Greywater Recycling System for Hotels and Societies

Introduction: The Water You Use Twice

Every building drains two kinds of wastewater. Blackwater comes from toilets and carries faeces, urine and the pathogens that go with them. Greywater comes from showers, bathtubs, wash basins, laundry and, in some definitions, kitchen sinks. It is dirtier than clean water but far cleaner than sewage, and it makes up a large share of what a building discharges, often more than half of the domestic wastewater.

This is a resource that most buildings throw away. A hotel, hospital or housing society buys water, uses it once for a shower, then sends it to the sewer or to the STP, and buys more water to flush the same building's toilets. Greywater recycling closes that loop: it collects the lightly polluted water, treats it to a safe quality and sends it back for flushing, gardening, cooling or cleaning.

The case is getting stronger. Water prices and tanker costs keep rising. Large water users may face reuse obligations if the draft Liquid Waste Management Rules are finalised, as discussed in our guide to the Liquid Waste Management Rules. Green building ratings reward reuse. And greywater is easier and cheaper to treat than mixed sewage, since it has much lower BOD and no heavy faecal load.

This guide explains what greywater is, how much a typical building produces, what treatment train it needs, how to handle plumbing and safety, what it costs and what to ask a supplier, with a worked example for a 200 flat society. It is written for hotel owners, hospital administrators, society committees, builders and facility managers. Trity Enviro designs greywater recycling systems for such buildings, and the guide draws on that work.

What Greywater Is and How Much You Produce

Light and Dark Greywater

Designers often separate greywater into two grades:

• Light greywater comes from showers, bathtubs and wash basins. It carries soap, hair, skin cells and small amounts of organic matter. BOD is usually low, often in the range of tens to a hundred or so mg/L.
• Dark greywater includes laundry, dishwashing and kitchen sink water. It carries detergents, food particles, fats and oils, and its BOD and COD are higher. Kitchen water, with grease, is the hardest part.

Many buildings recycle only light greywater, because it is the simplest to treat. Others combine laundry and some kitchen water with a grease trap and stronger treatment. Hospitals and some industrial uses require extra care, since their greywater may carry disinfectants and pathogens.

A Worked Example for a 200 Flat Society

A housing society has 200 flats with four residents each, 800 people in all. Assume domestic water use of 135 litres per person per day, a common design figure.

• Total water use: 800 × 135 = 108,000 L/day, or about 108 KLD
• Greywater share: If bath, basin and laundry water is about 60 percent of the total, greywater is about 65 KLD
• Toilet flushing demand: Flushing often accounts for 30 to 40 percent of domestic use. At about 45 litres per person per day, flushing needs 800 × 45 = 36,000 L/day, or 36 KLD
• Result: The 65 KLD of greywater is enough to cover all flushing with about 29 KLD to spare, which can go to gardening, car washing and cooling tower make-up

On these assumptions, a greywater plant could cut the society's fresh water demand by about a third. Use your own occupancy and metered data for a real design. The same approach works for hotels, where showers and laundry produce much greywater and cooling towers add another big demand. Our guide to how to calculate STP capacity explains how to estimate flows.

The Treatment Train

Screening, Grease Removal and Biological Treatment

Greywater carries hair, lint and fats that block pipes and pumps, so the treatment train begins with protection:

1. Screens and a hair and lint trap at the collection point
2. Grease trap or oil skimmer for kitchen and laundry streams. See our oil skimmer page
3. Equalization tank with gentle mixing, sized for morning and evening peaks, as covered in our guide to equalization tank design
4. Biological treatment: Even light greywater contains enough organic matter to go septic if stored, so it is usually treated biologically. MBBR is popular because it is compact, copes with variable loads and is easy to operate. See our MBBR sewage treatment plant page. MBR gives very high quality in minimal space, as described on our MBR sewage treatment plant page.
5. Clarification: a tube settler or membrane stage

Filtration and Disinfection

After biology, polishing steps make the water safe and pleasant to use:

• Pressure sand filter and activated carbon filter to remove suspended solids, colour and odour. See our multi grade filter and activated carbon filter pages
• Ultrafiltration, where very clear water is needed or space is tight
• Disinfection with chlorine or UV, and a small residual in the storage tank to prevent regrowth

Typical targets for flushing and gardening are low turbidity, little colour and odour, low BOD and TSS and a disinfectant residual, together with a faecal coliform count at or below the limit your local authority or consent sets. Check what applies in your city. Our article on tertiary water treatment for industrial reuse covers the quality side in more detail, and our grey water treatment plant page describes standard systems.

