Atmospheric conditions and environmental impact of swine rearing facilities re improved by adding alum (aluminum sulfate) in a swine manure processing system. In an embodiment, alum is added to flush water used to flush away manure which has temporarily collected on at least a portion of a floor of the facility, such as in a flushing trough. The flushed manure and water are drained and delivered to a holding pond. Preferably, the flush water is then recycled from the holding pond for subsequent flushing. In another method, alum is added to a manure slurry in a manure collection pit disposed under a slatted floor on which the swine reside. In either method, alum is added in an amount sufficient to substantially inhibit ammonia volatilization and to decrease soluble phosphorus present to provide a healthy and environmentally safe swine rearing facility and an improved agricultural fertilizer.