Can Autocatalytic Pyrolysis of Wastewater Biosolids be Energy Neutral and Generate Value-Added Products?

Over eight million metric dry tons of wastewater biosolids are produced annually from water resource recovery facilities (WRRFs) in the United States. WRRFs are facing multiple challenges including energy generation, nutrient recovery, and pollutant removal requirements. Autocatalytic pyrolysis of wastewater biosolids is a promising process to improve energy generation and product recovery while removing pollutants. In particular, it can generate biochar (a valuable soil amendment) as well as high-yield pyrolysis gas, which is a renewable clean energy to complement the energy requirement at WRRFs. An energy analysis of autocatalytic pyrolysis was conducted with the assumption of 10% heat loss and using the highest catalyst loading. The results showed that the autocatalytic pyrolysis at 600°C was slightly exothermic but was endothermic at 700°C and 800°C. Therefore, some py-gas was used to supply the heat for 700°C and 800°C operation. However, the remaining fraction of py-gas still reduced the energy for biosolids drying by approximately 70%. At pyrolysis temperatures of 600°C, the remaining py-gas could cover 40% of the energy for biosolids drying. In summary, autocatalytic pyrolysis of wastewater biosolids can be energy neutral and generate the value-added product, biochar.