What is Sewage Treatment Plant and How does It Work?
Sewage treatment plants accept waste from residential, commercial, and industrial sources and treat it to eliminate toxins that are harmful to water quality and pose a risk to public health and safety when released onto land or into receiving systems. It is a group of unit activities and unit processes created to meet the effluent criteria of the regulatory body while treating sewage to acceptable levels.
In the treatment process, sewage undergoes several stages to remove solids, organic matter and nutrients before the treated effluent is discharged to water bodies or reused. The key processes include preliminary treatment to screen and remove large solids, primary sedimentation to allow suspended solids to settle out, secondary biological treatment to breakdown organics, and secondary clarification to remove biological solids produced, with additional tertiary treatment and disinfection used in some plants before final discharge.
You will learn all there is to know about sewage treatment plants in this article, from the raw sewage that enters the facility to the effluent removed after several treatment stages. It will undoubtedly enhance your knowledge. Let’s start learning
Working Process in Details
Primary treatment, secondary treatment, and tertiary treatment are the three stages that make up the wastewater treatment process. Let’s learn about each process in detail.
The typical flowchart of the sewage treatment plant is described below.
Process flow diagram
Primary Treatment:
Removing some of the organic debris and suspended particulates from sewage is the first step in the treatment process. After pre-treatment, there are three stages of wastewater treatment: primary, secondary, and tertiary. Removing items from waste water that will float to the surface or settle due to gravity is the primary purpose of primary treatment.
It includes these steps:
Screening:
Coarse screens or bar racks are used first to remove large floating objects like rags, sticks, and plastics that may clog pipes or damage equipment.Fine screens can also be used to remove more minor suspended matter. Screens trap the debris, which is then manually or mechanically cleaned and removed.
Grit Removal:
Grit chambers or grit channels allow dense inorganic particles like sand, gravel, and coffee grinds to settle down by gravity.A grit collector mechanically agitates the wastewater to facilitate settling. Grit is then removed as slurry and landfilled.
The skimming tank in the sewage treatment plant:
Sewage treatment plants include skimming tanks to remove oil and grease from the wastewater—which, if left behind, prevents the growth of the microorganisms needed for the biological treatment. These tanks are located before the main sedimentation tank in sewage treatment facilities. When compressed air is introduced from the bottom of a tank used for skimming, it creates rising bubbles that coagulate foreign grease particles and transport them to the surface, where they are readily skimmed off. Since oil and grease particles do not set at high temperatures, skimming tanks are not commonly utilised in India. The detention period for skimming tanks is three minutes.
Primary Sedimentation:
Large circular tanks called primary clarifiers provide calm conditions for settling.Settled organic solids like food particles, human waste, oils and grease are removed as primary sludge. This is pumped out from the bottom and undergoes further treatment.The clarified effluent then proceeds to secondary biological treatment.
These physical processes remove around 50-70% of suspended solids and 25-40% of BOD in primary treatment.
Secondary Treatment
The main purpose of secondary treatment is to substantially degrade the biological content of the sewage, such as human waste, food scraps, oils, soaps and other organic matter. It employs biological processes and includes these main phases:
Aeration:
The primary effluent is mixed and aerated with oxygen to facilitate the growth of aerobic microorganisms into an activated sludge. Diffused aeration systems bubble air from the bottom to mix and oxidise the wastewater. Mechanical aerators also mix and add oxygen.
Biological Oxidation:
Bacteria and other microbes consume the organic matter for growth and reproduction as food source. This oxidation of organics is called bio-degradation.Up to 90% of organic matter measured as BOD and COD is removed by converting it into additional cells and gases.
Secondary Clarification:
The activated sludge mixture then flows into secondary settling tanks, allowing the biological flocs to settle out from the treated water. The clarified liquid overflowing from the top is the treated secondary effluent. The settled activated sludge is pumped back to mix with new incoming sewage to maintain a sufficient microbial population.
Tertiary treatment may follow secondary processing if higher-quality effluent is required. Over 85% of BOD and solids are removed after secondary treatment.
Tertiary Treatment:
Tertiary or advanced treatment is an additional step following secondary treatment to remove specific contaminants left in the effluent like nitrogen, phosphorus, other suspended solids, heavy metals and organic toxins. The goals of tertiary treatment include:
1- Further, improve effluent quality before discharge to more sensitive environments
2- Additional nutrient removal to prevent eutrophication in receiving waters
3- Remove specific pollutants like pesticides, metals and dyes
4- Disinfect effluent to destroy pathogens and make it safe for reuse
Major tertiary processes include:
1- Filtration: Rapid sand filters, micro screens, and membrane filters remove almost all residual suspended solids and achieve high clarity.
