Two stages: anaerobic digestion of harvested azolla biomass produces raw biogas, then Pressurized Water Scrubbing (PWS) upgrades it to DM-X CBM quality — without exotic chemistry, without membranes, without proprietary solvents.
Two of the 18 concrete cylindrical tanks (6 m diameter × 1 m deep) are being sealed and fitted with gas-collection infrastructure to operate as pilot anaerobic biodigesters. At commercial scale, purpose-built CSTR digesters of 100–200 m³ each are deployed. Harvested azolla biomass is loaded as substrate; anaerobic bacteria break it down over 25–30 days, producing raw biogas.
Azolla is an ideal digester substrate: high moisture content (~90%), soft cellular structure (no lignin to resist biological breakdown), and a favourable carbon-to-nitrogen ratio of approximately 10:1 — within the productive methanogenic range. The symbiotic Anabaena azollae cyanobacterium that gave the fern its nitrogen during growth now provides the digester with a nitrogen-rich substrate that supports robust microbial activity.
Raw biogas composition from azolla digestion:
~50% CH₄ (methane) · ~50% CO₂ (carbon dioxide) · 200–2,000 ppm H₂S · trace N₂ and water vapor.
This 50/50 split is typical for fresh herbaceous biomass substrates and is entirely consistent with downstream PWS upgrading design parameters.
| Biodigester Parameter | Pilot Value |
|---|---|
| Number of digester tanks | 2 |
| Tank dimensions (each) | 6 m Ø × 1 m deep |
| Volume per tank | ~28.3 m³ |
| Total active digester volume | ~56.6 m³ |
| Digester type | Sealed CSTR (continuously stirred) |
| Operating temperature | Ambient (~28–34°C, mesophilic) |
| Hydraulic retention time | 25–30 days |
| Organic loading rate | 1.5–2.0 kg VS/m³/day |
| CH₄ yield (azolla) | ~220–280 L CH₄/kg VS |
| Daily VS input (design) | ~85–113 kg VS/day |
| Estimated biogas output | ~40–80 Nm³/day |
| Biogas CH₄ content | ~50% vol |
| Gas collection | HDPE ring manifold + dome seal |
| Digestate use | Liquid N-rich organic fertilizer |
Pilot scale output. Commercial-scale deployment (per Phase 2/3 roadmap) replaces the two converted tanks with purpose-built 100–200 m³ CSTR digester vessels sized to the local azolla supply chain.
This is the full DM-X gas train: raw azolla biogas enters from the left, pure biomethane exits right at 200 bar. Gold dashed lines show biogas; white dashed lines show upgraded biomethane; blue shows the water regeneration loop; grey shows vent streams. Click any piece of equipment to see its tag, service, specifications, and inlet/outlet stream composition.
Raw biogas has a lower calorific value than natural gas and is not itself explosive in storage; but at 200 bar and in the presence of air it is. The plant is therefore engineered to fail safely at every stage. Every hazardous area is zone-classified per IECEx / PNS IEC 60079; every pressure vessel has independent pressure relief; every compressor has an emergency shutdown (ESD) tied to gas detection. The plant does not rely on operator vigilance to be safe.
| Hazard | Consequence | Engineered Mitigation |
|---|---|---|
| Over-pressure of T-101 | Vessel rupture, gas release | Dual-redundant PSVs at 9.5 bar(g); rupture disc at 10.5 bar; pressure transmitter on DCS trip |
| Biogas leak in digester area | Flammable cloud formation | Continuous LEL monitoring; Ex-rated equipment; forced ventilation; ESD on 25% LEL |
| H₂S exposure to operators | Asphyxiation / toxicity | Fixed + portable H₂S monitors; 10 ppm TWA alarm; SCBA for confined space entry |
| Compressor seal failure (K-102) | High-pressure CBM release | Seal gas monitoring; vibration trip (ISO 10816-3 Zone B); automatic isolation |
| Cylinder over-fill | Cylinder rupture | Mass flow meter + pressure transmitter redundant fill control; 10% over-pressure rupture disc |
| Water contamination in product | Downstream corrosion, low quality | V-104 twin-tower dryer; on-line dew point analyzer; ≥ −20 °C dew point spec |
| Power failure during operation | Loss of ventilation, ESD systems | UPS on DCS and gas detection (30 min); fail-safe SDVs; emergency vent on depressurization |
| Digester overload (shock feeding) | Foam-over, pH crash, production loss | Gradual feed ramp-up; pH + VFA monitoring; controlled feed pumps on DCS |
Pressurized Water Scrubbing (PWS) exploits a simple physical fact: at 8 bar(g) pressure, CO₂ is approximately 26 times more soluble in water than methane. Pressurize raw biogas, wash it with cold water, and the CO₂ dissolves preferentially — leaving a gas stream enriched to ≥97 % CH₄. No solvents. No membranes. No chemical regeneration. The water is recycled continuously in a closed loop; the only consumable is make-up water (~5 % of circulation) and electricity.
