Effect of bulking agent on the reduction of NH3 emissions during thermophilic composting of night-soil sludge.

Night-soil sludge contains a high percentage of nitrogen and releases large amounts of ammonia when it is composted. In this research, three types of bulking agents, sawdust, perlite, and activated carbon, were used, and the effects of these bulking agents on the reduction of NH3 emissions during thermophilic composting were evaluated. It was found that not only is sawdust the most effective agent in reducing NH3 emissions, but that it also effectively promotes organic matter decomposition. Increases in the mixing ratio of sawdust in the range adopted in the present research, from 70% to 92% on a dry-weight basis, appeared to cause no adverse effects on the decomposition of sludge itself. And the higher the mixing ratio of sawdust, the more effective the reduction in NH3 emissions, however this effect was not enough to completely suppress these emissions, even at the highest mixing ratio.

A cryptic plasmid, pAO1, from a compost bacterium, Bacillus sp.

The complete nucleotide sequence of a new cryptic plasmid, pAO1 isolated from a compost bacterium Bacillus sp., has been analyzed. Analysis of the PCR-based 16S rRNA sequence showed the bacterium harboring pAO1 was closely related to Bacillus pallidus. The plasmid pAO1 was 3,325 bp in size. Two open reading frames, ORF1 and ORF2, encoding putative polypeptides of 248 and 290 amino acids, respectively, were identified within the sequence. The ORF1 has a limited sequence similarity to an integrase/recombinase, while the ORF2 has high similarity with the replication protein of pBC1 from Bacillus coagulans. A putative origin sequence for a plus-strand was located between ORFs. Southern blot analysis indicates this plasmid replicates via a rolling circle-type mechanism.

A new operation for producing disease-suppressive compost from grass clippings

This study evaluated the use of grass clippings discharged from golf courses as the raw material for production of a suppressive compost to control Rhizoctonia large-patch disease in mascarene grass. Bacillus subtilis N4, a mesophilic bacterium with suppressive effects on the pathogenic fungus Rhizoctonia solani AG2-2, was used as an inoculum in a procedure developed with the aim of controlling composting temperatures and inoculation timing. The population density of mesophilic bacteria in the raw material was reduced to around 5 log10 CFU/g (dry weight) of composting material in the self-heating reaction at the initial stage of composting by maintaining a temperature of 80 degreesC for 1 day. The inoculum was applied immediately, and the composting material was maintained at 40 degreesC for 3 days. This served both to highly concentrate the suppressive bacterium and to achieve sporulation. The temperature was then raised to 60 degreesC and maintained, enabling hygienic, high-speed composting while maintaining the population density of the suppressive bacterium as high as 8 log10 CFU/g (dry weight) in the compost. The suppressiveness of compost made in this way was confirmed in a turf grass disease prevention assay.

Dynamic modeling of immobilized cell reactor: application to ethanol fermentation.

A mathematical model has been developed for the unsteady-state operation of an immobilized cell reactor. The substrate solution flows through a mixed-flow reactor in which cells immobilized in gel beads are retained. The substrate diffuses from the external surface of the gel beads to some internal location where reaction occurs. The product diffuses from the gel beads into liquid medium which flows out of the reactor. The model combines simultaneous diffusion and reaction, as well as cell growth, and it can predict how the rates of substrate consumption, product formation, and cell growth vary with time and with initial conditions. Ethanol fermentation was chosen as a representative reaction in the immobilized cell reactor, and numerical calculations were carried out. Excellent agreement was observed between model predictions and experimental data available in the literature.

Effect of temperature on composting of sewage sludge.

The effect of temperature on the composting reaction of sewage sludge was investigated at 50, 60, and 70 degrees C. The total amount of CO(2) evolved and the final conversion of volatile matter were maximum at 60 degrees C., suggesting that the optimal temperature for composting was around 60 degrees C. The specific CO(2) evolution rate (moles of CO(2) evolved per hour per viable cell) was maximum at 70 degrees C. The isolated thermophilic bacterium which was dominant at 60 degrees C but did not grow at 70 degrees C showed that the rate of O(2) consumption measured on the agar plate at 70 degrees C was four times higher than that at 60 degrees C. This showed that the energy yielded from catabolism is rather uncoupled with the anabolism at 70 degrees C in the metabolism of microorganisms indigenous in the compost. A higher respiratory quotient was observed at 70 degrees C than at any other temperature.

Effect of seeding during thermophilic composting of sewage sludge.

The effect of seeding on the thermophilic composting of sewage sludge was examined by measuring the changes in CO2 evolution rates and microbial numbers. Although the succession of thermophilic bacteria and thermophilic actinomycetes clearly reflected the effect of seeding, no clear difference was observed in the overall rate of composting or quality of the composted product.

Characteristics of Mesophilic Bacteria Isolated during Thermophilic Composting of Sewage Sludge.

The degree of inactivation by UV irradiation was different between vegetative cells and spores of bacteria isolated from sewage sludge composting at 60 degrees C. By using this property, a method to estimate the spore ratio of a mixture of vegetative cells and spores was presented. This UV irradiation method was applied to the estimation of the spore ratio of sewage sludge compost samples collected at several stages of composting. The spore ratio of mesophilic bacteria in the samples obtained at the thermophilic stage of 60 degrees C was 40% at most. The vegetative form of mesophilic bacteria showed a thermotolerance property at 60 degrees C by forming colonies but showed no respiratory activity at that temperature.

Change in Microbial Numbers during Thermophilic Composting of Sewage Sludge with Reference to CO(2) Evolution Rate.

Dewatered sewage sludge was composted in a laboratory-scale autothermal reactor in which a constant temperature of 60 degrees C was kept as long as possible by regulating the air feed rate. The change in CO(2) evolution rate was measured continuously from the start up through the cessation of compositing. The succession of mesophilic bacteria, thermophilic bacteria, and thermophilic actinomycetes was also observed during the composting. Specific CO(2) evolution rates of thermophilic bacteria and actinomycetes in the constant-temperature region of 60 degrees C were assessed quantitatively. It was found that the CO(2) evolution rate was attributed to thermophilic bacteria at the initial stage of 60 degrees C and to thermophilic actinomycetes at the later stage of 60 degrees C.