated carbon adsorption is a process of attracting and capture suspended solids onto the surface of the activated carbon. Activated carbon adsorption can be used to remove BOD, COD and suspended solids as well as some of other impurities.
Chlorination
Chlorination is normally employed for disinfection of the treated effluent. The process involves injecting chlorine gas or liquid into the treated effluent killing the microorganisms in it. Beside disinfection, chlorination is also one of the chemical oxidation methods.
Ozonation
Ozonation is a process of employing ozone gas to either disinfect the treated effluent or oxidize the pollutants in the wastewater. Ozonation is very effective in both disinfection and oxidation. However it capital, operation and maintenance costs are high.
Biological Treatment Systems
a. Trickling Filter
Trickling Filter is a type of attached growth biological treatment systems that is used mainly to remove BOD and COD. It can also be used to remove ammoniacal nitrogen that is present in the wastewater. A clarifier is required thereafter to separate the sludge produced from the treated effluent.
b. Activated Sludge Process
Activated Sludge is one of the many types of suspended growth biological treatment system is used to removed BOD and COD as well as ammoniacal nitrogen. Over the years, the Activated Sludge has been improved and modified into many other systems. A clarifier is required thereafter to separate the sludge produced from the treated effluent.
– Extended Aeration
Extended Aeration is one of the suspended growth biological treatment systems that are modified from the Activated Sludge. It is modified to provide a more stable system and less sludge production. However, it requires bigger footprint compare to the Activated Sludge. This system also requires a clarifier to separate the sludge produced from the treated effluent.
– Complete Mix Aeration
The quantity of the biomass required depends strongly on the load and the effluent quality to be met. Once the quantity of the biomass is known, the oxygen command (OC) can be determined and the aeration tank can be designed. The aeration tanks can be subdivided in complete mix, plug flow and circulator systems. In plug flow systems mixing is mainly concentrated in some parts of the tank, while in complete mix and circulator systems the mixing affects the whole tank. Therefore the concentrations of oxygen and pollutants differs much more in plug flow systems than in complete mix systems. This has important effects on the biological process.
c. Sequential Batch Reactor
Sequential Batch Reactor is another modified Activated Sludge system that provide smaller footprint than the Activated Sludge system. It is very versatile and can be adjusted to suit different conditions. The system is automated. This system eliminates the requirement of a clarifier.
d. Membrane Bio-Reactor (MBR)
Membrane Bioreactor combines the Activated Sludge with membrane filtration, therefore eliminates the need for a clarifier. Because this modified system is able to operate at a more concentrated condition, it reduces the size of the treatment system and the footprint is smaller than the Sequential Batch Reactor. The treatment efficiency is also higher than any other biological treatment systems.
e. Submerged Aerator Filter
The submerged aerated filter (SAF) is constructed in a very similar way to the BAF plants except that they have a settling tank to clarify the solids that slough from the filter rather than using back-washing. The plant has a 1-4m deep bed of filter media on which to grow a biomass.