H₂S odorant retention — the clever bit: Standard PWS would remove virtually all H₂S. DM-XTech retains approximately 50 ppm by means of a precision bypass needle valve (XV-102) that blends a calibrated fraction of raw biogas into the purified product stream. This eliminates the need for synthetic THT mercaptan odorization — saving ₱80,000–₱150,000 per year in chemical costs while providing a fully natural safety odorant with the exact same rotten-egg smell that alerts households to an LPG leak. Bypass fraction formula: x = (C_target − C_out) / (C_feed − C_out)
Slide the input to any azolla feed rate and see the full downstream chain — from fresh biomass to dry matter to volatile solids to methane to CBM cylinders to LPG equivalent and peso value. All conversion factors are standard literature values for azolla-based anaerobic digestion.
The scrubbing water is continuously regenerated in a closed-loop system — no liquid waste is discharged to the environment. The four-step regeneration cycle:
| Tag | Service | Key Specification | Standard |
|---|---|---|---|
| D-101 | Anaerobic biodigester (CSTR) | Commercial 100–200 m³ · 25–30 d HRT · mesophilic | — |
| K-101 | Feed gas compressor | 2-stage oil-free recip. · 15 kW · 1→8 bar(g) | ASME B19.3 |
| T-101 | PWS absorption column | DN250 × 9.0 m · 5.0 m PP Pall rings · SS316L | ASME VIII Div.1 |
| V-104 | Twin-tower desiccant dryer | 4Å mol. sieve · −20 °C dew point · 8-h auto cycle | — |
| K-102 | CBM compressor | 4-stage oil-free · 18.5 kW · 8→200 bar(g) · 50 Nm³/h | ASME B19.3 |
| V-103 | CBM cylinder filling manifold | 50-L Type-I steel · 200 bar · LPG thread connector | DOT-39 or eq. |
| V-105 | Flash depressurization tank | DN600 × 2200 mm · 0.5 bar(g) | ASME VIII Div.1 |
| T-102 | Atmospheric air stripper | DN300 × 4500 mm · 2.0 m PP Pall rings | — |
| V-106 | Caustic scrubber (H₂S abatement) | DN250 × 2000 mm · 10 % NaOH | — |
| P-101 A/B | Process water pumps (duty/standby) | 15 m³/h · 90 m head · 7.5 kW each · SS316L | ISO 5199 |
| E-102 | Process water cooler (PHE) | 50 kW duty · < 20 °C outlet · SS316L plates | — |
| XV-102 | H₂S bypass needle valve (odorant retention) | Calibrated raw-biogas blend · 50 ppm H₂S target in product | — |
Total installed electrical load (50 Nm³/h CBM hub basis): approximately 49 kW running / 57 kW connected. Total process water inventory (circulating): ~6 m³. Make-up water: ~5 % of circulation (from municipal or rainwater harvesting). For the complete engineering design basis, refer to the companion Engineering Design Document (PDF, available from the Engage page).
During the Month 5 to Month 7 commissioning window (see the pilot.html 12-month timeline), the plant undergoes a structured sequence of acceptance tests — each with a pre-agreed pass criterion, applicable standard, and linkage to a specific commissioning milestone. The bank and any other lender retains the right to witness these tests or require independent verification.
