Water Quality Calculator
Professional BOD, COD, k-rate calculations with Thai PCD effluent standards compliance checking. Built for environmental engineers.
Select Calculation Mode
Swipe to see all 9 modes →
BOD5 Calculator — Input Parameters
Source-specific Thai Effluent Standards
Verified profiles from the official community-system and building-effluent publications. Select by legal applicability, not by desired limit.
ระบบบำบัดน้ำเสียรวมของชุมชน
Combined community wastewater treatment system
For a qualifying combined community wastewater treatment system whose final unit is not the pond exception below.
ระบบบำบัดน้ำเสียรวมของชุมชน — หน่วยสุดท้ายเป็นบ่อ
Combined community system — pond final unit
The same community instrument, applying its explicit stabilization/oxidation-pond exception.
น้ำทิ้งจากอาคาร ประเภท A / ก
Building wastewater — Type A / ก
Source-specific limits for a building classified as Type A / ก; the building use and size thresholds in the instrument must be checked before selection.
น้ำทิ้งจากอาคาร ประเภท B / ข
Building wastewater — Type B / ข
Source-specific limits for a building classified as Type B / ข; the building use and size thresholds in the instrument must be checked before selection.
น้ำทิ้งจากอาคาร ประเภท C / ค
Building wastewater — Type C / ค
Source-specific limits for a building classified as Type C / ค; the building use and size thresholds in the instrument must be checked before selection.
น้ำทิ้งจากอาคาร ประเภท D / ง
Building wastewater — Type D / ง
Source-specific limits for a building classified as Type D / ง; the building use and size thresholds in the instrument must be checked before selection.
น้ำทิ้งจากอาคาร ประเภท E / จ
Building wastewater — Type E / จ
Source-specific limits for a building classified as Type E / จ; the building use and size thresholds in the instrument must be checked before selection.
Key Formulas
BOD5
BOD5 = (D1 - D2) x DF
DF = Bottle Volume / Sample Volume
Ultimate BOD
BODu = BOD5 / (1 - e^(-k*5))
k = first-order rate constant
COD (Dichromate)
COD = (A - B) x N x 8000 / V
A=blank, B=sample, N=normality
BOD/COD Ratio
>0.5: Easily biodegradable
0.3-0.5: Moderate
<0.3: Difficult
Temp Correction
kT = k20 x theta^(T-20)
theta = 1.047 (typical)
Removal Efficiency
E = (Cin - Cout) / Cin x 100%
Cin=influent, Cout=effluent
Why Use This Calculator?
Source-specific Screening
Assess complete samples against the selected community-system or building-effluent publication
Environmental Protection
Identify exceedances and missing evidence before a discharge decision
9 Calculation Modes
BOD5, COD, k-rate, loading, efficiency, and more
APHA Methods
Standard Methods for Water and Wastewater analysis
Instant Results
Get calculations in milliseconds with step-by-step solutions
Visual Compliance
Clear pass, exceedance, and not-assessed states with evidence gaps
Frequently Asked Questions
What is BOD (Biochemical Oxygen Demand)?
BOD measures the amount of oxygen consumed by microorganisms to decompose organic matter in water over 5 days at 20C. Higher BOD indicates more organic pollution. BOD5 is the standard 5-day test used worldwide.
What is COD (Chemical Oxygen Demand)?
COD measures the total quantity of oxygen required to oxidize all organic material in water using a strong chemical oxidant (dichromate). COD is always higher than BOD because it includes non-biodegradable organics.
What does the BOD/COD ratio tell us?
The BOD/COD ratio indicates how biodegradable the wastewater is. Ratio >0.5 means easily biodegradable (suitable for biological treatment). Ratio <0.3 means difficult to biodegrade (may need chemical/physical treatment first).
What are Thai effluent standards?
Thai effluent limits depend on the legal source category. This calculator currently implements the official combined community wastewater-system publication and the building-effluent publication (building categories A-E). Choose the profile by applicability; the building letters are not industrial severity classes.
What is the k-rate in BOD calculations?
The k-rate (deoxygenation rate constant) describes how fast organic matter is decomposed. Typical values range from 0.1-0.3/day. Higher k means faster decomposition. It varies with temperature, waste type, and microbial activity.
Explore More Water Engineering Tools
A complete suite of water supply and wastewater engineering calculators
Quantify organic load and water quality from lab data: BOD, COD, reaction-rate (k), temperature correction and removal efficiency — then assess complete samples against the selected Thai effluent standard.
ประเมินภาระสารอินทรีย์และคุณภาพน้ำจากผลแล็บ: BOD, COD, ค่า k, การแก้อุณหภูมิ และประสิทธิภาพการบำบัด พร้อมประเมินข้อมูลที่ครบตามมาตรฐานน้ำทิ้งไทยที่เลือก
When to use
- Preparing EIA / monitoring reports from BOD/COD bottle tests
- Checking effluent or surface-water compliance against Thai PCD classes
- Converting lab BOD at non-standard temperatures to 20 °C basis
How to use
- 1Pick the calculation mode (e.g. BOD5, COD, removal efficiency).
- 2Enter measured values with correct units; watch the validation hints.
- 3Read the result card and the compliance badge against the selected standard.
Key formulas
BOD₅ (dilution method)
BOD₅ = (D₁ − D₂ − seed) × DF
D₁,D₂ = initial/final DO (mg/L); DF = bottle vol / sample vol
Ultimate BOD
BOD_t = BOD_u · (1 − e^(−k·t))
k = deoxygenation rate (1/d); t = time (d)
Temperature correction
k_T = k₂₀ · θ^(T−20), θ ≈ 1.047
Arrhenius-type correction (Streeter–Phelps)
Removal efficiency
η = (Cᵢₙ − C_out) / Cᵢₙ × 100%
BOD₅ from a diluted sample
- Initial DO (D₁)
- 8.0 mg/L
- Final DO (D₂)
- 2.0 mg/L
- Sample volume
- 10 mL
- Bottle volume
- 300 mL
DF = 300/10 = 30 → BOD₅ = (8.0 − 2.0) × 30 = 180 mg/L
References
- • APHA, Standard Methods for the Examination of Water and Wastewater (23rd ed.)
- • Metcalf & Eddy (2014), Wastewater Engineering, 5th ed.
- • Thai PCD — Surface Water Standards (B.E. 2537)
Continue Your Workflow
VerWater integrates the full water cycle in one platform