Inflation, cold dark matter, and the central density problem

A problem with high central densities in dark halos has arisen in the context of LCDM cosmologies with scale-invariant initial power spectra. Although n=1 is often justified by appealing to the inflation scenario, inflationary models with mild deviations from scale-invariance are not uncommon and models with significant running of the spectral index are plausible. Even mild deviations from scale-invariance can be important because halo collapse times and densities depend on the relative amount of small-scale power. We choose several popular models of inflation and work out the ramifications for galaxy central densities. For each model, we calculate its COBE-normalized power spectrum and deduce the implied halo densities using a semi-analytic method calibrated against N-body simulations. We compare our predictions to a sample of dark matter-dominated galaxies using a non-parametric measure of the density. While standard n=1, LCDM halos are overdense by a factor of 6, several of our example inflation+CDM models predict halo densities well within the range preferred by observations. We also show how the presence of massive (0.5 eV) neutrinos may help to alleviate the central density problem even with n=1. We conclude that galaxy central densities may not be as problematic for the CDM paradigm as is sometimes assumed: rather than telling us something about the nature of the dark matter, galaxy rotation curves may be telling us something about inflation and/or neutrinos. An important test of this idea will be an eventual consensus on the value of sigma_8, the rms overdensity on the scale 8 h^-1 Mpc. Our successful models have values of sigma_8 approximately 0.75, which is within the range of recent determinations. Finally, models with n>1 (or sigma_8 > 1) are highly disfavored.Comment: 13 pages, 6 figures. Minor changes made to reflect referee's Comments, error in Eq. (18) corrected, references updated and corrected, conclusions unchanged. Version accepted for publication in Phys. Rev. D, scheduled for 15 August 200

A Decontamination Process to Remove Metals and Stabilise Montreal Sewage Sludge

The Montreal Urban Community (MUC) treatment plant produces approximately 270 tons of dry sludge daily (tds/day) during physicochemical wastewater treatment. The sludges are burned and contribute to the greenhouse effect by producing atmospheric CO2. Moreover, the sludge emanates a nauseating odour during its thermal stabilisation and retains unpleasant odours for the part (25%) that is dried and granulated. To solve this particular problem, the treatment plant authorities are currently evaluating an acidic chemical leaching (sulfuric or hydrochloric acid) process at a pH between 2 and 3, using an oxidizing agent such as ferric chloride or hydrogen peroxide (METIX-AC technology, patent pending; [20]). They could integrate it to a 70 tds/day granulated sludge production process. Verification of the application of METIX-AC technology was carried out in a pilot plant set up near the sludge production plant of the MUC. The tests showed that METIX-AC technology can be advantageously integrated to the process used at the MUC. The residual copper (274 ± 58 mg/kg) and cadmium (5.6 ± 2.9 mg/kg) concentrations in the treated sludge meet legislation standards. The results have also shown that odours have been significantly eliminated for the dewatered, decontaminated, and stabilized biosolids (> 97%) compared to the non-decontaminated biosolids. A high rate of odour elimination also was obtained for the liquid leached biosolids (> 93%), compared to the untreated liquid biosolids. The fertilising value (N and P) is well preserved by the METIX-AC process. Dissolved organic carbon measurements have showed that little organic matter is brought in solution during the treatment. In fact, the average concentration of dissolved organic carbon measured in the treated liquid phase is 966 ± 352 mg/l, whereas it is 1190 ± 325 mg/l in untreated sludge. The treated sludge was first conditioned with an organic polymer and a coagulant aid. It was successfully dewatered with various dehydration equipments (filter press, rotary press, centrifuge)