CSTR Digester
A CSTR Digester (Continuous Stirred Tank Reactor) is one of the most common and reliable digesters used in biogas / Bio-CNG plants—especially relevant for agri-waste and organic waste projects like the ones you’re exploring. Let’s break it down cleanly and practically.
What is a CSTR Digester?
A CSTR digester is a closed, cylindrical tank where:
Organic slurry is fed continuously
Contents are mechanically mixed
Anaerobic bacteria convert waste into biogas (CH₄ + CO₂)
H2S Removal System
An H₂S (Hydrogen Sulfide) removal system is a must-have in any biogas / Bio-CNG plant—especially if you’re running a CSTR digester on agri-waste, press mud, or dung. Let’s explore it from practical plant reality, not textbook theory.
Why H₂S Removal Is Critical
Biogas typically contains 50–3,000 ppm H₂S (sometimes higher). If untreated, it causes:
⚠️ Corrosion of pipelines, compressors, engines
⚠️ Catalyst poisoning in CBG upgrading systems
⚠️ Health hazards (toxic, rotten-egg smell)
⚠️ Failure to meet OMC / BIS CBG specs
Water Scrubber
A water scrubber is one of the most proven, regulator-friendly, and widely used systems for biogas upgrading to Bio-CNG—especially in Indian agri-waste projects. Let’s explore it from plant design + operation + decision-making angles.
What Is a Water Scrubber?
A water scrubber removes CO₂ and H₂S from biogas by physical absorption in water under pressure.
Key principle:
CO₂ and H₂S dissolve in water much more easily than methane (CH₄).
PSA Purification Plant
A PSA Purification Plant (Pressure Swing Adsorption) is a high-precision biogas upgrading technology used to convert raw biogas into Bio-CNG (≥95% CH₄). It’s more “engineering-intensive” than a water scrubber—but when done right, it delivers excellent gas quality with minimal water use.
What Is a PSA Purification Plant?
PSA separates gases based on their different adsorption behavior on solid adsorbents under pressure.
CO₂, H₂S, moisture, O₂, N₂ → adsorbed
CH₄ → passes through as product gas
The system works in cycles using pressure changes—no chemicals, no water.
Membrane Biogas Separation
Membrane Biogas Separation is a modern, modular way to upgrade biogas into Bio-CNG–grade methane using selective gas-permeable membranes. It sits neatly between water scrubbers and PSA in terms of CAPEX, footprint, and automation—and it’s gaining traction in India for mid-to-large plants.
What Is Membrane Biogas Separation?
A membrane system uses polymer membranes that let CO₂, H₂S, H₂O, O₂, N₂ pass through faster than CH₄.
Permeate side: CO₂-rich gas
Retentate side: CH₄-rich product gas
No chemicals. Minimal water. Continuous operation.
Organic Fertilizer
Organic fertilizer from biogas plants is not a by-product—it’s a second revenue stream when designed properly. Since you’re exploring CSTR digestion and upgrading systems, this closes the loop on waste → energy → soil health.
What Is Organic Fertilizer (from Biogas)?
After anaerobic digestion, the leftover material is called digestate. It is:
Rich in N, P, K
Biologically stabilized
Low odor
Pathogen-reduced
With proper processing, digestate becomes market-ready organic fertilizer.
Compressed Biogas
Compressed Biogas (CBG)—also called Bio-CNG—is the final, high-value product of the whole biogas chain you’ve been exploring (CSTR → H₂S removal → upgrading → fertilizer). This is where energy, policy, and revenue meet.
What Is Compressed Biogas (CBG)?
CBG is purified biogas with:
≥95% methane (CH₄)
Compressed to 200–250 bar
Stored and transported like CNG
Chemically, CBG ≈ Natural Gas, but it’s renewable and carbon-negative.
Biogas From Waste
Biogas from Waste is the foundation of everything you’ve been exploring—CSTR digesters, H₂S removal, upgrading, fertilizer, and finally CBG. Think of it as waste management + energy production + soil restoration rolled into one system.
What Is Biogas from Waste?
Biogas is produced when organic waste decomposes anaerobically (without oxygen), yielding:
Biogas: 50–65% methane (CH₄)
Digestate: nutrient-rich organic fertilizer
Pellets from Biogas Plant Waste
Pellets are solid bio-products made by drying and compressing digestate (the leftover slurry after biogas production). They are nutrient-rich, easy to handle, and environmentally friendly.
Raw Material Source
Biogas plant digestate from:
Agricultural waste
Cattle dung
Food & organic waste
Solid fraction separated using screw press / decanter