2- Nutrient Removal: Biological or chemical methods reduce excess nitrogen and phosphorus levels to prevent overgrowth of algae and eutrophication.
3- Adsorption: Passing through activated carbon removes organic pollutants like oil, grease and heavy metals through adsorption.
4- Disinfection: Chlorine, UV radiation or ozone treatment kills bacteria and pathogens to produce a safe effluent for discharge or reuse.
Advanced treatment systems are tailored to remove site-specific contaminants using different physical, biological and chemical combinations. With tertiary processing, treated effluent quality can approach drinking water standards.
How many types of Sewage Treatment Plants are there?
Sewage treatment facilities come in various types, and their methods for treating wastewater vary. They often fall into one of the following categories of systems:
Activated Sludge Plant
The activated sludge process is a vast aerobic biological treatment system in which a mixture of wastewater and sludge (microbes) called the activated sludge is aerated and agitated to decompose the organic pollutants in wastewater as food for the bacteria. This mix passes through a secondary clarifier, where the bacterial mass settles out and recycled back to the aeration tank for mixing with new wastewater to sustain optimal microbial population over time.
Rotating Disc System
The rotating disc system utilises large rotating discs placed at approximately 40% submergence in wastewater. The discs provide a surface for the growth of bacterial biofilm, which degrades organic load; the slow speed rotation exposes the biofilm alternatively to the organic matter in sewage and atmospheric oxygen to maintain aerobic conditions - creating excellent overall biological treatment and BOD removal with relatively less energy input versus other systems.
Trickling Filter
Wastewater is sprayed over and trickles through a stationary bed of media such as rocks, gravel or plastic pieces on which a biological film layer of microorganisms develops over time. The organic pollutants in the sewage are broken down by the microbes as the wastewater contacts this film while trickling through the voids in the media bed, requiring a large surface area but less power consumption.
Submerged Aerated Filter (SAF)
The submerged aerated filter is a treatment system in which wastewater flows through a tank filled with support media while air is pumped through the bottom of the bed. The press provides a surface for microbial growth, which forms a biological film layer that degrades organics. The influent wastewater comes in contact with the film, allowing the aerobic breakdown of pollutants. Typical media used include sand, gravel, granular activated carbon and specially designed plastic pieces. It provides efficient biological treatment in a compact space.
Suspended Media Filter (SMF)
The suspended media filter utilises proprietary broken growth media such as tiny high-surface area plastic balls or discs held in suspension within an aerated bioreactor tank. Microorganisms grow as a film on these suspended media, which are designed to aggregate together after a planned contact period to facilitate separation. The treatment involves alternate cycling of the press between aeration to achieve BOD reduction and settlement to separate and recycle back the media containing the active biomass.
Sequencing Batch Reactor (SBR)
The sequencing batch reactor (SBR) carries out the functional processes of equalisation, aeration, clarification, etc., in a time sequence rather than space within a single batch reactor. The batch cycles of fill, react (aerate), settle (clarify), decant and idle are programmable to achieve the desired treatment. It requires control systems to automate movement between sequences but provides flexibility to deal with flow fluctuations in a relatively smaller footprint.
Natural Systems
Use constructed wetlands, lagoons and stabilisation ponds. These are less expensive to build and operate. These systems require more land area.Removal efficiency can be variable in these systems.
What are the STP Technologies, and which one is better to install?
Several sewage treatment technologies can be used for installing STPs. Some of the leading technologies include:
1- Activated Sludge Process (ASP):
This technology is the most commonly used. It uses aeration and a biological floc of microorganisms to reduce BOD and COD. Produces high-quality effluent but is energy intensive.
2- Trickling Filters:
Wastewater is sprayed over a fixed bed of media like rocks or plastic on which biofilm forms. Organisms in this film break down organics. It is simple and efficient but requires a large land area.
3- Sequencing Batch Reactor (SBR):
Uses a fill-and-draw approach in a single batch reactor through sequences thereby avoiding the need for separate clarifiers. Has flexible operation.
4- Rotating Biological Contactors:
Use rotating discs on which biofilm grows which contacts wastewater and air alternately. Requires less energy and space.
5- Natural Systems:
Consist of constructed wetlands, stabilization ponds, and lagoons for low-cost treatment. Require large land area, climatic dependence.
