Sewage Treatment :
Sewage is a contaminated water discharged from domestic, industrial, municipal and other sources. Sewage treatment plant is designed to remove the contaminants from the water so that they can be recycled and reused. Both organic and inorganic contaminants are removed by using different physical, chemical and biological processes. The treatment plant produces waste stream which is a treated effluent and a solid waste or sludge which are reused.
Sewage is collected and transported via a network of pipes and pump stations to a municipal treatment plant. Normally three stages are involved for treating sewage- primary, secondary and tertiary. After being treated the effluent can be reused to flush toilets, greening parks, or for recharging ground water.
Sewage is collected and transported via a network of pipes and pump stations to a municipal treatment plant. Normally three stages are involved for treating sewage- primary, secondary and tertiary. After being treated the effluent can be reused to flush toilets, greening parks, or for recharging ground water.
Pre-Treatment of Sewage Water
In the process of pre treatment, the waste is collected from the sewage wastewater before putting it into pumps. THis actually protects the pumps from clogging and other such problems. In this sewage treatment the methods of screening, grit removal, fat and grease removal are practized.
Stages of Sewage Treatment
Sewage treatment is accomplished in three stages which are as follows:
Primary Sewage Treatment
In a primary sewage treatment wastewater is relieved from the contaminants like coarse sands, pebbles, organic and inorganic wastes, fatty substances etc. The wastewater consist of large objects like rags, cans, tin etc which are removed by screen. This is necessary because the presence of these objects can harm the sensitive parts of the plant. Followed by the screen there is a a grit chamber that are used for removing sand and other heavy inorganics. The materials so collected in the grit chamber are collected and bagged for disposal.
The liquid being freed from grit is passed to through the fixed or rotating screens in order to get rid of floating and larger materials. Some plants use sedimentation stage in which the sewage is passed through large tanks which are called as primary clarifiers or primary sedimentation tanks. In these tanks floating materials are removed and homogeneous liquid is ready for the biological treatment whereas, the sludge is is separated for the separate treatment. Primary tanks consist of scrapers that drive the sludge towards a hopper in the base of the tank. From here the sludge is pumped out for treatment.
The liquid being freed from grit is passed to through the fixed or rotating screens in order to get rid of floating and larger materials. Some plants use sedimentation stage in which the sewage is passed through large tanks which are called as primary clarifiers or primary sedimentation tanks. In these tanks floating materials are removed and homogeneous liquid is ready for the biological treatment whereas, the sludge is is separated for the separate treatment. Primary tanks consist of scrapers that drive the sludge towards a hopper in the base of the tank. From here the sludge is pumped out for treatment.
Secondary Sewage Treatment
Secondary sewage treatment method uses aerobic biological processes to degrade the biological content of the sewage like human waste, food waste, soaps and detergent. In this method bacteria and protozoa convert the biodegradable soluble organic contaminants into floc.
In Secondary sewage treatment systems two methods viz. fixed film and suspended growth are used. In these methods, sewage passes over the surface of the biomass which grows on the media. Of these two systems fixed film system is preferred as it can easily cope with drastic changes in the amount of biological material and can provide higher removal rates for organic material and suspended solids than suspended growth systems.
For strong organic loads sometimes Roughing filters used. These filters usually consists of tall, circular filters which are filled with open synthetic filter media where sewage is applied at a relatively high rate. These filters are fabricated to for high hydraulic loading and a high flow-through of air.
In Secondary sewage treatment systems two methods viz. fixed film and suspended growth are used. In these methods, sewage passes over the surface of the biomass which grows on the media. Of these two systems fixed film system is preferred as it can easily cope with drastic changes in the amount of biological material and can provide higher removal rates for organic material and suspended solids than suspended growth systems.
For strong organic loads sometimes Roughing filters used. These filters usually consists of tall, circular filters which are filled with open synthetic filter media where sewage is applied at a relatively high rate. These filters are fabricated to for high hydraulic loading and a high flow-through of air.
