Using four hazardous dispersion models, the ability to predict Lower Flammability Distance (LFD), the distance from a release through which the released gas is present in concentration below flammable range, has been evaluated using a set of large‐scale propane release field experiment data. The four models evaluated were the DEGADIS model, the SLAB model, the OME Simple Gas model and the OME Heavy Gas model (1983). The observed LFDs were compared with the predicted LFDs for three atmospheric conditions. The complete data set was broken into two parts: (1) the cyclone type releases (representing instantaneous release situations) and (2) the nozzle type releases (representing horizontal jet releases). A procedure based on the USEPA guidelines on air quality models was followed to evaluate the models.
The complex models (DEGADIS and SLAB models) appear unreasonably weak in predicting LFD's compared with the relatively simple Gaussian model used in the OME Simple Gas model for instantaneous releases. The OME simple gas model is significantly better than the DEGADIS and SLAB models for cyclone type (instantaneous) releases under unstable and neutral atmospheric conditions; and the DEGASIS model is significantly better than the SLAB model for nozzle type (horizontal jet) releases under stable atmospheric conditions. Since the size of the data set is not large enough (n = 20 for cyclone type release and n = 18 for nozzle type release), it is difficult to show 95% significant differences between models.
A series of experiments has provided data which indicate that treatment of municipal wastewater sludge cakes with 35 % kiln dust (cement, CKD or lime, LKD), alone or with a small amount of quicklime, will reduce the pathogenic microbial population in the sludge to below the U.S. Environmental Protection Agency's (USEPA) Process to Further Reduce Pathogens (PFRP) standard (USEPA, 1989). Both laboratory and large-scale field tests show that maintaining treated sludge at 52°C for 12 h, while the pH exceeds 12.0, kills viable indigenous and seeded populations of salmonella, poliovirus, and ascaris ova.
The addition of the cement or lime kiln dust results in a granular, easy-to-handle, soil-like material that is then treated in one of two methods. In one alternative no heating is necessary, while in the other, sludge cake is heated to 52°C for 12 h. In both, the pH must exceed 12.0 for a defined period. After this, the alkaline treated sludge is air dried through intermittent turning of windrows.
These patented (N-Viro) and USEPA's PFRP-approved pasteurization processes leave approximately 106 indigenous microorganisms per 5 g dry weight sludge, which help maintain the treated sludge in a nearly odor-free, stable, soil-like form. The specific chemical and physical effects of cement and lime kiln dust on municipal sludge cakes are presented to explain the mechanisms of the pasteurization process. Sludges from over twenty cities have been processed to make N-Viro Soil and all of them have achieved the PFRP criteria.
This process helps to prevent metal release in leachate by fixing the heavy metals present in the product and converting them to insoluble metal hydroxides. Data will show the degree to which alkaline treatment renders insoluble the heavy metals present in sludge. The modified EP Tox test was used to quantify the metal fixation accomplished by the mixing of kiln dust and sludge.
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