# Wastewater Surcharge BOD and TSS Calculator

> Source: https://netray.co/tools/wastewater-surcharge-bod-tss-calculator
> Publisher: Netray (netray.co), AI and integration engineering for ERP and manufacturing systems.
> Section: Free Tools

## Short answer

Compute industrial sewer surcharges for BOD and TSS above permit limits and test pretreatment savings.

## Category

ehs-workforce

## Industry

Discrete Manufacturing

## Audience

- EHS manager
- Environmental engineer
- Plant manager
- Facilities manager

## Tool

**Kind:** calculator

**Currency:** $

**Inputs:**

#### Discharge flow

**Key:** flow

**Type:** number

**Default:** 300

**Min:** 0

**Step:** 10

**Unit:** m3/day

#### BOD5 concentration

**Key:** bod

**Type:** number

**Default:** 900

**Min:** 0

**Step:** 10

**Unit:** mg/L

#### BOD5 base limit

**Key:** bod_lim

**Type:** number

**Default:** 300

**Min:** 0

**Step:** 10

**Unit:** mg/L

**Help:** Level above which your utility applies a surcharge. See your permit.

#### TSS concentration

**Key:** tss

**Type:** number

**Default:** 600

**Min:** 0

**Step:** 10

**Unit:** mg/L

#### TSS base limit

**Key:** tss_lim

**Type:** number

**Default:** 300

**Min:** 0

**Step:** 10

**Unit:** mg/L

#### BOD surcharge rate

**Key:** bod_rate

**Type:** number

**Default:** 0.45

**Min:** 0

**Step:** 0.01

**Unit:** $/kg

#### TSS surcharge rate

**Key:** tss_rate

**Type:** number

**Default:** 0.3

**Min:** 0

**Step:** 0.01

**Unit:** $/kg

#### Discharge days per year

**Key:** days

**Type:** number

**Default:** 300

**Min:** 1

**Max:** 365

**Step:** 5

**Unit:** days

#### Pretreatment removal of excess

**Key:** removal

**Type:** slider

**Default:** 60

**Min:** 0

**Max:** 100

**Step:** 5

**Unit:** %

**Outputs:**

#### BOD load

**Key:** bod_load

**Expr:** flow * bod / 1000

**Format:** decimal

**Description:** kg per day. One mg/L equals one g per m3.

#### BOD above limit

**Key:** bod_excess

**Expr:** flow * max(0, bod - bod_lim) / 1000

**Format:** decimal

**Description:** kg per day.

#### TSS above limit

**Key:** tss_excess

**Expr:** flow * max(0, tss - tss_lim) / 1000

**Format:** decimal

**Description:** kg per day.

#### Daily surcharge

**Key:** daily

**Expr:** bod_excess * bod_rate + tss_excess * tss_rate

**Format:** currency

#### Annual surcharge

**Key:** annual

**Expr:** daily * days

**Format:** currency

**Primary:** true

#### Annual saving from pretreatment

**Key:** saving

**Expr:** annual * removal / 100

**Format:** currency

**Primary:** true

**Chart:**

#### Annual surcharge vs BOD concentration

**Type:** line

**X:** bod

**From:** 100

**To:** 2000

**Steps:** 20

**Series:**

- annual

**Disclaimer:** Surcharge formulas differ by utility. Some bill on pounds, some on tiered concentration bands. Use the rate sheet in your discharge permit.

## Content

**Intro:** Many utilities charge industrial users extra when wastewater strength exceeds a base level, usually for BOD and TSS. This calculator turns your concentrations and flow into daily loads and annual surcharge, and tests the value of pretreatment.

**Sections:**

#### How to use the calculator

**Body:** Enter average daily flow and the average concentrations from your compliance sampling. Then enter the base limits and the per kilogram surcharge rates from your utility's rate schedule or permit. Set the number of discharge days per year and the share of the excess you expect pretreatment to remove. The results show loads, the surcharge per day and per year, and the saving. Run it again with the highest sample results to see worst case exposure.

**Bullets:**

- Use flow-weighted averages, not a single grab sample
- Check whether the surcharge applies to the excess only or to the whole load
- Include only the parameters your utility charges for

#### The math

**Body:** Because 1 mg/L equals 1 g/m3, the load in kg per day is flow in m3 per day times concentration divided by 1000. The excess load uses the concentration above the base limit, floored at zero. The surcharge is excess kg times the rate for each parameter, summed for BOD and TSS, then multiplied by discharge days. The chart sweeps BOD and shows that annual surcharge rises linearly once you pass the limit and stays flat below it.

#### Reading the result

**Body:** At defaults, the plant discharges 270 kg of BOD per day with 180 kg above the limit and 90 kg of TSS above the limit. That is roughly 108 dollars per day or about 32,000 dollars per year. Pretreatment such as equalization, dissolved air flotation or screening that removes 60% of the excess would save around 19,000 dollars per year, before capital and operating cost. Compare that to the equipment payback to decide.

#### Common mistakes

**Body:** Mixing mg/L with lb per 1000 gallons, or using gallons with a metric rate, is the top source of error. Another is using the annual average when the utility bills monthly on peak samples. Surcharges may also have minimum fees. Keep sampling results, flow meter readings and invoice dates in one record so you can challenge disputed bills and prove compliance.

**Bullets:**

- Match units to the rate sheet
- Check the sampling method in your permit
- Validate flow with meter data

**Cta:** Netray can connect lab results, flow meters and utility invoices from your ERP and files into a searchable environmental record, kept private on your servers.

**Faq:**

#### What is BOD5?

**Answer:** Biochemical oxygen demand over five days is the oxygen microorganisms consume breaking down organic matter in a water sample at 20 C. It measures how much organic load your wastewater puts on the treatment plant.

#### How do I convert mg/L to kg per day?

**Answer:** Multiply the concentration in mg/L by the flow in m3 per day, then divide by 1000. For US units, multiply mg/L by flow in million gallons per day by 8.34 to get pounds per day.

#### Does every utility charge the same way?

**Answer:** No. Some charge only the excess above a base strength, some bill tiered rates, and others charge a flat strength factor. Use the formula in your utility's ordinance or rate schedule and adjust the inputs accordingly.

#### What reduces BOD and TSS cheaply?

**Answer:** Good housekeeping, dry cleanup before washdown, spill containment, screening and equalization often cut load before any capital-intensive process. Dissolved air flotation or biological pretreatment follows if the savings justify it.

## Search terms

wastewater surcharge calculator, BOD TSS surcharge, industrial sewer surcharge, pretreatment savings calculator, BOD loading kg per day, mg/L to kg per day, industrial user surcharge fee, wastewater strength charge

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