The consistent increase in India’s population growth rate and unprecedented urbanisation have led to increased demand for water.The problem of access to safe water and sanitation facilities in India's urban areas is also a significant concern. In this context, appropriate reuse of treated wastewater can help meet water demand to some extent. However, there is a lack of wastewater treatment facilities to serve a growing population. The lack of sufficient infrastructure, services and funds to support the water and wastewater treatment facilities required for an urban area exacerbates the problem. Moreover, drainage and solid waste collection services are inadequate in most urban areas. The systems are poorly planned and designed, or are operated with inadequate maintenance. The natural capacities of soil and vegetation (green infrastructure) can be used to absorb and treat wastewater. Natural systems are more cost-effective and require low building, labour, and maintenance costs..IS 1172:1993 – Basic requirements for water supply, drainage, and sanitation.IS 12314:1987 – Code of Practice for sanitation with leach pits for rural communities.IS 2470 (Part 1):1985 – Code of Practice for installation of septic tanks: design criteria and construction.IS 2470 (Part 2):1985 – Code of Practice for installation of septic tank: secondary treatment and disposal of septic tank effluent.IS 9872:1981 – Precast concrete septic tanks.IS 5611:1987 – Code of Practice for waste stabilization ponds (facultative type).IS 10261:1982 – Requirements for settling tanks (clarifier equipment) for wastewater treatment.IS 13496:1992 – General requirements for suction machines for cleaning sewers, manholes and so on..Modern Sewage Treatment Plants (STPs) maximise efficiency and water reuse by integrating advanced biological processes, ultra-fine filtration, and smart automation. Leading methods include Membrane Bioreactors (MBR), Moving Bed Biofilm Reactors (MBBR), and IoT-based monitoring to ensure high-quality treated water..1. Membrane Bioreactor (MBR) TechnologyHow it works: MBR merges conventional biological treatment with microfiltration or ultrafiltration membranes. Instead of relying on gravity for settling, the treated water is sucked through microscopic membrane pores (usually 0.04 to 0.4 microns).Benefits: Produces the highest possible effluent quality; removes virtually all suspended solids, bacteria, and pathogens; and requires a significantly smaller physical footprint..2. Moving Bed Biofilm Reactor (MBBR)How it works: This system uses thousands of small, specifically engineered plastic carriers (biofilm media) floating in the aeration tank. These carriers provide a large surface area for bacteria to grow and efficiently degrade organic pollutants.Benefits: Exceptionally robust, resilient to fluctuating sewage loads, and easy to upgrade within existing tank structures without expanding the plant's footprint.3. Sequencing Batch Reactor (SBR)How it works: An SBR treats wastewater in a single batch within one tank through sequential phases: fill, react, settle, decant, and idle.Benefits: Highly automated, requires less space than traditional activated sludge systems, and offers immense flexibility in handling varying daily flow volumes..4. Smart Plant Automation and IoTHow it works: Modern plants utilise IoT sensors, PLCs, and SCADA (Supervisory Control and Data Acquisition) systems to monitor parameters like dissolved oxygen (DO), pH, flow rates, and turbidity in real-time.Benefits: Optimises energy consumption by automatically adjusting blowers and pumps, enables predictive maintenance, and ensures uninterrupted compliance with pollution standards..5. Decentralised and Modular SystemsHow it works: Systems prefabricated package plants treat wastewater close to the point of generation (such as residential complexes or commercial buildings).Benefits: Minimises the need for massive underground piping networks, reuses water on-site for landscaping or flushing, and operates odour-free with a very small visual impact..Modern Effluent Treatment Plants (ETP) priorities high-recovery, low-footprint systems that combine Advanced Biological Treatment Systems with smart automation. These include Membrane Bioreactors (MBR) for superior filtering, Zero Liquid Discharge (ZLD) to recycle 100% of water, and IoT-enabled cloud monitoring for real-time compliance and predictive maintenanceUpgrading to modern technology optimises energy consumption, minimises manual intervention, and significantly reduces the operational footprint of industrial facilities. Core technologies driving this evolution include.1. Advanced Biological and Membrane ProcessesMembrane Bioreactors (MBR): Combines traditional biological treatment with membrane filtration. It produces a high-quality effluent ideal for water reuse and requires much less physical space than conventional settling tanks.Moving Bed Biofilm Reactor (MBBR): Uses floating plastic bio-carriers to increase the surface area for bacterial growth. This allows the plant to handle higher organic loads in a smaller basin.Upflow Anaerobic Sludge Blanket (UASB): Highly effective for treating high-strength organic industrial waste, converting organic matter into biogas while breaking down pollutants..2. Advanced Oxidation Processes (AOP) and Electrochemical TreatmentAOP Systems: Utilises a combination of ozone, hydrogen peroxide, and UV light to break down complex, non-biodegradable organic pollutants.Electrochemical Methods: Deployed effectively in sectors like textiles to reduce toxic organic compounds and improve techno-economic feasibility, this process uses electrical currents to coagulate and separate