Biosolids
Biosolids (also called sludge) is the byproduct of wastewater treatment. Biosolids are predominately organic, and serve as an excellent feedstock for gasification.
Sludge is traditionally disposed of by land spreading, depositing in landfills, or dried to produce fertilizer. Each of these disposal methods has financial and environmental impacts. Changing state and federal regulations reflect a trend in public policy to secure better alternatives.
BIOSOLIDS CONVERSION – TWO APPROACHES:
1) At an Individual Treatment Plant:
A MaxWest integrated gasification system is suitable for individual wastewater treatment plants with a wide range of capacities. Treatment plants as small as 3 million gallons per day (GPD) may produce sufficient sludge to benefit from a MaxWest system. Small plants may also include biosolids from other small plants or other types of feedstocks. Plants of any size with operating dryers should consider a MaxWest System to lower fuel costs (as compared to natural gas), or to reduce costs and operating problems related to digester gas.
At individual treatment plants, the MaxWest system can accept digester gas, fats, oils, and greases (FOG), and grit and bar screenings on site. These materials get delivered to the gasifier material handling system or to the thermal oxidizer. An individual wastewater plant may utilize its MaxWest system to expand acceptance of FOG and septic tank effluent.
For larger individual wastewater plants, MaxWest’s conversion to thermal energy may include generation of renewable electric power. Excess steam or other heat energy can be utilized in a variety of ways to improve treatment efficiency, sometimes to the point of re-rating for an increased treatment capacity at no additional capital cost. As part of its standard preliminary engineering assessment, MaxWest will survey each wastewater plant with the operators and engineers to evaluate potential uses of thermal energy and other cost savings.
The MaxWest system will typically begin with sludge dewatered to some degree, then dry it and/or mix it with a drier material.
2) At a Regional Sludge Disposal Facility:
A MaxWest integrated gasification system is equally suitable for utilization as a regional sludge disposal facility servicing multiple jurisdictions. In most cases, a regional approach will ensure a large enough facility to produce renewable electric power along with thermal energy to be used for other purposes. Some regional facilities will be located at individual wastewater treatment plants; other regional facilities will be located at landfill sites. In many cases, some amount of methane and other wastes will be available as additional feedstock to produce more electric power and thermal energy.
As a general rule, a regional facility will best be located where power transmission lines (69 KV or larger) are convenient in order to minimize interconnection costs. Proximity to potential users of excess thermal energy is also desirable.
Clean construction debris (free of metal, glass and concrete), yard wastes, land clearing debris and other woody biomass all have excellent gasification characteristics. In the case of land clearing debris, dirt and sand do not interfere with the gasification process – no need for fuel cleaning, only chipping.
Larger gasification facilities do achieve some economies of scale. Multiple wastes typically provide feedstock for more electric power generation and more thermal energy. MaxWest will plan and engineer facilities to accommodate future growth during the term of the contract and beyond. At regional locations, MaxWest will consider utilizing feedstocks extracted or prepared from municipal solid wastes and other sources.