24 November 1995

Recycled slurry flushes clean…

By Jonathan Riley

DAILY flushing of slurry channels under pig houses with aerated slurry has reduced ammonia concentrations by as much as 66% in a collaborative study between ADAS and Silsoe Research Centre.

Roger Kay, research consultant at ADAS Terrington, Norfolk, says: "Manual cleaning of slurry channels below slats while the pigs are still in the pens is impractical."

This leaves two options – remove manure to control odours and ammonia concentrations, using scraper blades or flushing with large quantities of liquid.

"Liquid flushing would be easier to install in existing buildings, but using clean water would increase the volume of slurry to be handled and stored," says Mr Kay.

Therefore, the project set out to establish whether using recycled, aerated slurry would reduce odour and ammonia emmissions.

"Australian based research showed that pumps operating in the top 1m of a 9m deep slurry lagoon created an aerated layer that acted as a non-odourous cover for anearobic, denser contents beneath," says Mr Kay.

The MAFF-funded work at Terrington has proved that similar results can be achieved in above-ground tanks, more typical in the UK.

Known as stratified aeration, the process minimises the costs associated with aerating the entire contents of large above-ground slurry tanks and provides a layer of liquid for flushing channels.

In the study at Terrington, three pumps were positioned half way between the tank wall of a 4m (17ft) deep above-ground slurry tank and its centre. The pumps were then used to aerate the slurry to a depth of 1m (3.3ft).

A modified tanker was used to strip any remaining ammonia or odour from the recycled aerated slurry before flushing at 78 litres/sec for three seconds a day.

Substantial changes in the concentrations of ammonia in the building were achieved with regular daily flushings, reducing ammonia concentrations by up to 66% in the house.

Outside conditions, ventilation and the age of the pigs in each building affected ammonia and odour levels. But, compared with a conventional unflushed building over the year, an average reduction of about 20% in ammonia concentrations was recorded.

Also, at higher ventilation rates which raise ammonia emissions from pig housing, flushing reduced ammonia emissions by up to 45%.

As pigs grew the effectiveness of the flushing at removing manure from a relatively unmodified channel was reduced. "Further research is needed with better channel designs to determine how much more ammonia emission can be reduced," says Mr Kay.

But, air quality in the flushed house was noticeably improved and stock carers felt able to spend longer inside.

"Though not quantified in this study, stock could benefit if staff are more comfortable and willing to spend more time in an improved environment looking after the pigs," he says.

&#8226 Up to 66% reduction of ammonia concentrations in houses.

&#8226 Ammonia emission from house reduced by 45%

&#8226 No extra water to be stored.

&#8226 Stock carers more willing to spend more time with pigs.