Activated sludge plants are also used in secondary sewage treatment that use use dissolved oxygen to promote the growth of biological floc which aids in the removal of the organic material. It is also capable of trapping particulate material and can, convert ammonia to nitrite and nitrate ultimately to nitrogen gas. If plant is receiving more variable loads then trickling filter beds can be used.
In secondary treatment Biological Aerated Filter (BAF) is also used which consist of reactor filled with a filter media. The media supports highly active biomass that is attached to it and filter suspended solids. Carbon is reduced and ammonia is converted in aerobic mode.
In the final stage of secondary treatment biological floc is settled and material is filtered. The sewage water so produced after this treatment contains very low levels of organic material and suspended matter.
When the sewage is passed through rotating biological contractors (RBCs) the microorganism which covered the surface of the RBCs reduce the BOD and further remove suspended matter from the wastewater.
Tertiary Sewage treatment
Wastewater is given tertiary treatment to further enhance its quality before they are discharged in the environment. The popular methods that are used in this stage are filtration, lagooning, removal of chemicals like nitrogen and phosphorus etc.
Different sewage treatment processes are required to remove nitrogen and phosphorus. Nitrogen is removed through the biological oxidation of nitrogen from ammonia to nitrate, followed by denitrification, the reduction of nitrate to nitrogen gas which is removed to the atmosphere. Phosphorus on the other hand can be removed by using two process that is by the use of specific bacteria, called polyphosphate that accumulate large quantities of phosphorus within their cells they are removed from the water ans are used as fertilizer. Chemical precipitation can also be used to remove phosphorus. Wastewater is sometimes further disinfected by using chlorine, ozone gas and ultraviolet light.
Water Clarification
Clarifiers are used for the purpose of clarification of wastewater. Clarification is the widely accepted and the oldest used method in the effective treatment of water and wastewater. This operation includes removal of sediment, floating material and turbidity from raw wastewater.
Along with this water clarification is also done by the action of chemicals, filtration and disinfection. Water clarification for wastewater is different from that of drinking water as the later requires less chemicals. Also in wastewater treatment biological processes like sludge treatment is carried out for water clarification.
One is circular center feed clarifier that operates with the effluent entering through a center stilling well. It ensures proper residence time of the water in the clarifier to allow for the settling of the solids. The water rises and exits through a wall mounted weir.
Other type of clarifier is the circular peripheral flow clarifier. It operates with the water flow entering the system at the periphery. The water flow is distributed evenly and spirals down around the annulus of the clarifier. It is done by means of a specially designed baffle skirt. This configuration provides maximum settling of solids toward the sludge pick-up.
Sludge treatment equipment is a set of machines and equipment that are used to treat sludge and wastewater. The consistent efforts to design sludge & wastewater treatment facilities and the increasingly strict regulations for safe management of sludge are creating the requirement for new as well as superior sludge treatment facilities. A comprehensive range of sludge treatment equipment are available in the market that serve different functions and requirements.
Some of the important sludge treatment equipment include -
Functions
Sludge treatment equipment are designed and engineered to serve different functions and requirements of sludge treatment. Some of the important functions of sludge treatment equipment include -
Sludge treatment is a critical issue, which affects both the environment and the economic stability of various treatment sectors. It is a problem, which brings various factors into play – the quantities produced, the treatment processes involved and the various reprocessing sectors involved (energy and biological). A major factor that contributes to the increasing demand for sludge treatment equipment is extensive population growth. With increasing population, the sludge generation volumes are continuing to rise, thereby pushing the manufacturers to seek further solutions for sludge treatment.
According to a report, dewatering equipment and thickening equipment, jointly account for about 68% of total sales of sludge treatment equipment. Municipalities are the main source of revenues for the sludge treatment equipment market accounting for about 76%, while the pulp & paper and the food & beverages dominate the industrial applications in the sludge treatment industry. However, the present industry regulations and public demands are affecting both the municipalities as well as industrial end users. Trends suggest that in future, industrial end users will It has also been observed that in the future, industrial end users will grow in importance, as the awareness on the benefits of using the sludge treatment equipment for sludge processing is compounding with the attempts to conform regulations as well as to gain cost efficiency by recycling wastewater.
