System boundaries and production process
For the calculation of environmental impacts, standard life cycle assessment (LCA) research method was used, based on guidelines and requirements delineated in ISO 14044:2006 – Environmental management – Life cycle assessment, reviewed and confirmed in 2022 (International Standard, 2006).
All information regarding the cultivation system and process, from inoculation up-to facility gates was obtained from the Hellisheidi Spirulina facility in Hellisheidi geothermal park, located in the region of Hengill, South West Iceland, N64°2'12" W21°23'53".
In the facility, Spirulina (UTEX 3086) is cultivated in modified Zarrouk medium (Rajasekaran et al., 2016). Cultivation is conducted in modular production units, each consists of a bundle of 80, 180-L flat panel airlift PBRs. Culture is kept under agitation pneumatically induced by i of CO2-enriched air, with flow aeration of 0.5 vvm (air volume/medium volume/minute). Temperatures are maintained at 31 ± 2 °C. pH is kept at 10.8 ± 0.2. Culture in PBRs is grown under red/blue/UV illumination (USP # 63/026,764) at 3.5 W/l.
Light emitting diodes (LED) are used for artificial illumination allowing spectral control of light, and augmentation of photosynthesis (Schulze et al., 2014; Ooms et al., 2016). Considering energy-to-light LED efficiency and light-to-algae-biomass conversion efficiency, it was previously calculated that the energy required per Spirulina algal biomass is 143 kWh per 1 kg of ash free dry weight (AFDW) (Ooms et al., 2016). This figure corresponds the data obtained from the Hellisheidi Spirulina PBR facility. Moreover, approximately 50% of the electrical energy converts into light, with the remaining energy converted into heat (Ooms et al., 2016). In the production facility, residual heat is removed by liquid-liquid heat exchange using geothermal cooling water. Cooling pass-through water is provided by Hellisheidi geothermal park, alongside a stream of geothermal CO2 for biofixation in the culture (see Figure 1).
During a continuous daily harvest, approximately 15% of the culture in each production unit is transferred to a rotation sieve set for harvest, washing and downstream processing (micro and ultrafiltration membranes). Residual medium water is treated on site and recycled back to cultivation (using micro and ultrafiltration membranes). After washing, wet biomass is transferred to pasteurization. Hot geothermal waste stream is used as a heat source. After the pasteurization and cooling cycle, wet biomass is being parceled and packaged on site before it leaves factory gates.
Electricity for illumination, liquid pumping, gas blowing, culture harvesting and washing, water treatment, packaging and clean-in-place (CIP), is supplied by a single source, an electric direct connection to Hellisheidi geothermal power station. Cold and hot water streams used in the facility are integrated within Hellisheidi geothermal plant streams. Transportation inside facility gates are negligible and do not count toward the LCA.
In terms of construction materials, a facility producing 150,000 kg of edible wet Spirulina per year, including all production phases up-to facility gates, is made from stainless steel, galvanized steel, carbon steel, aluminum, fiberglass, silicone, polypropylene, viton, polyethylene, PVC-U, and includes LED systems. The energy requirements and CO2-eq emissions for construction are calculated based on the facility bill of materials, in the following. Production process details are presented in Figure 1.
Resource streams in Hellisheidi geothermal park are presented in Figure 2.
Figure 2. Hellisheidi geothermal park and resource streams including resources used as inputs in the Spirulina production facility. Based on in situ analysis and on Orka náttúrunnar (ON Power) Geothermal Park Reykjavík (Orka náttúrunnar, 2022).
The functional unit (FU), toward which all environmental impacts are allocated, is 1 kg of edible Spirulina biomass (i.e., wet biomass with 61% water content) cultivated in the geothermal park. In this analysis, this Spirulina is referred to as "GeoSpirulina" in tables and figures. Laboratory analysis (conducted by Eurofins Scientific SE) shows the main nutritional content of GeoSpirulina wet biomass in Table 1, highlighting Water, Protein, Essential Amino Acids (EAAs), and Iron, Fe, per 100g, alongside the nutritional content of ground meat from beef cattle (USDA, 2022).
