Autocatalytic Pyrolysis of Wastewater Biosolids for Product Upgrading

The main goals for sustainable water resource recovery include maximizing energy generation, minimizing adverse environmental impacts, and recovering beneficial resources. Wastewater biosolids pyrolysis is a promising technology that could help facilities reach these goals because it produces biochar that is a valuable soil amendment as well as bio-oil and pyrolysis gas (py-gas) that can be used for energy. The raw bio-oil, however, is corrosive; therefore, employing it as fuel is challenging using standard equipment. A novel pyrolysis process using wastewater biosolids-derived biochar (WB-biochar) as a catalyst was investigated to decrease bio-oil and increase py-gas yield for easier energy recovery. WB-biochar catalyst increased the py-gas yield nearly 2-fold, while decreasing bio-oil production. The catalyzed bio-oil also contained fewer constituents based on GC-MS and GC-FID analyses. The energy shifted from bio-oil to py-gas, indicating the potential for easier on-site energy recovery using the relatively clean py-gas. The metals contained in wastewater biosolids played an important role in upgrading pyrolysis products. The Ca and Fe in WB-biochar reduced bio-oil yield and increased py-gas yield. The py-gas energy increase may be especially useful at water resource recovery facilities that already combust anaerobic digester biogas for energy since it may be possible to blend biogas and py-gas for combined use.