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In every sewage or effluent treatment plant across India, one by-product is inevitable: sludge. Left untreated, this wet, heavy mass becomes a costly liability. A single 100 KLD residential STP can generate 2,000–3,000 litres of 1–2 % solid sludge every day, and disposing of it in its raw form now costs anywhere between ₹2,800 and ₹4,500 per tanker load in most states.
Sludge dewatering changes the equation completely by removing water mechanically and turning that same volume into a manageable 80–150 kg of semi-dry cake that is easy to transport, store, or even sell to farmers.
Dewatering is therefore not an optional add-on; it is the step that decides whether your treatment plant stays within budget, remains compliant with the Solid Waste Management Rules 2016, and keeps neighbours happy by eliminating odour and leachate problems.
What Exactly Is Sludge Dewatering and Why Every Indian Plant Needs It
Fresh biological sludge contains 97–99 % water. After dewatering, the same sludge reaches 18–35 % dry solids, meaning its volume shrinks by 70–90 %. The savings are real and immediate: fewer tankers, lower disposal charges, reduced risk of fines from the pollution control board, and in many cases, revenue from farmers who willingly pay ₹800–₹1,800 per ton for 25–30 % dry cake as an organic soil conditioner.
Common Dewatering Technologies Available in India Today
Several proven systems are widely used, each with its own strengths:
- Centrifuges spin the sludge at 2,500–3,500 RPM, generating forces thousands of times gravity to throw solids against the bowl wall while clear water exits through perforations.
- Belt filter presses sandwich conditioned sludge between two moving porous belts and squeeze water out through a series of rollers of gradually reducing diameter.
- Screw presses slowly push sludge forward inside a perforated screen while increasing pressure, releasing water with remarkably little energy and wash water.
- Recessed-plate or membrane filter presses pump sludge into chambers formed between filter cloths, then close the plates hydraulically and apply 8–16 bar pressure; membrane versions add a final high-pressure squeeze with air or water to achieve the highest dryness.
- Geotextile bag dewatering, still common in labour camps and small townships, relies on gravity and natural drainage after polymer conditioning.
How the Major Technologies Compare in Real Indian Conditions
Centrifuges consistently deliver cake dryness of 22–32 % and work well in large plants above 200 KLD that run continuously. They consume 15–25 kWh per ton of dry solids and require no wash water, but noise levels are high and wear parts need replacement every 8,000–12,000 operating hours. Capital cost for a 100–150 kg/hr machine usually falls between ₹55 lakh and ₹90 lakh.
Belt presses remain popular for medium-sized plants and sticky sludges because they are relatively inexpensive (₹35–60 lakh for similar capacity) and achieve 18–25 % dryness. However, they need generous wash water (20–40 % of throughput), belts wear out every 2,000–4,000 hours, and someone must watch belt tracking daily.
Screw presses and Volute units have become the first choice for housing societies, hotels, hospitals, and commercial complexes in the 20–150 KLD range. They produce 18–28 % dry cake using only 1.5–4 kWh per ton of dry solids, require almost no wash water, operate almost silently, and occupy just 8–12 m² of space. Polymer consumption is the lowest at 2–5 kg per ton of dry solids, and moving parts last 10,000–15,000 hours. Investment ranges from ₹40 lakh to ₹70 lakh.
Membrane filter presses deliver the highest dryness — often 28–40 % — making them ideal when landfill gate fees are high or when the plant plans to send cake for co-processing in cement kilns. Power consumption is moderate (3–8 kWh per ton), wash water requirement is low, and filter cloths last years with proper care. Budget ₹60 lakh to ₹1.1 crore for a 100–150 kg/hr unit.
Special Advantage of SKF Elixer Vulcan Plants
Because the Vulcan series uses Attached Growth Bioreactor (AABR) technology, the biological sludge produced is more granular and less sticky than conventional activated-sludge or MBBR plants. This translates into 30–40 % lower sludge yield to begin with (0.4–0.6 kg dry solids per cubic metre of sewage treated) and easier dewatering behaviour.
Customers regularly achieve 28–34 % cake dryness with simple screw presses and polymer dosages below 3 kg per ton of dry solids — numbers that older plants struggle to match.
Practical Tips to Select the Right System for Your Project
First, calculate expected dry solids production: a 100 KLD domestic STP typically generates 40–60 kg DS per day, while a food-processing ETP can produce three to five times more.
Second, decide the disposal or reuse route early. Farmers happily take 20–25 % dry cake from a belt or screw press, but cement plants and secure landfills demand minimum 25–30 % dryness, pushing you toward membrane filter presses or centrifuges.
Third, measure available space honestly. Basement installations in Gurugram, Bengaluru and Mumbai high-rises almost always end up with screw presses because of their tiny footprint and whisper-quiet operation.
Fourth, run a five-year total cost calculation that includes polymer at ₹280–₹420 per kg, electricity at commercial rates, spare parts, and labour. In most residential and commercial projects, a slightly higher initial investment in a screw press pays back faster than a cheaper belt press.
Fifth, insist on jar tests and pilot trials with your exact sludge. Reputed manufacturers conduct these free of charge and provide guaranteed performance numbers before you commit.
Finally, think one step ahead: if zero-liquid discharge or tertiary polishing is in your future roadmap, you will soon have additional filter-backwash sludge to handle. Choose equipment that can accept mixed streams without major modification.
The Bottom Line
In 2025 India, sludge dewatering has shifted from being a regulatory burden to a genuine profit centre. With tanker charges rising every year and freshwater costs following suit, a correctly sized, low-energy dewatering system typically pays for itself in 24–36 months through disposal savings alone. Add water-reuse credits and green-building points, and the return on investment becomes even more attractive.
Whether you are building a 5,000-apartment township in Hyderabad, a 300-room resort in Goa, or a 150-bed hospital in Indore, allocate 10–15 % of your total sewage treatment budget to the right dewatering technology from day one. Contact SKF Elixer to receive a quotation for sewage treatment plant
Frequently Asked Questions (FAQs)
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1. How much does a sludge dewatering machine cost in India in 2025?
A 50–100 kg DS/hr screw press costs ₹38–65 lakh, a 1 m³/hour membrane filter press ₹70–95 lakh, and a high-speed centrifuge of similar capacity ₹80 lakh–₹1.4 crore (ex-factory prices).
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2. Which technology uses the least electricity and polymer?
Screw presses and Volute-type units typically consume only 1.5–4 kWh and 2–4 kg polymer per ton of dry solids — the lowest among all mechanical options.
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3. Is natural drying in beds still allowed?
Drying beds require large open land and 15–30 days per cycle, making them impractical in urban areas. Most state pollution boards discourage or prohibit them during monsoon months.
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5. How much money can proper dewatering save a 100 KLD apartment complex?
By converting 2–3 % wet sludge to 25–30 % cake, societies routinely save ₹4–7 lakh annually in tanker and disposal charges, often achieving full payback on the dewatering unit within 30 months.
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