Different pretreatments for increasing the anaerobic biodegradability in swine manure.

The effect of three methods (mechanical, chemical, and thermal pretreatment) were tested to improve methane production and anaerobic biodegradability of swine wastes. The first experiment was designed to determine the biodegradability enhancement through the separation of liquid and solid matrix by using a 0.25mm pore size screen (mechanical pretreatment). The second approach was the treatment of swine waste by the addition of a flocculant agent and strong chemicals such as acid (HCl) and alkali (NaOH). The third pretreatment studied was thermal application (170 degrees C provided by vapor). The soluble COD was increased by 57% and 32% during the pretreatment period with alkali and thermal application, respectively. In addition, these two pretreatments gave the highest enhancement on methane production with regard to the untreated sample. Meanwhile, the addition of a flocculant improved the methane production of the liquid fraction but not the solid one. On the other hand, mechanical pretreatment did not show any important enhancement. Biodegradability percentage followed the same trend as methane productivity.

Solids and nutrients removals from the liquid fraction of swine slurry through screening and flocculation treatment and influence of these processes on anaerobic biodegradability.

A correct separation of solids from liquid fraction is crucial for a successful treatment of swine manure. For this reason an in-depth study of flocculant addition on different livestock wastewaters was carried out. Two flushed swine manure matrices, namely the mixture from nursery and feeder-to-finish pigs and the feeder-to-finish slurry alone, were tested for solids and nutrients removals from liquid fractions. The separation techniques applied were sieving and flocculation. 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.