1. Water Cost and Availability for
Algae Cultivation- Salinity Issues
ERIK R. VENTERIS AND MARK S. WIGMOSTA
June 10, 2013 1
Spatial Modeling Research Engineer
2. June 10, 2013 2
Key issues- water availability, quality, and associated costs
Relevant PNNL Biomass Assessment Tool (BAT) capabilities (open ponds)-
Algae productivity from climate and salinity data (M. Huesemann, PNNL)
Evaporative water demand (met data, pond state simulation)
Water source characterization, availability and costs
salinity <2,000 mg L-1, relatively shallow <1,000 ft, municipal and/ or agricultural use
Non-competitive saline water
salinity generally too high for crops (>2,000 mg L-1), depth <3,280 ft
unlimited supply, salinity ~35,000 mg L-1, consistent ion chemistry
National trends in freshwater availability and groundwater salinity
What is the best operating salinity to balance production value and water costs?
For organism X and salinity of water source, what are supply and saline disposal costs
(CAPEX and OPEX)?
Note that we do not follow NRC model of freshwater + brackish mix
3. Competitive water (Fresh) Availability
Details in Venteris et al., 2013, Environmental Science and Technology
Strong E/W gradients, especially for southern half of the US 3
4. Salinity trends in competitive (fresh) waters
Geostatistical simulation based on nearly 200,000 data points
Patterns related to interaction between geology and climate
Even waters defined as “fresh” have significant salt content
5. Salinity trends in non- competitive
(brackish/ saline) groundwater
Less data (21,000 data points), more clustering, more uncertainty
Higher salinity waters related to sedimentary basins, oil-gas occurrence 5
6. June 10, 2013 6
Tradeoff Modeling- Operating Salinity
What is best compromise between growth rate and water costs?
As pond operating salinity goes up, in general-
Algae growth rate and biofuel production decreases (Chlorella, N. salina)
Total makeup water and associated costs decrease (blowdown)
Fewer supply wells
Less saline concentrate for disposal (by geologic injection or evaporation ponds)
Costs based on pipelines (seawater) or wells and pipelines (ground waters)
GIS models connect each farm site to optimal water source
Calculate (biofuel production value – water costs) for range of salinities
8. 16,024 485 Ha Unit Farms
38,678 485 Ha Unit Farms
Operating Salinity- Chlorella and competitive waters
June 10, 2013 8
Southwestern US Southeastern US
5-7 g kg-1 2-3 g kg-1
9. Operating Salinity- Chlorella and saline waters
June 10, 2013 9
Southwestern US Southeastern US
Use Chlorella or more salt-resistant species?
10. June 10, 2013 10
Conclusions, future directions
Regional trends in salinity impact water availability and costs
Understanding interactions between organism growth and water source
geochemistry is critical.
Elevated water source salinity and evaporation rates in SW require that ponds
be operated at a higher salinities than in the SE.
Many water issues remain to be addressed, including-
Regulatory constraints on freshwater supplies and saline concentrate disposal
Temporal trends in competitive uses (development, climate change, etc.)
Brackish and saline groundwater sustainability (volumes, recharge etc.)
Growth performance vs. pH, ion chemistry, etc. (for example, NaCl water vs.
Brief overview of PNNL’s efforts in water resource modeling.Discuss national patterns in groundwater salinityHow do these impact overall water costs? (Supply and concentrate disposal)
Freshwater availability model based on average discharge measured at stream gauges.Supply limited to 5% total dischargeEach dot is 485 ha unit farm, black supplied, gray unsupplied. Priority on water supply costsEW gradients
Low salinity waters in east and south east, some areas of upper Midwest, Pacific NorthwestSalinity of competitive waters much higher in the south west, Rockies, Great Plains.Saline concentrate disposal essentially unavoidable.
Non compete less information, generally deeper, higher salinity, etc.
As an approximation, utilization of non-compete waters requires roughly 2x increase in operating salinity.