## 1 Introduction  
During poultry production on farms, poultry litter (or broiler litter) is generated as a mixture of poultry exceta (or manure), bedding materials (e.g., wood shavings, sawdust, peanut hulls, and rice hulls), spilled feed, dead birds, bones, and feathers [1; 2]. Over the past few decades, there have been increasing mass quantities of poultry litter produced all over the world due to the increasing demand for animal and protein products in human's daily diet. In 2009, about 25 million tons of total poultry litter were produced in Europe and in the U.S. [1]. The U.S. is the world's largest broiler chicken producer with an annual production approximately between 8.4 billion (in 2012) and 8.9 billion (in 2017) [3]. Using the assumption of poultry litter production between 1.1 and 1.4 tons per 1000 birds, the U.S. alone annually produces around 9.24-12.46 million tons of poultry litter [1; 4]. Brazil is the second largest producer of broiler chickens. It is estimated that the annual volume of poultry litter generated by Brazil is annually around 8-10 million tons [5]. In most cases, poultry litter is applied to the croplands as an organic fertilizer due to its rich nutrients, such as nitrogen, phosphorous, calcium, and potassium [5]. However, excessive overtime application and indiscriminate use have been blamed for eutrophication, pathogen contamination, nuisances (e.g., flies and odors), fish death, and other negative effects on human and animal health [1; 5; 6]. Increment of poultry litter production in the Delmarva Peninsula and all its challenges have stimulated the process of developing and seeking more efficient, cost-effective, environment-friendly, and sustainable poultry litter disposal methods and technologies. Several technical reviews were conducted to compare and summarize alternative poultry litter disposal technologies for energy production and to identify existing technical challenges. [PERSON] et al. [7] found that three main alternative disposal routes--composting, anaerobic digestion, and combustion--may increase the opportunities to produce market energy and nutrient ash by furthering the advancement in disposal routes while providing financial incentives. In 2010, [PERSON] et al. [8] reviewed environmental and social issues from using poultry litter as a feedstock for energy production by four techniques, anaerobic digestion, combustion, co-firing (or co-combustion), and gasification. Recently, [PERSON] et al. [5] analyzed characteristics of poultry litter as a fuel and discussed the main thermal-chemical processes (e.g., anaerobic digestion, combustion, gasification, and pyrolysis) for energetic conversion. The study then proposed measures to improve its performance as a sustainable biomass fuel. Literature reviewed and pointed out that the thermal-chemical processes are effective disposal routes from both technical and environmental points of view to generate useful energy from poultry litter with lower emissions. Combustion is widely considered as one of the most simple, cost-effective, and environmentally benign thermal-chemical processes to date. It provides space heating and large-scale power generation, as well as combined heat and power [6; 7; 9]. In the U.S., there are currently several European-based companies which have constructed commercial centralized combustion systems. For instance, Ireland-based Biomass Heating Solutions Inc. has constructed a manure to combined heat and power plants in Maryland, where the combustion systems use poultry litter as an energy resource to produce useful energy [10]. However, there are several technical challenges of burning U.S. poultry litter in current combustion units. This is because U.S. poultry growers typically clean out poultry litter up to a certain depth, and then proceeds to put a fresh layer of bedding materials on the existing layers for an extended number of flocks. On the other hand, the EU government requires broiler sheds to be completely cleaned out after each flock [11].