Effects of cycle-frequency and temperature on the performance of anaerobic sequencing batch reactors (ASBRs) treating swine waste.

Anaerobic digestion of animal waste is a technically viable process for the abatement of adverse environmental impacts caused by animal wastes; however, widespread acceptance has been plagued by poor economics. This situation is dismal if the technology is adapted for treating low strength animal slurries because of large digester-volume requirements and a corresponding high energy input. A possible technology to address these constraints is the anaerobic sequencing batch reactor (ASBR). The ASBR technology has demonstrated remarkable potential to improve the economics of treating dilute animal waste effluents. This paper presents preliminary data on the effects of temperature and frequency-cycle on the operation of an ASBR at a fixed hydraulic retention time (HRT). The results suggest that within the parameter range under consideration, temperature did not affect the biogas yield significantly, however, higher cycle-frequency had a negative effect. The biogas quality (%CH(4)) was not significantly affected by temperature nor by the cycle-frequency. The operating principle of the ASBR follows four phases: feed, react, settle, and decant in a cyclic mode. To improve the biogas production in an ASBR, one long react-phase was preferable compared to three shorter react-phases. Treatment of dilute manure slurries in an ASBR at 20 degrees C was more effective than at 35 degrees C; similarly more bio-stable effluents were obtained at low cycle-frequency. The treatment of dilute swine slurries in an ASBR at the lower temperature (20 degrees C) and lower cycle-frequency is, therefore, recommended for the bio-stabilization of dilute swine wastewaters. The results also indicate that significantly higher VFA degradation occurred at 20 degrees C than at 35 degrees C, suggesting that the treatment of dilute swine slurries in ASBRs for odor control might be more favorable at the lower than at the higher temperatures examined in this study. Volatile fatty acid reduction at the two reactor temperatures and cycle-frequencies, from a high of 639+/-75 mg/L to a low of 92+/-23 mg/L, greatly reduced the odor and the odor-generation potential in post-treatment storage. The nutrients (both N and P) in the waste influent were conserved in the effluents.

Biodegradation of Red B dye by Bacillus sp. OY1-2.

Batch tests were employed to investigate the effects of aerobic and anoxic conditions on the biodegradation of Red B dye by Bacillus OY1-2. Results from batch experiments demonstrated anoxic conditions were beneficial for rapid biodegradation of Red B dye in comparison to aerobic conditions. Biodegradation is a major mechanism in the decolorization of Red B dye in comparison with biosorption, which accounted for only 8% of the total decolorization efficiency. Reactors packed with granular activated carbon (GAC) and inoculated with Bacillus OY1-2 were investigated to treat a synthetic wastewater under anoxic conditions. In the absence of cosubstrates, Red B dye was degraded; however, a significant improvement in degradation resulted with the addition of cosubstrates.

Impact of long chain fatty acids on glucose fermentation under mesophilic conditions.

The effects of three long chain fatty acids (LCFAs) on glucose fermentation at 37 degrees C were examined during this study. Linoleic acid (LA) was more inhibitory than oleic acid (OA) and stearic acid (SA). During glucose fermentation, the carbon flow was diverted towards the production of more reduced volatile fatty acids (VFAs) in cultures fed with unsaturated LCFAs. In cultures inoculated with LA and OA, butyrate was produced with elevated levels observed in cultures inoculated with LA. Propionate degradation was unaffected by the presence of SA; however, elevated levels and longer removal times were observed in cultures receiving LA and OA. Acetate accumulation indicated the acetoclastic methanogenic population was affected only by OA and LA.

Kinetics of glucose fermentation by a mixed culture in the presence of linoleic, oleic, and stearic acid.

The effects of long chain fatty acids (LCFAs) on glucose degradation were examined at 21 degrees C. A competitive inhibition model was used to determine the kinetics of glucose degradation. Half velocity constants (Ks) were a function of LCFA concentration only at 100, 300 and 500 mg l(-1). The inhibitor constants (KI) for individual and mixed LCFAs were statistically the same. Glucose degradation rates for cultures receiving saturated (stearic acid (SA)) and monounsaturated (oleic acid (OA)) LCFAs were statistically the same but statistically different when compared to cultures fed with a polyunsaturated LCFA (linoleic acid (LA)). Individual and mixed LCFAs inhibited glucose degradation at threshold levels of 300 and 500 mg l(-1), respectively.

Anaerobic degradation and methanogenic inhibitory effects of oleic and stearic acids.

Oleic acid, an 18 carbon acid with one double bond (C18:1) was degraded anaerobically to palmitic (C16:0) and myristic (C14:0) acid by-products at 21 C by a culture unacclimated to long-chain fatty acids. These by-products were degraded to acetate and ultimately to methane. In comparison, no long-chain fatty acid by-products were observed in unacclimated anaerobic cultures receiving stearic (C18:0) acid although slow removal of stearic acid occurred. Oleic acid concentrations above 30mg l(-1) inhibited acetate degradation but stearic acid up to 100 mg l(-1) did not inhibit aceticlastic methanogenesis. Hydrogenotrophic methanogenesis was slightly inhibited by oleic and stearic acids. A thermodynamic basis for comparing anaerobic C18 acid degradation and predicting by-products is presented.