The techniques for sludge treatment and disposal have been subject to rigorous testing and inspection, which is due to the strict policies governing the treatment processes suitable for final disposal routes. The regulatory factors act as dominant forces and present an important market opportunity for equipment manufacturers. The urban wastewater treatment directives drive the market to meet legislative requirements, thereby boosting the demand for treatment equipment. However there is a need for superior technology capability and knowledge of industry.
Flexible and innovative services are also expected to ensure future growth in the regulated market of sludge treatment wherein the environmental consciousness in rising. Considerable opportunities remain in upstream efficiencies adaptability and innovation is a key for success. The most progressive technologies, like drying and dewatering, continue to be beneficial to companies compelled to look for methods to reduce the amount of water content in sludge in order to minimize the transportation and disposal costs. Sludge drying is expected to earn huge demand and revenues with continuously increasing safety regulations and restrictions being placed on disposal alternatives such as landfills.
Different sewage treatment processes are required to remove nitrogen and phosphorus. Nitrogen is removed through the biological oxidation of nitrogen from ammonia to nitrate, followed by denitrification, the reduction of nitrate to nitrogen gas which is removed to the atmosphere. Phosphorus on the other hand can be removed by using two process that is by the use of specific bacteria, called polyphosphate that accumulate large quantities of phosphorus within their cells they are removed from the water ans are used as fertilizer. Chemical precipitation can also be used to remove phosphorus. Wastewater is sometimes further disinfected by using chlorine, ozone gas and ultraviolet light.
Screening Equipment
Screening equipment are one of the important equipment used in the water and wastewater treatment plants. They are used for the purpose of removal of bulk of the non biodegradable matter, such as plastics, woven materials, pieces of wood, metallic items and other solids from the water stream. The screening equipment helps in improving the plant operational efficiency as well as it prevents damage to other components. Screening equipment require a higher level of maintenance in comparison to other plant equipment components. It occurs due to the harsh conditions under which they operate.
All water treatment plants and wastewater treatment plants have some type of preliminary screening machines and devices, used for the removal of debris and large particles. Some plants use separate pieces of equipment for the removal of debris and grit from the influent while some combines them into one unit, offering a saving of equipment, space, and cost.
The selection of the type of screening equipment should be based on the variety and amount of material that is expected to enter the plant through the influent water. The purpose of the screen is to accept influent water containing a mixture of particles of different sizes. The screens separate the water into two parts, one is underflow that is passed the screen and other is overflow that is rejected by the screen. A perfect screen would separate the influent water into two parts such that the smallest particle in the overflow would be just larger then the largest particle in the underflow.
What is Screening?
In water treatment plants, screening is the process of retention of particles by a grid or longitudinal bars having smaller openings than the particles to be removed. It is the method of separating particles according to the size. The smaller particles are removed by screens with small openings while bigger particles need equipment with larger openings.
Types of Screening Equipment
Screening equipment have a wide range of forms and ranges from microscreens to trash racks. The designing of screens involve selection of materials, mechanical appurtenances, structural calculations, hydraulics, conveyance of screening wastes, disposal of screenings and other processes.
All water treatment plants and wastewater treatment plants have some type of preliminary screening machines and devices, used for the removal of debris and large particles. Some plants use separate pieces of equipment for the removal of debris and grit from the influent while some combines them into one unit, offering a saving of equipment, space, and cost.
The selection of the type of screening equipment should be based on the variety and amount of material that is expected to enter the plant through the influent water. The purpose of the screen is to accept influent water containing a mixture of particles of different sizes. The screens separate the water into two parts, one is underflow that is passed the screen and other is overflow that is rejected by the screen. A perfect screen would separate the influent water into two parts such that the smallest particle in the overflow would be just larger then the largest particle in the underflow.
In water treatment plants, screening is the process of retention of particles by a grid or longitudinal bars having smaller openings than the particles to be removed. It is the method of separating particles according to the size. The smaller particles are removed by screens with small openings while bigger particles need equipment with larger openings.
