High Solid Content Biomass and Biosolid Feedstock Preparation Using a Hydro-Thermal Pretreatment

Biosolid sludges discharged from municipal waste water treatment plants typically have a solid content that can vary from 0.25% to 25% by weight. It is conventionally disposed of through land farming or landfills although it needs to be de-watered prior to disposal. This adds significant cost to the disposal process. There is considerable effort to find other methods of disposal of biosolids to minimize both energy and capital costs. Biosolids contain energy that could be reutilized. In fact, gasification of comingled biomass and biosolid feedstocks offers a renewable and environmental friendly pathway of utilizing waste to produce energy. However, the handling and transport of high solid content biomass and biosolid mixtures pose technological problems. The College of Engineering, Center for Environmental Research and Technology (CE-CERT) has developed a Hydro-Thermal Pretreatment (HTP) process that produces high solid content biosolid slurry either alone or comingled with biomass. This process shows considerable promise for efficient handling of biosolid slurries.

The objective of this research is to systematically investigate HTP of biomass and biosolid mixtures. The purpose is to determine optimized operational conditions and to assess the rheological properties of biomass and biosolid slurries with different solid content and different particle size. In addition, the energy content of the pretreated biomass and biosolid slurries are also evaluated to determine the potential for fuel production. It is found that, after HTP, the volumetric density of biosolid increases. The solid fraction in biosolid condenses and free water is available for mixing with biomass particles. Two different mixing procedures are applied to mix biomass with biosolid: untreated biomass mixed with pretreated biosolid and pretreated biomass mixed with pretreated biosolid. It has shown that comingled pretreated biomass and pretreated biosolid slurry gives acceptable solid content and viscosity values so that it can be utilized as a feedstock in the CE-CERT hydro-gasification process. Estimates of the chemical and physical properties of various biosolids/biomass mixtures, such as low heating value, proximate analysis and elemental analysis, will also be presented.