The Effects of Hydraulic Retention Time and pH on Slaughterhouse Wastewater Acidification

Abstract

Slaughterhouse effluent has not been treated properly in Thailand and two-phase anaerobic treatment was appeared to be advantageous for long-term operation.  The present work was thus investigated on slaughterhouse wastewater acidification in a continuously-stirred tank reactor (CSTR) under ambient temperature according to the limitation of acid-forming study and to enhance the overall performance of two-phase anaerobic treatment. A 3-l acidogenic CSTR was applied throughout the experiment.  It was firstly operated under hydraulic retention time (HRT) in the range of 4-24 hr without pH control and was secondly applied with pH ranging between 5.11-6.57 and 8 hr of HRT to evaluate the effects of operational HRT and pH variation, respectively.  An acidification efficiency was significant affected by HRT under non-pH control scenario (pH=6.99).  An operational HRT of 8 hr was found to be the optimum operational HRT as a maximum percentage of acidification of 10.0% and acid production rate of 0.398 g COD/l.d were achieved.  pH changing was found to be an unimportant influence on acid-forming activity as both of the percentage of acidification and the acid production rate were not considerably changed.  An adjustment of operational pH would be negligible.  HRT of 8 hr with non pH adjustment is thus appeared to be the optimum operational condition for slaughterhouse wastewater acidification in a CSTR.  Acetic acid was a predominant product while propionic, butyric acid were also commonly generated but in less quantity.