Table 1. Comparison of nutritional content of GeoSpirulina wet biomass produced in Hellisheidi facility with ground meat from beef cattle.
|
Spirulina wet biomass
(g / 100g)
|
Meat from beef cattle, ground
(g / 100g)
|
Solids (including EAAs, protein and Iron)
|
39.0
|
44.0
|
Water
|
61.0
|
56.0
|
EAAs (Threonine, Valine, Isoleucine, Leucine, Phenylalanine, Lysine, Histidine, Methionine, Tryptophan)
|
10.2
|
10.2
|
Protein
|
27.2
|
25.8
|
Iron, Fe
|
0.03
|
0.02
|
In this research, system boundaries cover the processes from input production up-to factory gates. The cultivation process described here produces a wet paste of edible Spirulina biomass. Outside factory gates, algal paste may be consumed as whole food (raw) or serve as an ingredient in the preparation of other foods.
The land use category includes the land requirements for Spirulina cultivation in this particular site, including cultivation, downstream processing and miscellaneous needs (e.g. maintenance, storage). Indirect land use associated with the production of carbon and non-carbon inputs for the production units, namely the land used for geothermal energy production, CO2 stream for biofixation, and hot- and cold- water streams, are not included in this study because these have pre-existed to algal cultivation, remain under-utilized, and otherwise would have been wasted or emitted to the environment. Moreover, there are no competing demands for lands in Hengill area, for agricultural purposes or otherwise, as described in the following.
Decommissioning of the facility is not included in the calculation as construction materials would be possible to salvage, recycle and reuse.
The LCA further accounts for the GHG emissions of producing Nitrogen fertilizer, Phosphorus fertilizer and Iron sulfate, used as nutrients for Spirulina production at ratios of 0.44, 1.26 and 0.16 kg FU -1, respectively (Papadaki et al., 2017), as well as for the production of a cleaning agent (Lye) for CIP of the production system.
Data
Allocations
The production of animal source foods, including beef meat, often cover several co-production processes to provide a variety of goods which may include meat cuts, fat, bones, and hide (i.e., leather from cattle). In LCAs, co-production processes require allocation of environmental impacts between different by-products (Nijdam et al., 2012). Considering that the Hellisheidi Spirulina production facility is a manufacturing system with just one stream of products (edible biomass in the form of wet paste), the environmental impacts in this study need only to account for this output. Therefore, allocations and sensitivity analyses are not included in this research.
Land inputs
An environmental impact assessment conducted by the European Investment Bank for Hellisheidi power plant determined that geothermal power production in this region has negligible effect on land and ecosystems, flora, fauna, and biota of hot springs, water resources, air quality, as well as cultural remains, residential, transport or agricultural development. Lands in Hengill area are marginal and moss-covered with little-to-no vegetation. Animal life is scarce. Moreover, land and climate conditions make the region unsuitable for crop cultivation (EIB, 2008). This assessment applies to all facilities situated in the geothermal park, including Hellisheidi Spirulina integrated production facility, therefore the land use change value is zero.
In terms of direct, though non-arable land resources, 0.0378 m2 are required to produce 1 kg edible biomass year –1. Table 2. shows land allocation by production phases.
Table 2. Land footprint of Hellisheidi Spirulina PBR facility per 1 kg biomass year –1.
Production phase
|
Production machinery
|
Land Footprint
m2/(metric) kg year -1
|
Cultivation
|
Production units
|
.0292
|
Downstream processing
|
Harvest and washing; water recycling; Pasteurization; Packaging
|
.0033
|
Storage
|
Biomass storage inside facility gates
|
.0026
|
Other
|
Miscellaneous
|
.0026
|
Total
|
|
.0378
|
Water inputs
In accounting for freshwater uses, this study relies on a common framework (Milà i Canals et al., 2009) distinguishing between blue water (i.e., groundwater and surface), green water (i.e., rainwater), and grey water (i.e., water assimilating pollutants), used directly and indirectly in production processes.
Considering the production process analyzed in this research, surface and rainwater were excluded from the calculation, as well as grey water, since freshwater are mostly recycled with only a negligible volume (0.015 m3 kg-1), defined here as "waste", is generated consisting of biomass and nutrient residuals, with no toxins and no runoff.
Similar to land uses in the geothermal park, streams of hot- and cold- freshwater from groundwater sources are already used for industrial purposes. The Spirulina PBR facility benefits from these resource streams, which otherwise would have remained under-utilized.