6- Membrane Bioreactor (MBR):
It combines an activated sludge process with membrane filtration like ultrafiltration. Produces the best quality effluent with small footprint but energy intensive and membrane fouling issues.
The choice depends on cost, land availability, discharge standards, ease of operation and energy requirements. MBR, ASP variants or SBR adapted to local conditions are best for performance. Trickling filters and natural systems suit low-cost needs.
What is the cost-effective Technology in STP?
The most cost-effective sewage treatment technology for an STP depends on the specific needs and constraints of a site, but some typically cost-effective options include:
1- Waste Stabilization Ponds: Large shallow basins filled with wastewater rely on natural oxidation and microbial action. These include:
Facultative ponds: Allows both anaerobic and aerobic activities
Aerobic/maturation ponds: Allow mainly aerobic microbial action
Anaerobic ponds: Allow septic conditions for initial BOD reduction
They have very low construction, operational and maintenance costs but require a large land area. Overall, it is cost-effective, where land availability is not an issue.
2- Trickling Filters: Use rocks, gravels, or other media for biofilm growth and breaking down organics. Have low installation, operational and maintenance costs given the more straightforward mechanical equipment. It can be designed modularly to handle higher organic loads in the same land area.
3- UASB Reactors: Upflow anaerobic sludge blanket reactors allow sludge granulation and anaerobic processing of concentrated waste. Has lower installation, operational and maintenance costs for high organic load wastewaters. Biogas production for energy recovery provides additional cost savings.
Thus, stabilisation ponds, trickling filters, and UASB reactors are typically the most cost-effective conventional treatment technologies used in STPs when economics is a crucial criterion.
What are the major components of Sewage Treatment Plants and Write all equipment details of MBBR Technology.
An organization that generates wastewater and then has to treat it can profit from a moving bed biofilm reactor (MBBR) system. A biological wastewater treatment technology known as a moving bed biofilm reactor has several distinct features that set it apart from more conventional techniques like activated sludge or trickling filters. When it comes to aspects like efficiency, flexibility, and convenience, MBBR is outstanding.
This is a more thorough explanation of the MBBR procedure. A useful approach to comprehending this procedure is to think about the several MBBR design elements that come together to enable this method.
Basin: Also referred to as an aeration tank or reactor, a basin is where the MBBR process is carried out. The amount of filtration that a specific plant requires determines how big this container should be. After entering this basin for treatment, the influent could go on to another basin for more MBBR processing or for another kind of water treatment procedure. This is an aerobic filtering method since the top of the MBBR aeration tanks is open, exposing the water to the outside air.
Media: Also known as carriers, the basin contains hundreds of tiny plastic chips. The media might use up to 50–70% of the tank. Their shape makes the most of the surface area they offer for biofilm growth. A lot of carriers have the shape of rotelle or pasta with wheels. Instead of floating or sinking, they are able to mix throughout the fluid since they have the same density as water.
Aeration grid: An aeration grid is another device that facilitates the efficient movement of media throughout the tank. This apparatus, which is situated at the base of the reactor tank, is basically a fan. The aeration grid facilitates the movement of carriers, allowing them to come into touch with all waste materials and break them down effectively. It increases the amount of oxygen in the tank.
Sieve: One can ask how the media stays in the tank instead of leaving through the exit while imagining the MBBR system that has been previously explained. If the tank's sieve wasn't installed, it may be an issue. Water can travel through the mesh material, but it retains the plastic carriers inside the basin.
It is simple to comprehend how MBBR operates once one has a basic understanding of the constituent parts. The water is made cleaner and safer for reuse or disposal when the microbes affixed to the tank's medium devour garbage. The kind of waste that has to be removed will determine what kind of microorganisms are added to the tank. MBBR isn't limited to consuming regular waste. In addition, it contributes to denitrification and nitrification. Denitrification is the process by which nitrate is transformed into nitrogen gas through the metabolism of oxygen. Nitrification is the process by which ammonium is converted into nitrate. MBBR is a great method of supporting both processes because they are both biological in nature. Once more, the kinds of microorganisms supplied will depend on the objectives of the MBBR process. In the case of denitrification, for instance, it is advisable to utilize denitrifiers such as Pseudomonas, Paracoccus or Alcaligenes.
If a biological process is needed to enhance the wastewater's quality, MBBR is a useful approach to take into account.
How do you calculate STP Capacity?
