EFFECTS OF 4-NITROPHENOL ON H-2 AND CO LEVELS IN ANAEROBIC PROPIONATESYSTEMS

Parameters used for anaerobic process control include volatile acids, COD, gas volume and composition. Measuring headspace trace gases (hydr ogen and carbon monoxide) are becoming more common in anaerobic resear ch. For economy, it is important to know whether a single parameter (h ydrogen, carbon monoxide or volatile acids) can be sufficient for proc ess control. In this research, 4-nitrophenol (4-Np) inhibited, anaerob ic, propionate fed, chemostats were used to study the limitation of us ing (i) headspace hydrogen (or carbon monoxide) or (ii) effluent volat ile acids (acetate and propionate) as monitoring parameters. It was fo und that hydrogen utilizing methanogens were not affected with up to 6 6 mg/l 4-Np at 16-day SRT and with up to 33 mg/l at 10-day SRT. This l ed to no hydrogen accumulation even though acetate and propionate accu mulated significantly showing inhibition of both propionate-utilizing acetogens and acetate-utilizing methanogens. This shows that hydrogen measurements alone would be misleading in this case. Measurement of bo th volatile acids and hydrogen is recommended unless prior comparative knowledge is available on the effects of a toxicant on propionate-, a cetate- and hydrogen-utilizers. CO went up to 3 ppm from 0.8 ppm with a spike of 66 mg/l 4-Np at 16-day SRT. In most cases CO was not very u seful as a monitoring parameter.