66 EFFLUENT
EFFLUENT
Dealing with effluent solids By Logan Bowler
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olids management for some farms is a bit hit-and-miss. I see farms that have extremely poor systems resulting in troublesome FDE irrigation, and I also see some farms that have solids management overkill. So, what’s the right system for your farm? That comes down to what volume of solids are generated on your farm – does the farm have a feedpad or not, and how is the liquid FDE system set up on-farm? If the farms FDE system gravity feeds all FDE from the shed to the pond and then liquid FDE is pumped from the pond, there will be considerably more solids put into the pond than a farm that has a sump before the pond and irrigates fresh FDE to pasture on most days the soil conditions allow. On these days the solids are all suspended in the liquid and are put back on the paddocks. If half the days per season were irrigation days (soil conditions are good for FDE irrigation) then the farm storage is only capturing half the annual solids generated. If the farm is on low-risk soils, then as many as 80% of the days could be irrigation days. If you paid for a solids separator or a stirrer to manage solids in the pond, then it doesn’t have a lot of work to do. On small farms the capital cost of FDE systems can be extremely large when compared to large farms, and the costs are compared on a per cow basis. We need to be thinking smarter than just throwing more money at the system. On our 250-cow farm at home, we have a feedpad that is predominantly used over winter. All solids are scrapped into a weeping bunker, where most of the solids are held back, and a large portion of the liquid migrates through the slats to be pumped into storage. The dairy shed effluent gravity feeds to a sump and then from there is either pumped up into the pond or irrigated fresh. When we want to remove effluent from the pond a valve is opened and effluent gravity feeds from a pipe 200mm above the floor of the pond into the sump then pumped to the irrigator. We have no solids separation for the
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If the farm generates lots of solids then often the most cost effective way is to separate solids before they are added to the storage pond.
dairy shed FDE. We are on high-risk soils so store much more effluent than a similar farm on low-risk soils. We have no stirrer on our pond and our pond is now five years old. We have not seen a build-up of solids in the pond to the point where it is impacting storage volumes and we have no crusting. When solids build up to a point that they are impacting on storage volumes, we will get a contractor in to stir the pond and pump it out. In my mind, this system costs significantly less, has less repairs and maintenance, has lower running costs and is simple. Unstirred ponds should have slightly lower greenhouse gas losses and any phosphorus held in the sludge will not diminish over time, so while there might be a delay in getting the phosphorus onto the paddocks, there are no losses from storage. Basically all the potassium stays in solution in the liquid, so there is no delay or losses there and for nitrogen (N), a significant proportion has stayed in the liquid so that portion of N is still going back onto pasture regularly with irrigated FDE. Regardless of whether the pond is stirred or not, in my opinion a stirrer in the sump is a must. It helps to prevent troublesome solids building up in the
sump, which can then create irrigator blockages. Small (less than 1kw) submersible stirrers do a fantastic job in an average 20m3 sump and are cheap to run. If your farm generates lots of solids, then often the most cost effective way is to separate solids before they are added to the storage pond. If you’re not generating lots of solids, then think seriously about whether you need the additional cost of your own stirrer. It could well be that periodic stirring from a hired PTO stirrer might manage solids in the pond, or it could be done much less frequently by a contractor. Just because a salesperson wants to sell you a solids separator or a stirrer does not necessarily mean you need one on your farm. Make an informed decision and use your hard-earned capital where it’s needed most. n
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Logan Bowler is the owner of Agblution Solutions Ltd offering common sense, independent advice on effluent systems. Not being affiliated to any company or any product allows him to offer completely independent advice. He and his wife own and operate a dairy farm at Marton so understand and experience effluent management on a daily basis at home.
DAIRY FARMER
November 2021
26/10/21 1:02 PM