Types of Screening Equipment
Screening equipment have a wide range of forms and ranges from microscreens to trash racks. The designing of screens involve selection of materials, mechanical appurtenances, structural calculations, hydraulics, conveyance of screening wastes, disposal of screenings and other processes.
Grit Separators
Grit separators are systems designed to remove grits, trash, debris, sediment, and some amount of oil and grease from the influent water stream. These separators are specifically suited to capture particulates and hydrocarbons from small and highly impervious areas. They are best for small areas which produce heavy loads of sediment and hydrocarbons, such as parking lots, roads, gas stations and convenience stores. The grit separators operate on the principles of sedimentation. They are also known as oil separators.
Besides creating blockage problems, grits are a constant source of wear & tear of the downstream units and equipment. There are different kinds of grit separation equipment to fulfill specific job requirements. They are optimally designed for the required hydraulics to ensure maximum grit separation even at peak hydraulic load. The grit withdrawal section is designed in such a way that it removes the settled grits without disturbing the settling in the main section. It lifts the water contents so that grit disposal does not pose excessive water spillage problem. The grit separators are usually cleaned by pumping out the contents of each chamber to a tanker trunk.
Working of Grit Separators
Grit separators are also known as gravity separators. They are hydrodynamic separation devices that are designed to remove grit and heavy sediments, etc from water through gravitational settling and trapping. These units contain a permanent pool of water. Typically they consist of an inlet chamber, separation or storage chamber, and an access port for maintenance purposes. The influent water enters the inlet chamber where heavy sediments and solids drop out. Subsequently the flow moves into the main gravity separation chamber, where suspended solids are settled further. The grease and oil are skimmed and stored in a waste oil storage compartment for future removal. The clarified runoff is discharged after moving in the outlet chamber.
Types of Grit Separators
Besides creating blockage problems, grits are a constant source of wear & tear of the downstream units and equipment. There are different kinds of grit separation equipment to fulfill specific job requirements. They are optimally designed for the required hydraulics to ensure maximum grit separation even at peak hydraulic load. The grit withdrawal section is designed in such a way that it removes the settled grits without disturbing the settling in the main section. It lifts the water contents so that grit disposal does not pose excessive water spillage problem. The grit separators are usually cleaned by pumping out the contents of each chamber to a tanker trunk.
Grit separators are also known as gravity separators. They are hydrodynamic separation devices that are designed to remove grit and heavy sediments, etc from water through gravitational settling and trapping. These units contain a permanent pool of water. Typically they consist of an inlet chamber, separation or storage chamber, and an access port for maintenance purposes. The influent water enters the inlet chamber where heavy sediments and solids drop out. Subsequently the flow moves into the main gravity separation chamber, where suspended solids are settled further. The grease and oil are skimmed and stored in a waste oil storage compartment for future removal. The clarified runoff is discharged after moving in the outlet chamber.
Types of Grit Separators
- Square Grit Collectors: They are the most common used units because of its simplicity in design and its operational reliability. These units come either with Screw Classifier or with Rake Classifier.
- Rectangular Grit Collectors: These grit collectors are useful when the plant layout does not allow the square units or where there are certain process considerations. These units are usually provided with moving scrappers driven through the chain.
- Aerated Grit Channel: It is an efficient concept for optimal performance of any grit removal system. The grit separation is controlled by means of air circulation across the baffle.
Water Clarifier/ Water Clarification
What is Water Clarification?
Water is a great solvent that dissolve almost anything. Water clarification and its filtration are the main processes that are carried out on drinking water and the water that is to be used for other specific purposes or for draining. Untreated water contain many kinds of harmful contaminants which must be removed before the end use of water.Water Clarification
Clarifiers are used for the purpose of clarification of wastewater. Clarification is the widely accepted and the oldest used method in the effective treatment of water and wastewater. This operation includes removal of sediment, floating material and turbidity from raw wastewater.
