Swine manure cleanup criteria calculation for odor causing volatile organic compounds based on manure-to-ventilation air exposure pathway.

A mathematical model was derived to calculate swine manure cleanup criteria for odor causing volatile organic compounds (VOCs) so that acceptable total dose would not exceeded through the inhalation of ventilation air in swine housing for workers and pigs. A hypothetical scenario was used which assumed that subsurface contaminant in swine manure diffuses through a layer of manure-air interface then is swept into the ventilated airspace via advection, where long-term inhalation of contaminant was assumed to occur. The philosophy of the transport model is to incorporate the age distribution of contaminated air and a first-order decay of contaminant sources into the diffusion model for simulation of air concentrations of VOCs and total exposure dose. A closed-form solution is presented to allow a series of numerical experiments for investigating the effects of adsorption characteristics between manure gas and manure, the mean age of contaminated air, effective diffusivity, and degradation coefficient on total dose. Swine manure cleanup criteria based on non-exceedence of the total hazardous dose corresponding to an acceptable risk from indoor inhalation of four selected VOCs of p-cresol, hexane, toluene, and xylene were calculated in a typical pig unit. The model can be used in the future to compute the relative effectiveness of VOCs filtration systems and/or altered ventilation rates on the VOC exposure problem in animal housing.