Biological Wastes最新文献

Stimulatory, inhibitory and antagonistic roles of heavy metals in anaerobic digestion are reviewed. Partitioning and speciation, variety of biotic and abiotic detoxifying mechanisms as well as acclimation are shown to hinder an accurate prediction of response based on a given total metal concentration.

The purpose of this study was to evaluate the inhibitory effect of representative wood resin compounds on the activity of methanogenic bacteria. Resin is by definition the mixture of wood components that are extractable with apolar solvents. Major resin constituents are long-chain fatty acids, terpenes, resin acids, lignans and apolar phenols. The methanogenic inhibition was determined at a temperature of 30°C in standardized toxicity assays utilizing anaerobic granular sludge. An apolar phenol, 4-hydroxystilbene, was the most toxic of the compounds studied, with a 50% inhibiting concentration of 20 mg/litre. Resin acids and volatile terpenes were also highly toxic to methanogenic activity. Concentrations causing 50% inhibition ranged from 43 to 330 mg/litre. In contrast, triterpenes were non-toxic at relatively high concentrations, 1000–1300 mg/litre. These results suggest that wood resin constituents play an important role in the anaerobic inhibition exerted by several forest industry wastewaters.

Effects of the acidity and of metal ions on metabolic activity of activated sludge from waste cheese whey biological treatment have been determined. The 10% and 50% inhibitory concentrations (IC₁₀ and IC₅₀) were evaluated for each ion. In a decreasing order of toxicity two groups were found: Hg²⁺ > Cd²⁺ > CrO₄²⁻ > Cr³⁺ > Cu²⁺ and Pb⁴⁺ > Zn²⁺. The discrepancy in results of other toxicity stufies reveals the impossibility of defining on an absolute scale an order of toxicity for these ions.

A very strong synergistic effect was noted in the mixed Cu and Zn studies, thus pointing out the difficulty of setting a water-quality standard based on single toxic chemicals.

In four full-scale bunker silos were ensiled 16·5 tons of different mixtures of swine waste, wheat straw and cane molasses. One mixture had 22% swine waste, and the other one 44% (DMB). Swine waste was collected from an open concrete growing-finishing swine feedlot. During the first six weeks samples were taken from the silos and analyzed for pH, lactic acid, total coliforms, clostridia and aerobic and lactic acid bacteria. After three months, silos were opened and evaluated for physico-chemical, microbiological and nutritional characteristics. Two performance trials on sheep were conducted, one to determine the nutritive value of the silages with 22 and 44% of swine waste and the other one to evaluate the inclusion of the silage with 44% swine waste at 20, 40, 60 and 80% (DMB) in sheep diets. Dry matter, crude protein, acid detergent fiber and neutral detergent fiber digestibilities were determined for silages with 22 and 44% swine waste in eight sheep. Evaluation of storage stability in samples from different levels in bunker silos indicated low stability in surface, bottom and side wall samples and fairly good stability in samples from 50 cm depth. Those samples had a pleasant aroma and appearance similar to that of a good quality haylage. Typical manure aroma was not present in waste silages. Twenty-two percent swine waste silage reached an average pH 4·4 while 44% swine waste silage reached an average pH4·6. After 7 days of fermentation, total coliforms were completely destroyed. Clostridia and aerobic bacteria tended to be decreased by ensiling. Average daily gain and digestibility of crude protein were higher for sheep fed 44% swine waste silage than sheep fed 22% swine waste silage, but lower than sheep fed basal diet (P < 0·01). Feed efficiency was different for the three diets (P < 0·01). Dry matter intake was similar for sheep fed 44 and 22% swine waste silage (P > 0·01) but lower than sheep fed basal diet (P < 0·01). Average daily gain and dry matter intake decreased with increasing levels of 44% swine waste silage (P < 0·01). Feed efficiency was not different between the four treatments (P < 0·01).

Production of citric acid on wastes from leaf-protein production fortified with molasses and potassium ferrocyanide appears to be a commercial proposition.