PubMed · 3583145
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V Pokorný. 1987. A water filter for electron microscopes.. https://pubmed.ncbi.nlm.nih.gov/3583145/
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The three operational modes of pressurised liquid extraction (PLE) (namely, static, dynamic and static-dynamic) have been applied for the extraction of nitrated polycyclic aromatic hydrocarbons from both spiked and natural contaminated soils. A comparison of the three modes in terms of experimental set-up used, extraction time needed for total removal of the analytes and precision has been carried out. The use of a flow-injection manifold as interface between every pressurised extractor and a filtration-preconcentration system has allowed the partial automation of the proposed approaches. Efficiencies close to 100% have been provided by the three operational modes. However, the static-dynamic mode has been proved as the most suitable alternative providing the shortest extraction time (25 min) versus the static (30 min) and the dynamic (50-70 min) modes. Gas chromatography with MS-MS ion preparation mode has been used providing both high selectivity (no interferences were observed) and sensitivity (detection limits of low pg). The comparison of the proposed approaches with the reference method 3540 of the US Environmental Protection Agency (EPA) has shown that both methods provide similar efficiencies with an important shortening in the extraction time (25-70 min by PLE versus 24 h by the EPA method). The use of water as leaching agent has avoided the use of organic solvents providing an environmentally friendly method.
Municipal and industrial wastewater treatment plants produce large amounts of sludge, containing organic and mineral components and being mechanically dewatered to e.g. 20-25% DS in centrifuges. Both the reduction of the amount of sludge produced and improving its dewaterability are hence of paramount importance. Hot acid hydrolysis can meet these objectives. The current paper describes the results of detailed investigations with respect to acid hydrolysis of thickened sludge (5-6% DS content). A comparison with traditional thermal hydrolysis is also included. As a result of the experimental investigations, it can be concluded that hot acid hydrolysis is efficient in both reducing the residual sludge amounts and improving the dewaterability. Under the proposed optimum conditions it is found that (i) the amount of hydrolysed DS is approximately 70% lower than the initial untreated amount, (ii) the DS-solid content of the dewatered cake is increased from 22.5% (initial untreated) to at least twice this value, (iii) the rate of mechanical dewatering is not significantly affected. The preferential release of ODS into the water phase, and the increased BOD/COD-ratio through hydrolysis, turn this recycle water phase into a possible carbon-source for nitrification/denitrification. Heavy metals and phosphates are also released in the water phase, and can be subsequently precipitated.