Investigation of the influence of hydraulic retention time on acidogenesis in aerobic treatment

Abstract

Anaerobic processes are one of the most important biological waste treatmentprocesses. In recent years, interests in anaerobic treatment has expanded considerablybecause the methane by product can serve as a useful fuel to help offset a growing demandfor energy. Unfortunately, this and other attributes have been clouded by certain drawbacks,such as prolonged periods required for start-up and the process instability, which results inthe failure of operating digesters. In order to increase the stability of anaerobic digestion,two-phase anaerobic systems have been introduced.The aim of this study is to investigate the influence of hydraulic retention time on theconversion of the substrate to volatile acids and on the composition of the reactor effluent.The experimental work comprised two major parts; the acclimation of obtained acidogenicsludge to glucose in four steps (these were 5000, 10000, 15000 and 20000 mg COD/L) andinvestigation ofthe influence of hydraulic retention time (HR.T). It was found that HR.T hasan impact on the conversion of the substrate to volatile acids and on the composition of thereactor effiuent. In HRT= 4 days, main products of the reactJrs were acetic (HAc),propionic (BPr), butyric(HBu) and valeric (HVal) acids; where as in HRT=10 days, mainproducts of the reactors were BPr, HVal, HBu and HAc. Moreover, in HRT= 4 days;percentage of acidification and VF As: Alkalinity were in the proper range; 6% for A reactor,11% for B reactor and 0.85 for A reactor, 0.56 for B reactor, respectively. In contrast to 4days HRT, in HRT= 10 days, above values were respectively, 1% for A reactor, 1% for Breactor and 0.28 fur A reactor, 0.28 for B reactor.These data presented failure of theprocess. Therefore, in comparison to 10 days hydraulic retention time, 4 days HR.T wasbetter for lab-scale semi continuous reactors which were used glucose as carbon source.