3.2.11 Primary Treatment Tanks
This section details the primary treatment tanks at the WWTP: Primary Tank 1 (PT-1), Primary Tank 2 (PT-2), and Pre-Anoxic Tank (AT-1), plus the alkalinity dosing system. Based on the LBC OWMS O&M Manual V1.1.
Overview
Primary treatment of raw wastewater is performed using existing septic tanks at the site plus 66,000 L of new primary treatment capacity at the WWTP. All tanks are installed below ground with waterproof lids and risers. They capture and process more than two-thirds of gross solids, grease, and oils. Desludging intervals are expected at approximately 6–8 years.
Primary Tank 1 (PT-1)
Specifications
| Item | Detail |
|---|---|
| Capacity | 22,000 L concrete tank |
| Coating | Internal epoxy coating (H₂S attack prevention) |
| Manufacturer | Taylex Tanks (Fastcall Plumbing NT) |
| Lids | 2 × fibreglass lids and risers (Orenco) |
| Venting | Venting lid with activated carbon odour suppression kit |
| Access | Tank shield anti-access grate |
| Float Assembly | MF4P-VC, 39" length (Orenco) |
Function
Receives raw wastewater from the collection network (SPS1/SSP1 and SPS2/STEP tank). Treatment occurs via settling and anaerobic digestion. Can typically achieve BOD removal of >50% and TSS removal of >90% when using an effluent filter.
Operating Logic
Passive operation — no automated controls.
Primary Tank 2 (PT-2)
Specifications
| Item | Detail |
|---|---|
| Capacity | 22,000 L concrete tank |
| Coating | Internal epoxy coating (H₂S attack prevention) |
| Manufacturer | Taylex Tanks (Fastcall Plumbing NT) |
| Lids | 2 × fibreglass lids and risers (Orenco) |
| Effluent Filter | Biotube Filter, 12" (FT1260-36, Orenco) |
| Access | Tank shield anti-access grate |
Function
Provides equalisation and stability by levelling out flow peaks and allowing consistent loading of the AdvanTex AX100 filters. Further primary treatment occurs before effluent exits via gravity through the effluent filter, retaining all solids and debris greater than 3 mm.
Operating Logic
Passive operation — primary treated effluent gravity flows from PT-1 into PT-2.
Pre-Anoxic Tank (AT-1)
Specifications
| Item | Detail |
|---|---|
| Capacity | 22,000 L concrete tank |
| Manufacturer | Taylex Tanks (Fastcall Plumbing NT) |
| Lids | 2 × fibreglass lids and risers (Orenco) |
| Pump Package | Orenco Biovault (PVU84-2425-L) with Biotube 24" cartridge |
| Discharge Pumps | 2 × Orenco PF(50Hz)300534 — 1/2 hp, 30 gpm, 380 V 3Ø |
| Water Meter | 50 mm HR MultiJet with 10 L pulse reed output (Thinkwater NT) |
Function
Effluent gravity transfers from PT-2 into AT-1. A portion of treated effluent is pumped back from the AdvanTex Recirculation Tank, creating an anoxic environment for denitrification (conversion of NO₃ to N₂ gas by facultative heterotrophic bacteria).
Effluent is discharged to the downstream AdvanTex Recirculation Tank via duty/standby submersible pumps with float-controlled operation.
Operating Logic — Pre-Anoxic Pumps
Controls pumps (2), PF(50Hz)300534, 380 V 3Ø, 1/2 hp (1.1 A each) in duplex alternating, on-demand mode.
Float Operation:
| Level | Action |
|---|---|
| High Level Alarm / Lag Pump Enabled | Lead Pump On |
| Mid level | Pump(s) Off |
| Redundant Off / Low Level Alarm | — |
Settings:
| Parameter | Value |
|---|---|
| High Level Delay | 5.00 seconds |
| Lag Enable | O/F |
| Minimum Run Time | 30.00 seconds |
| Pump High Amp Alarm | 4.10 A |
| Pump Low Amp Alarm | 0.50 A |
| Pump 1 Liters per Minute | 113.56 LPM |
| Pump 2 Liters per Minute | 113.56 LPM |
Alkalinity Dosing
Purpose
Nitrification in the AdvanTex system requires alkalinity to buffer the process (7.14 mg/L alkalinity per 1 mg/L ammonia-N). For complete nitrification, pH must remain between 7.5 and 8.5, always above pH 7 (nitrification ceases at pH 5).
Equipment
| Item | Detail |
|---|---|
| Chemical | Sodium bicarbonate |
| Feed Unit | Fiberglass Liquid Chem Feed Unit (LCF-C, Orenco) with internal mixer |
| Feed Pump | Peristaltic alum feed pump (Orenco) |
| Target Residual | Minimum 80 mg/L; preferred 100 mg/L |
Sodium bicarbonate is dosed into the pre-anoxic tank upstream of the AdvanTex system. The Liquid Chem Feed Unit features an internal mixer to ensure adequate chemical mixing.
Operating Modes
Flow Pace (default): Peristaltic pump activation tied directly to pre-anoxic pump activation. Mixer activates prior to peristaltic pump (3 min pre-run default). Feed rate manually adjusted on peristaltic pump based on operator flow calculations.
Timer: Programmable ON/OFF times (factory default 1 min ON, 59 min OFF). Activated when LCFA RO float is up.
Maintenance
| Task | Action | Frequency | Responsible |
|---|---|---|---|
| Check Biotube® Effluent Filters (PT-2); clean as required | Inspect 12" filter | Quarterly | ENVR |
| Visual inspection of liquid levels in all tanks | Check all primary and anoxic tanks | Quarterly | ENVR |
| Sludge accumulation assessment | Measure sludge and scum levels in Primary Tanks; organise de-sludge if required | Quarterly | ENVR |
| Inspect, test and clean all floats | All tank float assemblies | Quarterly | ENVR |
| Inspect and clean intakes of all submersible pumps | Pre-anoxic discharge pumps | Annually | ENVR |
See 3.2.15 for the full maintenance program and contingency controls for declining TN/pH.
Version Control
| Version | Date | Description |
|---|---|---|
| 2.0 | 2026-06-22 | Initial Release per O&M Manual V1.1 |
| 2.0.1 | 2026-06-22 | Added primary and anoxic tanks diagram |
Next Review Date: 2026-12-22