1. Scope and Purpose
This maintenance manual covers the three critical subsystems of industrial wastewater treatment plants as standard in manufacturing companies in the DACH region (automotive, chemical, food):
- Ventilation system: Rotary lobe blower (15–75 kW), membrane aerator (fine/coarse bubble), air distribution lines DN80–DN300
- Sludge pumps: Eccentric screw pumps and rotary lobe pumps for primary/surplus sludge (flow rate 5–80 m³/h)
- pH value control: Inline pH probes, dosing pumps, calibration systems
Implementation times: Ventilation system every 2,000 operating hours or quarterly. Slurry pumps every 1,500 hours of operation. pH calibration weekly to fortnightly according to DIN 19268.
Normative bases: DIN EN 12255 (sewage treatment plants), DIN EN 12723 (pumps), VDI 2035 (water treatment), DIN 19268 (pH measurement), VDE 0100-710 (electrical systems in medically used areas - here analogous for moist/corrosive environments), ATEX Directive 2014/34/EU for explosive areas for digester gas.
2. Safety instructions
WARNING - LOCKOUT/TAGOUT (LoTo): Before any work on fans, pumps or electrical components, a complete isolation must be carried out in accordance with DIN EN ISO 14118. All energy sources (electrical, pneumatic, hydraulic) must be disconnected and secured against being switched on again.
WARNING - CHOKING HAZARD: In closed pools and shafts there is a risk of oxygen deficiency due to H₂S and CH₄. Before entering: Carry out a gas measurement (O₂ > 19.5% vol., H₂S < 5 ppm, CH₄ < 10% LEL). Release certificate required according to DGUV Rule 113-004.
WARNING — BIOLOGICAL HAZARD: Wastewater contains pathogenic germs. Avoid skin contact. Disinfect immediately after contact. Hepatitis A vaccination recommended for maintenance personnel.
WARNING — ATEX ZONE: ATEX zones 1/2 apply in the area of digestion towers and closed sludge collectors. Only use approved tools and measuring devices (ex protection category II 2G).
Required PPE
- Chemical Resistant Gloves (EN 374, Type A)
- Safety glasses with side protection (EN 166)
- Safety shoes S5 (EN ISO 20345) — waterproof, puncture-proof
- Disposable protective suit type 4/5 (EN 14605) for mud work
- Respiratory protection: Half mask with ABEK filter when working in shafts, alternatively air-independent respiratory protection when driving
- Gas detector 4-gas (O₂, H₂S, CH₄, CO) - calibrated, test < 6 months old
3. Tools and materials
| Tool/Material | Specification | number |
|---|---|---|
| Torque wrench | 10–50 Nm, ratchet 3/8" | 1 |
| Torque wrench | 40–200 Nm, ratchet 1/2" | 1 |
| multimeter | True RMS, CAT III 600V, insulation measurement ≥ 500 V DC | 1 |
| Vibration meter | Frequency range 10-1000 Hz, resolution 0.01 mm/s | 1 |
| Infrared thermometer | Range -30 to +500 °C, emissivity adjustable | 1 |
| Pressure gauge | 0–1 bar, accuracy ±0.5%, connection G1/4" | 2 |
| pH calibration solutions | pH 4.01 / pH 7.00 / pH 10.01 (DIN 19266, traceable) | 250 ml each |
| Stator lubricant | Food-grade lubricant (NSF H1) for progressive cavity pumps | 1 tube 400 ml |
| Membrane diffuser seal set | EPDM, Ø depending on the aerator type | 10 pcs. reserve |
| flange gaskets | EPDM, DN80–DN150, PN10/16 | 2 each |
| Gas detector | 4-Gas (O₂/H₂S/CH₄/CO), ATEX II 1G | 1 |
| Feeler gauge | 0.02-1.00mm, 20 sheets | 1 sentence |
| Strobe | Flash frequency 60-99,999 FPM | 1 |
| Cable lugs/tools | Crimping pliers 0.5-6 mm², insulated cable lugs | 1 set |
4. Pre-maintenance inspection checklist
| No. | Checkpoint | Exam | Acceptance criterion | Remark |
|---|---|---|---|---|
| 4.1 | LoTo status | Visual control of all separation points | All switches open, locks in place, zero voltage test confirmed | Sign the protocol |
| 4.2 | Gas free measurement (during shaft work) | 4-gas measurement at working depth | O₂ 19.5-23%, H₂S < 5 ppm, CH₄ < 10% LEL, CO < 30 ppm | Repeat every 30 minutes |
| 4.3 | Fan housing temperature | IR thermometer on pressure side | ≤ 120 °C (rotary blower), ≤ 80 °C (side channel blower) | Exceedance → Clarify cause before maintenance |
| 4.4 | Fan vibration level | Radial vibration measurement on the bearing housing | ≤ 4.5 mm/s (ISO 10816-3, group 2) | If > 7.1 mm/s: immediate action |
| 4.5 | Slurry pump leakage | Visual inspection of shaft seal | No visible leakage, maximum moisture film | Dripping seal → plan replacement |
| 4.6 | Pressure loss ventilation network | Pressure gauge before/after distributor | Differential pressure ≤ 50 mbar at nominal air volume | Higher value → constipation likely |
| 4.7 | pH probe condition | Visual inspection of the glass electrode | No cracks, no deposits on the diaphragm, electrolyte level OK | Replace broken probe immediately |
| 4.8 | Electrical connections | Visual inspection of terminals, cable entries | No corrosion, no loose terminals, IP protection intact | Replace corroded terminals |
5. Step-by-step procedure
5.1 Ventilation system — inspection and maintenance
Disconnect the fan electrically. Main switch to OFF, attach LoTo lock. Perform a zero voltage test on the multimeter (AC V, range 0-600 V). Release residual pressure via vent valve (target pressure: 0 bar overpressure).
Common mistake: Forgetting the pneumatic residual pressure in the pressure line. Always read the pressure gauge before loosening flanges.
Check and clean the intake filter. Open the filter housing (4× M8 screws, torque when reinstalling: 15 Nm). Remove filter element. Document differential pressure during operation (acceptance: ≤ 25 mbar clean, change at ≥ 50 mbar). Blow out or replace the filter element with compressed air (max. 3 bar, nozzle distance ≥ 150 mm) from the inside to the outside.
Visual indicator: Filter material evenly bright, no oil stains, no cracks.
Check V-belt/belt drive (if present). Check belt tension: Depth of indentation at 10 N force = 3–5 mm per 100 mm free span length. Check wear markers on belt flanks. Belt alignment with laser alignment device (tolerance: ≤ 0.5°/0.5 mm parallel offset).
Common error: Excessive belt tension leads to bearing damage on the fan. Observe manufacturer's instructions.
Document the bearing temperature and vibration. Measure IR thermometers at both bearing locations. Acceptance: Storage temperature ≤ 80 °C (ambient + 40 K). Radial and axial vibration measurement on each bearing. Enter values in trend map.
Check the membrane aerator in the pool. Partially empty the pool (if possible) or use a diver/camera. Observe the aerator pattern when the fan is running: Uniform bubble formation over the entire pool surface. Individual “dead
