# Physical Properties of Dairy Manure Pre- and Post-Anerobic Digestion
## 1 Introduction
More recently, [PERSON] et al. [21] developed a relationship between manure density and TS content, but focused on manure with a high TS content from 10% to 50%. A summary of previous studies that related TS content and density of animal manure is presented in Table 1.  
The physical characteristics of manure depend on multiple factors and practices before and after excretion. These factors include animal diet, animal type, manure collection and storage systems, processing technology, and water or other by-products added to the manure stream [24]. These practices have changed significantly in the last two decades [25], and this could have an impact on the manure density results presented by the studies listed above, as well as the relationship between manure density and TS. Dairy cattle today produce much more milk and are fed more grains for supplying energy [26]. Many facilities have also incorporated manure processing and storage which may have an impact on previously collected data. Manure characteristics can also change from one handling stage to the other, especially if there is manure processing such as AD. [PERSON] et al. [27] measured an 80% VS degradation during a two-stage AD process. The breakdown of organic compounds changes the composition of TS and thus, the density of manure after AD. Sampling manure at each stage from \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Manure Studied**} & \multirow{2}{*}{**Equation or Value Predicting Density of Manure**} & **TS** & **Authors** \\  & & **Range** & \\ \hline \multirow{4}{*}{Beef} & \(\rho=16.02(20.41-0.3648M+0.01972M^{2}+0.00001036M^{3}\) – & \multirow{4}{*}{15–75\%} & \multirow{4}{*}{[PERSON] et al. [18]} \\  & 0.00001304M\({}^{4}\) & & \\  & where: \(\rho\) = bulk density (kg m\({}^{-3}\)); M = moisture content (\%) & & \\  & \(\rho=17\)-0.0003575 & & 0–16\% & \\  & where: \(\rho\) = bulk density (kg m\({}^{-3}\)); TS = total solids (\%) & & \\  & \(P_{quality}=0.023575^{3}+1.1975^{2}-11.275+1000\) & & \\  & \(P_{quality}=0.036775^{3}-2.3875^{2}+14.675+1000\) & & \\  & \(\rho_{alap}=0.008675^{3}-0.87375^{2}+8.975+1000\) & & \\  & where: \(\rho\) = bulk density (kg m\({}^{-3}\)); TS = total solids (\%) & & \\  & \(\rho_{alap}=0.702675^{2}-58.13275+1407.40\) & & \\  & where: \(\rho\) = bulk density (kg m\({}^{-3}\)); TS = total solids (\%) & & \\  & \(\rho_{alap}=0.081675^{2}-58.13275+1407.40\) & & \\  & where: \(\rho\) = bulk density (kg m\({}^{-3}\)); TS = total solids (\%) & & \\  & \(\rho_{alap}=162.375\) – 159.3 & & \\  & where: \(\rho\) = bulk density (ton m\({}^{-3}\)); TS = total solids (\%) & & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Summary of studies that related total solids (TS) content and density of animal manure. excretion to land application can become costly and time intensive for preliminary assessments and models. As a result, multiple dairy related LCA studies that evaluated the contribution of manure to different environmental impacts assumed no variation of the physical characteristics across manure stages [28; 29; 30]. This assumption can affect the precision of estimations given that some environmental impacts are directly related to manure characteristics. For example, CH\({}_{4}\) and ammonia (NH\({}_{3}\)) emissions from manure storage are highly dependent on VS content and surface area [13]. If physical changes in manure are not accounted for, modeled emissions of undigested and post-digested manure would be similar, which is not the case [10]. The aim of this paper is to relate manure TS to density for current dairy farming practices, particularly for those introducing AD. To better determine the density of manure pre- and post-digestion, the density, TS, and VS of manure were analyzed. These relationships and parameter changes are critical for planning decisions, infrastructure designs, evaluating equipment performance, and in developing models used for predictive purposes.