Biological Wastes最新文献

Corn (maize)—processing effluents, known as nejayote, were aerobically treated in a 50-liter laboratory-scale rotating biological reactor. Removal of organic compounds, evaluated as chemical and biochemical oxygen demand (COD and BOD), as well as reducing sugars, was monitored. Operating conditions were: feed COD, 6·4 g/liter; rotational disc speed, 16 rpm; hydraulic retention time, 2·5 days. A comparison with previous experiments, carried out in a 150liter reactor, to consider scaling-up effects (1:3) was performed. Final COD removal was 84·6%. The application of an exponential model to reducing-sugars degradation was highly satisfactory, and the value of the constant was −0·352. Generated biomass was bromatologically evaluated, and average results in per cent of total dry biomass were: protein content, 41·5; fat, 3·4; fiber, 14·8; ash, 15·1.

The average density of viable microorganisms in poultry pine-sawdust litter was 6·3 × 10⁷/g dry material (DP); 1·6% of the population were aerobic heterotrophic bacteria. Acidophile bacteria, aerobic spore-forming bacteria, actinomycetes and fungi were, respectively 4·8 × 10⁴, 8·1 × 10⁴, 5·2 × 10⁴ and 8·9 × 10⁴ CFU/g DP. However the latter did not have a measurable mycelium. Algae were in low densities (18/g DP) and cyanobacteria were not detected. Most of the population had proteolytic and ammonificant capacities, but there were very few ammonium oxidizers and nitrite oxidizers. Denitrifiers were in relatively high density and the anaerobic free-nitrogen fixers were more abundant than the aerobic ones. Aerobic cellulolytics were scarce, but anaerobic cellulolytics, amylolytics and pectolytics showed a similar, and relatively high average density. Sulphate reducers and anaerobic mineralizers of organic sulphur were more abundant than the elementary-sulphur oxidizers, and sulphide oxidizers were not detected. Except for algae, microbial populations generally tended to decrease with time of use of the litter. This decline affected mainly nitrifiers, anaerobic and aerobic cellulolytics and amylolytics while sulphate reducers and anaerobic free-nitrogen fixers increased.

Seven mixtures from four organic residues—aerobic sewage sludge, city refuse, peat residue and grape debris—were made up to study the influence of the composting and maturation processes on the extractability of Fe, Cu, Ni, Zn, Cd, Pb, Cr and Mn by a chelating agent (diethylenetriaminepentaacetic acid, DTPA) and a neutral salt solution (0·05m CaCl₂) from the residues.

Composting and maturation increased the concentration of heavy metals in the materials due to the loss of weight of the materials during these processes. The metals also became more insoluble, and extractants employed removed larger amounts of metals from the raw composts than from the mature composts. In general, CaCl₂-extractable metals did not correlate significantly with the metal content of the composts. With DTPA-extractable metals, the only ones that showed significant correlations between the quantity of metal extracted by DTPA and the metal content of the samples in nearly all the composts studied were Pb and Zn.

The load of ‘zinc equivalent’ increased with the composting and maturation processes, and the Cd/Zn ratio decreased with those processes.

An integrated system for biogas production from mango-processing wastes and utilization of biogas effluent for production of major carp Rohu, (Labeo rohita) and common carp (Cyprinus carpio) was studied. Mango peels produced 0·21 m³ of biogas per kg of total solids. Biogas effluent of mango peels, when used at 34 kg/100 m² area in ponds as the sole source of feed for carps, yielded 8·35 kg/100 m² of fish which had acceptable colour, flavour and taste every 120 days.

Surface (0–20 cm) samples from five soils amended with pig slurry, sewage sludge or cattle slurry were separated into four macro- and three micro-aggregate fractions by dry sieving. Relative to the controls, these amendments decreased the apparent density and dispersibility of the aggregates, increased slightly their water-retention capacity at —0·03 MPa tension, but had no significant effect on intra-porosity and particle-size distribution of the aggregates. On average, pig slurry reduced aggregate dispersibility by 34% in the sandy loam and 8% in the sandy clay loam Modena soils. Sewage sludge and cattle slurry reduced dispersibility by 41% and 26%, respectively, in the sandy loam Lamporecchio and sandy clay loam Cremona soils. The organic carbon contents of the aggregates accounted for 73–98% of variability in their tendency to disperse, whereas their silt plus clay contents accounted for 38–96% of variability in the moisture they retained at —0·03 MPa tension.

Four anaerobic fluidised-beds were started-up on a dairy-type effluent of 5000 mg COD litre⁻¹ using different regimes: (a) two-phase; (b) Ca²⁺ addition; (c) polymer addition; and (d) control. Substrate removal efficiencies reached 76–92% at 9·4 kg COD⁻³ day⁻¹ in the two-phase, calcium- and biopolymer-amended reactors. The data suggest that removal efficiency and biomass concentration peaks were variable but mature biofilms, which were dependent on the protocol applied, were developed in the above-mentioned three reactors. Volatile fatty acids concentrations were reflected by intermediary/partial alkalinity variations.

Eight common aquatic weeds Salvinia molesta, Hydrilla verticillata, Nymphaea stellata, Azolla pinnata, Ceratopteris sp. Scirpus sp. Cyperus sp. and Utricularia reticulata were digested anaerobically to produce methane. The carbon to nitrogen (C/N) ratio, carbon to phosphorus (C/P) ratio, and the volatile solids (VS) content of the weeds varied widely. No trend between these factors and the methane yield was discernable; the possible reasons are discussed.

The energy potential of the weeds per unit area of the weed crop was worked out. Natural stands of salvinia, such as the one employed in the present investigation, would yield energy (methane) of the order of 10⁸ Kcal ha⁻¹ year⁻¹.