Cell Immobilization on Lignin–Polyvinylpyrrolidone Material for Anaerobic Digestion

摘要

Immobilization of bacterial cells on carriers ensures the stability and intensity of biochemical transformations. The choice of the right carrier is often decisive to the success of the biotechnological process. So far, a relatively small group of materials has been tested in the anaerobic digestion (AD) process and the experiments produced different results. In this study, lignin grafted with polyvinylpyrrolidone (PVP) was used for the first time as an innovative microbial carrier in the AD process due to its particularly positive properties such as porosity, thermal stability, and availability. PVP improved cell adhesion to the carrier surface. Waste wafers (WAF) and sewage sludge (SS) were tested as separate samples. The process was carried out in the batch mode under mesophilic conditions. Monitoring of key process parameters such as pH, the volatile fatty acids (VFA), and the VFA-to-total alkalinity (VFA/TA) ratio proved the stability of digestion both in variants with and without the carrier. Results of microbiological and biochemical analyses proved that the addition of lignin-PVP material considerably increased the proliferation of eubacteria in the wafer sample (by 77%) and increased the enzymatic activity, especially in the SS sample (by 30%). Scanning electron microscope observations revealed the presence of microbial colonies on the lignin surface. Improvement of microbiological and biochemical parameters resulted in a natural increase in the amount of biogas/methane produced, that is, an increase of 33.9% in the WAF sample (1,201.45 m3/Mg volatile solids [VS] of biogas, including 685.53 m3/Mg VS of methane) and an increase of 46.8% in the SS sample (746.82 m3/Mg VS of biogas, including 379.60 m3 Mg/VS of methane). As lignin grafted with PVP was proven to have positive effect on the condition of bacterial flora and AD efficiency, the material can be used as a microbial carrier.