Biological Wastes最新文献

Eupatorium odoratum L. is a prolific producer of biomass among the weeds introduced into India and it can be used for energy production. Since freshly harvested biomass contains inhibitors of microorganisms involved in methanogenesis, the effects of leaching and partial aerobic decomposition of the weed before anaerobic digestion were studied (1·0 m³ pilot-scale batch fermenters) in relation to biogas production. About 70% more biogas was produced by the pretreated waste, and it also gave a higher count of cellulolytic and methanogenic bacteria than the untreated material.

In the food industry, where effluents contain very high concentrations of dissolved organic matter, in-situ treatment systems have been recommended. These systems require simple and inexpensive control parameters. According to the literature, to evaluate the system performance an inexpensive method is the microscopic observation of different protozoal species, combined with personal judgement of evaluators.

For a four-stage laboratory rotating biological reactor treating diluted corn-processing effluents, ciliated protozoa as indicator organisms of system performance were studied. Temperature, pH and dissolved oxygen were monitored. Dissolved organics, measured as chemical and biochemical oxygen demand (COD and BOD₅), gradually decreased along the reactor. Twelve protozoal species were identified. From them, 10 have been reported in the literature as commonly found inhabitants of aerobic municipal wastewater treatment plants. A correlation between six of the species with BOD₅ concentrations in the wastewaters along the reactor was found.

Nitrogen losses during the storage of liquid livestock manures were measured in short- and long-term model experiments (35–68/191–200 days) with cattle and pig slurries. The true nitrogen losses were strongly correlated with the storage time. They were also often higher than they were previously thought to be, even without aeration. Calculated on the ash content they ranged between 1·4 and 20·5% of the total nitrogen content after 35 days, and between 17·1 and 53·6% after 180 days. The differences did not depend on the species of animal, but on the origin of the slurries. Furthermore, they seemed to depend on the pH-value. Other alternating effects between the N-losses (ammonia volatilization) and any other parameter (e.g. mineralization rate) could not be derived from this investigation.

Maturation during composting was investigated in three composts prepared from lignocellulosic wastes. We used the cress seed germination (Lepidium sativum L.) bioassay and phytotoxicity assays of Helianthus annuus plants to determine a series of physiological parameters. Germination of Lepidium sativum and leaf weight of Helianthus annuus revealed increasing maturity of all three composts during the initial period of composting, i.e. the thermophilic period. In general, the data then showed a period of transition, followed by a substage of mesophilic activity (30–60 days) when compost reached optimum ripeness, and a second mesophilic substage during the final period of composting (60–90 days). The results of cress germination tests during these periods suggest that the rate of maturation tended to stabilize, whereas some of the Helianthus annuus physiological parameters indicated a slight decrease in the quality of the matured compost. Stem length of sunflower plants was found to be too insensitive as an indicator to detect changes in the degree of maturation during composting.

The potentiality of some plant wastes plus poultry litter as feedstocks for biogas production was determined. Some wastes could substitute for cowdung when dung is in short supply.

The aerial parts of Vicia faba collected at seed maturation stage have no economic utility and are, therefore, discarded. However, these leaves and stems contain a considerable amount of flavonol glycosides. Two extraction procedures have been assayed: one using methanol-water as extraction solvent and another using alkaline water. The extraction yield (about 1 g of flavonoid/kg fresh plant material) was slightly higher when extracting with alkaline water, but this extraction hydrolyzes the acetyl derivatives, leaving almost exclusively the deacetylated compounds.

The mechanism of degradation of paper-mill sludge containing lignin and cellulose was studied, for establishing a technology for the bioconversion of paper-mill solid wastes and waste lignins to useful materials and for protecting the environment from lignin-related pollutants. The degradation of cellulose by Pleurotus sajor-caju was rapid at the initial stages of growth. The activities of endoglucanase, exoglucanase and β-glucosidase were maximum at 8, 12 and 26 days of growth, respectively. The activities of lignin-degrading enzymes were maximum at the later stages of the growth. Such a delignification process is considered to have potential applications in the cinversion of paper-mill sludge into food, animal feed and fibre products.

Aerobic digestion of primary and secondary sludges was studied in airlift bioreactors at mesophilic and thermophilic temperatures. The experimental studies were conducted with a laboratory U-shape airlift reactor (operating volume 23 liters) and in a pilot U-shape airlift reactor of 1150 liters operating volume. In the laboratory reactor, with cold (6°C) and concentrated (3–4% solids) feed of primary and secondary municipal sludge, a 30% volatile suspended solids (VSS) reduction was achieved with a hydraulic retention time (HRT) of 2·5 days. A VSS loading rate of 8·2 kg VSS/m³/day was achieved. This loading is comparable to that obtained in a pure-oxygen sparged, mixed reactor.

In the pilot-plant reactor at mesophilic temperature (31–33°C), a VSS loading rate of 7·9 kg VSS/m³/day and a VSS reduction of 40% were achieved with a HRT of 4 days.

Methane production from waste of dairy cattle fed diets containing 72% roughage (dry matter basis) was investigated in anaerobic reactors at 60°C with retention times (RT) set at 3, 6 and 9 days. Influent concentrations of volatile solids (VS) were increased in steps of 2% from 4 to 14% VS or until the reactor failed due to excess substrate. Gas production was measured and samples of effluent taken for six consecutive days after allowing three volume turnovers for each increment of VS. The maximum concentration of VS in the substrate for highest volumetric fermentation efficiency was 8–10, 10–12 and 12 for RT of 3, 6 and 9 days, respectively. Destruction of VS for these and lower substrate concentrations was 19–24, 26–27 and 30–33% for 3-, 6- and 9-day RT reactors, respectively. The corresponding methane production rates were 0·09-0·12, 0·11-0·14 and 0·11-0·16 liters/day/g of VS in substrate. The gas contained 51–56% methane with the rest mainly carbon dioxide. Increasing the percentage of feed VS beyond the values indicated resulted in greatly decreased VS destruction and methane production.

The dairy cattle waste contained the following constituents as percent of dry matter: Volatile solids (VS) 85, Na 0·37, K 3·8, P 1·0, Si 2, non-ammonia N expressed as crude protein (CP) 18, NH₃N 0·3, cell wall constituents 46, acid detergent fiber 32, hemicellulose 13, cellulose 21, lignin 10, acetate 3·1, lactate 6·6 and ether extract 4. Detailed analyses for organic acids indicated that the efficiency of methanogenesis was, in general, good until increasing organic loading rates caused total organic acid concentration to reach 120–150 mm. As loading rates increased, propionate was the first acid to increase but did not exceed levels higher than 27 mm. Acetate was the second acid to increase and reached levels as high as 150 mm at high reactor loading rates. Butyrate was low or absent initially but was produced at high loading rates, reaching levels of 30–40 mm. Inhibition of methane did not appear to be associated with a change in any specific acid. Isobutyrate and isovalerate plus 2-methylbutyrate, indicative of protein catabolism, accumulated in amounts as high as 5 and 7 mm, respectively, when 10–14% of VS were fed. Little n-valerate, n-caproate, formate or succinate accumulated.