Concentrated animals feeding operations (CAFOs) are the objective of many studies since they pose an important environmental risk. The most common practice in farms involves manure flushing and consecutive collection in anaerobic lagoons. The final effluent is usually applied to cropland as fertilizers. However, this practice is becoming a problem because nutrients are spread out constantly in the same area, with the subsequent soil saturation. Some of the negative effects that hog manure causes are gas emissions (which affects animals and humans health), accumulation of heavy metals on soils, groundwater pollution due to leaching as well as contamination of surface water. Therefore an effluent treatment must be implemented before swine waste dischargement. Many techniques used nowadays for treating manure are developed in order to reduce nutrients (biological systems), to generate energy (anaerobic digestion), or to use the manure as solid fertilizer (compostage). In this context, a correct pre-treatment involving the separation of solids from liquid and treating each matrix separately is crucial for the success of the above-mentioned techniques. Mechanical separation and addition of chemicals (coagulants and flocculants) are the common techniques used for the separation of matrices. The inconvenience that mechanical separation exhibits is the impossibility to retain the fine suspended matter that contains the organic nutrients (nitrogen and phosphorus) in swine wastewater (Vanotti and Hunt, 1999). Therefore, many chemicals like ferric chloride and aluminium sulphate (Zhang and Lei, 1998) as inorganic coagulants and polyacrylamides and chitosan as organic polymers have been tested for separation enhancement. Among the organic polymers, polyacrylamides (PAM) have been widely studied during the last years in swine wastes by different authors. The objective of this study was to evaluate the optimal PAM dosage in two different livestock matrices, namely the mixture of hog manure from feeder-to-finish and nursery and from feeder-to finish alone. In order to determine and enhancement on methane productivity, biodegradability assays were carried out using the liquid and solid fraction separately obtained by two different processes; sieving and flocculation followed by sieving. A range of 80–200 ppm of polyacrylamide (PAM) followed by screening was employed in the case of flocculation treatment. The best results were observed when using the highest PAM dose in the matrix correspondent to the mixture of slurries. The removal rates in the liquid fraction were 73% for total solids, 87% for volatile solids, 98% for suspended total and volatile solids, 71% for chemical oxygen demand, 40% for total Kjeldahl nitrogen, and 34% for soluble phosphorus. Once the best PAM dose (120 ppm) was chosen, an anaerobic biodegradability study was performed in order to check the increase of methane production in the separated fractions by using the flocculant and the screen. The assay determined that the solid fractions biodegradability was constant at 79%. Meanwhile for the liquid fractions, an increase of 9% points was achieved with PAM-amendment when compared with 82% reached for the liquid fraction obtained by screening.

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