Resources and Conservation最新文献

In continuous fermentation, more than 90% conversion of glucose and 86% conversion of xylose were achieved in a continuous stirred tank reactor (CSTR) for a 72-h retention time and a 30-g/L total sugar concentration. The fermentation in the CSTR was shown to be about four times faster than in the batch reactor. More than 92% conversion of glucose and 75% conversion of xylose were found at a 28-h retention time in an immobilized-cell reactor (ICR). Also, about 67% of the sugar can be converted into organic acids in this reactor, yielding more than 20 g/L of organic acids. High sugar concentrations were tested in the ICR, yielding a 54% conversion of glucose with a 10% sugar concentration. In fermenting concentrated solutions in the ICR, P. acidi-propionici showed a preference for glucose over xylose. In comparing the CSTR and ICR, the fermentation in the ICR is about 5 to 8 times faster than in the CSTR. Thus, the ICR system is the better system for organic-acid production by fermentation of sugars. Based on laboratory results, a 5-Gg/y plant for the production of organic acids from rice straw is proposed. The capital and operating costs of this plant are estimated.

Silver carp, bighead, grass carp and common carp were stocked at a total density of 3000 fish/ha in the proportion of 7:5:6:6 and cultured in two oxidation ponds at the Shek Wu Hui pilot sewage treatment plant. One pond received secondary effluents from the activated-sludge process and the other a mixture of effluents from both the activated-sludge and high-rate biological filter systems. The silver carp and bighead grew at a faster rate in the oxidation ponds than in a commercial pond as control. The growth of the common carp was satisfactory but that of the grass carp was poor. The stocking density of 3000 fish/ha could be increased further provided that the final effluent quality can be controlled. The mixture of effluents from the activated-sludge and the biological filter systems enhanced fish growth as compared with the activated-sludge system alone. However, the increase in BOD, chlorophyll a, and ammonia levels, together with the decrease in dissolved oxygen in the effluents from the biological filter system in the later stage of the trial caused heavy mortality of fish. Bacteria and heavy metals found in the fish were within safety limits for human consumption. More investigation is necessary to explain the exceptionally high mercury level.

Juvenile tilapia, Sarotherodon mossambica, was cultured in two oxidation ponds at the Shek Wu Hui pilot sewage treatment plant. One pond received the secondary effluents from the activated sludge process and the other a mixture of effluents from both the activated-sludge and high-rate biological filter systems. S. mossambica grew and survived well in the oxidation ponds. The respective yield rates were 1114 kg/ha-y and 1527 kg/ha-y without feeding at stocking densities of 2000 fish/ha and 1000 fish/ha, respectively. The stocking density could be considerably increased if the water quality of the culture medium could be controlled. Only male tilapia should be used for culturing, so as to avoid wild breeding. The mixture of effluents from the biological filter and activated sludge systems of the pilot plant contained higher nutrient contents than the effluent from the activated-sludge system alone. The former was found to be more productive. Bacteria and heavy metals in fish muscle were found to be within the safety limit for human consumption. More detailed investigation is recommended if large-scale production is to be introduced.

In Papua New Guinea large quantities of crop residues (228,494 Mg) and animal wastes (492,638 Mg) are available for conversion into fuel, fertilizer and feed. It is estimated that a total of 5303, 3384 and 7136 Mg of N, P and K are available from crop residues and animal wastes with an approximate fertilizer value (in kina) of K12,329,117 (approximately US$ 13 million). Fertilizer trials with root crops, legumes and cereals responded to application of wastes and the percentage increase in yield over the control treatment ranged from 6 to 247% and the application rate at which maximum yield was obtained was different for different crops. Pyrethrum mare, evaluated for its feed value in sheep, has indicated its potential nutritive value as medium-quality forage for ruminants. The following recommendations are suggested: (1) research on the development of an integrated system to utilize waste for pollution control, livestock production and food production for both large and small holdings; (2) utilization of wastes for developing high-protein sources for human and livestock; utilization of coffee, cocoa and oil palm waste for mushroom production; (3) development and testing of simple, cheap and adaptable equipment for small farms for biogas and direct combustion for drying agricultural products; (4) residual and toxic effects from crop residues should be evaluated, e.g. continuous feeding of animals with coffee pulp and pyrethrum mare and its effect on the physiology in animals; and (5) studies combining composted wastes and inorganic fertilizers should be evaluated for mixed and plantation cropping systems.

A 30-ha farm was developed in the Southern Philippines along the line of integrated farming systems. Livestock-fish-crop modules were set up and trials were conducted on their viability. Utilization of goat and sheep manure by crops and fish was linked with utilization of crop products and byproducts by goats and sheep to establish the cycle of integration. It is computed that the net income per ha of a livestock-fish-crop module is P27,852/y. Similarly, the rice-fish-crop module gave a yearly net income of P21,473.40/y. The integration of livestock with coconut, grains (corn) and pasture production showed that the fertilizer cost was reduced by 50%, using goat and sheep manure while gross production yield was comparable with the yield of a system using 100% inorganic fertilizer. The integrated farming system using the organic wastes of livestock shows that farm production levels can be raised, at the same time maximizing farm resources.

Pilot-scale experiments were conducted under ambient, tropical conditions to investigate the physico-chemical characteristics of fish pond water fed with septic-tank sludge (septage). Four concrete ponds were loaded daily with septage at 75, 150, 300 and 450 kg COD/ha-d, and tilapia (a herbivorous fish) were stocked at 5 fish/m² in each pond. The septage loadings between 75 and 150 kg COD/ha-d resulted in pond water characteristics suitable for tilapia growth, and the maximum extrapolated yield of 7530 kg/ha-y was obtained in the 150 kg COD/ha-d loaded pond. The phenomena of septage sedimentation and solubilization to the pond water are discussed.

A brief overview is given of the present efforts and future prospects in waste management for organic waste utilization, including the utilization of water hyacinth (Eichhornia crassipes (Mart.) Solms). Special emphasis is reported on the technical aspects, continuous availability of raw material, marketability, other economic aspects, and environmental risks and benefits in the utilization of water hyacinth, with or without other organic wastes, as raw materials for cardboard and pulp production.

This paper argues that the importance and nature of organic recycling in rural and urban areas in Asia is little understood. Many proposals for large-scale waste recycling are formulated without consideration of the consequences of diverting resources from the use of poorer sections of the community, and stores of traditional knowledge and experience are overlooked. An important aspect of future social research on organic waste recycling should be a study of current practices as the starting point for understanding the role of recycling in communities and the potential for beneficial development. Non-governmental organizations working at the grassroots can be sources of valuable information on community practices and attitudes.

Growth rates of fry of Oreochromis mossambicus were studied in a dug-out pond in Muthurajawela swamp, which had been fertilized with cowdung and poultry waste. This swamp is characterized by waters with very low pH, low dissolved oxygen and low values of primary productivity. The addition of fertilizer increased the gross primary production from 0.18 g C/m²-day to 1.08 g C/m²-day in about 40 days, with pH and dissolved oxygen values becoming favourable for growth of fry. The average growth rate of 0.04 g/day was comparable to the growth rates attained in favourable habitats in Sri Lanka.