Treatment characteristics of two phase anaerobic system using an UASB reactor

• Main Author: Ramos, Elsa Dolores Chacin
• Published: University of Birmingham 1993
• Subjects: 628.3
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.633074

During this project, the treatment of a simulated wastewater from soluble starch by a two-phase anaerobic system using an UASB reactor was examined under mesophilic conditions. Prior to seeding the reactors, the pregranulated sludge which was to be used as the inoculum for the acidogenic reactor, was acidified to pH 4.3, using a mixture of volatile fatty acids, to improve the spatial bacteria separation in the system. The two-phase system was studied, first under different organic loads and secondly, in terms of its resistance to the addition of heavy metals. For the first experimetal studies, different organic load were applied to the system, and changes to the microbial ecology of the acidogenic and the methanogenic phase was assessed. The biomass in the methanogenic reactor was mainly composed of fluorescent methanogenic bacteria. In the acidogenic reactor after the start-up period elapsed, no fluorescent bacteria were observed. Two different runs were performed and for each individual run, different OLR were used. For the first run, the organic loads applied to the system were from 3.83 to 30.63 kg COD/m3d, this gave organic loads for the methanogenic reactor of between 4.56 to 44.3 kg COD/m3d. In the second run, the OLR used were from 10 to 16.6 kg COD/m3d for the overall system, and from 13 to 23.35 kg COD/m3d for the methanogenic reactor. Organic loads greater than 15 kg COD/m3d, caused biomass wash-out from both the acidogenic and methanogenic reactor. The best COD removal efficiencies and gas production rates were achieved by the system under OLR of 13.31 kg COD/m3d, with pCOD removal efficiency of 95 % and methane production of 80.2 %. The biogas production was 0.33 m3CH4/kg COD removed. Under high applied organic load, the microbial population of the methanogenic reactor changed, and filamentous foaming bacteria were isolated both from the sludge and the foam that was produced. The species found to be responsible for the foam formation in the anaerobic methanogenic reactor was Microthrix parvicella, which was identified using the Neisser test and Scanning Electron Microscopy (SEM). For the second part of this experimental work, copper and lead were used as toxic elements. These two heavy metals were choose due to the fact that they are subproducts of many industries and can cause significant environmental problems. Copper and lead were used as the acetates and chlorides to study the effect of these heavy metals when they were combined with different anions. It was found that the combination of copper and lead as chlorides were more toxic to the anaerobic treatment than when they were present as acetate. Also, it was found that the two heavy metals used were toxic to the acidogenic phase and not to the methanogenic phase.