Agricultural Wastes最新文献

Willow-dust is one of the solid cellulosic textile mill wastes available in large quantities. A batch fermentation method to process this material for the production of biogas and biomanure has been previously standardised. This process involves an initial aerobic fermentation of willow-dust treated with sodium hydroxide (1% w/w) and inoculated with slurry from anaerobically digested willow-dust followed by anaerobic fermentation with a substrate to liquid ratio of 1:6. With a 100 kg capacity biogas plant 17 m³ of biogas could be generated in 30 days. The spent slurry served as a good manure. The present work showed that it was possible to produce biogas as effectively as before with a substrate to liquid ratio of 1:1·5. The process was further improved by replacing most of the sodium hydroxide with lime to obtain an agriculturally suitable biomanure without affecting the biogas yield.

An anaerobic digester, operated semi-continuously in order to retain high concentrations of biomass in the digester, was used to treat wool scouring wastewater. At a space load of 9·9 kg COD m⁻³ day ⁻¹ (hydraulic retention time, 2·8 days) >56% of the COD and >47% of the grease were removed. At these efficiencies, this rate was estimated to be at least 2·5·3· times greater than that which would be achieved in a continuously stirred digester. Preliminary studies of enzymatic pretreatment of the scouring effluent showed that significantly improved treatment rates and/or efficiencies could be achieved—i.e. >70% removal of both the COD and grease at a space load of 12 kg COD m⁻³ day⁻¹. It is unlikely that any substancial levels of flocculation would develop in this system and it is expected that the moderate use of polyelectrolytes would be required to help maintain the VSS concentration in the reactor.

From a number of yeast strains capable of fat biosynthesis on a medium with beet molasses, Candida curvata D was selected as being most efficient. The optimum conditions for fat biosynthesis by C. curvata D were pH, 5·4; temperature, 30°C; sucrose content of the medium, 25 g litre⁻¹.

Cultivation of C. curvata D on a medium with beet molassed and whey gave food fat and biomass fields. The biomass, preserved separately or together with the spent medium, could be used as a fat-protein component of feeds for poultry, pigs or cattle.

Our previous experiments showed that flowering Chinese cabbage (Brassica parachinensis) and Chinese radish (Rhaphanus sativus) var. longipinnatus grown in soil amended with sewage sludge and animal manure accumulated Pb, Cu, Zn and Mn. In this experiment, caterpillars of the common white butterfly (Pieris canidia) were fed with the waste-grown vegetables. Caterpillars fed with sewage sludge-grown vegetables had a lower body weight and a higher level of heavy metals than those fed with animal manure-grown vegetables (average fresh body weights of caterpillars fed with waste-grown leaves of Chinese radish were 75, 122, 186 and 196 mg for activated sludge, digested sludge, chicken manure and pig manure, respectively). Those fed with flowering Chinese cabbage accumulated a higher level of heavy metals than those fed with Chinese radish (Pb, 6·7-fold, Cu, 6·0-fold, Zn, 6·8-fold and Mn, 5·7-fold in treatments with activated sludge). As a whole, the accumulation of heavy metals in the caterpillars, in descending order, was from vegetables manured with activated sludge, digested sludge, chicken manure and pig manure.

Caterpillars, even though ingesting an enormous amount of the leaves, accumulated a lower level of Pb, Cu and Zn than that found in the vegetables. The route of elimination was not verified but it was suggested that the egestion of faeces might play an important role.

Urea and wheat straw moistened to 70% was stacked in the open for 12 or 9 days' natural fermentation. The urea was added at the rate of 4% on a dry straw basis. The fermentation was carried out by turning the stacks at 3- or 6-day intervals, or the stacks were not turned for the entire periods. About 84% to 87% was degraded during the fermentation, resulting in microbial-protein enrichment of the treated straw. A high stack temperature developed (65°C to 73°C) and the ammonia released penetrated the cell wall sufficiently to loosen the ligno-cellulose bonds. The microbes utilized hemicellulose and cellulose, without effecting the lignin content.

The daily dry matter intake (7·96kg) during a 4-month acceptability trial, using 12 day fermented straw with 2·0 kg fresh green fodder and minerals, showed the straw was palatable and was able to maintain the six adult buffaloes without affecting their body weight or health. Further metabolic trials with the different straw preparations showed that digestibilities of DM, OM, CF and cellulose, and N retention, were significantly (P < 0·01) improved in 9 day fermented straw as compared with the other straw preparations.

The results showed that, by 9 days' fermentation of wheat straw, the cellulose digestibility and apparent biological value were improved to the extent that fermented straw supplemented with adequate vitamins and minerals could be used as a sole maintenance ration for ruminants.