As with any production process, algal biofuel will undoubtedly have an impact on the environment relating to land use, water use, atmospheric emissions and terrestrial/water emissions. One of the key aims of biofuel production is to produce a fuel with fewer environmental impacts than conventional fossil fuels [100]. The intensive processing of the biomass, however, could result in a fuel with greater environmental impacts.

When considering environmental impacts of a product, many factors are taken into account. One of the main impact categories which is con­sidered is the greenhouse gas emissions (GHG) in kg CO2 equivalent, ef­fectively the benchmark for how “green” a product is. In the best case, a biofuel can have a negative greenhouse gas emission in that during its pro­duction more carbon dioxide is taken up than is released during produc­tion and use of the fuel. Many studies have been carried out assessing the greenhouse gas emissions of various fuel types from different feedstocks. Recent studies which have investigated the production of algal biofuel have found that, under most circumstances, algal biofuels are likely to have a net positive greenhouse gas emissions [77, 87, 96]. This is in con­trast with many other biofuels produced from conventional first and sec­ond generation feedstocks which are produced uptaking more greenhouse gases than are emitted in the process [101-103]. A comparison of carbon dioxide emissions from algal biofuel and alternative feedstocks is shown in Table 9. The table shows the CO2 emissions per MJ of energy recov­ered as biofuel. The LCA method is included showing at which point the study stopped i. e., at fuel production (well to fuel) or at combustion (well to wheel). The data displayed in table 8 exhibits how poorly algal biofuel currently performs when compared to alternative feedstocks whether they are processed to bioethanol or biodiesel. One of the studies finds algal biodiesel to provide a negative GHG balance [95], nevertheless this is in contrast to the majority [77, 87, 96]. The different termination points of the study make comparison more difficult as predictably there are GHG emis­sions associated with the transport and combustion of the fuel.

The majority of greenhouse gases in algal biofuel production are emit­ted as a result of energy production. Clarens et al. [87] for example dem­onstrated that CO2 procurement demands 40% of total energy consump­tion and 30% of GHG emissions. Any electricity required will create GHG emissions at the point of generation. In their more recent study Clarens et al. [97] compared the greenhouse gas emissions of two scenarios: algal biodiesel with bioelectricity generated from residual biomass and just bio­electricity generated from the biomass. The results were compared with biodiesel and bioelectricity from canola and bioelectricity from switch — grass. The energy from algae scenarios both performed well with direct bioelectricity from algae producing the least GHG emissions. The process stream configuration greatly affects the energy requirements. The greater the number of processes (particularly those including lipid extraction and digestion) required more energy and thus also produced greater green­house gas emissions.

GHG emissions may be the most common impact category yet there are many others that also require consideration including eutrophication potential, global warming potential, land use and human toxicity. In their life-cycle analysis Lardon et al. [77] investigated the environmental im­pacts of their algal-biofuel best-case scenario (low N, wet processing) to alternative feedstocks (rapeseed, soybean, palm, diesel). In some areas the algal biofuel performed well (such as in land use and eutrophication) how­ever it did not compare well for the majority of categories, particularly for photochemical oxidation, ionizing radiation, marine toxicity, acidification and abiotic depletion. In the study published by Clarens et al. [87] a fewer number of categories were investigated but the results are similar for eu­trophication and land use, both of which are favourable in comparison to corn, canola and switchgrass. Clearly improvements need to be made to minimise the adverse impacts that would be caused by the production and combustion of algal biofuels. These impacts are unlikely to ever be non-existent but it is important that the concept can perform favourably in comparison to alternatives regarding environmental impacts.