The management and purification of sewage prior to its discharge back into the environment is a critical function of sewage treatment plants. Finding the right capacity to manage the incoming wastewater flow is a crucial part of constructing a sewage treatment facility that works.
Here,we will explore the fundamental formulae and factors that every STP buyer should be aware of as we dive into the realm of sewage treatment plant capacity calculation.
Here are the typical steps to calculate the capacity of a Sewage Treatment Plant (STP):
Estimate sewage inflow rate
Collect data on the water supply rate to the area to be served by the STP
Add a leakage and infiltration factor (typically 15-30% of water supply)
This gives the estimated sewage inflow rate in m3/day
Determine average and peak flow rates
Average Flow Rate = Total daily inflow ÷ 24 hours
Peak Flow Rate = Average flow × Peak Factor (typically 1.5-2.5 x average flow)
Based on disposal norms and the water body to receive treated effluent, decide on the quality standards to achieve at the STP outlet for parameters like BOD, COD, TSS, N, P, etc.
Select appropriate sewage treatment technology based on sewage characteristics and effluent standards.
Calculate reactor volumes and area requirements for each unit operation using process design criteria and selected technology specifications. Common units include - Screen channels, Grit chambers, Primary clarifiers, Reactors (activated sludge process, trickling filters, etc.), Secondary clarifiers, and Chlorine contact tanks.
Design sludge handling, pumping stations, utilities etc.
Add factor of safety and space provisions for future capacity expansions.
The cumulative capacity of all designed STP units to match peak inflow rates and meet quality criteria determines the STP treatment capacity. Typically, a 20-30% factor of safety is added.
How to Calculate Power Requirements for STP Plant?
Designing a reliable and efficient power supply system is crucial to Sewage Treatment Plant engineering. An adequately powered STP ensures smooth and continuous operation of all process units for collection, pumping, screening, aeration, treatment, clarification, disinfection and sludge management. The load demand must account for peak wastewater flow capacity, the operation of all motors, blowers, aerators and auxiliary equipment, and expanded future capacity. The power requirement depends significantly on treatment technology options, equipment selection and degree of automation. Generally, an STP has continuous base loads for crucial equipment and large intermittent loads. A detailed load list and demand calculation procedure must be developed during STP design to determine the reliable power capacity needed for optimal functioning. The connected electrical loads have to categorise essential and non-essential equipment and provide backup systems for the former.
Here are the key steps involved in calculating the power requirement for a Sewage Treatment Plant (STP):
Determine flow rate capacity and treatment system details:
Average and Peak wastewater flow rates
Treatment units - Pumping, Aeration, Mixing, Sludge handling
Prepare process flow diagrams and mass balances for the selected treatment system
Calculate dynamic head requirements for pumping in various stages of treatment (e.g. Inlet works, sludge recirculation, effluent discharge)
Estimate hydraulic retention time and oxygen demand for aeration systems in line with process design guidelines
Decide equipment details - motors, blowers, pumps, gearboxes - their numbers, capacities, efficiencies
Determine mixing power requirements based on tank dimensions and mixing intensity needs
Estimate load requirements of auxiliary equipment - lighting, instrumentation and controls
Calculate intermittent, continuous and average power consumption of all electrical equipment
Add appropriate safety factors, consider plant expansion plans, optimize design
Select optimum motor rating and numbers for reliability and redundancy
Calculate overall plant load demand and connected load capacity required
By aggregating the power needs of all process units, utilities, and ancillary systems through these steps, the total electrical power requirement of the STP can be determined. This forms the basis for the electric system and distribution design.
What are the Fixed cost and variable cost in the Sewage Treatment Plant?
The total cost of an STP comprises fixed and variable costs over its service lifetime. The fixed costs refer to one-time infrastructure, equipment and administrative expenses during the STP setup, which do not change significantly with day-to-day functioning or sewage influent volumes. These predominantly include the capital investment required for land, civil structures like inlet works, screening channels, collection tanks, treatment reactor basins, secondary clarifier tanks, chlorine contact tanks, administration buildings, pump houses etc. Additionally, significant costs are incurred in procuring and installing electro-mechanical equipment like bar screens, grit removal systems, pumps of various types, large aeration blowers, decanters, dewatering presses, etc., along with associated piping, valves, instrumentation and electrical systems. Supplementary project expenses include engineering consultancy, site development, and construction management, while a portion of project contingency funds will also likely be utilised.
