Manometric test system

For the determination of gas production resulting from the biodegradation of the test materials, two different test systems each containing 12 reaction vessels were set up. The volumetric test system of TUHH (Fig 1) and a manometric test system (Sensomat, Fig 2) of the company Aqualytic, 63201 Langen, Germany, were applied as test systems. The test vessels used were modified SOO ml glass flasks (Schott). 

The gas production in the manometric test system were measured automatically and semi-continuosly every 120 minutes by measuring the pressure in the headspace of the reaction vessel. The limit of the measured pressure is 350 mbar. By using an IR-sensor the data can be registered by a data logger and transferred to a computer. Sampling of liqmds is carried out via the septum at the reaction vessel itself. Samples are mixed discontinuously using magnetic stirrers. 

Figure 2. Principle outline of the manometric test system Sensomat, Company Aqualytic, Germany ...

Comparing both test systems different biogas quantities were analysed by addition of HCl at the end of the test. This can be attributed to the fact that test setups of both systems show different ratios between headspace and volume of inserted medium. In the manometric setup, ratio is approx. 1 1, in the volumetric setup average is 1 5. The CO2 concentrations are lower in the gas phase of the manometric setup also leading to a smaller part of dissolved CO2 in die aqueous phase. However, stripped gas quantities could clearly be recorded and quantified with both test systems. 

Various aspects of in vitro gas production test have been reviewed by Getachew et al. [33], and these authors reported that gas measurement were centered on investigations of rumen microbial activities using manometric measurements and concluded that these methods do not have wide acceptability in routine feed evaluation since there was no provision for the mechanical stirring of the sample during incubation. Another in vitro automated pressure transducer method for gas production measurement was developed by Wilkins [34], and the method was validated by Blummel and Orskov [35] and Makkar et al. [36]. There are several other gas-measuring techniques such as (i) Flohenheim gas method or Menke s method [37] (ii) liquid displacement system [38] (iii) manometric method [39] (iv) pressure transducer systems manual [40], computerized [41], and combination of pressure transducer and gas release system [42]. 

A9.4.3.5.6 Volatile substances should only be tested in closed systems as the Closed Bottle test (OECD Test Guideline 30ID), the MITI I test (OECD Test Guideline 301C) and the Manometric Respirometry test (OECD Test Guideline 30IF). Results from other tests should be evaluated carefully and only considered if it can be demonstrated, e.g. by mass balance estimates, that the removal of the test substance is not a result of volatilization. 

Fig. 4.2 Testing apparatus for manometric measurements of the absorption rate in C/L systems in any liquid and any pure gas (not gas mixtures ) from [624],...

Obemosterer [402] systematically investigated the effect of several non-ionic and ionic tenside classes on fei. values in the water/aeral oxygen system. He also used the Manometric (pressure gauge) measuring technique and determined the m-values as a function of the nature and concentration of the tenside under constant test conditions. 

The rate of reduction of cytochrome a was examined by addition of various chemical reductants such as p-phenylenediamine, hydro-quinone, and ascorbic acid. These were then tested as substrates for the cytochrome oxidase, the activity of which was measured manometrically. Onlyp-phenylenediamine reduced cytochrome a, while the other reagents tested, except sodium dithionite, had weak reductive activity. In Fig. 11, it is shown that cytochrome a is oxygenated under aerobic conditions and is reduced under anaerobic conditions by addition of 10 Af/>-phenyl-enediamine and the trace of borohydride, used to decrease the concentration of oxygen in the solution in the cuvette. When a trace of oxidized cytochrome c is added to either system, both forms of cytochrome a are instantaneusly oxidized. As shown in Table IX (see Section III.C), the cytochrome a acquires an oxidase activity in cooperation with cytochrome c when the oxygen consumption is measured manometrically in the presence and absence of cytochrome c. 

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