Polyhydroxyalkanoates (PHA) biosynthesis from kraft mill effluents in a moving bed bioreactor (MBBR): operational factors, biomass origin and nutrients effect

摘要

In the MBBR operation, nutrient diffusion into the biofilm layer is highly limited, which the bacterial populations adopt specific survival strategies. In particular, cells often accumulate organic carbon as internal polymers, such as polyhydroxyalcanoate (PHA). In this work the operational factors and nutrient effect on the biosynthesis of PHA were studied using kraft effluents and MBBR technology, as well as three kind of sludge origin was studied using batch system. The MBBR was operated during 225 days in five phases. The Hydraulic Retention Time (HRT) was reduced from 48 to 4.8 h between phases Ⅰ and Ⅳ, the BOD_5:N:P ratio (100:5:1 and 100:1:0.2) was evaluated as an operation strategy in phases Ⅳ to Ⅴ. Inocula were obtained from activated sludge plants from sewage (SAS), paper mill (PAS) and kraft (KAS) for batch assays. The maximum PHA accumulation was obtained under a BOD_5:N:P relationship of 100:1:0.2 using KAS sludge with 30.40% of cells. Yields obtained ranged from 0.10-0.14 mg PHA/mgCOD. In the MBBR operation the maximum absolute fluorescence against the proportion of cells accumulating PHA was obtained for a OLR of 1.19 ± 0.04 kgBOD_5/m~3·d and a BOD_5:N:P relationship of 100:1:0.2. The increase of PHA biosynthesis is due to the OLR increase and it is not attributable to the increase of cell concentration, which is maintained constant in stationary status during bioreactor operation. However the sludge performance when the HRT was reduced from 48 to 4.8 h shown that the fraction of suspended biomass decreased (33.4%) and biofilm growth in the MBBR increased to 84%.