Water Clarification Unit Processes
Water clarification process is not the one process but the combination of different processes. Large suspended solids get settle down by gravity. For non-settleable material removal is done through coagulation, sedimentation and flocculation. All these three processes are collectively called conventional clarification or the water clarification.- Rapid mix for coagulation
- Moderate mixing for flocculation
- Solid-liquid separation
Types of Clarifier
There are two types of clarifiers.One is circular center feed clarifier that operates with the effluent entering through a center stilling well. It ensures proper residence time of the water in the clarifier to allow for the settling of the solids. The water rises and exits through a wall mounted weir.
Other type of clarifier is the circular peripheral flow clarifier. It operates with the water flow entering the system at the periphery. The water flow is distributed evenly and spirals down around the annulus of the clarifier. It is done by means of a specially designed baffle skirt. This configuration provides maximum settling of solids toward the sludge pick-up.
More Types of Water Clarifier
On the basis of applications water clarifiers can be categorized as:Equipment for Biological Treatment of Water
Water used for drinking and household use, even water from a ground water supply, should be treated before it is used to ensure it is safe and aesthetically pleasing. Biological water treatment is one of the innovative methods of water treatment. This process involves the use of naturally occurring micro-organisms in ground water to improve water quality. In optimal conditions, the micro organisms break down material in the water such as dissolved organic carbon and iron. In this way it improves water quality.
The biological treatment of water is well suited to treat some common problems to ground water supplies, such as iron, arsenic, and dissolved organic carbon (DOC). It also treats colour and turbidity. It has been proved that the biological treatment system, including a slow sand filter and biological activated carbon filter, effectively reduces colour, turbidity, DOC, as well as iron and arsenic.
How will biological treatment improve water quality?
Biological treatment of ground water enhances the water quality by decreasing the amount of arsenic and iron, which are health and aesthetic problems, respectively. This process also reduces the turbidity and color and also the concentrations of DOC. All these factors can cause helath problems in chlorinated water. The decreased level of DOC enhances the taste and odour of the water, and it can also reduce the amount of chlorine needed for disinfection.
Machines for Biological Treatment
The biological treatment of water is well suited to treat some common problems to ground water supplies, such as iron, arsenic, and dissolved organic carbon (DOC). It also treats colour and turbidity. It has been proved that the biological treatment system, including a slow sand filter and biological activated carbon filter, effectively reduces colour, turbidity, DOC, as well as iron and arsenic.
Biological treatment of ground water enhances the water quality by decreasing the amount of arsenic and iron, which are health and aesthetic problems, respectively. This process also reduces the turbidity and color and also the concentrations of DOC. All these factors can cause helath problems in chlorinated water. The decreased level of DOC enhances the taste and odour of the water, and it can also reduce the amount of chlorine needed for disinfection.
Machines for Biological Treatment
Sludge Treatment Equipment
Sludge treatment equipment is a set of machines and equipment that are used to treat sludge and wastewater. The consistent efforts to design sludge & wastewater treatment facilities and the increasingly strict regulations for safe management of sludge are creating the requirement for new as well as superior sludge treatment facilities. A comprehensive range of sludge treatment equipment are available in the market that serve different functions and requirements.
Some of the important sludge treatment equipment include -
- Anaerobic Digester
- Digester Mixer
- Dissolved Air Flotation Thickener
- Rotary Vacuum Drum Filter
- Gravity Thickener
- Belt Filter Press
Sludge treatment equipment are designed and engineered to serve different functions and requirements of sludge treatment. Some of the important functions of sludge treatment equipment include -
- Mixing of municipal industrial wastes, deep tank blending of high viscosity fluids, de-icing applications.
- Filtration of industrial liquid.
- Handling of concentrated municipal and industrial sludges, dewatering and lifting devices for heavy solid uses and applications.
- To remove water from the liquid wastewater residues and to form a non-liquid material.
- Sludge flotation
- Anaerobic digestion for the volume and mass reduction of input material.
Sludge treatment is a critical issue, which affects both the environment and the economic stability of various treatment sectors. It is a problem, which brings various factors into play – the quantities produced, the treatment processes involved and the various reprocessing sectors involved (energy and biological). A major factor that contributes to the increasing demand for sludge treatment equipment is extensive population growth. With increasing population, the sludge generation volumes are continuing to rise, thereby pushing the manufacturers to seek further solutions for sludge treatment.
