Advanced Trickling Filter Design Calculator

Input Data

Design basis

Average flow (m³/day)

Peak factor

Influent BOD₅ (mg/L)

Target effluent BOD₅ (mg/L)

Primary clarification removal (%)

Recirculation ratio, R = Qr/Q

Filter depth (m)

Design organic loading (kg BOD/m³·day)

Design hydraulic loading (m³/m²·day)

Safety factor

Distributor arms

Media void ratio

Wastewater temperature (°C)

Example Data Table

Basis	Flow (m³/day)	Influent BOD (mg/L)	Primary Removal (%)	Recirculation Ratio	Depth (m)	Organic Loading	Hydraulic Loading
Standard rate	2,500	220	30	1.0	2.0	0.35 kg/m³·d	12 m³/m²·d
High rate	5,000	180	28	1.5	1.8	0.85 kg/m³·d	25 m³/m²·d
Plastic media	7,200	240	35	2.0	6.0	1.80 kg/m³·d	40 m³/m²·d

Formula Used

Applied influent concentration after primary clarification:

S_applied = S₀ × (1 − P/100)

BOD mass loading to the filter:

W = Q × S_applied / 1000

Required filter volume by selected organic loading:

V_org = (W / L_org) × SF

Required surface area by selected hydraulic loading:

A_hyd = (Q × (1 + R) / L_hyd) × SF

Hydraulic-governed volume and governing size:

V_hyd = A_hyd × D, and V = max(V_org, V_hyd)

Equivalent circular diameter:

d = √(4A/π)

Recirculation factor used in the NRC screening check:

F = (1 + R) / (1 + 0.1R)²

Single-stage NRC screening form used for estimated removal:

E = 100 / (1 + 0.0085 × √(W / (V × F)))

This calculator is intended for preliminary sizing and comparison. Final design should still verify distributor hydraulics, ventilation, media choice, solids handling, seasonal temperature effects, and local code requirements.

How to Use This Calculator

Choose a design basis that matches the media and operating style.
Enter average flow, BOD values, primary removal, and recirculation ratio.
Set trial organic loading, hydraulic loading, depth, and a safety factor.
Run the calculation to compare organic-governed and hydraulic-governed sizes.
Review the result panel above the form for quick sizing outputs.
Check the warnings section before accepting the trial design.
Use the detailed table for reporting, CSV export, or PDF printing.
Refine the assumptions until the design basis and target performance align.

Frequently Asked Questions

1. What does this calculator mainly size?

It estimates filter volume, plan area, circular diameter, hydraulic loading, organic loading, recirculation flow, and a screening effluent check for BOD performance.

2. Why include primary clarification removal?

Primary settling reduces the BOD applied to the media. That changes organic loading, required filter volume, and the removal efficiency you must achieve afterward.

3. Why is recirculation important?

Recirculation improves wetting, can stabilize performance, and affects hydraulic loading. It also changes the recirculation factor used in the NRC screening estimate.

4. What is the governing design size?

The calculator compares the volume needed for organic loading against the volume implied by hydraulic loading and depth. The larger requirement controls the reported size.

5. Is the NRC result a final guarantee?

No. It is a screening estimate for preliminary design. Final design should include media selection, temperature correction, ventilation, secondary clarifier limits, and regulatory review.

6. Can I use this for plastic media towers?

Yes, as a preliminary check. Choose the plastic media basis and enter realistic depth and loading values for the selected packing and manufacturer recommendations.

7. Why does the calculator show an equivalent square side?

Some concept layouts start with square plans instead of circular filters. The square side helps compare site fit, civil layout, and structural options quickly.

8. When should I increase the safety factor?

Increase it when influent variability, cold weather, uncertain pretreatment, future growth, or stricter effluent targets make the early-stage design more conservative.