The degradation rate describes the rate at which organic or inorganic substances in water or wastewater are degraded by physical, chemical or biological processes. In industrial water and wastewater treatment, the degradation rate is an important parameter for evaluating the efficiency of purification processes, particularly with regard to the removal of pollutants and the treatment of biodegradable substances.
Table of contents
Technical background
The degradation rate is often considered in connection with biological wastewater treatment, in which microorganisms break down organic contaminants. Here, the degradation rate describes how quickly these microorganisms convert the organic substances into less harmful end products such as carbon dioxide (CO₂) and water (H₂O). The speed of this process depends on several factors, including
Substrate concentration:
Higher concentrations of organic substances increase the activity of the microorganisms and thus the degradation rate until a saturation point is reached.
Temperature:
The biological degradation processes are temperature-dependent, with most microorganisms working most efficiently at temperatures between 20 °C and 35 °C.
pH value:
Microorganisms are dependent on a stable pH value. At pH values outside the neutral range (6.5-7.5), the degradation rate can drop significantly.
Oxygen supply:
In aerobic systems (such as the activated sludge process), a sufficient supply of oxygen is crucial for the degradation rate, as oxygen is required for biological degradation.
Degradation rate in practice
In practice, the degradation rate is measured using various methods, depending on the wastewater to be treated and the required purification targets. Two frequently used parameters for assessing the degradation rate are
Biochemical oxygen demand (BOD): The BOD indicates how much oxygen microorganisms consume in a defined period of time (usually 5 days, BOD5) in order to break down the organic substances contained in the water. A high degradation rate leads to rapid oxygen consumption.
Chemical oxygen demand (COD): COD measures the amount of oxygen required to chemically oxidize all organic compounds in a water sample. Although it does not exclusively reflect biological degradation processes, COD can serve as an indicator of the overall degradation potential of wastewater.
Degradation rate in various processes
Aerobic processes: In plants such as activated sludge systems (e.g. ALMA BHU BIO) and membrane bioreactors (ALMA BHU MBR), the degradation rate is heavily dependent on the oxygen supply. Here, continuous aeration ensures that microorganisms can work effectively and break down organic substances quickly.
Anaerobic processes: In processes such as digested sludge treatment (e.g. in biogas plants such as the ALMA BHU GMR), microorganisms work in the absence of oxygen. The degradation rate tends to be slower in anaerobic processes, but these processes produce biogas as a by-product, which can be used to generate energy.
Chemical and physical degradation rate: In processes such as ozonation or UV oxidation (e.g. ALMA OXI UV), pollutants are degraded by chemical or physical methods. The degradation rate in these processes depends on the dose of the oxidizing agent used (e.g. ozone) or the energy source (e.g. UV light).
Influence on the system design
Knowledge of the degradation rate is crucial for the design of water and wastewater treatment plants. A low degradation rate often requires longer retention times in reactors or basins to ensure that the pollutants are sufficiently degraded. In contrast, high degradation rates can allow for smaller basin volumes and shorter retention times, resulting in a more compact and cost-efficient plant design.
Example: Degradation rate in the food industry
The food industry, especially the dairy industry, produces wastewater with a high content of organic compounds such as fats, proteins and carbohydrates. The degradation rate of these substances in biological wastewater treatment plants is crucial to ensure the efficiency of the plant. A slow degradation rate can lead to an overload of the biological processes, which is why sufficient aeration and optimized temperature conditions must be ensured.
Conclusion
The degradation rate is a key parameter in water and wastewater treatment that describes the rate of degradation of pollutants and organic compounds. It influences the design and operation of treatment plants and depends on various factors such as substrate concentration, temperature, pH value and oxygen supply. Understanding the degradation rate is crucial for optimizing purification processes and ensuring compliance with environmental regulations in industrial water and wastewater treatment.
