RECIRCULATION OF FILTERED AIR IN PIG BARNS

Recirculating air filtration systems were tested to reduce dust and ba cteria levels inside the feeder barns of a hog farm in the Fraser Vall ey of British Columbia. Design of the air filtration systems had to be reconciled with the existing structures and ventilation system in the barns. Multiple fabric filters and a high-voltage, plate-type electro static precipitator were selected as dust collection devices for the g rower and finisher barns, respectively. Each barn was partitioned into two halves with one serving as the experimental unit equipped with th e air filtration system aid the other as the control unit. Recirculati on air flow rate was set at 20 air changes per hour which lies between the summer and winter ventilation rates. Monitored parameters include d air quality indices (respirable and inhalable dust levels, bacteria counts, and, ammonia level), environmental and operating parameters (t emperature, relative humidity, filter pressure drop, and air flow rate ), and animal performance (average growth rate, carcass grading, anti necropsies). Visits to the farm were conducted regularly once a week d uring the first 9 months and subsequently once every two weeks during the rest of the 18-month period of the study. The air filtration syste ms effectively reduced dust levels and aerial bacteria counts inside t he pig barns although their efficiency was dependent ripen air recircu lation flow rate, location, size, and number of inlets and outlets, an d humidity. Although the effect on indoor ammonia level was indetermin ate, air filtration resulted in reduced prevalence of enzootic pneumon ia and atrophic rhinitis among the pigs. It also accelerated animal gr owth as evidenced by an increase in average daily mass gain which tran slated to a shorter number of days to market. Air filtration showed no significant effect on the temperature and humidity inside the barn. T he electrostatic precipitator exhibited :higher dust removal efficienc y during winter and spring time and was almost as effective as the fab ric filter during the other seasons of the year. In terms of bacteria reduction, the electrostatic precipitator was consistently more effect ive than the fabric filters.