impurities..3. Smart Automation and IoTReal-Time IoT Monitoring: Modern ETPs use cloud-connected sensors to continuously track critical water quality parameters (COD, BOD, TDS, pH) in real-time.Automated Chemical Dosing: PLC/SCADA systems monitor the incoming effluent load and precisely dose necessary chemicals, reducing chemical waste and human error..4. Zero Liquid Discharge (ZLD) SystemsEvaporators & Crystallizers: Combines RO, Mechanical Vapour Compression (MVR) evaporators, and Agitated Thin Film Dryers (ATFD) to concentrate brine and completely eliminate liquid waste from the facility, turning residues into solid salts..Effluent Treatment Plants (ETP) use a strategic combination of physical, biological, and chemical processes to treat industrial wastewater. Different treatment phases use different chemicals, such as coagulants for suspended solids and acids/bases for pH control. For a detailed breakdown of chemical requirements and their specific functions, consult resources..Essential chemical applications across the different stages of an ETP include:1. Primary Treatment: Coagulation and FlocculationThis stage targets suspended solids, oils, and colloidal matter by clumping them into larger, heavier particles (flocs) that settle easily.Coagulants: Destabilise particle charges. Common options include Poly Aluminum Chloride (PAC), Aluminum Sulfate (Alum), and Ferric Chloride.Flocculants: Bridge the destabilised particles together. Typically, synthetic water-soluble polymers known as polyelectrolytes (Anionic, Cationic, or Non-Ionic) are used..2. pH Adjustment and NeutralisationIndustrial wastewater often fluctuates between highly acidic and highly alkaline levels. Because downstream biological processes and discharge regulations require neutral conditions (typically pH 6.5 to 8.5), exact chemical dosing is essential.For Acidic Effluents: Caustic Soda (Sodium Hydroxide / NaOH), Lime (Calcium Hydroxide /(Ca(OH)_2)), and Sodium Carbonate.For Alkaline Effluents: Sulfuric Acid ((H_{2}SO_{4})) or Hydrochloric Acid (HCl)..3. Biological Treatment (Secondary Phase)This stage relies on specialized microorganisms (bioculture) to break down dissolved organic pollutants. Chemical use is mostly supportive:Nutrients: Microbes may require supplementary nitrogen and phosphorus to thrive.Defoamers: Excessive foaming or frothing often occurs in aeration tanks. Silicone-based or organic defoamers are used to suppress this foam and keep the process stable..4. Tertiary Treatment: Disinfection and PolishingThis final step eliminates pathogens, removes colour, and reduces the chemical oxygen demand (COD) before the water is safely discharged or recycled. Disinfectants: Sodium hypochlorite, calcium hypochlorite, or ozone gas. Odour and Colour Removal: Hydrogen peroxide or Activated Carbon..Automation Systems of STP and ETPETP (Effluent Treatment Plant) and STP (Sewage Treatment Plant) automation integrates PLCs, SCADA systems, and smart sensors to replace manual monitoring. This approach optimises chemical usage, cuts energy consumption, and ensures compliance. Streamline your operations with smart systems, utilising Dosimix Technologies to reduce polymer consumption, Inovar for strategies to lower operational costs, and IJATES for large-scale treatment design..Key Benefits and Core Automation Systems1. Energy OptimisationAutomated Aeration Control: Biological treatment is the most power-hungry phase, with blowers accounting for \(40\%\) to \(60\%\) of total energy OPEX. Automation uses Dissolved Oxygen (DO) sensors to dynamically adjust blower speeds, matching exact biological demands and eliminating over-aerationVFD Integration: Variable Frequency Drives (VFDs) modulate pump speeds based on continuous flow and level data, preventing motor burnout and saving energy..2. Chemical Cost ReductionPrecision Dosing: Manual dosing of coagulants, flocculants, and pH adjusters leads to chemical waste and excess sludge. Automated Polymer Dosing Systems and smart pH sensors adjust the chemical mix in real time based on water-quality feedback.Sludge Management: Precise dosing generates well-formed flocs, reducing sludge handling and disposal costs..3. Real-Time Compliance and MonitoringMultiparameter Analyzers: Continuous measurement of inlet/outlet variables ensures the final discharge meets pollution control standards.SCADA Systems: Supervisory Control and Data Acquisition (SCADA) systems log data, send alarm-driven SMS/GSM alerts to operators, and generate compliance reports automatically.Benefits of Reusing Treated Wastewater:Wastewater recycling and reuse for “all buildings having a minimum discharge of 10,000 litres and above per day. The recycled water should be used for horticultural purposes”. Handbook on Service Level Benchmarking by MoHUA proposes a benchmark of 20% extent of recycling and reuse of sewage for urban areas.There are several benefits to wastewater recycling for cities, industries, agriculture and others, which are explained here:.An additional source of water: Recycled wastewater reduces freshwater demand in the city, in industry, and in agriculture. This option is generally less expensive than other options for augmenting existing water supplies from distant sources or through expensive treatment, such as desalination. .Using treated or untreated wastewater for agriculture has historically been prevalent in India; however, there is a need to understand the economic, environmental, social, and health implications of using untreated wastewater and to mitigate any deleterious effects. In coastal areas, reclaimed wastewater (discharged to the sea) is an additional resource to meet irrigation demand, and in upstream