My parents own a dairy operation is SW Quebec.  They milk 85 cows, total herd is ~ 150 heads.  They own 300 acres of land, most of which is used to feed the cows; this includes alfalfa, timothy, silage and grain corn, and seed oats (only crop that's sold).  Acreage is becoming a problem for manure.  Because of all the environmental rules (application dates, maximum rates, etc) it is becoming increasingly difficult to apply all the manure produced on the farm.  Crop rotation further complicates the situation: can't apply manure on alfalfa (won't stand the compaction on super heavy clay soils).  So we're out looking for a solution.  Buying land would be the first option, but land is expensive ($6000+ per acre) and there's nothing for sale in the area.  And buying more land also means buying more work.  Another option I thought about would be to use a manure separator to remove the solids, and put a cover on the Slurrystore to eliminate the additional water from rain (area gets ~35" of rain a year).  
Has anyone ever put a cover on a Slurrystore manure storage structure?  It's 81' diameter and 19' tall.  Not interested in inflatable covers or roofs (too windy for inflatable cover, and roof means a complex structure).  I was thinking of a floating cover that goes up and down with manure.  I have seen some which accumulate rain water on top, and a small put takes care of pumping it out.  It sounds like a good idea, but I just don't know if it can be done on a Slurrystore and how much it costs.

As for manure separators, what do you recommend?  Screw type?  I have seen a GEA Houle separator at work... it's a whole different concept: a rotary sieved cage, followed by rollers that further extract liquid from manure.  I like that concept.  We use around 2500 small 50 lbs straw bales a year, we would extract most of that, plus the solid fraction of manure.  Just not sure of what kind of price to expect for a separator.  It would be fairly easy to sell the solid part or transport it to far away fields.  

Combination of separator and roof on storage would reduce the quantity of manure we have to deal with by as much as 20-25%.  Of course the liquid part would be more concentrated, but I think we can deal with that.  Most phosphorus would be exported in the solid part.

What do you think, does this plan make sense vs. buying more land.  Financially I am pretty sure it is advantageous to go with the manure separation plan, but I still have to crunch numbers to confirm that.  Any opinion on the feasablity of such a project, or suggestions of alternative solutions to this manure problem?

TIA

Nick