Laserfiche WebLink
3422es_e.htm at mend20enrcan.gc.ca • Page 2 of 4 <br /> study the effects of natural sludge aging. <br /> • Sampling plans were developed prior to the collection of sludge cores to ensure a <br /> representative composite sample of aged sludge. The number of samples was based in <br /> large part on the volume of disposed sludge, while the sampling stations were defined <br /> after a review of site-specific characteristics including pond dimensions and patterns <br /> of disposal within the pond. A commercially available hand corer with extension was <br /> used to reach depths of up to 6 in and is recommended for collection of cores in <br /> shallow water and/or sampling through an ice cover in winter. <br /> Sludge characterization <br /> Physical characterization and leaching tests were performed on the wet samples. The <br /> remaining analyses (chemical, mineralogical and thermal) were done using the <br /> freeze-dried material. <br /> The pH values for the sampled sludges were alkaline and ranged from 8.2 to 10.8. In <br /> most cases aged sludges showed a lower pH than their fresh counterparts. Eh values <br /> ranged from 58 to 315 mV with the aged sludges commonly recording the lower <br /> values. <br /> Denser sludges, generally produced using the High Density Sludge (HDS) process, <br /> displayed both smaller median particle sizes and narrower particle size distributions. <br /> Many of the sludges produced from conventional or basic treatment processes <br /> • exhibited bimodal particle size distributions. In all but one case, the measured particle <br /> size was greater for the aged sludge. <br /> The solids content of the sludges ranged from 2.4% to 32.8%. In almost all cases at <br /> least a 25% increase in solids content was seen from the fresh to the aged material. <br /> Based on the samples tested, no correlation was observed between the degree of <br /> densification and either the age of the deposited sludge or the presence (or absence) of <br /> a water cover on the sludge pond. <br /> Neutralization potential values for the sludges collected ranged from 108 to 725 tonnes <br /> CaCO3 equivalent per 1000 tonnes sludge. While low NP values are attractive in <br /> terms of plant efficiency, sludges with high NPs have more neutralization capacity <br /> which directly impacts on long term sludge stability. Calcium content in the sludges <br /> varied from 3.8% to 27%; calcium is present in two main forms, as calcite or gypsum. <br /> The metals content of sludge can be viewed as potential recoverable assets or a source <br /> of leachable metals. Zinc recovery may be possible for some sludges ([Zn]>14%). <br /> Zinc concentrations ranged from 0.019% to over 14.4%. The low concentrations <br /> observed for copper and nickel (generally less than 1%) do not justify their recovery. <br /> Aluminum ranged from 0.1% to 11%. Copper, arsenic, boron, cadmium, chromium, <br /> mercury, lead, and selenium occur only in trace amounts, generally less than 0.01%. <br /> Iron ranged from 1.5% to 28% in the sludges. <br /> • All the sludges contained sulphate, in some cases greater than 30%. The sulphate <br /> content correlated directly with the amount of total sulphur in most of the sludge <br /> http://mend2000.nrcan.ge.ca/reports/3422es_e.htm 1/18/99 <br />