locations, the use of reclaimed water in agriculture frees up freshwater for domestic and industrial consumption. By 2030, treated wastewater from Class I and II cities can meet about a quarter of the current industrial water demand..Source of revenue for utilities: Utilities with well-functioning STPs are in a position to sell treated effluent to industrial customers, depending on demand and the availability of other water sources. Utilities may charge these industrial customers for this recycled wastewater based on the required level of treatment provided and the quality of wastewater. Therefore, it is desirable therefore, that cities, whenever possible, should promote the use and sale of recycled wastewater to industrial customers, even making this practice mandatory through changes in the state/local regulations.Reduction in groundwater pumping requirement: The use of treated wastewater for irrigation also can to reduce groundwater irrigation, hence pumping and the associated energy requirement, GHG emissions, and associated costs. An estimated 1.75 million MWh of electricity, which is equivalent to reducing about 1.5 million tonnes of CO2e (tCO2) GHG emissions can be avoided by reduced pumping every year in India.While treated wastewater presents potential economic and environmental benefits to consumers (industrial, agricultural), city governments and states–an assured and reliable water supply, the nutrients present in the wastewater, and avoided costs of groundwater pumping – utilities and state/ city governments will need to develop more sustainable business models. These models should aim at different user categories – industry, agriculture, institutions/commercial establishments–which in collaboration with partner agencies ensure financial viability, follow water allocation rules and support peri-urban agriculture..The treated water from Sewage Treatment Plants (STP) and Effluent Treatment Plants (ETP) is critical for conserving freshwater and preventing environmental contamination. Reusing this water lowers the demand on natural aquifers, helps industries and municipalities comply with government regulations, and eliminates toxic health risks..Why Treated Water Matters: STPSewage Treatment Plants process domestic wastewater from residential and commercial buildings..Disease Prevention: Untreated sewage contains pathogens that cause cholera and typhoid; treating it makes the water safe for non-potable use.Water Recycling: Treated STP water is perfectly suited for landscaping, toilet flushing, construction curing, and agricultural irrigation.Environmental Protection: Discharging raw sewage into water bodies depletes oxygen and creates dead zones. Proper treatment allows safe environmental release or reuse..Why Treated Water Matters: ETPEffluent Treatment Plants treat toxic, chemical-laden wastewater from industries such as pharmaceuticals, textiles, and manufacturing.Pollutant Neutralisation: ETPs remove heavy metals, toxic dyes, and chemicals that would otherwise contaminate soil and groundwater. Industrial Sustainability: Treated effluent can often be recirculated into factory cooling towers or equipment cleaning, reducing overall freshwater consumption.Regulatory Compliance: Proper treatment ensures industries avoid heavy penalties from local environmental boards by meeting strict discharge limits..Utilisation of treated waterThe best utilisation of treated water includes large-scale agricultural irrigation, industrial cooling, and groundwater recharge. To design a safe, localised system, explore resources such as the Food and Agriculture Organisation for agroforestry and the Urban Green-blue Grids to review urban reuse.The ideal reuse application depends on the water's treatment level (primary, secondary, or tertiary). Top applications include:.1. Agriculture and AgroforestryCrop Irrigation: Treated water is highly suitable for agricultural lands and peri-urban farming. It supplies essential macro- and micro-nutrients such as nitrogen and phosphorus, acts as a natural fertiliser, and often increases yields.Energy Plantations and Fodder: Using treated water for non-edible crops, forestry, and animal fodder safely manages wastewater without exposing human food chains to heavy metals.2. Industrial ProcessesCooling Towers: Large manufacturing plants, textile facilities, and power plants require massive volumes of water for cooling.Process Water: Instead of drawing from vulnerable groundwater or freshwater reserves, many industrial clusters use treated wastewater as their primary supply..3. Urban and Municipal UseLandscaping and Parks: Recycled water is ideal for golf courses, sports fields, and urban parks. It is particularly effective when applied through subsurface drip irrigation to prevent human contact.Toilet Flushing and Construction: Non-potable treated water is commonly piped back into municipal buildings for flushing toilets and used as a water source in concrete mixing..4. Environmental and Ecological RestorationGroundwater Recharge: Highly treated water (often following tertiary treatment and UV sterilisation) can be pumped or naturally infiltrated into depleted underground aquifers to prevent saltwater intrusion and land subsidence.Wetland Creation: Sustaining artificial wetlands and recreational lakes supports wildlife habitats while keeping water within the natural ecosystem..ABOUT THE AUTHORSanjay Singh Kushwaha is a General Manager with 31 years of experience in the field of Project/Plant Operation and maintenance of Steel and Power Plant and Petrochemical Industries. Bachelor in Mechanical & Metallurgical Engineering Mr Sanjay can be contacted by email, sanju_7in@rediffmail.com
