In-Situ Acid Dosing: The Precision Recovery of MBR Aeration Efficiency

By: Kate Chen
Email: [email protected]
Date: Mar 19th, 2026

In-situ acid cleaning is the localized injection of organic acids into the active air stream to dissolve mineral scaling (calcium carbonate) and biological foulants from disc diffuser membranes without tank drainage. This process restores the Standard Oxygen Transfer Efficiency (SOTE) and reduces blower backpressure, typically cutting aeration energy consumption by 15–25% for fouled systems.

The Technical Strategy: Why In-Situ Dosing is Mandatory

In MBR and high-load industrial plants, draining tanks is operationally disruptive and expensive. In-situ cleaning leverages the air distribution grid as a delivery vehicle. By atomizing concentrated Formic Acid (HCOOH) or Acetic Acid (CH₃COOH) into a fine mist, the chemical is forced through the membrane pores from the inside out, chemically “softening” the debris that causes pore-clogging.

Operational Comparison: Cleaning Methods for Industrial Aeration

Acid Dosing: Best for inorganic scaling and mineralized biofilms.
Pressure Bumping: Best for loose biological growth and physical debris.
Manual Scrubbing: Last resort for irreversible fouling (requires drainage).

Feature	Liquid Acid Dosing (In-Situ)	Physical “Pressure Bumping”	Manual Scouring (Ex-Situ)
Primary Target	Calcium Carbonate / Struvite	Soft Biofilms / Sludge Flakes	Irreversible Scaling / Silt
Operational Impact	Zero (Process remains online)	Zero (Process remains online)	High (Requires tank drainage)
Recovery Rate	80–95% of Design SOTE	40–60% of Design SOTE	90–100% of Design SOTE
Chemical Req.	85% Formic or Acetic Acid	None	Water / Detergents
Risk Factor	Corrosion of non-plastic pipes	Membrane rupture if over-pressured	Mechanical damage to pores

Step-by-Step Technical Protocol (SOP)

Baseline Diagnostics: Record the Blower Discharge Pressure and Airflow (SCFM) at a fixed motor frequency.
Acid Selection: Use 85% Formic Acid for maximum potency. It is more acidic than acetic acid and more effective at breaking down complex industrial scales.
The Dosing Calculation: Allocate 60ml to 100ml of acid per 9-inch disc.
- Example: For a grid of 500 diffusers, use 30–50 Liters of acid.
Injection Phase: Use a chemical metering pump to inject acid into the air header after the check valve. Maintain a “Cleaning Flow” (approx. 3.5 m³/h per disc) to ensure the mist travels the full length of the lateral pipes.
Permeation: The acid reacts with the scale, releasing CO₂ gas. Monitor the pressure drop in real-time.
Flushing: Run blowers at high speed for 30 minutes post-injection to clear residual acid from the piping.

Critical Material Compatibility for Acid Cleaning

Component	Compatible Materials	Warning / Non-Compatible
Membrane	EPDM / PTFE-Coated EPDM	Silicone (limit concentration to <50%)
Piping Grid	PVC / Stainless Steel (304/316)	Galvanized Steel (Immediate Corrosion)
O-Rings	Viton / EPDM	Natural Rubber (Degrades in acid)
Blowers	N/A (Keep acid downstream)	Fumes can damage blower impellers

The “Alpha Factor” (α) Recovery Logic

Fouling doesn’t just block air; it increases bubble size (coalescence). Larger bubbles have a lower surface-area-to-volume ratio, which crashes the Oxygen Transfer Efficiency. Successful acid dosing restores the micro-perforation integrity, returning the bubble size to the optimal 1–3 mm range. This shift is what restores the α value of the wastewater, allowing the plant to maintain Dissolved Oxygen (DO) with significantly lower blower RPM.