The Decision-support for Digester-Algae IntegRation for Improved Environmental and Economic Sustainability (DAIRIEES) model is being developed to track the carbon, nitrogen and phosphorus flows through the system, quantify the amounts and values of the products, and assess the annual cost on a per cow basis. The model allows the user to evaluate different process configurations and calculate whether the implementation of the integrated system is economically viable. The model requests certain inputs such as herd size, the year, market values for certain products, capital costs and several other variables. Based on the experimental data obtained, the overall reduction in GHG emissions is determined along with whether or not the system makes sense from an energy balance point of view. If no values are entered, default values are used to calculate the outcomes of the system. Several assumptions are also used in the model to fill gaps and supply data not provided by the experimental data.
Sub-models were created for each process and incorporated into the DAIRIEES model. Appropriate default values were researched and included on the same worksheet as the user-defined inputs. Examples of default parameters include the amount of manure produced per cow per day, volume of reactor needed to hold all of the manure, amount of algae required to adequately sequester carbon and nutrients, yield of PHAs per kg of VFA, the marketable value of bio-oil, and annual cost of dewatering algae ponds, etc. The Excel-based model is designed to be navigable and intelligible by general users familiar with the basic unit level operations. To this end, summary tables, graphs and figures are generated to supply basic information for investigating the potential implementation of the integrated manure treatment system. A separate worksheet for each system, fermenter, AD, PHA reactor, algae cultivation, hydrothermal liquefaction and pyrolysis summarize the mass flows for each process. Additional worksheets detail the economic and environmental analysis.