Pig slurry was treated in an upflow anaerobic sludge blanket (UASB) reactor. To maintain a stable operation, the organic loading rate (OLR) applied to the system was increased stepwise by decreasing the dilution ratio of the pig slurry. Finally, during the last operational stage, no dilution was applied to the influent. The reactor maintained a soluble chemical oxygen demand (CODs) removal efficiency of 82% when OLRs lower than 1.73 g CODs l(-1) d(-1) were applied, although its efficiency fell to 55% when operated at 2.48 g CODs l(-1) d(-1). System performance was not affected by the presence of free ammonia (concentrations up to 375 mg NH3 l(-1)). The distribution of the different molecular weight fractions changed significantly during anaerobic digestion. Proteins contained in the fractions higher than 10,000 Daltons are less degraded than those belonging to the lower fractions. An important percentage of both COD and BOD5 in the effluent were observed in the lowest fraction, probably caused by the presence of volatile fatty acids (VFA).

Differences in biodegradability can affect the treatment of slurry before its use in spraying. The objective of this study was to evaluate the effect of the generation and physical-chemical characterization of swine and dairy cattle slurries on different biological treatment technologies. This research involved monthly sampling (number/composition) for 1 year of 24 swine farms (16%), cattle farms (38%), and mixed swine and cattle farms (46%). The results obtained showed differences in feeding (3 l water kg(-1) food for cattle and 5 l water kg(-1) food for swine) and assimilation (0.6 kg food kg (-1) milk produced and 3 kg kg(-1) weight gain), which may influence the generation of slurry (57 l animal(-1)d(-1) in cattle and 31 l animal(-1) d(-1) in swine) and its composition. In addition, the composition of swine slurry [23 g chemical oxygen demand (COD) l(-1), 3 g total nitrogen (TN) l(-1)] is significantly different (P < 0.01) to cattle slurry (4 g COD l(-1), 0.3 g TN l(-1)). Finally, the composition and the S index applied to swine slurry [COD N(-1) = 8, biological oxygen demand (BOD)5 COD(-1) = 0.3, S index > 0] and cattle slurry (COD N(-1) = 16, BOD5 COD(-1) = 0.6, S index < 0) show a difference on the biodegradability of both slurries. Suitability of anaerobic and aerobic treatment was assessed based on the findings.

No abstract