I've just bumped into this. Trent claims he wants this to scale to present petroleum consumption scales, and 5000 gallon/acre-year production values. Let's take those as given.
The US consumes roughly 6 billion barrels (252 billion gallons) of petroleum annually.
Using GNU units, and solving for square kilometers:
You have: 6 billion barrels / (5000 gallon/acre)
You want: km^2
That's 78,800 mi^2.
Square roots will give us the length of this on a side: 280 miles, or 450 km.
Assuming you wanted to park this alongside the Pacific and Atlantic coastlines of the US, roughly 1,000 miles (1600 km) each, you're looking at an algae bag field about 80 miles, or 130 km, across. I don't see his separation columns or freshwater supplies scaling out here.
The Gulf of Mexico might be a better siting location, at 1.5 million km^2. Trent's scheme would occupy 13% of it.
You could decide this is too ambitious and scale everything down, but you're then talking about a vastly smaller output. Even 10% of production (roughly: aviation and marine transport fuel demands, on the low side) would require 20,400 km^2 or 7,900 mi^2, call it about 80 miles on a side, or 140 km. Again, you could scale depth to keep the structures close to shore -- but you're still
talking structures extending roughly 13 km or 8 mi out to sea.
The scale of biofuels operation is something I just don't see working out.
More on that:http://redd.it/28k1w5http://redd.it/29qk9o