Agricultural Wastes最新文献

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.

Waste from a local hatchery was processed by cooking it with water at a ratio of 2 waste to 1 water and then dehydrating the product (‘processed hatchery waste’, PHW). PHW was subjected to proximate, mineral and amino acid analyses: it was found to contain 22·8% crude protein 21·48% true protein, 22·64% Ca and 2706 kcal kg⁻ metabolizable energy. The product was incorporated at 2·5% and 5·0% levels in broiler rations and at 4%, 8% and 12% in laying hen diets as a substitute for soyabean meal, meat meal and ground limestone. In the broiler trials, body weight gains, feed consumption and feed efficiency were comparable for birds on all diets. The optimal inclusion level of PHW in broiler rations is around 2·5%. In the laying hens trial, body weights, egg production rates, feed consumption and efficiency, and egg size were not adversely affected by including PHW in diets.

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.

Farmers are increasingly concerned to maximise the fertiliser potential of slurry applied to pasture. The availability of the nitrogen in cow slurry for grass growth has been investigated by a number of workers and values from 14% to 84% have been reported for the season after application. Results are presented for 7 field experiments undertaken in southern England on four different farms in the harvest years 1977–1979. Spring and summer slurry applications were 25–30% as effective as ammonium nitrate in promoting dry matter yield of ryegrass swards and winter applications somewhat less at around 15%. When combined with applications of ammonium nitrate the average response was similar but there were appreciable differences in responses between sites. The apparent recovery of slurry nitrogen in herbage was 13% averaged over all treatments.

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.

A 4 t heap of aerobic sewage cake was stored exposed to the weather in a temperate maritime climate and examined over a period of 60 weeks. Salmonellae were not isolated after 11 weeks storage. Coliforms and faecal streptococci were not isolated from surface samples after 23 and 46 weeks, respectively, but were both isolated from the interior for 60 weeks.

One competitive solution to the slurry handling problem of some intensive pig houses is described. The system is based on mechanical and chemical separation techniques. The solids produced are easy to store until they can be spread on neighbouring land and their smell is inoffensive. The liquids produced are greatly reduced in bulk, by evaporation, and in polluting potential, thereby reducing the problems of their eventual disposal.

A treatment plant has operated for 3 years in a 500 place finishing piggery in such a way that slurry was flushed from the channels hourly and passed through a mechanical separator to remove the coarse particles. Separation enabled a high rate biological filter to treat the separated liquid reliably without blockages and also increased the pump life tenfold. The treated separated liquid was then flocculated, and the conbined effect of the mechanical separation and the flocculation was to leave up to 40% of the input slurry as a semi-solid at 15% dry matter (DM) together with a clear filtrate liquid, much of which was evaporated by diverting air from the ventilation system around the treatment plant and through an air scrubber/evaporator. Thus, only 30% of the original slurry had to be discharged as liquid. With design modifications to the treatment plant and close control of water wastage this figure 30% can be reduced to zero, i.e. an output of solids only can be attained.