For decades, wastewater labs have worked under a contradiction—testing for pollution using chemistry that creates waste. The methods are established, regulator-approved, and still widely used. But as labs take on more samples with fewer resources, the trade-offs are harder to overlook.
Total Organic Carbon (TOC) and Total Bound Nitrogen (TNb) analysis provide a faster, more scalable alternative to traditional wastewater testing methods. This summary, based on a technical webinar led by Bernd Bletzinger, product manager for the TOC/TNb portfolio at Analytik Jena, explains how these systems generate dependable data while lowering long-term costs tied to reagents, labor, and downtime.
What COD and BOD₅ Can’t Handle Anymore
To assess contamination, wastewater labs often estimate how much oxygen a sample would use as its organic matter breaks down. That oxygen demand helps determine if discharge poses a risk or violates regulatory thresholds. Most labs rely on two standard methods: Chemical Oxygen Demand (COD) and Biochemical Oxygen Demand over five days (BOD₅).
COD simulates chemical breakdown by boiling the sample with carcinogenic potassium dichromate and sulfuric acid, often with toxic mercury salts. BOD₅ uses a biological approach, incubating the sample for five days to measure oxygen consumed by microbes digesting organic matter. Both methods have downsides—COD generates hazardous waste and requires careful handling, while BOD₅ is slow, variable, and demands significant space for controlled incubation and storage.
How TOC and TNb Quantify Organic Load
TOC analysis measures carbon by oxidizing organic compounds into carbon dioxide, using either high-temperature combustion or UV light with chemical oxidants. An infrared detector then quantifies the CO₂ to determine total organic carbon. This approach captures a complete carbon load and avoids the interferences that affect oxygen demand tests.
Nitrogen is also critical in wastewater analysis. High levels of ammonia or organic nitrogen can trigger algal blooms and strip oxygen from surface waters. TNb analysis captures that full nitrogen load in one step. The sample is thermally decomposed, releasing nitrogen compounds as nitric oxide, which then reacts with ozone to produce light. A chemiluminescence detector measures that light, producing a stable signal unaffected by common interferences.
Why Wastewater Samples Challenge TOC Systems
Wastewater samples often contain fats, oils, particulates, or high salt loads, which can complicate TOC analysis. To avoid damaging their instruments, many labs filter or dilute samples or analyze only the supernatant. These steps reduce wear but also remove solids that carry a significant portion of the organic load.
TOC instruments developed for clean applications, such as drinking water or pharmaceutical testing, often underperform when faced with real wastewater. Narrow capillaries, small-bore needles, and unprotected valves can clog or wear down. Oxidation systems not built for complex loads often miss solids and underreport total organic carbon. For industrial or municipal labs, this can lead to sample loss, erratic measurements, and more frequent service interruptions.
Inside the multi N/C Series: Built for Tough Samples
The design of a TOC system determines how well it can handle real wastewater. Injection method, flow path, and sample preparation all affect whether solids pass cleanly through the system, oxidation completes fully, and key components stay protected. Analytik Jena’s multi N/C series is built with these demands in mind, offering models adapted to different matrix complexities.
The multi N/C 3300 is suited for routine wastewater monitoring (Figure 1). It uses a loop injection system, where the syringe fills a separate loop that delivers the sample into the furnace, avoiding direct contact and reducing wear. The system handles particles up to 800 microns, supported by 0.8 mm tubing and a ceramic valve. A reverse rinse function clears the aspiration needle after each run to prevent blockages.
For more challenging loads, the multi N/C 2300 employs top-to-bottom direct injection, sending the sample straight into the combustion tube (Figure 2). Its short, valve-free path ensures full transfer of solids up to 700 microns through a 0.7 mm syringe needle. Automatic rinsing prevents carry-over and the septum-free injection port maintains leakage-free operation. Reinforced catalyst beds support performance in brines, sludges, and high-strength industrial waste—all within a compact footprint.
Real-World Results with TOC/TNb
Design matters, but results are what convince analysts. In the webinar, Bletzinger highlighted a sugar producing company that replaced COD with TOC for weekly wastewater analysis. The switch saved €29,000 annually by reducing reagent costs, disposal volume, and manual workflows. ROI was achieved in just over a year. The analyzer ran on 51 × 55 cm of bench space, replacing a setup that once depended on full-scale incubator rooms to process the same sample load.
Another example came from a contract lab using the multi N/C 3300 to validate TOC performance under EN ISO 20236 and EN 1484. The lab performed cellulose recovery tests using a 100 mg/L suspension with particle sizes up to 100 µm. Results showed TOC recoveries between 95 and 100 percent, with relative standard deviations below 0.5 percent. These outcomes exceeded the required thresholds of ±10% recovery and ≤10% RSD, confirming the system’s suitability for regulated wastewater applications.
A QC lab in the pulp and paper sector adopted the multi N/C 2300 to handle both wastewater compliance and product testing on the same platform. The system measured TOC and TNb across low and high concentrations without changing methods or setups. COD values were estimated using NPOC (Non-Purgeable Organic Carbon), calculated directly within the system software using conversion factors, a feature that allowed the lab to maintain continuity with existing reporting formats.
Conclusion
Analytik Jena’s TOC/TNb systems are built for long-term performance in high-demand wastewater labs. Calibration remains stable for up to a year, reducing downtime and routine rework. Autosampler features such as sealed sample vials and automated stirring support unattended runs without compromising sample integrity.
For labs managing difficult matrices, the ability to retrofit older analyzers with high-salinity kits extends system life and protects against corrosive damage. Combined with software-based COD/BOD₅ conversion and stable recovery across a wide range of concentrations, the multi N/C series offers a durable, future-ready platform for regulated workflows.
To access the free webinar and hear directly from Bernd Bletzinger, visit Analytik Jena online.
Meet the Expert
 | Bernd Bletzinger Bernd Bletzinger received his MS in Technical and Analytical Chemistry at Friedrich Schiller University Jena & Dublin City University in Ireland. He has been with Analytik Jena since 2006, first as an application specialist, then as a product specialist, and is the product manager for the TOC/TNb product line. |
