Waste Particle Size Research Articles

Empirical measurements of parameters critical to modelling benthic impacts of freshwater salmonid cage aquaculture

Although the waste dispersion models used in salmonid marine cage aquaculture could potentially be applied in freshwater cage aquaculture, much of relevant data on the waste particle parameters are unavailable. The present study provides new data on the wet densities of diets, the fall velocities of diets, the fall velocities of faecal matter and waste particle size. A significant increase of densities caused by the immersion time in water was observed. The wet density obtained from 60-s immersion time was found to be the effective settling density of diets. Fall velocities of salmonid diets were non-Stokesian and ranged from 0.02 to 0.12 m s(-1). These fall velocities did not significantly vary with water temperature. Fractionation of collected solid wastes from experimental tanks revealed that almost 60% by mass was retained on 2000-, 1000- and 500-micrometers meshes. The fall velocities of these fractions were found to vary between 0.015 and 0.030 m s(-1). The waste fraction that passed through a 500-micrometers mesh had an estimated median diameter of 114.4 micrometers. The observed fall velocities of both diets and solid wastes were lower than those commonly used in modelling waste dispersion in the marine environment. However, because of the relatively slow current velocities in most freshwater environments, it is expected that the wastes will tend to accumulate locally at cages.

Evaluation of municipal solid waste composting kinetics

Most modern municipal solid waste (MSW) composting operations have emphasized the enhancement of decomposition of the organic fraction of the waste to comply with strict environmental regulations. This can be achieved once the composting process kinetics are well understood. This study examined process kinetics through experimentation with bench-scale reactors under controlled composting conditions to show the interdependence between biological, chemical and physical factors during composting of MSW. The effects of temperature, moisture content, waste particle size and carbon to nitrogen (C/N) ratio on process kinetics were evaluated. The results obtained revealed that these factors should be carefully controlled in order to achieve optimum process performance. It has been found that the organic matter degradation during composting follows a first-order kinetic model.

An estimation of the size distribution of amalgam particles in dental treatment waste.

Regulations have been adopted in several countries of the European Union which prescribe that dental treatment waste water must be discharged via an amalgam separator device. Since the effectivity of the device strongly depends on the size of the amalgam waste particles, this size was evaluated in waste water samples from eight dental offices. Per sample, all solid particles were separated from the waste water by pressure filtration, then dried and divided into six fractions by being sieved over five sieves with decreasing mesh width. Of the particles in each fraction, the density was determined by picnometry, the mass by weighing, and the area and width by image analysis. For this analysis, width was defined as the dimension perpendicular to the length of the particles. By combining the density, area, and width determinations of all fractions, we obtained mass distributions per waste particle width of the samples. The proportional amalgam mass of the distributions was estimated with the measured density of the particle fractions and with a number of assumptions for the density of amalgam particles only and of other waste particles only. Each waste sample has its own characteristics with respect to the mass and density of the particle fractions. The size distribution of waste particles has a bimodal shape and consists of a distribution of small (width, 2 to 90 microns) and large particles (width, 160 to 5500 microns). For small particles with a width up to 60 microns, the influence of the assumptions on the estimation of the proportion amalgam of the waste mass distribution is minor when compared with the sampling error. By averaging the estimations over the samples, one can estimate the weight of amalgam particles with a width < 10 microns and < 50 microns, respectively, between 4 and 15% and between 15 and 30%. The smallest particles comprising 5% of the amalgam mass have an estimated width of up to 15 microns.

Combustible carryover predictions for a wood-waste boiler

An analytical model of a spreader-stoker type wood-waste fired boiler is used to predict the flight times and mass reductions of combustible particles entrained by the flow of furnace gases. The predicted mass ratio, initial char mass to final char mass at the furnace exit, is coupled with literature values for wood waste particle size distribution in order to predict furnace exit particle mass loading and size distribution. Only the combustible fraction of carryover is considered in these calculations, and it is assumed that the entrained combustible particle size distribution is the same as the entrainable fraction of the fuel. A simple analytical expression for the efficiency of a multicyclone-type particulate collector is applied to the predicted furnace exit loading and size distribution in order to predict stack particle loading and size distribution of the combustible fraction. This procedure is repeated for various boiler operating and fuel conditions. The influence of steam generation rate, excess air, and initial fuel moisture on stack mass loading and particle size distribution is shown to be relatively minor. It is further shown that the influence of the initial fuel size distribution has a very pronounced effect on the predicted results both for the furnace exit and for the stack.