The fixed expenses category further encompasses non-tangible costs like obtaining permits and clearances, detailed project reporting, transport studies, and providing for rehabilitation of displaced families if applicable. The assets created have quantifiable depreciation, which forms a recurring fixed yearly expenditure. The STP setup also requires substantial capital raised through equity or debt, entailing committed interest and principal repayments. After commissioning, the staff for administrative functions, managers, supervisors, technicians and security personnel will draw wages as permanent salaries, irrespective of actual sewage treated. Licenses and insurance for the plant and equipment have preset charges. Routine overheads spent on site upkeep, security, administration workflows, general stores and inventory also belong to inflexible outlays.
In contrast, the variable costs of running an STP fluctuate with the operational capacity or the amount of sewage treated. These primarily comprise expenditures linearly linked to actual treatment operations like energy consumption across equipment, periodic replacement of damaged parts, and consumables like filters, lubricants, etc. The costs of chemicals, viz. chlorine, alum, and polymers, vary depending on the influencing sewage characteristics. More excellent manpower or outsourced workers may be deployed to handle increased maintenance workload during peak loads. The quantum of sludge generated and requiring further handling, transport, and tipping depends on plant throughput. Effluent testing charges increase if additional quality checks become necessary beyond compliance levels. Thus, fixed and variable costs constitute key considerations while evaluating an STP's operational viability.
Operation and maintenance cost of Sewage Treatment Plant
The efficient and continuous operation of a sewage treatment plant is crucial for cleaning the sewage from large residential and industrial areas to meet environmental discharge standards. However, the functioning of an STP incurs significant recurring expenditures across vital aspects like competent staffing, energy supply, adequate treatment chemicals, routine equipment upkeep and sludge disposal facilities. Regular testing and compliance checks also form a cost factor. While capital investments in infrastructure and equipment comprise the fixed one-time installation expenses, the daily operational and maintenance costs determine the budgeting needed for optimal, uninterrupted treatment performance. The manpower, material, power and regulatory resources complement the asset structures to remove pollutants, neutralise toxins, and safely dispose of high volumes of sewage via sustainable mechanisms adopted in an STP facility.
Here is a detailed overview of the typical operation and maintenance costs associated with a Sewage Treatment Plant (STP):
1- Staffing Costs: Salaries, wages and benefits of plant supervisory staff, technicians, mechanics, electricians, labourers and security personnel form a significant chunk of STP operating costs. Their strengths depend on capacity, complexity of treatment and automation level. Staff quarters and facilities may add to costs.
2- Chemical Costs: Costs incurred in the procurement of treatment chemicals like alum, lime, claimants, chlorine gas/liquid for disinfection, polymer solutions etc., based on actual usage. Cost depends on STP process chemistry needs and fluctuating market rates.
3- Energy Costs: Significant power consumption across pumping, aeration, and mechanical equipment like centrifuges, belt filter presses, etc. STP unit operations rely heavily on uninterrupted power. Cost depends on electricity tariffs, operational capacity and efficiencies.
4- Consumables and Spares: Regular replenishment of lubricants, activated carbon, filter media/cartridges, laboratory reagents, protective gear, and spare parts to minimise equipment downtime.
5- Effluent Monitoring: Mandatory compliance testing of treated effluent calls for sampling kits, field test equipment, or external laboratory analysis services.
6- Sludge Handling: Disposal costs of accumulating waste sludge, including loading, transport charges, incineration (if applicable) in the presence of lime and additives or tipping fees.
7- Maintenance Costs: Preventive (AMC) and breakdown maintenance costs through internal teams or external agencies for specialised repairs and overhauls.
8- Miscellaneous Costs: Transport vehicles, inventory, site administration costs for record-keeping, communication, etc. are also required.
Thus, fixed and variable cost components spanning staff, chemicals, energy, equipment maintenance and regulatory requirements encompass STP operations. Effective utilisation of funds improves sustainability.
Consumables cost in Sewage Treatment Plant
The routine operation of a sewage treatment plant requires continuous purchase and replenishment of various chemicals, materials and parts, which are collectively termed consumables. These include specialised treatment chemicals like aluminium sulphate, ferrous sulphate, lime, anti-foaming agents, and polymer solutions which play essential roles in dewatering, conditioning, and meeting discharge limits. Additionally, regular testing of sewage quality mandates laboratory supplies, including reagents, culture media and titrants. Maintenance costs are mitigated through properly inventorying frequently changed parts like pump coupling rubbers, bearings, seals, and valve stem packings. Refilling of lubricants and hydraulic oils as per scheduled services also helps optimise asset lifespans. Fuel charges for transport vehicles and diesel generators have become necessary during load shedding. Other consumables comprise compressed process air cartridges, activated carbon charges, analytical kits, tubular filtration candles, and protective gear like gloves, masks, etc. Renewal of granular biofilter media may also be included periodically. While asset depreciation covers capital equipment, all such chemicals, spare parts, testing supplies, fuel additives, and laboratory items covered under consumables may account for 15-20% of the yearly operating budget, depending on STP capacity. Establishing proper forecasting, tracking systems and order schedules helps maintain adequate stock of essential consumables, furthering uninterrupted plant functioning.
