Agricultural Wastes最新文献

Rapid pyrolysis of rice hull was studied in a Curie-Point pyrolyzer with heating rates between 1500 and 2000°C s⁻¹, depending upon the Pyrofoil used. Primary pyrolysis occurred vigorously between 400 and 600°C to yield tar, light organics, H₂O, CO₂ and CO. As temperature went over 600°C a small amount of heavier primary products was further cracked into CO and light hydrocarbons. The amount of char residue decreased with temperature and finally reached an asymptote of 24%; this value was about 10% lower than that obtained in a slow heating thermogravimetric analyzer (TGA). Below 800°C the effect of residence time on rice hull devolatilization was significant whereas, at higher temperatures, the pyrolysis was so rapid that it virtually completed during the heating up period. Pyrolysis of cellulose and lignin yielded liquid tar and solid char, respectively, as the major products; the yield of char and total volatiles from the pyrolysis of rice hull could be estimated from their yields in the pyrolysis of cellulose and lignin.

Organic soil amendments in the form of chopped shoots of some weeds gave significant reductions in the population build-up of the root-knot nematode Meloidogyne incognita and the stunt nematode Tylenchorhynchus brassicae on a strong host, eggplant cv. ‘Pusa Purple Long’. The most effective was soil treated with Solanum xanthocaroum followed by Calotropis procera, Datura metel, Croton bonplandianum and Argemone mexicana. These treatments also inhibited significantly root galling. The plant growth of eggplant was also improved by the amendments; however C. bonplandianum showed some phytotoxicity at higher dosage.

Samples of raw liquid pig manure, anaerobic digester effluent, screened digester solids, screened digester effluent, anaerobic digestion residue derived by centrifugation of the screened digester effluent, the centrifuge centrate and the final stored liquid effluent were collected at monthly intervals for 9 months from an anaerobic digestion system operated at a 375-sow pig farm. Porcine enteroviruses were isolated on pig kidney-cell cultures, most frequently from the raw manure, and significantly less frequently from the screened digester solids, anaerobic digestion residue and the final liquid effluent. It was concluded that the anaerobic digestion system resulted in significant, but incomplete, reductions in viral infectivity.

In continuous-culture aeration, heterotrophic activity varied with mean treatment time and treatment temperature but was unaffected by the level of dissolved oxygen provided it was maintained above 1% of saturation. At temperatures from 15 to 50°C most of the slurry odorants were removed even after very short treatment times. Below 1% of dissolved oxygen saturation, heterotrophic activity, in particular the oxidation of odorants and other BOD₅ material, varied with the oxygen concentration as well as mean treatment time and temperature. The oxygen concentration was no longer detectable by the Mackereth-type electrode and was controlled and measured indirectly through redox potential within the range −500 to 0 mV E_cal (pH 7·8). At 35 and 50°C total residual COD and BOD₅ were both similarly related to changes in redox potential. At 15°C only the total residual BOD₅, not the total residual COD, was related to redox potential. This could indicate that at lower temperatures some fermentative activity occurs at low aeration rates. Treatment times must normally exceed 7 days and redox potential during treatment must be higher than −200 mV E_cal (pH 7·8) if the rapid regeneration of odorants after treatment is to be avoided.

Rice straw was treated with 4% urea (w/w) dissolved in water to result in straw to water ratios of 1:1, 1:0·3 and 1:0·1. The methods of urea solution application were: uniform mixing of straw and solution, mixing of 10% of the straw with solution stacking the rest of the straw above this and adding urea solution on to straw after stacking. Assessments were based on the distribution of total nitrogen added, water-soluble and free ammonia nitrogen and IVOMD of the treated material.

When urea solution was uniformly mixed with straw the total nitrogen, water-soluble NH₃-N and IVOMD of the straw treated with a straw to water ratio of 1:1 or 1:0·3 were not significantly different (IVOMD values, 52% and 53%). Water at 1:0·1 resulted in significantly lower (P < 0·01) N contents and IVOMD values.

Addition of urea solution on to stacked straw or mixing of solution with a limited quantity of straw resulted in N and digestibility gradients within the stack.

Orange peels at 21·2% dry matter were ensiled in airtight containers for 92 days at 26°C. In one experiment in which there was release of gases and seepage, total DM losses reached 33·7 ± 1·98% (9·8% seepage, 23·9% gases). In another experiment, in which only gas was released, DM losses were 26·5 ± 0·04%. The dynamics of gas and seepage release and the chemical changes of stored seepage are described.

This paper evaluates the most important agronomic characteristics of the sewage sludge from the Tenerife wastewater treatment plant and the compost obtained by composting of this sludge with the organic fraction of municipal refuse. A comparative study is also carried out on several commercial products used as organic dressings on the island's agricultural soils.

From the results obtained, the direct use (after sterilization) of sewage sludge could be very interesting from the agricultural point of view. The compost obtained, because of its high total (43·6%) and oxidisable (37·3%) organic matter content, its high fertilizer elements concentration (N, 2·8%; P, 1·3%; K, 1·6%; Ca, 5·2% and Mg, 1·1%), its balanced essential elements content and moderate toxic heavy metals levels, can be considered a good organic fertilizer whose use could represent a great saving in chemical fertilizers and replace the manures formerly used, which are now almost non-existent. In addition, it could compete advantageously with the products at present on sale in the island because of its lower cost and better agronomic quality.