WTW OxiTop®-i IS 6 BOD Analyzer

Overview

The WTW OxiTop®-i IS 6 BOD Analyzer is a laboratory-grade, manometric respirometric system engineered for precise, unattended determination of Biochemical Oxygen Demand (BOD) over standard incubation periods of 1 to 7 days. Unlike titrimetric or electrochemical methods, the OxiTop®-i IS 6 operates on the principle of pressure differential measurement in sealed vessels: microbial oxidation of organic matter consumes dissolved oxygen, while concurrently generated CO₂ is chemically trapped by sodium hydroxide pellets. This results in a quantifiable negative pressure change proportional to oxygen depletion—directly converted and displayed as mg/L BOD. The system adheres to internationally recognized protocols including ISO 5815-1:2019 (Water quality — Determination of biochemical oxygen demand after n days — Part 1: Dilution and seeding method) and EN 25815, ensuring data integrity for regulatory reporting, wastewater treatment plant performance evaluation, and environmental impact assessments.

Key Features

• Six independent, self-contained sensor heads—each with integrated LCD graphic display—enabling parallel analysis of up to six samples without cross-channel interference.
• Automatic temperature equilibration logic: sensor heads detect thermal drift and defer measurement initiation by 1–3 hours until sample temperature stabilizes within ±0.3 °C, minimizing thermal artifact-induced error.
• Programmable incubation duration (1–7 days) with automatic daily data logging—seven time-stamped values stored per channel, eliminating manual intervention during extended assays.
• Flexible unit selection (mg/L O₂, ΔhPa, hPa, or raw digit output) supports both regulatory compliance reporting and internal process monitoring workflows.
• Color-coded sensor heads (blue for influent, gray for effluent) facilitate rapid visual identification and reduce procedural errors in sequential sampling schemes.
• Modular design compatible with standard 250 mL or 500 mL BOD bottles; scalable range extension to 4,000 mg/L achieved via volumetric adjustment or serial dilution without hardware modification.

Sample Compatibility & Compliance

The OxiTop®-i IS 6 accommodates a broad spectrum of aqueous matrices, including raw sewage, secondary effluents, surface waters, industrial discharges, and biologically treated leachates. Its sealed-bottle configuration prevents atmospheric oxygen intrusion and eliminates headspace equilibration bias common in open-circuit systems. Each measurement cycle complies with GLP documentation requirements: timestamps, incubation duration, ambient temperature logs, and final BOD values are retained onboard and exportable via IR interface. The system meets foundational metrological criteria for ISO/IEC 17025-accredited laboratories and supports audit readiness for EPA NPDES permit monitoring, EU Urban Wastewater Treatment Directive (91/271/EEC), and ISO 14001 environmental management systems.

Software & Data Management

Data retrieval occurs via infrared (IR) optical link to the optional OxiTop® Control Software (Windows-based), enabling batch export to CSV or PDF formats with embedded metadata (sample ID, operator, calibration date, sensor serial number). The software enforces user-level access control, generates electronic signatures compliant with FDA 21 CFR Part 11 (when paired with validated IT infrastructure), and maintains immutable audit trails for all parameter changes and result exports. No cloud dependency or subscription model is required—data sovereignty remains fully under laboratory control.

Applications

• Performance verification of activated sludge, trickling filter, and MBR wastewater treatment units.
• Regulatory BOD₅ compliance testing for municipal discharge permits (e.g., US EPA Method 405.1, UK EA MCERTS).
• Biodegradability screening of new chemical formulations under OECD 301 series guidelines.
• Long-term stability assessment of constructed wetlands and anaerobic digesters.
• Educational use in university environmental engineering labs for teaching respirometric kinetics and oxygen mass balance principles.

FAQ

How does the OxiTop®-i IS 6 eliminate CO₂ interference in BOD measurement?

It uses solid NaOH absorbent pellets placed inside each sealed BOD bottle; CO₂ produced during microbial respiration reacts irreversibly to form Na₂CO₃, preventing partial pressure contribution and ensuring measured pressure loss reflects only O₂ consumption.
Can the system be used for BOD₅ only, or is non-standard incubation supported?

The instrument supports fully customizable incubation durations from 1 to 7 days—BOD₅ is simply one preconfigured option. Extended periods (e.g., BOD₇, BOD₁₀) are programmable and logged with equivalent traceability.
Is calibration required before each run?

No routine recalibration is needed; the pressure transducers are factory-calibrated with NIST-traceable references and retain stability for ≥12 months under normal lab conditions. A zero-point verification using air-saturated deionized water is recommended prior to critical campaigns.
What happens if power fails during a 7-day measurement?

All sensor heads contain non-volatile memory—time-stamped BOD values recorded prior to interruption remain intact. Upon power restoration, the system resumes timestamping without data loss or clock drift.