| # | Test | Acceptance Criterion | Standard | Milestone |
|---|---|---|---|---|
| 1 | Hydrostatic pressure test · all vessels | 1.5 × working pressure, 30 min, no leak | ASME VIII Div.1 | M5 Q1 |
| 2 | Gas pipe pressure leak test | ≤ 1 % volume loss in 24 h at 10 bar | ASME B31.3 | M5 Q2 |
| 3 | Electrical insulation resistance | ≥ 1 MΩ (line-to-earth) | IEC 60364-6 | M5 Q2 |
| 4 | Grounding continuity | ≤ 0.1 Ω plant-wide bond | PNS IEC 60364 | M5 Q3 |
| 5 | Ex-rated equipment certification | All Zone 1/2 devices bear IECEx / PNS mark | IECEx · PNS IEC 60079 | M5 Q3 |
| # | Test | Acceptance Criterion | Standard | Milestone |
|---|---|---|---|---|
| 6 | Digester biogas yield | ≥ 40 Nm³/day raw biogas at pilot scale (≥ 50% CH₄) | VDI 4630 | M6 Q1 |
| 7 | K-101 compressor performance | 100 Nm³/h raw biogas @ 8 bar(g), specific power ≤ 0.15 kWh/Nm³ | ASME PTC 10 | M6 Q2 |
| 8 | T-101 PWS purity — sustained | ≥ 97 % CH₄ at product outlet · 30 continuous operating hours | ISO 6976 (gas analysis) | M6 Q2 |
| 9 | Water consumption (make-up) | ≤ 5 mL per Nm³ CBM produced | Plant spec | M6 Q3 |
| 10 | V-104 dryer dew point | ≤ −20 °C at 8 bar product outlet | ASTM D1142 | M6 Q3 |
| 11 | K-102 compressor performance | 50 Nm³/h CBM @ 200 bar(g), specific power ≤ 0.30 kWh/Nm³ | ASME PTC 10 | M6 Q4 |
| 12 | Compressor vibration (K-101 & K-102) | ≤ 4.5 mm/s RMS (ISO 10816-3 Zone B) | ISO 10816-3 | M6 Q4 |
| # | Test | Acceptance Criterion | Standard | Milestone |
|---|---|---|---|---|
| 13 | H₂S odorant retention (XV-102) | 50 ± 5 ppm H₂S in product stream | ASTM D5504 | M7 Q1 |
| 14 | Cylinder fill validation | 10.0 ± 0.1 Nm³ per cylinder at 200 bar and 15 °C | ISO 11439 | M7 Q2 |
| 15 | Emergency shutdown response | All SDVs closed ≤ 30 s from trip signal | IEC 61508 / SIL-2 | M7 Q2 |
| 16 | Gas detection calibration | CH₄ at 25/50/100 % LEL; H₂S at 10/20 ppm TWA/STEL | OSHA 1910.146 | M7 Q3 |
| 17 | Fugitive emissions baseline | ≤ 0.5 % of product stream · OGI camera survey | EPA Method 21 | M7 Q3 |
| 18 | Final product gas composition | ≥ 97 % CH₄ · ≤ 3 % CO₂ · ≤ 0.01 % H₂O · 50 ± 5 ppm H₂S | ISO 6974 / 6976 | M7 Q4 |
The plant has exactly six vent points. The CO₂ released is biogenic — carbon that the azolla fern absorbed from the atmosphere four weeks earlier — and therefore not net anthropogenic emission. Residual methane slip is minimized to ≤ 2 % of product. Trace H₂S is neutralized before atmospheric discharge. The inventory below is the starting basis for Gold Standard VER baseline calculation and for DENR environmental permitting.
| Tag | Stream | Composition & classification | Rate |
|---|---|---|---|
| V-105 VENT | Flash tank CO₂ | Biogenic CO₂ (net zero) · 98% CO₂ · trace H₂O | ~920 kg CO₂/day |
| T-102 VENT | Stripper off-gas | Biogenic CO₂ + trace CH₄ slip (≤2% product) · routed via V-106 | ~380 kg/day · 20 Nm³ CH₄/day slip |
| V-106 STK | Caustic scrubber stack | Post-H₂S-abatement atmospheric vent · < 0.1 ppm H₂S | ~400 Nm³/day |
| PSV DISCH | Safety relief vents | Vent stack > 8 m · only during abnormal trip (normally zero) | 0 (normal op) |
| FUG EM | Fugitive (flange / seal) | ≤ 0.5 % of product CH₄ · OGI-verified baseline · LDAR program | ~5 Nm³ CH₄/day |
| D-101 RELIEF | Digester over-pressure vent | Biogas (50% CH₄ · 50% CO₂) · only during abnormal operation | 0 (normal op) |
Per Gold Standard methodology GS-TCCB-A-07 for biomethane displacing fossil LPG. At 287 MT LPG displaced per hub per year: ~860 tCO₂e/yr avoided.
Less residual methane slip at GWP₁₀₀ = 29.8 (~220 kg CH₄ × 29.8 = ~6.5 tCO₂e subtraction). Net ~854 tCO₂e/yr is the defensible VER claim.
PWS systems typically show 1.5–2.5 % methane slip. The V-106 caustic scrubber is positioned downstream of T-102 specifically to abate slip-bound H₂S before atmospheric discharge, but CH₄ itself passes through.
Continuous methane slip measurement at T-102 vent using a tunable diode laser absorption spectroscopy (TDLAS) monitor. Monthly calibration against reference gas.