SE--Structure and Environment Practicalities, Costs and Effectiveness of a Floating Plastic Cover to reduce Ammonia Emissions from a Pig Slurry Lagoon

The objectives of this research were to assess the practicalities and costs of covering a lagoon of pig slurry, with a maximum slurry surface area of 525 m2. The lagoon was covered with 0·5 mm thick reinforced ultraviolet (UV) stabilized black, opaque polyethylene. During the covering operation, several practical difficulties were identified. Since the lagoon was full, it was difficult to estimate the size of the material required to cover the lagoon whilst ensuring sufficient space to allow the lagoon to fill and empty. The covering operation itself required a calm day and was very labour intensive. Covering lagoons larger than the one covered in this study may necessitate them to be empty, which is often not practical in commercial pig units. The total cost of covering the lagoon was £8400 which equated to £16 m-2of slurry surface covered. If larger lagoons are covered, economies of scale come into effect and the material costs per unit area of slurry surface are likely to reduce, although the labour cost may increase. Ammonia emissions were measured from both an uncovered lagoon and covered lagoon. The ammonia emissions were measured using hoods, each covering a surface area of 0·5 m2. Each hood was fitted with an inlet pipe and outlet pipe. Air was forced into the hood using a 12 V fan which gave a superficial air velocity of 0·4 ms-1across the measured surface. The ammonia flux was measured into and out of the hoods by Ferm tubes situated in the inlet and outlet pipes. The ammonia emission rates (corrected for wind speed) from the uncovered lagoon ranged from 0·63 to 3·66 gm-2d-1. The floating plastic cover prevented nearly 100% of these emissions.