In addition, influences of algal cultivation and production on total annual water production in the Hellisheidi site, in terms of thermal management (liquid-liquid heat exchange, using water in the facility for cooling and heating) is insignificant taking into account the ~127.5 million m3 annual hot- and cold- water production of the power station and geothermal park (Reykjavík Energy, 2020). Therefore, water circulated for cooling (for heat removal) and heating (during pasteurization) does not count toward the LCA.
As showed in Figure 1, freshwater is used for cultivation, primarily as culture medium, and for washing of biomass. The system suffers no water losses. Table 3. provide freshwater use figures in the production of biomass.
Table 3. Water footprint of Hellisheidi integrated Spirulina production facility per 1 kg edible biomass
Production phase
|
Water type
|
Water Footprint
m3/(liter) kg -1
|
Cultivation
|
Blue
|
5.320
|
Washing (cleaning)
|
Blue
|
2.280
|
Other (miscellaneous)
|
Blue
|
0.760
|
Total
|
|
8.360
|
Energy inputs and GHG emissions
Energy inputs for facility operations and GHG emissions for facility operations, construction materials of the facility, and nutrient production are calculated for one FU (1 kg edible Spirulina biomass). Primary energy includes both renewable (i.e., geothermal) and nonrenewable energy sources. GHG emissions were assessed as global warming potential by using the conventional 100 years' time scale (GWP100).
Data for production operations were retrieved from publicly available analyses (2020) issued by Reykjavík Energy (Orkuveita Reykjavíkur) (Reykjavík Energy, 2020), the utility operating Hellisheidi geothermal power station and park. Data for amounts and GHG intensities of construction materials were based on the facility's bill of material and database retrieved from Mannvit Engineering, Iceland. Previously calculated GHG emissions of production of N fertilizer (Marques et al, 2009; Bäuerle, 2017), P fertilizer (Randall et al., 2016; Chen et al., 2018), and Iron sulfate (Randall et al., 2016) were used in this study. N and P fertilizers used in the Hellisheidi PBR facility are sourced from open-pit mines, and are not based on energy intensive ammonia-based fertilizers.
The carbon fixed by Spirulina cells during cultivation contributes toward the LCA and is regarded as negative (-0.702 kg CO2-eq kg -1 biomass), as otherwise it would have been released into the atmosphere. For this reason, it offsets positive CO2 emissions relating to the production process.
Energy inputs and GHG emissions are presented in Table 4.
Table 4. Energy inputs and GHG emissions of Hellisheidi integrated Spirulina production facility required to produce 1 kg edible biomass.
Construction materials
|
|
CO2-eq kg -1
|
Fiberglass
|
0.051
|
Stainless steel
|
0.021
|
Galvanized steel
|
0.013
|
Carbon steel
|
0.008
|
Polypropylene
|
0.001
|
Viton
|
0.002
|
Polyethiline
|
0.001
|
Aluminum
|
0.037
|
LED systems
|
0.055
|
PVC-U
|
0.012
|
Silicone
|
0.001
|
Total
|
0.201
|
|
Energy consumption
|
Production phase
|
kWh / kg
|
CO2-eq kg -1
|
Lights (LED)
|
Cultivation
|
122
|
0.395
|
Pumps
|
Cultivation and downstream processing
|
6
|
0.027
|
Blowers (Air, CO2)
|
Cultivation
|
8
|
0.026
|
Harvesters
|
Harvest and washing
|
3
|
0.010
|
Water treatment
(Microfiltration and UV radiation)
|
Water recycling
|
0.5
|
0.002
|
Other
|
Pasteurization and packaging
|
0.2
|
0.001
|
Total Energy consumption
|
0.460
|
|
Nutrient consumption
|
|
CO2-eq kg -1
|
Nitrogen fertilizer
|
0.009
|
Phosphorus fertilizer
|
0.020
|
Iron sulfate
|
0.000
|
Total
|
0.028
|
Cleaning agent consumption
|
Lye
|
0.004
|
|
Carbon dioxide biofixation
|
kg / kg DW
|
CO2-eq kg -1
|
CO2 uptake
|
-1.8
|
-0.702
|
|
Total CO2-eq kg -1 balance
|
-0.008
|