Sludge - Alternative Pathways For Sludge Reuse

Alternative Pathways For Sludge Reuse

Feridun of the United Sludge Free Alliance suggests that sludge can be recycled in a variety of ways that are both environmentally beneficial and sustainable, and which do not involve application of biologically active materials to croplands that humans live close to. These include using anaerobic digestion to produce biogas, pyrolysis of the sludge to create syngas and potentially biochar, or incineration in a waste-to-energy facility for direct production of electricity and steam for district heating or industrial uses. Synergies from these processes include a far lower, controlled level of methane release (an extremely potent greenhouse gas) to the atmosphere from the pyrolyzed/digested/combusted sludge rather than the uncontrolled release of methane from untreated sludge. If methane is captured rather than allowed to outgas, it can be used for fuel, closing the carbon cycle. Thermal or anaerobic processes greatly reduce the volume of the sludge, as well as achieve remediation of the biological concerns. Direct waste-to-energy incineration systems require multi-step cleaning of the exhaust gas, to ensure no hazardous substances are released. In addition, the ash produced by incineration is difficult to use without subsequent treatment due to its high heavy metal content; solutions to this include leaching of the ashes to remove heavy metals followed by reuse of the ash as aggregate for concrete, or if biochar is used, the heavy metals may be fixed in place by the char structure. Another way to use dried sewage sludge as an energy resource is to burn it together with coal in coal-fired power stations. This is considered as biomass co-firing, which allows power stations to produce the same amount of electricity with less carbon-dioxide emissions.