Proper chemical dosing system sizing is critical for treatment performance and operating cost optimization. Overdosing wastes chemicals (up to $50,000/year excess cost), while underdosing fails to meet discharge standards. This technical guide provides the calculation methods and design parameters for accurate dosing system specification.

Coagulant Dosing Calculation

Step 1: Determine Required Dosage

Application	Typical Dosage (mg/L)	Common Chemical
Primary Coagulation	20-150	PAC (Polyaluminum Chloride)
Phosphorus Removal	10-50	Ferric Chloride (FeCl3)
pH Adjustment (acid)	5-50	Sulfuric Acid (H2SO4)
pH Adjustment (alkali)	10-100	Sodium Hydroxide (NaOH)
Disinfection	2-15	Sodium Hypochlorite (NaOCl)

Step 2: Calculate Daily Chemical Consumption

Formula: Daily consumption (kg/day) = Flow (m3/day) x Dosage (mg/L) / 1000

Example: 2,000 m3/day flow, 50 mg/L PAC dosage

Daily consumption = 2,000 x 50 / 1,000 = 100 kg/day PAC (as 100% concentration)

Step 3: Size the Dosing Pump

Formula: Pump capacity (L/h) = Daily consumption (kg/day) / (Solution concentration x Operating hours x Density)

For PAC at 10% solution, 24h operation, density 1.18 kg/L:

Pump capacity = 100 / (0.10 x 24 x 1.18) = 35.3 L/h

Select pump at 130% of calculated capacity = 46 L/h (next standard size: 50 L/h)

Polymer Dosing for Sludge Dewatering

Dewatering Type	Polymer Dosage	Solution Concentration
Screw Press	2-4 kg/t DS	0.1-0.3%
Belt Press	3-5 kg/t DS	0.1-0.5%
Centrifuge	4-8 kg/t DS	0.2-0.5%

Polymer Preparation System Sizing

• Batch system: Size for 1-2 batches per 8-hour shift
• Continuous system: Size for 120% of peak sludge flow
• Maturation time: 30-60 minutes required after dissolution
• Tank material: PE or SS316L (polymer is corrosive in concentrate form)

Complete Dosing Skid Design Parameters

Component	Specification
Dosing Pumps	Diaphragm type, ATEX if required, PTFE wetted parts
Solution Tanks	PE/SS with level switches and mixer
Control	Flow-proportional or PID-controlled (SCADA-ready)
Safety	Drip tray, leak detection, emergency shower nearby
Calibration	Calibration column with graduated scale
Redundancy	Duty/standby pump arrangement for critical dosing

Common Sizing Mistakes

1. Ignoring polymer aging: Prepared polymer loses 50% effectiveness after 24 hours – size for fresh batches
2. Underestimating peak flows: Storm events can double plant flow in minutes
3. Wrong solution concentration: Too concentrated = poor mixing; too dilute = oversized tanks
4. Missing duty/standby: Critical dosing points (disinfection) need redundant pumps

Feiran EP Dosing Skid Solutions

Feiran EP provides pre-assembled, factory-tested chemical dosing skids with Siemens PLC control, complete with calibration columns, drip trays, and SCADA integration. Available in single-chemical and multi-chemical configurations.

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