Plumbing, Reuse and Safety

Dual Plumbing and Storage

The treated water has to travel from the plant to the point of use, which needs its own pipes. In a new building, plan a dual plumbing system from the start: one network for fresh water, and a second, clearly marked network for recycled water to flushing cisterns, taps for garden use and similar points. Use a distinct pipe colour, labels and tags, and never connect the two networks.

In an existing building, retrofitting dual plumbing to every flat can be expensive and disruptive. Many societies choose a partial approach: use the treated water for gardening, car washing, common area cleaning and cooling towers, and add flushing for new blocks or for common toilets. Provide a treated water storage tank with a cover and a chlorine residual, a pump and a pressure set, and an overflow to a safe discharge, as the volume of greywater and the volume of demand rarely match. Keep a fresh water make-up connection with an air gap so that flushing never runs dry.

Where Treated Greywater Can and Cannot Be Used

Suitable uses: toilet flushing, gardening and landscaping, car and floor washing, construction water, cooling tower make-up after further treatment, and some process uses.

Not suitable: drinking, cooking, bathing, laundry in contact with people unless designed for it, swimming pools and any use in patient care, food contact or sterile areas of a hospital.

Safety rules are simple and strict. Label every reuse tap, lock them where children might use them, post signs and train staff. Test the treated water regularly for turbidity, residual chlorine, BOD, TSS and coliform. Spray irrigation should avoid windy periods and contact areas. In hospitals, keep greywater reuse away from clinical zones and discuss design with infection control.

Cost, Planning and Choosing a Partner

Budget and Payback

The cost of a greywater system comes from the treatment plant, tanks, pumps, filters, disinfection, instrumentation, civil work, dual plumbing and installation. Plumbing is often the largest and most variable part in existing buildings. Running cost includes power, chemicals, filter media and membranes, operator time and maintenance.

Payback comes from fresh water avoided, valued at your true cost of water including tankers and pumping, and from lower sewage load. In the society example, saving about 36 KLD of flushing water at a water cost of Rs 50 per KL, for illustration only, would be worth about Rs 6.6 lakh a year, before running costs. Use your own cost and quantity. New buildings usually have much better economics, because dual plumbing costs little when it is built in.

Design the system to grow. Hotels and hospitals change use over time, so leave room for extra modules and ultrafiltration if needed.

Questions to Ask Before You Order

• What flow data and greywater sources did you design for, and which streams are included?
• What reuse quality do you guarantee, and what tests will prove it?
• How are grease, hair and detergents handled?
• What storage, pumping and plumbing is included, and what does a retrofit need?
• How do you protect against cross connection and misuse?
• What are the power and chemical consumption and maintenance needs?
• What operation, training and AMC support do you provide?

Trity Enviro designs greywater and sewage treatment systems for hotels, hospitals and societies, with wastewater recycling system options for larger sites, and an annual maintenance contract keeps the system safe and efficient. Our sewage treatment plant for hospital page covers special considerations in healthcare.

Operation and Monitoring Routine

Treat the system like any treatment plant, with a daily logbook. Check screens and the grease trap daily, DO and pH in the biological tank, filter pressure gauges and chlorine residual in the treated water tank. Test turbidity daily and send BOD, TSS and coliform samples to a laboratory monthly, or as your authority requires. Backwash filters on schedule, inspect diffusers and pumps and clean the storage tank at least once a year. Keep a spare set of filter media, a chlorine supply and pump parts in stock. Trity Enviro's AMC visits include sampling, a written report and a check of reuse points, so that problems such as odour, staining or low residual are caught before residents notice.

Industry Comparison / Operational Parameter Table

Why Choose Trity Enviro

Trity Environ Solutions is an ISO 9001:2015 certified and QCI-approved greywater treatment plant and wastewater recycling system manufacturer and supplier in India, delivering robust, high-efficiency systems engineered for CPCB and SPCB regulatory compliance.

Every installation is supported by pan-India Annual Maintenance Contract and Operation and Maintenance services.