A perennial problem with any LCA is identifying reliable and representative data sources. LCI data are available for many common raw materials (e. g., polyvinyl chloride) and manufacturing processes (e. g., extrusion), and, generally speaking, the more common a process, the better characterized it is from an LC perspective. Naturally, having multiple sources of data for a single process allows the user to evaluate the reliability of each source. In the production of algae, there are a large number of materials and processes that have been modeled from a life cycle stand­point that are quite useful. For example, reliable inventory data for a number of fertilizers, flocculants, and other industrial chemicals is readily available from a number of sources as highlighted in Table 3. Similarly, unit operations like pumping centrifugation can be easily modeled from first principles to derive energy use under conditions relevant to the specific process of interest [22].

As discussed earlier, current studies are somewhat limited by the fact that few full-scale algae-to-energy facilities are in operation. This makes it difficult to esti­mate the emissions from specific applications. For example, fugitive emissions from open ponds are expected to be nontrivial, and loss of this nutrient-rich medium could impact nearby receiving waters. Estimating this potential for eutrophication is highly speculative until actual ponds are in place from which data can be collected.

Similarly, there is little data to support assumptions about how often tubular photobioreactors would crack and require replacement, or the extent to which geotextiles are needed at the bottom of an open pond to prevent seepage of growth medium into the subsurface. Most of these estimates will be generally unreliable until some pilot plants are built in the coming years. In the meantime, analogous processes can sometimes be used to approximate the emissions associated with algae-related unit operations. For example, belt filter presses in wastewater treatment sludge handling can be used to approximate the impacts from an algae-to-energy unit operation, and as such, have been used by a number of authors [8, 31].