Area requirement for different sizes of Sewage Treatment Plant And How to calculate the Area for Sewage Treatment Plant?
Sewage treatment plants are one alternative for disposing of wastewater if your property is not linked to the central sewage system. But it's crucial to get it correctly if you plan to install a sewage treatment plant. Sewage disposal issues can be unpleasant for you and your neighbours. Still, they can also damage the surrounding ecosystem, be costly to resolve, and get you in trouble with the local government.
One of the most important things to consider when choosing which sewage treatment plant to construct is its size. To guarantee that it functions effectively, the sewage treatment plant needs to be able to process the household wastewater by demand sufficiently.
Here are some critical points about calculating the area requirements for sewage treatment plants of different sizes:
1- The area required depends on the plant's capacity (flow rate it is designed to handle) and the treatment processes/technologies used.
2- Generally, conventional activated sludge plants require about 0.05 to 0.1 acres per million gallons per day (MGD) capacity. For example, a 5 MGD plant would need around 0.25 to 0.5 acres.
3- Advanced treatment processes like membrane bioreactors, tertiary filtration etc. tend to have higher space requirements. A rough estimate would be 0.1 - 0.2 acres per MGD.
4- Primary treatment plants (mainly sedimentation tanks) have lower area requirements of about 0.03 acres per MGD. Only primary treatment may be provided for small towns or initial phases of large plants.
5- Land is also needed for pre-treatment units, sludge handling/dewatering, administrative offices, roads etc. These can add 25-50% more area, depending on the scope.
To calculate the area:
1- Estimate design capacity required (flow rate based on projected population, service area etc.).
2- Decide on treatment processes to be used - primary, secondary (activated sludge), tertiary etc.
3- Allocate land for specific units based on flow and thumb rules for space requirement per MGD.
4- Add buffer land for expansion, landscaping, etc. Typically 25-50% extra area is added.
So, a 10 MGD secondary treatment plant would need approximately 10 x 0.05 to 10 x 0.1 = 0.5 to 1-acre core area. Add 0.15 to 0.5-acre buffer area for a total of 0.65 to 1.5 acres.
What is the purpose of STP?
Everyone wants to live in a healthy atmosphere, don't they? For this reason, disposing of garbage in sewers or dumpsters is insufficient. To prevent water pollution and preserve a healthy ecology, we must ensure that sewage waste are cleaned up before being deposited.
Wastewater from houses and businesses and perhaps pre-treated industrial waste make up sewage. One can select from a variety of sewage treatment methods. Sewage treatment is a sort of wastewater treatment that keeps raw sewage discharges from contaminating water by removing pollutants from the wastewater and producing an appropriate effluent for reuse or release to the environment. The main objective of sewage treatment is to produce an effluent that can be reused beneficially or released into the environment with little water contamination.
Here are some of the critical purposes of sewage treatment:
1- Remove solids and pollutants: STPs are designed to remove contaminants like organic matter, nutrients (nitrogen, phosphorus), toxic chemicals and solid waste from the sewage. This treated effluent has reduced environmental impact.
2- Protect public health: Treating sewage helps remove infectious organisms and pathogens that can cause diseases. This helps protect communities from waterborne diseases like cholera, typhoid, and dysentery that spread via raw sewage contamination.
3- Improve water bodies: The load of polluting organic matter is significantly reduced by treating sewage before discharge into rivers, lakes or seas. This helps maintain dissolved oxygen levels and supports aquatic ecosystems.
4- Allow water reuse: The tertiary treatment processes in advanced STPs can produce treated effluent of purification standards that allow reuse for applications like agricultural irrigation and industry process use. This saves freshwater.
5- Recycle nutrients: Modern plants utilise processes like anaerobic digestion, sludge treatment, and biogas generation to recycle energy and nutrients from waste.
