Application of biogranules in the anaerobic treatment of distillery effluents

[摘要] ENGLISH ABSTRACT: The distillery industry produces large volumes of waste water with a high organiccontent throughout the year. These effluents must be treated in some mannerbefore being discharged or recycled in the factory. Several treatment options arein use presently, but they all have disadvantages of some nature, such as longretention times, bad odours or the need for large areas of land. Considerableinterest has been shown in the application of anaerobic digestion, especially theUASB design (upflow anaerobic sludge blanket), to treat this high strength wastewater. Thus, the aim of this study was to investigate the efficiency of an upflowanaerobic sludge blanket (UASB) bioreactor using full-strength distillery effluent.The activity of the bacteria in the biogranules was also evaluated by developing aneasy and reliable activity method to estimate the general biogas andmethanogenic activity and to calibrate this method using different anaerobicgranules from different sources.The influence of high strength distillery effluent on the anaerobic digestionprocess was investigated using a mesophilic lab-scale UASB bioreactor. Duringthe experimental study, the organic loading rate (OLR) was gradually increasedfrom 2.01 to 30.00 kgCOD.m-3.d-1, and simultaneously, the substrate pH wasgradually lowered from 7.0 to 4.7. It was found that at an OLR of 30.00 kgCOD.m-3.d-1,the pH, alkalinity and biogas production stabilised to average values of 7.8,6 000 mg.l-1 and 18.5 I.d-1 respectively. An average COD removal> 90% wasfound indicating excellent bioreactor stability. The low substrate pH holdsconsiderable implications in terms of operational costs, as neutralisation of thebiorector substrate is no longer necessary. The accumulation of fine solidspresent in the distillery substrate was found at the higher OLR's and resulted in thegranular bed increasing with subsequent biomass washout and a lowering inefficiency parameters. However, a possible pre-treatment filtration of these finesolids would eliminate this problem.The success of the upflow anaerobic sludge bed (UASB) process is mainlydue to the capability of retaining the active biomass in the reactor. Over the years,several methods have been developed to characterise and quantify sludge activitybut each has advantages and disadvantages. There is thus an increasing need for a rapid method to evaluate the activity of the granular biomass. The activitymethod of Owen et al. (1979) as adapted by Lamb (1995), was thus evaluated interms of efficiency and applicability in determining the activity of granular samples.The method was found to be inaccurate as well as time consuming and it was thusmodified. Results obtained with the modified assay method were found to be moreaccurate and the impact of the different test substrates (glucose, lactate, acetateand formate) on activity, was more evident. The activity of seven differentanaerobic granules, was subsequently evaluated. Biogas (Ss) and methanogenic(SM) activity was not measured in volume of gas produced per unit COD convertedor volatile suspended solids (VSS), but as tempo of gas production (ml.h-1) in astandardised basic growth medium. The activity data obtained were alsodisplayed as bar charts and calibration scales. This illustrative depiction ofactivity data gave valuable information about population dynamics as well aspossible substrate inhibition.The calibration scales can also be used to group the general biogas (Ss)and methanogenic activities (SM) of any new biogranule relative to active (O-type)and inactive (W-type) anaerobic granules, providing that the same method ofactivity testing is used. The calibration scales can thus be used to give a fastindication of how the activity value of one sample relates to the activity values ofother granules, even when using different test substrates.

[发布机构] Stellenbosch University