Fixed-bed Filters Research Articles

Aerosol collection in magnetically stabilized fluidized filters

An experimental study of aerosol filtration in a magnetically stabilized fluidized filter (MSFF) was conducted in order to compare the performance of MSFFs with fixed-bed filters. The experiments were carried out using polydispersed aerosols from which unit collector efficiencies for aerosols of different sizes (i.e., graded efficiencies) were determined. The experimentally determined unit collector efficiencies were compared with five empirical correlations of collection efficiencies of fixed-bed filters proposed by various investigators during the past decade. The comparisons yielded only order of magnitude agreement, suggesting that the similarity between MSFFs and fixed-bed filters is only approximate.

Analysis and anaerobic degradation of wool scouring and olive oil mill wastewaters

Two types of fatty industrial wastewaters, wool scouring effluents (WSE) and olive oil mill effluents (OME) were analysed (lipids, phenols and COD), and were then treated anaerobically in laboratory-scale fixed bed filters. Approximately 50% of the organic compounds in both wastewaters was degraded at two days of hydraulic residence time. A higher biogas production was obtained when using OME rather than WSE. This experimental study confirmed that anaerobic digestion can be considered as a roughing treatment in a multi-step process for industrial fatty wastewaters.

Oxygenation par le peroxyde d'hydrogene des biomasses fixees utilisees en traitement biologique des eaux

Because of their advantages as compared to flocculated biomass processes, there is now a revival of interest in fixed biomass processes: no mishaps due to bad flocculation, particularly with filamentous organisms (bulking) compact equipment owing to the ability to obtain greater biomass concentrations (several g l −1), which is impossible in flocculated biomass. In this paper, we will consider mainly bio-discs and submerged fixed bed filters. In bio-disc investigations, Hoehn and Ray's (1973), Kornegay and Andrew's (1968) now classical results showed that the bacterial film only acts on the surface, over a thickness which, at best, does not exceed 150 μm. At the same time, Bungay's (1969) very accurate measurements showed that the film active thickness coincides with the depth where the oxygen concentration in the film is higher than the critical oxygen concentration. In submerged filters, Elmaleh (1976) and Grasmick's (1978) theoretical studies permit one to define a Useful Column Height (UCH) which corresponds to the active part of the reactor and which is superposed on the height where oxygen concentration is higher than the critical oxygen concentration. In classical devices, the UCH is relatively low: approx. 0.50-1 m. In both cases, the system is provided with oxygen through an exchange between the air and the effluent to be treated, at a gas-liquid interface. This procedure limits the O 2 concentration to about 9 mg O 2 l −1, at the ambient temperature. Therefore, to increase the UCH of a submerged reactor or the active thickness of a bio-disc film by increasing the oxygen penetrating depth, the oxygen partial pressure in the gas phase should be increased by either using pure oxygen or increasing total gas phase pressure. These two methods are somewhat difficult to use and we prefer to use another method: bringing dissolved oxygen directly into the liquid phase without the exchange at the gas-liquid interface. This is feasible by using an oxygen liberating labile chemical reagent i.e. hydrogen peroxide. We consider two types of fixed biomasses: the bio-discs and the submerged filters. Bio-discs. The apparatus used is shown in Fig. 1. The utilization of H 2O 2 resulted in a very sharp increase in the substrate removal efficiency. It is observed that the substrate removal efficiency (Figs 5 and 6) and the reduced pollution flux (Figs 4 and 7) show a maximum when these are plotted as a function of the ratio: equivalent quantity of O 2 given by H 2O 2/O 2 demanded by the effluent and as a function of dissolved oxygen in the liquid phase. Moreover, these curves suggest that oxygen acts as an inhibitor and different attempts at modeling, based on standard models of inhibiting effects, lead to the exponential model giving the lowest deviation (Fig. 8). Submerged packed reactors. The apparatus used is shown in Fig. 3. This unit is fed by urban effluents and the oxygenation in the reactor is carried out by using diluted H 2O 2 (0.5-1.5 N).

Chemistry of conversion of alkylphenyl esters at high temperatures and pressures

At a progressive rate, small wastewater treatment plants in rural areas need to be equipped with an additional phosphorus removal stage in order to achieve a good chemical status in the receiving natural water bodies. A conventional regeneration method for ferric (hydr)oxides such as phosphate specific adsorbents, which can be applied to remove and recover phosphorus in fixed bed filters, was investigated and improved. It was shown that a loss of up to 85% of the initial capacity can be observed when regeneration with 1 M NaOH is implemented. The losses are caused by surface blocking with different calcium-containing compounds as revealed by an EDX analysis. These blocking compounds could be removed completely with an additional acidic regeneration step at pH = 2.5. During the alkaline desorption that followed, complete phosphorus removal and a full recovery of the adsorption capacity were achieved for goethite-rich Bayoxide® E 33 HC (E33HC) and akaganéite-rich GEH® 104 (GEH). The regeneration procedure was repeated up to eight times without any signs of further decline in the phosphate adsorption capacity or any changes in the specific surface area or pore size distribution of the adsorbent. In contrast to GEH and E33HC, ferric hydroxide- and calcite-rich FerroSorp® Plus (FSP) was partly dissolved during acid treatment.