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The Biodegradability Testing of Lubricants
Published in Leslie R. Rudnick, Synthetics, Mineral Oils, and Bio-Based Lubricants, 2020
Peter Lohmann, Ben Müller, Gerhard Gaule
As already mentioned, due to the great variability of unknown composition of inocula, biological tests are not very precise. Nonetheless, although an inoculum is a constituent of every biodegradation test, reproducibility varies a lot among different test methods. The biodegradation rate is expressed as a percentage; therefore, absolute values of reproducibility are used in this context. Table 31.1 shows the absolute reproducibilities of some biodegradation test methods. In summary, it is obvious that test principles measuring the decrease of a test substance, e.g. OECD 301 A and CEC L-103-12, reveal a reproducibility that is comparable to other tests used in the lubricant industry. Derived from the large values of absolute reproducibility, respirometric test methods show a poor reliability of results. For example, in a round robin test in 1988, OECD 301 B, by far the test used most to measure CO2 evolution, showed an absolute reproducibility of 19–40% for the water-soluble test substances (Hashimoto 1988). The round robin test of a CEN working group in 2017 specified a CO2 evolution test (prEN 17181:18), based on the OECD 301 B method, by an exact description of sample incorporation for poorly water-soluble substances. The overall absolute reproducibility of this test was 36% (Table 31.1). To clarify the meaning of such round robin test results, the following example gives information (Figure 31.6):
Gas Transfer Limitations in Environmental Respirometry
Published in Bell John W., Proceedings of the 44th Industrial Waste Conference May 9, 10, 11, 1989, 1990
Ricardo B. Jacquez, Fernando Cadena, Somavarapu Prabhakar, Martha I. Beach
The effect of thermal changes and water vapor are also important in respirometric determinations. For example, if an experiment is conducted at room temperature with a variation of ±2°C and a Vh:Vt ratio of 0.5, the BOD error will be approximately 8 mg/L which is significant if a low oxygen demanding substrate is used in the study. This error may be reduced to ±0.5–1.0 mg/L if the experiment is conducted in an incubator, assuming the temperature change is restricted ±0.5°C.
Mature landfill leachate treatment in a biological filter using scoria as media
Published in Journal of Applied Water Engineering and Research, 2023
German D. Jojoa-Unigarro, Simón González-Martínez, Óscar González-Barceló
Respirometry is the measurement and interpretation of the biological oxygen consumption rate under well-defined experimental conditions. Because oxygen consumption is directly associated with biomass growth and substrate removal, respirometry is a helpful technique for monitoring, modeling, and controlling biological processes (Vanrolleghem 2002; Im et al. 2016; Vitanza et al. 2016). The arrangement is shown in Figure 1. Because it is not possible to record the oxygen concentration directly inside filter bed reactors, the water is pumped to the oxygen meter outside the filter. This procedure was developed especially for this experiment to observe the changes in dissolved oxygen due to substrate consumption. Before performing every measurement, the influent pump was turned off to avoid new nutrients flowing into the filter. Immediately after that, the pump associated with the O2 measuring device was turned on, and the air supply was turned off; in this precise moment, the dissolved oxygen concentration inside the filter was maximal. The water inside the filter was forced through the filter media in a loop. The microorganisms consumed the oxygen as they used the substrate simultaneously, and the oxygen electrode was able to monitor the decreasing dissolved oxygen. With the pump associated with the O2 electrode running all the time, to observe the dissolved oxygen concentration, the air supply to the filter was cut for 15 min and then allowed again another 15 min to saturate the water inside the filter, during one whole HRT (3.7 h). Dissolved oxygen concentration was continuously recorded during the experiment due to substrate consumption (O2 probe, Figure 1). Considering that all the biofilm in the filter took place during the respirometric determinations and knowing the amount of substrate inside the filter, accurate substrate consumption could be determined.
The evaluation of COD fractionation and modeling as a key factor for appropriate optimization and monitoring of modern cost-effective activated sludge systems
Published in Journal of Environmental Science and Health, Part A, 2019
Jakub Drewnowski, Anna Remiszewska-Skwarek, Sylwia Fudala-Ksiazek, Aneta Luczkiewicz, Sheena Kumari, Faizal Bux
The Activated Sludge Models[5,6] commonly used by IWA Task Group, are developed based on the COD fractionation, nevertheless, a proper evaluation of COD fractionation, which is crucial for modeling and model predictions, is still under debate. In general, total COD in the wastewater consists of: readily (soluble) biodegradable organic substrates (SS), slowly (particulate) biodegradable substrates (XS), inert suspended organic matter (XI), and inert soluble organic matter (SI).[6] There are two main approaches for determining the COD fraction in wastewater; 1) based on their physical-chemical properties[7] and 2) microbial growth kinetics, viz., respirometric test based on oxygen uptake rate (OUR) and COD measurements.[8] Respirometric method was first introduced by Ekama et al.[9] in the 70’s of the last century and are still being used by many researchers. It is used mainly for determining SS, whether XS requires simulation modeling, which is adjusted to the batch experimental data. Additionally, the respirometric approach is highly influenced by experimental conditions and therefore to be reliable, it should be carried out with precision and careful maintenance. Alternatively, physico-chemical method, which is based on physical (particle size) and chemical (coagulation/flocculation) properties of organic matter present in wastewater are used. The disadvantage of this method is connected with imprecise definition of colloidal organic matter, which may contribute to both readily and slowly biodegradable fractions. Thus modification of physico-chemical method was proposed by Roeleveld and Loosdrecht,[10] which combined flocculation and filtration steps with BOD measurements (STOWA protocol).