The immediate effect of agitation and mixing a lagoon would be to suspend more of the solids in the liquid, which raises the solids content of the liquid and reduces the sludge volume somewhat during agitation, depending on the degree of agitation. If agitated lagoon contents are pumped out for irrigation, then solids suspended in the agitated liquid will be pumped out. and this could decrease the amount of sludge remaining in the lagoon. Agitation would also increase ammonia loss to some degree by stirring up the sludge and increasing ammonia concentration in the liquid and likely increasing the mass transfer coefficient of ammonia from the liquid surface during agitation. Agitation could also increase odor, at least temporarily. Whether agitation would enhance organic matter breakdown would be difficult to predict. The agitation would bring more solids into the warmer regions of the liquid column and increase the surface area exposure of the solids, so theoretically the bacterial action could be greater. However, good working lagoons normally have purple sulfur bacteria which are photosynthetic or phototrophic (bacteria that derive their energy from sunlight) and depend on light penetration, so stirring up sludge would decrease light penetration and likely reduce the action of purple sulfur bacteria. If the lagoon is agitated but no pumping out of contents occurs while agitated, it is likely that the lagoon liquid and lagoon sludge will return to their previous states (solids and nutrient concentrations) within a few days, but data to verify the effects of periodic agitation are lacking.
Author: Phil Westerman, North Carolina State University
