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Brazil is one of the most important countries in pork production worldwide, ranking third. This activity has an important role in the national economic scenario. However, the fast growth of this activity has caused major environmental impacts, especially in developing countries. The large amount of nitrogen and phosphorus compounds found in pig manure has caused ecological imbalances, with eutrophication of major river basins in the producing regions. Moreover, much of the pig production in developing countries occurs on small farms, and therefore causes diffuse pollution. Therefore, duckweed pond have been successfully used in the swine waste polishing, generating further a biomass with high protein content. The present study evaluated the efficiency of two full scale duckweed ponds for the polishing of a small pig farm effluent, biomass yield and crude protein (CP) content. Duckweed pond series received the effluent from a biodigester-storage pond, with a flow rate of 1 m3/day (chemical oxygen demand rate = 186 kg/ha day) produced by 300 animals. After 1 year a great improvement of effluent quality was observed, with removal of 96% of total Kjeldahl nitrogen (TKN) and 89% of total phosphorus (TP), on average. Nitrogen removal rate is one of the highest ever found (4.4 g TKN/m2 day). Also, the dissolved oxygen rose from 0.0 to 3.0 mg/L. The two ponds produced together over 13 tons of fresh biomass (90.5% moisture), with 35% of CP content, which represents a productivity of 24 tonsCP/ha year. Due to the high rate of nutrient removal, and also the high protein biomass production, duckweed ponds revealed, under the presented conditions, a great potential for the polishing and valorization of swine waste. Nevertheless, this technology should be better exploited to improve the sustainability of small pig farms in order to minimize the impacts of this activity on the environment. [ABSTRACT FROM AUTHOR]

1. Arylamidase activity was isolated from Enterolobium contortisiliquum seeds (2 U/g) using L-Leu-2-naphthylamide as substrate to monitor the purification. 2. The enzyme preparation was purified 733-fold by ammonium sulfate precipitation, and by ion exchange and gel filtration chromatography, in 6.6% yield. 3. SDS-Polyacrylamide gel electrophoresis after fast protein liquid chromatography on a Mono Q column, showed only one protein band with a molecular weight of 35 kDa. 4. The optimum pH for arylamidase activity was 6.5. Taking the hydrolysis rate of Lys-2-naphthylamide as one, the relative rates at which the other substrates were hydrolyzed were: Leu-2-naphthylamide, 30, Met-2-naphthylamide, 18, Arg-2-naphthylamide, 2, Ala-2-naphthylamide, 1.5, and L-Leu-p-nitroanilide, 26. 5. The arylamidase activity was inhibited 50% by 0.1 mM HgCl2, 0.1 mM MnCl2, 0.1 mM ZnCl2, 0.13 mM NiCl2, 0.2 mM o-phenanthroline and 1 microM sodium p-hydroxymercuribenzoate, and activated 35% by 5.0 microM EDTA. Iodoacetate (0.67 mM), dithioerythritol and 2-mercaptoethanol (3.3 mM), and chloride ions (0.2 M) had no effect on the enzyme activity.