Decline of Phosphorus, Copper, and Zinc in Anaerobic Lagoon Columns Receiving Pretreated Influent.

Confined swine production generates large volumes of wastewater typically stored and treated in anaerobic lagoons. These lagoons usually require a sludge management plan for their maintenance consisting of regular sludge removal by mechanical agitation and pumping followed by land application at agronomic rates to avoid nutrient and heavy metal contamination of ground or surface water. However, limited land area for sludge disposal may increase the risk of soil and water contamination by excess soil phosphorus and heavy metals. Accordingly, this risk could be reduced by pretreatment of liquid manure prior lagoon input. Our objective was to evaluate, in a 15-month meso-scale column study, the effect of liquid manure pretreatment on concentration and mass accumulation of phosphorus (P), copper (Cu), and zinc (Zn) in both lagoon liquid and sludge using: (i) enhanced solid-liquid separation with polymer (SS); and (2) solid-liquid separation plus biological nitrification-denitrification (SS + NDN) . A conventional anaerobic lagoon was included as a control. Liquid and sludge obtained from a 10-yr conventional anaerobic lagoon were used to replicate the anaerobic lagoon in the experimental lagoon columns. Concentrations of total suspended solid (TSS), total P (TP), soluble P (SP), Cu, and Zn were monitored during the course of the study, and the volumes of liquid and sludge were used to estimate TP, Cu, and Zn mass accumulation in the columns. The removal of solids by both pretreatments was effective to reduce Cu and Zn concentrations in the lagoon liquid; their concentrations were positively correlated (r = 0.79 to 0.90, n=16) with TSS concentrations. Even though both pretreatments significantly reduced P with solids removal, TP and SP were negatively correlated with the TSS in the liquid of lagoon columns receiving both pretreatments (r = - 0.51 to -0.87, n=16). These results suggest the possible dissolution of P from the sludge into the overlying lagoon liquid. The net mass accumulation (net mass = initial mass – final mass) of TP, Cu, and Zn in the lagoon columns declined with both liquid pretreatments with respect to the control: TP mass declined by 66% with SS and by 84% SS + NDN; Cu declined by 87% with SS and 100% with SS+NDN; and Zn declined by 72% with SS and 100% with SS+NDN. The reduction of solids input and decline in mass accumulation of TP, Cu, and Zn sludge can help to minimize sludge removal for lagoon maintenance and land area for disposal. As an additional benefit, solids removal by the pretreatments can offer the opportunity for recovery of nutrients and energy from manure.