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Title: Anaerobic membrane bioreactor technology for solid waste stabilization
Author: Trzcinski, Antoine Prandota
ISNI:       0000 0004 2680 8761
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2009
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In this study, a simulated Organic Fraction of Municipal Solid Waste (OFMSW) was treated inan anaerobic two-stage membrane process. The OFMSW feedstock was fed to a ten litre hydrolyticreactor (HR) where solid and liquid fractions were separated by a coarse mesh, whilethe leachate was fed to a three litre submerged anaerobic membrane bioreactor (SAMBR) within-situ membrane cleaning by biogas sparging beneath a flat sheet Kubota membrane. Theaim was to develop and optimize this two-stage process where the use of a membrane in bothreactors to uncouple the Solid and Liquid Retention Times (SRT and HRT) would allow us toimprove the current performances obtained with single stage designs. The Denaturing GradientGel Electrophoresis (DGGE) technique was used to monitor the microbial population in the reactorsand have a better understanding of the archaeal and bacterial distribution in a two-stageprocess. It was found that meshes with pore sizes of 10 microns and 150 microns were inappropriateto uncouple the SRT and HRT in the HR. In the former case, the mesh became clogged, whilein the latter case, the large pore size resulted in high levels of suspended solids in the leachatethat built up in the SAMBR. The most important parameter for Volatile Solids (VS) removal in theHR was the SRT. Maximum VS removals of 70-75% could be achieved when the SRT was equalto or greater than 50-60 days. This was achieved at a HRT of 9-12 days and an Organic LoadingRate (OLR) of 4-5 g the SRT to beyond 100 days did not significantlyincrease the VS removal in the HR. However, at an OLR of 10 g in the HR the SRThad to be reduced due to a build up of TS in the HR that impeded the stirring. Below 20 daysSRT, the VS removal reduced to between 30 and 40%. With kitchen waste as its main substrate,however, an OLR of 10 g was achieved with 81% VS removal at 23 days SRT and1.8 days HRT.The SAMBR was found to remain stable at an OLR up to 19.8 g at a HRT of0.4 day and at a SRT greater than 300 days, while the COD removal was 95%. However, theperformance at such low HRTs was not sustainable due to membrane flux limitations whenthe Mixed Liquor Total Suspended Solids (MLTSS) went beyond 20 g.l-1 due to an increase inviscosity and inorganics concentration. At 35 ?C the SAMBR was found to be stable (SCODremoval 95%) at SRTs down to 45 days and at a minimum HRT of 3.9 days. The SAMBRcould achieve 90% COD removal at 22 ?C at an OLR of 13.4 g and 1.1 days HRT(SRT = 300 days).The DGGE technique was used to monitor the archaeal and bacterial diversity and evolutionin the HR and SAMBR with varying SRTs, HRTs, OLRs and temperatures in the biofilm andin suspension. Overall, it was found that stable operation and high COD removal correlatedwith a high bacterial diversity, while at the same time very few species (2-4) were dominant. Only a few dominant archaeal species were sufficient to keep low VFA concentrations in theSAMBR at 35 ?C, but not at ambient temperatures. It was found that some of the dominantspecies in the HR were hydrogenotrophic Archaea such as Methanobacterium formicicum andMethanobrevibacter while the other dominant species were from the genus Methanosarcinaor Methanosaeta. The presence of hydrogenotrophic species in the HR could be fostered byreinoculating the HR with excess sludge from the SAMBR when the SRT of the SAMBR wasgreater than 45 days. Among the bacterial species Ruminococcus flavefaciens, Spirochaeta,Sphingobacteriales, Hydrogenophaga, Ralstonia, Prevotella and Smithella were associated withgood reactor performances.
Supervisor: Stuckey, David Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral