Integrated Wastewater Treatment in Lignocellulosic Biorefineries
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Production and use of bio-based products offer a number of advantages over conventional petrochemicals, yet the relatively high cost of production has restricted their mainstream adoption. Optimization of waste treatment processes could reduce capital expenditures, lowering the barrier to market entry for lignocellulosic biorefineries. This paper characterizes waste production from lignocellulosic ethanol production and analyzes potential wastewater treatment operations. It is found that organic material is intrinsic to bioconversion wastes, supplying up to 260 kilograms of biological oxygen demand per tonne of feedstock. Inorganic material, however, is largely added to waste streams throughout the bioconversion process as a result of pretreatment and pH adjustment operations which increase the inorganic loading by 44 kilograms per tonne of feedstock. Adjusting unit operations to limit addition of inorganic material can reduce the demands and therefore cost of waste treatment. Various waste treatment technologies – including those that take advantage of ecosystem services provided by feedstock production – are evaluated in terms of capital and operating costs, as well as technical feasibility. It is concluded that waste treatment technologies may be better integrated with conversion processes and even feedstock production. In general, there should be an effort to recycle resources throughout the bioenergy supply chain through application of ecosystem services provided by adjacent feedstock plantations and recovery of resources from the waste stream to reduce overall capital and operating costs of bioconversion facilities.
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