In summary, STPs are vital community infrastructure that safeguard public health, protect water resources and the environment, enable water reuse and support sustainability through resource recovery.
Which STP Technology is the leader and have most of the installation in India and comply the CPCB Norms?
Household trash gathering, processing, and disposal pose a significant issue in developed regions because many cities and towns produce substantial volumes of sewage, which is improperly treated and dumped in open sewers where it mixes with water bodies and travels downstream. Groundwater quality is frequently threatened by the heavy usage of groundwater and the massive amount of wastewater generated in modern life.
Therefore, to prevent the pollution of surface and groundwater bodies, among other things, residential wastewater must be adequately treated by installing sewage treatment plants (STPs) with sufficient capacity. A pioneer in decentralized sewage treatment, Netsol Water has designed and executed several successful STP installations across India through an end-to-end, customised technology approach tailored to Indian conditions. With expertise in process optimisation, automation and lifecycle support services, Netsol’s innovative solutions enable sustainable wastewater infrastructure to meet national stringent norms for many towns.
Here is a more detailed overview of why Netsol Water is considered a leading sewage treatment plant (STP) technology provider in India:
Technical Capabilities:
1- Patented Flocculator-Clarifier Design: This unique hydraulic flow pattern allows uniform flocculation and settling, leading to consistent sludge quality and clear effluent with <10 mg/L BOD and <20 mg/L TSS to meet pollution control board norms for inland or marine disposal.
2- Customized Process Design: Netsol has in-house expertise across biological treatment, filtration, disinfection and sludge management, allowing optimised process flow sheets tailored for municipal and industrial wastewaters.
3- Pollution Abatement: The plants incorporate tertiary treatment using chlorination, ozonation and activated carbon filters, enabling water reuse while treated biosolids are used as manure. Overall, the treatment trains ensure zero liquid discharge capability.
4- Automation & Controls: The plants have the capability for remote monitoring, electronic data logging and PLC/SCADA-controlled operation for minimal manual intervention. This ensures reliable and round-the-clock effluent treatment.
Implementation Success:
1- Large Install Base: Successful STP installations across 29 states/UTs treat billions of litres daily, making Netsol Water the current STP market leader. The experience allows them to handle a wide range of design capacities.
2- Turnkey Execution: As an integrated company, Netsol Water provides complete in-house design, engineering, equipment supply, construction and oversight, leading to timely, compliant plant installation.
Services Support:
1- Life Cycle Support: Comprehensive O&M services include plant upkeep, effluent testing, compliance reporting, inventory management, etc. This ensures optimal plant performance.
2- Operator Training: A facility for hands-on training on full-scale operational STPs allows the development of skilled manpower.
Thus, Netsol Water stands out through its technical expertise for customisation, field-proven solutions tailored for Indian conditions, successful project execution track record and life-cycle services support across 1500+ towns, making it a national leader in STP technology.
What are the STP Norms in India?
Sewage treatment facilities will be encouraged to recycle or reuse the treated wastewater with little to no requirement for extra treatment, as the NGT mandate requires high-quality effluent. This will assist in supplying the growing water demand from growing urban populations and industrial development. The fact that several Indian towns have already begun to take action in this area by recycling and reusing treated effluent for industrial and other uses at their STPs is encouraging.
The pace at which newly constructed sewage infrastructure keeps up with the amount of sewage generated shows that the administration intends to manage the nation's sewage discharges appropriately. India ensures that its wastewater is adequately cleansed before being released into the environment and expanding its infrastructure. Before 2015, the Central Pollution Control Board (CPCB), a Ministry of Environment, Forests & Climate Change (MoEFCC) department, published the General Standards for STP discharges that the Environment Protection Act controlled. The maximum limitations for discharges are determined by these criteria, which also contain restrictions for other contaminants, including pH, TSS, COD, nitrates, BOD and ammoniacal nitrogen. Certain towns set stricter rules for some of the pollutants previously included in the list, as well as limitations for new contaminants.
