Converting Biosolids to a Useable Fuel: The Emerging Technology of Biosolids Carbonization

Bolin, K., Kearney, R., Overstreet, E., Dooley, B.
EnerTech Environmental, Inc


EnerTech’s patented SlurryCarb™ process chemically converts biosolids into a high-energy, renewable solid fuel, providing
an environmentally and economically sound solution for biosolids management. The proven technology produces significant
savings in both operating and capital costs, and commercial installations of the process are currently under development.
Simplicity of operation is key to the SlurryCarb™ technology. Biosolids at up to 30% solids content are brought to a central
processing facility where they are processed as a pumpable slurry, creating savings in capital and operating costs. The
biosolids slurry is continuously pumped and pressurized above its saturated steam pressure to maintain a liquid state
throughout processing. Upon reaching the desired reaction pressure and temperature, the molecular structure of the biosolids
is reconfigured. The cellular structure of the biosolids ruptures and carbon dioxide gas splits off, a step called “carbonization.”
This reaction significantly reduces the size and improves the uniformity of the biosolids molecules. The reacted product
becomes extremely hydrophobic and can be mechanically dewatered to greater than 50% solids. By avoiding evaporation,
thermal energy inputs for the evaporation of water are minimized. The SlurryCarb™ process requires approximately 57.5%
less energy than traditional drying methods.

This dewatered, reacted product is concentrated in carbon, and over 80% of the original water present in the biosolids is
removed without evaporation. The reacted, dewatered product is dried to form a fuel that burns at up to 16,282 kJ/kg (7000
Btu/lb). This fuel, called E-Fuel, is exported to a customer and utilized as a renewable fuel. The filtrate from dewatering is
pretreated to the standards of the local wastewater treatment plant.

In addition to the energy savings, the SlurryCarb™ process removes key pollutants from the E-Fuel. Emissions from the
combustion of E-Fuel are well within emissions standards without extensive air pollution control systems. And, as a renewable
fuel, E-Fuel produces essentially zero net greenhouse gas emissions. The SlurryCarb™ process eliminates the release of
methane encountered by landfilling biosolids. The release of methane from landfills is a major source of man-made
greenhouse gases.

EnerTech has constructed a Process Development Unit (PDU) located in Georgia. EnerTech’s 54.5 l/h (14.4 GPH) PDU
includes all the necessary pumping, heating, depressurizing and dewatering systems necessary to simulate a commercial
scale SlurryCarb™ facility. The PDU has provided comprehensive engineering data from extended operations. The results of
these operations are summarized in this paper.

By avoiding the evaporation of water, the economics for the SlurryCarb™ technology are extremely competitive with current
methods employed by the industry. With operating experience and significant research conducted at the PDU, EnerTech and
its engineering partners have designed the 675 wet tons per day facility in the Los Angeles area. Construction of the Los
Angeles area facility has started, and users for the E-Fuel have been established. Significant progress has been made on the
Los Angeles area project over the past few months. This paper includes final design criteria and an update on the status of
the Los Angeles area project.

The need for environmentally and economically sound alternatives to traditional biosolids removal methods is becoming
increasingly evident. EnerTech’s ability to offer the municipal market and large private waste producers a low-cost,
sustainable, and environmentally-friendly solution that overcomes regulatory hurdles has already gained the company
widespread interest and support for its SlurryCarb™ process.

Biosolids, Carbonization, E-Fuel, Energy Production, Renewable Fuel, SlurryCarb™

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