Volatile acids toxicity

McCarty, P. L., McKinney, R. E., Volatile Acid Toxicity in Anaerobic... 

Handhng of this volatile and toxic matenal may be avoided by the clever use of the trimethylsilylated perfluorinated resinsulfonic acid [97] This solid reagent is prepared by treatment of the acid form of NAFTON 511 with chloro-tnmethylsilane This reagent exhibits sigmficant stabdity in air (equation 78)... 

Ruthenium dissolves anodically in alkaline solutions, as predicted by Pourbaix but its corrosion resistance when made anodic in acid solutions is variable. Under some conditions the volatile and toxic tetroxide is evolved. Osmium is even more reactive anodically than ruthenium. 

Fuels cells are of interest both from energetic and environmental considerations. When methanol is fed directly to an anode, as in Direct Methanol Fuel Cells , electric power is generated, making the devices suitable for small and lightweight uses [53], Alternative fuels such as polyhydric alcohols like ethylene glycol and glycerol are much less volatile and toxic, on the one hand, and electrochemically oxidizable on the other [54]. Therefore, the electrochemical oxidation of various polyhydric alcohols has been investigated in acidic as well as in alkaline conditions. 

Lawrence and McCarty (JO) also found that when toxicity was manifest, gas production fell off much more rapidly than volatile acids increased. This is indicative of equal toxicity to the acid formers and methane formers. This is unusual in that the methane formers are usually considered to be more sensitive than acid formers to environmental conditions. It is probable that the very high toxicity of heavy metals results in virtual elimination of both groups of organisms once a few milligrams/ liter excess of heavy metal are present. This is probably also the reason it is impossible to discriminate between the toxicity of individual heavy metals. 

Therefore, a prime objective in the operation of anaerobic waste treatment processes is maintenance of a proper pH range. The signal that trouble is imminent is a sudden rise in the volatile acids. One group of investigators has indicated that the proper action to take when the volatile acids rise suddenly is to add alkaline substances to maintain the buffer capacity 12, 13, 14), A second group led by Buswell 15) and Schlenz 16) contends that this is detrimental because the volatile acids themselves are toxic to methane bacteria but not to acid formers at concentrations of about 2000 mg/liter. The use of alkaline materials thus only stimulates acid production leading to even greater toxicity. This latter... 

This work, however, did not completely eliminate the controversy over the toxicity of volatile acids. Subsequently, Buswell and Morgan 20) reported that propionic rather than acetic acid was toxic to the methane bacteria. McCarty et al. (9) investigated the effect of various volatile acids on methane bacteria in order to clear up this controversy. They added 6000 mg/liter of acetic, propionic, and butyric acid (the three most common acids produced during anaerobic breakdown of complex substances) individually to laboratory scale sewage sludge digesters. Prior... 

The studies of McCarty and co-workers have shown clearly that volatile acids are not toxic to methane bacteria at concentrations that would occur in stuck or sour digesters. On the contrary, evidence has been elucidated which indicates propionate retards the acid formers. Thus, the use of alkaline substances to maintain an adequate buffer capacity in an anaerobic waste treatment unit is a valid procedure. A word of caution is necessary pH control is not a universal palliative. Its only advantage is to prevent a bad situation from getting out of hand. The basic cause of the digester biochemical imbalance must be discovered and rectified. Unless this is done, pH control is worthless in the long run. In addition, care must be exercised in selecting an alkaline material that will not produce a toxic reaction. 

Volatile Acid Determination. Part III. Toxicity of Propionic Acid, Tech. Paper No. 239, Florida Engineering and Industrial Experiment Station (1962) 16, 10. 

Failure can also be caused by the addition to the digester of inhibitory or toxic substances other than volatile acids. The model presented is not adequate to represent this type of failure. However, this could be accomplished by adding a death rate term to the organism balance (Equation 7) and establishing a material balance on the toxic material. 

The high volatility and toxicity of HF mean that very special precautions have to be taken to ensure that circuits are completely tight at flanges and valves. The essential nature of the measures taken in the acid section of the unit can be listed as follows ... 

ISOCyanatGS. Polymeric diphenylmethane diisocyanate (pMDI) is the most commonly used isocyanate wood adhesive mainly because of its lower volatility and toxicity when compared to other isocyanates such as toluene diisocyanate and dicylcohexylmethane diisocyanate. Some of the advantages enjoyed by pMDI include the fact that it is a liquid polymer, and so it does not require a solvent carrier for application, it is free of formaldehyde, and also it does not require acidic (the case with UF) or alkaline catalysts (the case with PF). It is an effective wood adhesive because the high reactivity of the isocyanate (—N=C=0) groups allows the resin to cure rapidly, and it has the potential to covalently bond directly to the wood by reacting with the hydroxyl groups on the wood surface (Fig. 5) (7,18-20). 

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