The Central Pollution Control Board (CPCB) has laid down the following sewage treatment plant (STP) discharge norms in India:
1- Inland Surface Water Norms:
Biochemical Oxygen Demand (BOD) - ≤30 mg/l
Total Suspended Solids (TSS) - ≤100 mg/l
Fecal Coliforms - ≤1000 MPN/100 ml
2- Public Sewers Norms:
Biochemical Oxygen Demand (BOD) - ≤350 mg/l
Total Suspended Solids (TSS) - ≤600 mg/l
3- Land for Irrigation Norms:
Biochemical Oxygen Demand (BOD) - ≤100 mg/l
Total Suspended Solids (TSS) - ≤200 mg/l
4- Marine Coastal Areas Disposal Norms:
Biochemical Oxygen Demand (BOD) - ≤100 mg/l
Total Suspended Solids (TSS) - ≤600 mg/l
Fecal Coliforms - ≤2500 MPN/100 ml
The norms are intended to control water pollution from sewage discharge to protect public health and the environment. STPs must be designed and operated to meet the prescribed concentrations for parameters like BOD, TSS and microbial indicators depending on where the treated sewage is reused or disposed. Regular monitoring by state pollution control boards ensures compliance. Advanced STPs can produce higher quality treated water fit for non-potable reuse applications.
What is the Use of STP Water and How can we use STP Water?
Town planners and city managers nationwide face a significant issue due to the growing urban population worldwide and the lack of fresh water, particularly in India. Since fresh groundwater is already in extremely low supply in India, efforts must be made to minimise its usage for non-potable uses, such as irrigating urban green spaces.It would be beneficial to promote the use of STP water for irrigating urban green spaces. This would conserve our finite supply of fresh water while promoting grass and plant development because the water has adequate macro and micronutrients.
Even though STP water contains organic and inorganic contaminants and heavy metals, it can be reduced to the proper levels by installing secondary filtration units.
Here are some of the common uses of treated STP water:
1- Irrigation - Treated STP water can irrigate non-food crops, gardens, parks, golf courses, and more. Using treated wastewater reduces the strain on freshwater supplies for irrigation.
2- Industrial Applications - Many industries can use treated STP water for their processes, cooling systems, washing, boiler feed, etc. Using recycled water conserves potable water for drinking.
3- Toilet Flushing - Flushed water from toilets can be recycled for flushing after treatment. This application saves a significant amount of drinking water.
4- Construction - STP water can be utilised for construction activities like concrete mixing, dust control, etc. This reduces the utilisation of valuable freshwater.
5- Fire Fighting Reserve - The treated wastewater can be explicitly stored for fire emergencies. This eliminates the need to use drinking water for fire suppression.
6- Groundwater Recharge - In some cases, the highly treated STP water replenishes groundwater aquifers by letting it percolate into the ground. This helps improve groundwater levels.
7- Wetland Restoration - Treated wastewater can be released in a controlled manner into wetlands to help restore habitats and ecosystems.
So, in summary, treated STP water has many non-potable applications that can significantly reduce the usage of freshwater supplies, thereby conserving water resources. Proper treatment and regulation is necessary to ensure safety when reusing wastewater.
Difference between STP and ETP and How STP is different from ETP?
It is equally important to treat sewage as handling effluent. However, these two categories differ significantly from one another. As a result, the plants that hold them—sewage treatment plants and effluent treatment plants—also vary. By handling garbage, both improve the health of the ecosystem. Nonetheless, they differ fundamentally. Let's now examine some of the distinctions between STPs and ETPs.
The key differences between STP (Sewage Treatment Plant) and ETP (Effluent Treatment Plant) are:
1- Source of Water - STPs treat domestic sewage from household and community sources. ETPs treat industrial wastewater that is produced during industrial and commercial activities.
2- Treatment Objective - The main aim of an STP is to remove solids, organic matter and nutrients like nitrogen & phosphorus before discharging treated water into the environment. ETPs focus on eliminating toxins, industrial chemicals and other hazardous pollutants from effluent water.
3- Treatment Mechanism - STPs involve sedimentation, filtration and biological oxidation processes. ETPs utilise additional chemical treatments like neutralisation, coagulation, and activated carbon absorption besides physical treatments.
4- Discharge Quality - Water discharged from STPs, while not potable, can be used for irrigation or groundwater recharge after disinfection. However, ETP output may still require dilution before it can be safely used for any purpose.
5- Infrastructure - STP infrastructure involves screen chambers, grit chambers, clarifiers, aeration tanks, secondary clarifiers and chlorine contact tanks. ETPs have additional components like neutralisation tanks, treated effluent tanks and specialised chemical dosing systems.
6- Operational Expertise - Running an STP requires expertise in biological processes, sludge disposal, etc. Expertise in industrial chemistry and effluent composition is crucial for efficient ETP operations.
In summary, ETPs usually involve more complex treatment processes, infrastructure and expertise than STPs due to industrial wastewater's challenging nature. STPs mostly deal with biodegradable organic matter from domestic sources