Life Cycle Environmental Impacts of Wastewater-Based Algal Biofuels

Abstract

Recent research has proposed integrating wastewater treatment with algae cultivation as a way of producing algal biofuels at a commercial scale more sustainably. This study evaluates the environmental performance of wastewater-based algal biofuels with a well-to-wheel life cycle assessment (LCA). Production pathways examined include different nutrient sources (municipal wastewater influent to the activated sludge process, centrate from the sludge drying process, swine manure, and freshwater with synthetic fertilizers) combined with emerging biomass conversion technologies (microwave pyrolysis, combustion, wet lipid extraction, and hydrothermal liquefaction). Results show that the environmental performance of wastewater-based algal biofuels is generally better than freshwater-based algal biofuels, but depends on the characteristics of the wastewater and the conversion technologies. Of 16 pathways compared, only the centrate cultivation with wet lipid extraction pathway and the centrate cultivation with combustion pathway have lower impacts than petroleum diesel in all environmental categories examined (fossil fuel use, greenhouse gas emissions, eutrophication potential, and consumptive water use). The potential for large-scale implementation of centrate-based algal biofuel, however, is limited by availability of centrate. Thus, it is unlikely that algal biofuels can provide a large-scale and environmentally preferable alternative to petroleum transportation fuels without considerable improvement in current production technologies. Additionally, the cobenefit of wastewater-based algal biofuel production as an alternate means of treating various wastewaters should be further explored.

Evaluation of Microalgae Biofuel Production Potential and Cultivation Sites Using Geographic Information Systems: A Review

“…As a downside, wastewater is prone to production of undesirable viruses and bacteria which can result in contamination and will increase cleaning and maintenance costs [65]. Considerable improvement in current production technologies are also required to make large-scale wastewater algal biofuel systems possible [66]. In addition, feasibility of the system with respect to available land area around wastewater treatment plants and infrastructure requirements, such as effluent storage and transportation, should be thoroughly examined [43].…”

Evaluation of Diverse Microalgal Species as Potential Biofuel Feedstocks Grown Using Municipal Wastewater

“…Regardless of the strain used (salt or fresh water), a nonsaline water supply will be required to make up for evaporative loss in an open-pond cultivation system. Lastly, off-setting part or all of the nutrient supply required to grow microalgae with non-petroleum-derived fertilizer such as municipal wastewater can help improve the carbon budget of microalgal-based biofuel production systems (Chisti, 2007;Wang et al, 2010;Bhatt et al, 2014;Dong et al, 2014;Mu et al, 2014).…”

“…Ideally, the wastewater could be used in its raw state or with minimal treatment so as to reduce the costs of the wastewater treatment plant (WWTP) (Pittman et al, 2011;Bhatt et al, 2014;Mu et al, 2014). Centrate, the liquid fraction after anaerobic digestion, offers a feed stream high in nitrogen and phosphorous, which are two of the main nutrients required for microalgae and also two compounds that cause high removal costs for most municipal WWTPs (Wang et al, 2010;Li et al, 2011a;Bhatt et al, 2014;Dong et al, 2014;Mu et al, 2014). In addition to decreasing the nutrient load to the plant, diverting centrate to algae production also decreases the treatment volume, thereby decreasing treatment costs of other chemical constituents (Li et al, 2011a;Mu et al, 2014).…”

“…Centrate, the liquid fraction after anaerobic digestion, offers a feed stream high in nitrogen and phosphorous, which are two of the main nutrients required for microalgae and also two compounds that cause high removal costs for most municipal WWTPs (Wang et al, 2010;Li et al, 2011a;Bhatt et al, 2014;Dong et al, 2014;Mu et al, 2014). In addition to decreasing the nutrient load to the plant, diverting centrate to algae production also decreases the treatment volume, thereby decreasing treatment costs of other chemical constituents (Li et al, 2011a;Mu et al, 2014). Metal content of wastewaters or centrate are unlikely to inhibit microalgal growth (Wang et al, 2010;Dong et al, 2014).…”

Nutrient removal from an anaerobic membrane bioreactor effluent using microalgae. Study and modeling of the process.

“…Yang et al (2011) calculated that 90% of freshwater, 94% of nitrogen and 100% of potassium, magnesium and sulfur could be saved when producing microalgal biofuels using wastewater as growth medium, and Mu et al (2013) confirmed the higher sustainability performance of microalgae grown in wastewater than cultures grown in freshwater.…”