According to a report, dewatering equipment and thickening equipment, jointly account for about 68% of total sales of sludge treatment equipment. Municipalities are the main source of revenues for the sludge treatment equipment market accounting for about 76%, while the pulp & paper and the food & beverages dominate the industrial applications in the sludge treatment industry. However, the present industry regulations and public demands are affecting both the municipalities as well as industrial end users. Trends suggest that in future, industrial end users will It has also been observed that in the future, industrial end users will grow in importance, as the awareness on the benefits of using the sludge treatment equipment for sludge processing is compounding with the attempts to conform regulations as well as to gain cost efficiency by recycling wastewater.
The techniques for sludge treatment and disposal have been subject to rigorous testing and inspection, which is due to the strict policies governing the treatment processes suitable for final disposal routes. The regulatory factors act as dominant forces and present an important market opportunity for equipment manufacturers. The urban wastewater treatment directives drive the market to meet legislative requirements, thereby boosting the demand for treatment equipment. However there is a need for superior technology capability and knowledge of industry.
Flexible and innovative services are also expected to ensure future growth in the regulated market of sludge treatment wherein the environmental consciousness in rising. Considerable opportunities remain in upstream efficiencies adaptability and innovation is a key for success. The most progressive technologies, like drying and dewatering, continue to be beneficial to companies compelled to look for methods to reduce the amount of water content in sludge in order to minimize the transportation and disposal costs. Sludge drying is expected to earn huge demand and revenues with continuously increasing safety regulations and restrictions being placed on disposal alternatives such as landfills.
Bio Gas Handling
Biogas that is generated during the process of anaerobic digestion is to be generally utilized by gas engines, boilers, incinerators or other devices requiring consistent and regular supply of gas. For this regular supply of gas, adequately sized biogas handling systems are crucial between the gas supplying units and the utility point. A comprehensive range of biogas handling systems are available in market for this purpose. Different set of machines and equipment that are used in biogas handling systems are -
- Flares (elevated + ground type)
- Blower stations
- Biogas desulphurization (chemical + biological)
- Biogas burners & dual fuel burners
- Steam + hot water boilers
- Biogas fired power generators
Sludge Handling/ Sludge Treatment Plant
Semisolid materials that are produced during the wastewater treatment. These materials are oftenly infected with organic or inorganic compound and hence should be treated well before they are discharged in an environment.
Sludge is treated with a motive to reduce the amount of organic matter and the microorganism which are the causative agents of many diseases. Sludge can be treated following processes:
Sludge is treated with a motive to reduce the amount of organic matter and the microorganism which are the causative agents of many diseases. Sludge can be treated following processes:
Anaerobic digestion
This is a bacterial process carried out in the absence of oxygen. There are two methods used in this process - Thermophilic digestion or Mesophilic digestion. In thermophilic digestion fermentation of sludge takes place in tanks at a temperature of 55°C whereas in mesophilic digestion fermentation takes place at a temperature of around 36°C. The process generates biogas that is used not only for heating the tanks but also to generate electricity.Aerobic digestion
Aerobic digestion takes place in the presence of oxygen. Organic matter is consumed by bacteria and convert it into carbon dioxide. The lack of organic matter leads to the death of bacteria. Once the bacteria dies they are used as food by other bacteria. Thus through this process solid reduction takes place. The cost of aerobic digestion is low with compared to anaerobic digestion as it consumes bacteria faster.
Anaerobic Digestion
| Preferences of wastewater sludge treatment Sludge can be treated by using from one of the available techniques-Aerobic digestion, Anaerobic digestion and composting. One can choose the treatment keeping in mind the amount of solids generated and other site-specific conditions. For smaller scale applications, composting method is applied whereas for large scale municipal applications, anaerobic digestion is preferred. |
Composting
Sludge can also be treated by composting method. It is basically aerobic process which involves mixing the wastewater solids with materials like sawdust, straw or wood chips which are the good source of carbon. Bacteria, in the presence of oxygen digest both the wastewater solids and the added carbon source.
Composting of Faccal Solid
