## 2 Methodology
### Life Cycle Input and Output Data for Each Biosolids Production Process
#### 2.2.1 Air Drying  
The inputs and outputs for Air Drying are summarized in Table 1. Air Drying begins with a belt filter press (Figure 1), which increases the biosolids to 22% total solids (Figure 2). The belt filter press requires the addition of a water-soluble polymer to increase the performance of mechanical dewatering by flocculating suspended solids and colloidal material [11]. The most commonly used polymers in mechanical dewatering are cationic polyacrylamide (PAM) polymers. Acrylonitrile was chosen to represent PAM within the Ecoinvent databasebecause it is used to manufacture acrylamide [15]. The amount of electricity required for dewatering was determined from the empirical relationship outlined in [16]. There are three sources of wastewater from a belt filter press that must be treated: (1) water for cleaning the belt, (2) water to dilute the dry polymer to 0.5%, and (3) water removed from biosolids. The LCA includes the inputs associated with the treatment of this wastewater within a small WRRF. Diesel fuel is needed to transport biosolids from the belt filter press to the Air-Drying pad in a dump truck, form windows with a front-end loader, and mix the windows \begin{table}
\begin{tabular}{p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \hline
**Parameter** & **Value** & **Unit** & **Ecoinvent Item/Comments** \\ \hline Inputs & & & \\ \hline Dewatering Electricity & 20,895 & kWh & US electricity, medium voltage, at grid mix \\ \hline Dewatering Polymer & 1252 & kg & Acrylonitrile, market \\ \hline Dewatering Water & 2490 & kg & Tap water, at user \\ \hline Wastewater to be Treated & 3437 & kg & Treatment, sewage, unpolluted, to wastewater treatment, class 3 \\ \hline Diesel Fuel & 610 & kg & Diesel, at regional storage \\ \hline Asphalt & 54,122 & kg & Asphalt 1  \\ \hline Transportation of Final Product & 48,664 & tkm & Transport, lorry 16-32t, EURO3 \\ \hline Outputs & & & \\ \hline CO\({}_{2}\), Biogenic & 119,619 & kg & Carbon dioxide \\ \hline CH\({}_{4}\), Biogenic & 3107 & kg & Methane \\ \hline N\({}_{2}\)O, Biogenic & 54 & kg & Nitro oxide \\ \hline CO\({}_{2}\), Fuel Combustion & 4270 & kg & Carbon dioxide \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Inputs and outputs for Air Drying LCA. Figure 2: Mass flow through Class A biosolids treatment process trains. Rectangles represent biosolids mass at each point in treatment train. Arrows represent unit processes. each week. To calculate the amount of diesel fuel needed, it was assumed that the Air-Drying pad is 2000 ft away from the belt filter press. The diesel fuel requirement for the window mixing equipment came from [17]. It was assumed that the windows are mixed once a week using a window turner machine. Diesel consumption and combustion from transportation to the Air-Drying pad were estimated using the assumed distance, driving speed, and fuel consumption of the equipment used (Supplemental Information). The impervious surface used for Air Drying is assumed to be an asphalt mixture of 10% bitumen and 90% gravel. The energy required to pave the pad was estimated using paving equipment data [18]. The quantity of asphalt was determined by calculating the size of the impervious pad needed to accommodate the volume of biosolids in windows. The assumed depth of asphalt was 0.5 feet. It was assumed that the lifetime of the asphalt pad is 25 years. The environmental impacts of the asphalt pad were distributed equally to all of the biosolids produced within the lifetime of the pad. Round-trip transportation (100 miles total) to the biosolids land application site was also included as an input within the system boundary for all processes under study to evaluate the effects of the moisture content of the end product and the addition of amendments on transport requirements and ultimate environmental impacts. In fact, the distances that WRRFs must transport biosolids varies widely.