WTW OxiTop-i IS 6 Pressure-Difference BOD₅ Analyzer

Overview

The WTW OxiTop-i IS 6 is a laboratory-grade pressure-difference BOD₅ analyzer engineered for precise, mercury-free biochemical oxygen demand measurement in accordance with ISO 5815-1:2019 and ASTM D5210–92 (reapproved 2021). It operates on the principle of closed-circuit respirometry: microbial oxidation of organic matter in a sealed, darkened sample bottle consumes dissolved oxygen, generating a proportional pressure drop across a calibrated sensor. This differential pressure—measured continuously over 1 to 7 days—is converted into BOD₅ concentration (mg/L O₂) using stoichiometric conversion and temperature-compensated algorithms. Unlike traditional dilution-and-inoculation methods (e.g., ISO 5815-2), the OxiTop-i IS 6 eliminates manual titration, volumetric dilution errors, and operator-dependent endpoint determination. Its robust architecture supports routine compliance testing for drinking water, surface water, groundwater, wastewater, and treated effluent under GLP and ISO/IEC 17025-accredited laboratory conditions.

Key Features

• Mercury-free, electro-mechanical pressure transducer technology ensures long-term stability and regulatory compliance with EU RoHS and Minamata Convention requirements.
• Six independent, optically isolated measurement channels—each equipped with a dedicated OxiTop®-i measurement head featuring dual-color (blue/gray) identification and integrated LED status indicators for real-time operational feedback.
• Standard brown glass bottles (250 mL or 500 mL) provide complete light exclusion to prevent photoinhibition of aerobic microorganisms and ensure method integrity.
• Integrated magnetic stirring base maintains uniform suspension of biomass and substrate, minimizing diffusion limitations and enhancing reaction kinetics reproducibility.
• Automatic temperature compensation adjusts start timing by 1–3 hours if initial sample temperature deviates from the standard incubation setpoint (typically 20 ± 0.5 °C), ensuring strict adherence to BOD₅ definition.
• Three-button interface enables intuitive navigation without software dependency; all measurements are stored onboard with timestamps and calculated BOD values displayed directly on the unit.

Sample Compatibility & Compliance

The OxiTop-i IS 6 accommodates undiluted samples across seven predefined BOD ranges: 0–40, 0–80, 0–200, 0–400, 0–800, 0–2000, and 0–4000 mg/L—enabling direct analysis of low-strength potable water and high-strength industrial effluents without manual dilution steps. It complies with ISO 5815-1 for standard BOD₅ determination and supports extended applications including soil respiration (ISO 21528-2), biodegradability screening (OECD 301 series), and anaerobic digestion monitoring via modified head configurations. All measurement heads meet CE and EMC directives. When paired with the Multi 3620/3630 IDS SET WL controller, the system supports audit-trail-enabled data management compliant with FDA 21 CFR Part 11 requirements for electronic records and signatures.

Software & Data Management

Data acquisition and visualization are supported through the optional Multi 3620/3630 IDS SET WL controller, which communicates wirelessly with OxiTop®-IDS measurement heads. The controller performs real-time calculation of BOD values, plots time-resolved pressure decay curves, and exports timestamped datasets in CSV format for integration into LIMS or statistical analysis platforms (e.g., R, Python pandas, or JMP). Onboard memory retains up to 180 days of logged data at configurable intervals (minimum 30-minute resolution). No proprietary drivers or cloud dependencies are required—data transfer occurs via USB or Bluetooth, preserving data sovereignty and network security in regulated environments.

Applications

• Routine BOD₅ monitoring in municipal and industrial wastewater treatment plants for process control and discharge compliance (e.g., EU Urban Wastewater Treatment Directive, US EPA NPDES permits).
• Drinking water quality assurance in distribution systems and source water assessment per WHO Guidelines and national standards (e.g., GB/T 5750.7–2006).
• Biodegradability testing of surfactants, pharmaceuticals, and agrochemicals per OECD 301B/C/D protocols.
• Soil microbial activity quantification in ecotoxicology studies and land remediation projects.
• Lab-scale anaerobic digestion trials measuring cumulative biogas potential and hydrolysis kinetics.

FAQ

What incubation temperature is required for BOD₅ measurement?
The standard incubation temperature is 20 ± 0.5 °C for five days, as defined in ISO 5815-1. The OxiTop-i IS 6 supports automatic temperature-based start delay to align with this requirement.
Can the system be used without the Multi 3620/3630 controller?
Yes—the OxiTop-i IS 6 operates autonomously with local display and data storage. The controller is optional and enhances remote configuration and advanced data visualization.
Is calibration traceable to national standards?
Pressure sensors are factory-calibrated against NIST-traceable reference manometers. Field verification can be performed using certified barometric references or zero-pressure checks under nitrogen purge.
How is stirring controlled during measurement?
Each unit includes a dedicated magnetic stirring base with continuous rotation (60 ± 5 rpm), ensuring homogeneous oxygen distribution and preventing sedimentation-induced underestimation.
Does the system support multi-day logging beyond 7 days?
Yes—data logging intervals range from 30 minutes to 180 days, enabling extended biodegradation kinetics studies or low-BOD matrix monitoring where slower oxidation rates apply.