Effluent treatment in steel plants is a critical challenge due to the high pollutant load, including organic compounds, heavy metals, and nitrogen. Online monitoring of parameters such as dissolved oxygen (DO), pH, and oxidation reduction potential (ORP) is essential to ensure the efficiency of biological degradation and contaminant removal processes.
This document explores the importance of these parameters in the operation of wastewater treatment plants, based on case studies and relevant technical references.
Context and Importance of Measurements
Dissolved oxygen (DO)
DO is a critical parameter in biological wastewater treatment. In steel plants, the presence of compounds such as phenol, thiocyanates, and ammonia requires efficient aerobic biodegradation processes. Bacteria such as Pseudomonas e Nitrosomonas are essential in the decomposition of pollutants and require adequate concentrations of oxygen to metabolize organic compounds.
The use of optical dissolved oxygen (DO) sensors, such as the VisiFerm DO Arc, ensures reliable measurements, even in effluents with high organic loads and suspended particles. These sensors minimize interference from CO2 and SO2 and require minimal maintenance.
VisiFerm DO Arc Sensor
- Optical technology: reliable measurements, no need for electrolyte or replaceable membrane.
- Low maintenance: minimum calibration and resistance to contamination.
- Durability: sensor cap lifespan exceeds two years.
- Digital integration: direct communication via 4-20 mA and Modbus.
pH
pH control is essential for the stability of biological and chemical processes. Values outside the ideal range can compromise microbial activity and affect the solubility of heavy metals, increasing their toxicity.
Sensors like the Polilyte Plus Arc allow for continuous monitoring, ensuring that the pH is maintained within the ideal range for pollutant removal and the efficiency of chemical and biological treatments.
Polilyte Plus Arc Sensor
- Accurate and stable measurements, even in environments with a high contaminant load.
- Reduced maintenance: sporadic calibration and integrated microtransmitter system.
- Offline calibration: data storage on the sensor itself for adjustments in the laboratory.
- Longer shelf life: approximately 18 months of operation.
ORP (oxidation-reduction potential)
ORP is a critical indicator of a medium's oxidation or reduction capacity, directly reflecting the efficiency of biological and chemical processes. Processes such as nitrification and denitrification require specific ORP ranges to occur efficiently:
- Nitrification: Requires a moderate positive ORP (~ +150 mV to +250 mV).
- Denitrification: occurs best under slightly reducing conditions (-50 mV to +50 mV).
Sensors like the Polilyte Plus ORP Arc provide accurate, low-maintenance measurements, ensuring that treatment processes are operating within optimal parameters.
Polilyte Plus ORP Arc Sensor
- High stability even in aggressive environments.
- Low calibration requirement, with data stored in the microtransmitter.
- Long shelf life, estimated at up to two years.
- Digital compatibility, allowing direct communication with automation systems.
Case study
There is a coke plant in one of the largest steel companies in Europe (and also in Brazil), where effluent treatment is carried out in four successive biological stages, using bacteria such as Pseudomonas, Thiobacillus, Nitrosomonas and Nitrobacter to degrade phenol, thiocyanates, cyanides, thiosulfates and ammonia.
Os Hamilton sensors (VisiFerm DO Arc, Polilyte Plus Arc and Polilyte Plus ORP Arc) are used in each of the biological tanks, ensuring precise control of operating conditions and maximizing treatment efficiency.
With this rigorous monitoring, the plant is able to remove 90% of the organic load (COD) and 75% of the nitrogen load, allowing for water recycling within the steelmaking unit itself.
Benefits of online wastewater monitoring
- Greater Operational Efficiency: Rapid response to parameter variations prevents process failures.
- Cost Reduction: Minimizes the use of chemical reagents and manual interventions.
- Sustainability: Ensures environmental compliance and reduces ecological impacts.
- Reduced Maintenance: State-of-the-art sensors require fewer calibrations and replacements.
The strategic importance of online wastewater monitoring.
Online monitoring of effluents — including variables such as dissolved oxygen (DO), pH, and orbital petroleum reductase (OPR) — has become indispensable for more efficient and sustainable treatment in the steel industry. By integrating advanced sensor technologies, such as the solutions provided by Alutal, it is possible to optimize pollutant removal, reduce operating costs, and ensure full compliance with environmental requirements.
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References
- “Zero Pollution with the Help of Bacteria” – Hamilton Bonaduz AG, 2014.
- Metcalf & Eddy, “Wastewater Engineering: Treatment and Resource Recovery”, 5th Edition, 2013.
- ISO 5667-10 standard: “Guidelines for biological sampling in water quality monitoring”.
