Bioaerosol reductions: paper pads versus wood chips in a multi-stage scrubber of a pig barn

A commercial three-stage scrubber of a pig barn usually used to reduce ammonia, odour and dust was investigated regarding the reduction of indicator bioaerosols (mesophilic bacteria, haemolytic streptococci, methicillin-resistant Staphylococcus aureus, endotoxins as well as molds and yeasts). The bio-scrubber stage (third stage), was filled half with wood chips and half with paper pads as an alternative material in order to compare the reduction rates. Air samples were taken simultaneously with emission impingers from the untreated air, downstream of the acid scrubber (second stage) and downstream of the two bio-scrubber halves (third stage). The total reduction rate of indicator bacteria was at least 93% throughout all stages. However, both materials in the bio-scrubber stage significantly reduced an additional portion of the bioaerosols and therefore contributed to the overall reduction. This applied equally for endotoxins downstream of the wood chips half. In contrast, the cultivable mold and yeast numbers were not significantly reduced and increased downstream of the wood chips. Considering the reduction of potentially pathogenic bacteria, resistant bacteria and endotoxins of approximately log10, it can be concluded that three-stage scrubbers can mitigate the risk of harmful bioaerosol emissions for residents and animals on neighbouring farms. In terms of the reduction of microorganisms, paper pads can be used as an alternative material to wood chips in the bio-scrubber stage.