Agricultural Wastes最新文献

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.

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.

Primary treated and anaerobically treated meat-processing wastes were irrigated onto pot lysimeters containing Horotiu sandy loam (Entic Dystrandept) and a ryegrass/clover sward. Four effluent application rates were used: 0, 500, 1000 and 2000 kg N ha⁻¹ year⁻¹. For primary and anaerobically treated effluent, pasture production was maximal at 2000 kg and 1000 kg N ha⁻¹ year⁻¹, respectively. Herbage from lysimeters receiving anaerobically treated effluent contained much higher concentrations of nitrate-nitrogen than that from lysimeters receiving primary treated effluent. Health problems may result when ruminants feed on high-nitrate materials. Based on ‘safe’ nitrate levels in the herbage, the upper loading limit would be about 500 kg N ha⁻¹ year⁻¹ for anaerobically treated effluent and about 1000 kg N ha⁻¹ year⁻¹ for primary treated effluent.

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.

The effects on slurry nitrogen of the aerobic treatment of pig and cattle excreta under various aerotion regimes are described. They were: high-rate aeration with dissolved oxygen >15% of saturation; low-rate aeration with dissolved oxygen 1–15% of saturation; and minimal aeration with dissolved oxygen <1% of saturation by control of redox potential at values <0mV E_cal. These had important effects upon the mineralised nitrogen components of the excreta. This nitrogen could be conserved as ammoniacal nitrogen, lost via ammonia stripping, oxidised to nitrate and conserved, or lost via denitrification. They also had important implications for energy conservation and odour regeneration. The energy requirement for aerobic treatment was minimal when the dissolved oxygen level was as low as possible and still consistent with adequate treatment. Conservation of the mineralised nitrogen as nitrate may prevent odour regeneration subsequent to treatment, but a dissolved oxygen level > 15% of saturation was required. In addition, the oxygen requirement for nitrification was equivalent to about 30–80% of the heterotrophic oxygen demand. Thus, with minimal aeration the efficiency was maximised, the extra oxygen demand for nitrification prevented and the nitrogen conserved as ammonia, but odour regeneration could be fairly rapid during storage.

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.

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.