Currently, the most common technique for treatment and storage of swine manure
in the Southeastern U.S. is by use of anaerobic lagoons. The life expectancy of
these 
lagoons is commonly fifteen to twenty-five years. Renovation techniques at the
end of this period include complete agitation and pumping or replacing the lagoon.
These methods are both costly and inefficient.
Complete agitation and pumping greatly disperses and dilutes the total nutrient content in the sludge. This creates problems for sludge use in off-site land application. Compounding this, very little is known of the nutrient concentration within the undiluted sludge. The research described here determined the physico-chemical characteristics of insitu sludge and any trends present within the sludge profile. The site evaluated was a fifteen-year-old lagoon at a farrow to wean swine operation.
The lagoon was 23.2m by 30.5m with a mean depth of 2m (Figure 1).
Figure 1: Lagoon Grid Layout
The depth of the sludge layer was determined at fifty-seven points using a self-constructed sludge-depth plate (Figure 2).
Figure 2. Active Lagoon Depth (m) Map
Undisturbed sludge samples were taken using a 5cm-diameter PVC tube with rotary gates placed at 1.5m intervals (Figure 4). The sludge sampler had sample ports placed at 0.3m intervals for removal of individual samples from the column. The sludge was characterized based on total, volatile, and fixed solids, particle size distribution, TKN, ammonia, organic nitrogen, total and ortho phosphate (TP and OP), potassium, and COD (Figure 5). The results of the characterization show three distinguishable strata within the sludge layer. These strata were defined as the CZ (concentrated zone), AZ (active zone), and DZ (dilute zone) (Figure 3).
Figure 3. Lagoon Sludge Depth (m) Map
An optional fourth stratum could also be defined as a sludge/supernatant interface. Samples of like depths from different columns showed no significant variance in nutrient characteristics. This is part of ongoing research to develop a technique to remove only the sludge volume without disturbing the supernatant from aged lagoons.
Figure 4. Sludge Core Sampler
Figure 5. Various Results
