Application of a modified OxiTop® respirometer for laboratory composting studies

Abstract

This study applied a modifi ed OxiTop ® system to determine the oxygen uptake rate during a 2-day respiration test of selected composting materials at different moisture contents, air-fi lled porosities and composition of composting mixtures. The modifi cation of the OxiTop ® respirometer included replacement and adjustment of a glass vessel (i.e. a 1.9-L glass vessel with wide mouth was used instead of a standard 1-L glass bottle, additionally the twist-off vessel lid was adjusted to attach the measuring head) and application of a closed steel mesh cylinder of 5 cm in diameter and 10 cm in height with the open surface area of the mesh of approximately 56.2%. This modifi cation allowed obtaining different bulk densities (and thus air-porosities) of the investigated composting materials in laboratory composting studies. The test was performed for apple pomace and composting mixtures of apple pomace with wood chips at ratios of 1:0.5, 1:1, 1:1.5 (d.w), moisture contents of 60%, 65% and 75% and air-fi lled porosities ranging from 46% to 1%. Due to diverse biodegradability of the investigated apple pomace and composting mixtures this test allows for the determination of the effects of different air-porosities (due to compaction in a pile) on the oxygen uptake rate for mixtures with a fi xed ratio of a bulking agent. The described method allows for laboratory determination of the effects of moisture content and compaction on biodegradation dynamics during composting.

Respirometric activities of unacclimatizedEnterobacter aerogenesand mixed culture bacteria in sequencing batch reactor systems in response to acrylamide and its biodegradation products

“…Finally, the pressure decreases linearly due to the steady microbial oxygen consumption. 22 The slope of linear pressure drop determined by linear regression was used to indicate the pressure drop per unit time (Δ P / t ), which subsequently was used to determine the oxygen uptake rate (OUR). The OUR was derived from the relationship between the number of moles based on the mass of oxygen and pressure drop according to the ideal gas law as follows: where Δ n is the change in mole of oxygen, Δ m is the change in mass of oxygen, V is the gas volume, M is the oxygen molecular weight (32 g mol −1 ), R is the general gas constant (8.314 J mol −1 K −1 ), T is the temperature in kelvin (K), t is the incubation time in hour, and Δ P is the pressure drop in hPa.…”

“…20 Typically, the pressure in the vessel increases during the rst 2-3 hours as a result of the temperature difference between sample and incubator. 21,22 Aer the sample has equilibrated with temperature in the incubator, it requires an acclimation period for microorganisms to adapt themselves to new conditions causing nonlinear reduction of pressure. Finally, the pressure decreases linearly due to the steady microbial oxygen consumption.…”

“…Finally, the pressure decreases linearly due to the steady microbial oxygen consumption. 22 The slope of linear pressure drop determined by linear regression was used to indicate the pressure drop per unit time (DP/t), which subsequently was used to determine the oxygen uptake rate (OUR). The OUR was derived from the relationship between the number of moles based on the mass of oxygen and pressure drop according to the ideal gas law as follows:…”

“…where Dn is the change in mole of oxygen, Dm is the change in mass of oxygen, V is the gas volume, M is the oxygen molecular weight (32 g mol À1 ), R is the general gas constant (8.314 J mol À1 K À1 ), T is the temperature in kelvin (K), t is the incubation time in hour, and DP is the pressure drop in hPa. Eqn (1) can be written as eqn (2), 21,22 but was modied in this study to apply the slope of linear pressure drop determined from the linear regression for the calculation of OUR (mg O 2 L À1 h À1 ). The OUR was subsequently divided by the MLVSS concentration to obtain the specic oxygen uptake rate (SOUR) in the unit of mg O 2 (mg VSS) À1 d À1 .…”

Assessment of Biodegradation Efficiency of Polychlorinated Biphenyls (PCBs) and Petroleum Hydrocarbons (TPH) in Soil Using Three Individual Bacterial Strains and Their Mixed Culture

“…Based on the O 2 consumption and/or CO 2 production rate, it is possible to estimate the rate of aerobic biodegradation of organic pollutant, i.e., the rate of substrate loss over time. Moreover, the results of respirometric tests illustrate the degree of metabolic activity of the polluted environment [87].…”