Hot water extraction with in situ wet oxidation: PAHs removal from soil

Hot water extraction with in situ wet oxidation: PAHs removal from soil
Dadkhah AA, Akgerman A
JOURNAL OF HAZARDOUS MATERIALS

93 (3): 307-320 AUG 5 2002

Abstract:
We are reporting the results of a small-scale batch extraction with and without in situ wet oxidation of soils polluted with polycyclic aromatic hydrocarbons (PAHs) using subcritical water (liquid water at high temperatures and pressures but below the critical point as the removal agent). Two types of soil; one spiked with four PAHs, and an aged sample were used. Experiments were carried out in a 300 ml volume reactor in the batch mode. In each experiment, the reactor was filled with 45-50 g of soil and 200-220 ml of double distilled water. For extraction without oxidation, the reactor was pressurized with nitrogen, while for those with the oxidation, an oxidizing agent (air, oxygen or hydrogen peroxide) was used.

The extraction only experiments were carried out at 230, 250 and 270 degreesC for spiked soil samples, and at 250 degreesC for aged soil samples, while all of the combined extraction and oxidation experiments were carried out at 250degreesC. Removal of PAHs from spiked soil in extraction-only experiments was from 79 to 99+% depending on the molecular weight of the PAH. This was in the range of 99.1% to excess of 99.99% for the combined extraction and oxidation. While 28-100% of extracted PAHs can be found in water phase in case of extraction alone, this reduces to a maximum of 10% if the extraction is combined with oxidation. With aged soil similar or comparable results were obtained. Based on these results, extraction with hot water, if combined with oxidation, would probably reduce the cost of post treatment for the water and can be used as a feasible alternative technique for remediation of contaminated soils and sediments. (C) 2002 Elsevier Science B.V. All rights reserved.

Author Keywords:
polycyclic aromatic hydrocarbons, hot water extraction, wet oxidation, soil remediation, water treatment

KeyWords Plus:
SUPERCRITICAL-FLUID EXTRACTION, SUBCRITICAL WATER, POLYAROMATIC HYDROCARBONS, POLYCHLORINATED-BIPHENYLS, SOLVENT-EXTRACTION, CONTAMINATED SOILS, POLLUTANTS, SEDIMENT, WASTES

Kinetic analysis of thermophilic anaerobic digestion of wastewater sludge
Alatiqi IM, Hamoda MF, Dadkhah AA
WATER AIR AND SOIL POLLUTION

107 (1-4): 393-407 OCT 1998

Abstract:
Conventional mesophilic anaerobic digesters are sometimes subject to process upset and have earned the reputation of being difficult to cope with sludge overloading. This study was conducted to examine the thermophilic process as a viable alternative.

An analysis of field data from an operating mesophilic sludge digester was conducted in parallel with experimental runs on a laboratory thermophilic reactor using similar sludge. The results showed that thermophilic anaerobic digestion was a viable alternative to the mesophilic process especially for overloaded digesters in warm climates. The optimum hydraulic retention time for the thermophilic process was 10 days which can lead to substantial savings in digester capacity. A simplified kinetic model was developed and applied in the analysis of steady-state operation of thermophilic anaerobic sludge digesters.

Author Keywords:
anaerobic digestion, kinetic models, thermophilic digestion, wastewater sludge

COMPARISON BETWEEN DYNAMICS AND CONTROL PERFORMANCE OF MESOPHILIC AND THERMOPHILIC ANAEROBIC SLUDGE DIGESTERS
ALATIQI IM, DADKHAH AA, AKBAR AM, HAMOUDA MF
CHEMICAL ENGINEERING JOURNAL AND THE BIOCHEMICAL ENGINEERING JOURNAL

55 (3): B55-B66 OCT 1994

Abstract:
Two anaerobic digestion schemes, namely mesophilic and thermophilic processes, have been analysed for process stability and controllability. As in any control problem, three types of variable are distinguished in this study, i.e. disturbance, manipulated and controlled variables. Substrate concentration S(i) and influent temperature T(i) are the disturbance variables. The manipulated variables are sewage sludge influent rate Q and specific heat addition rate G(u). The controlled variables are effluent substrate concentration S and digestion temperature T. A control system including a proportional-integral (PI) controller and variable groups is proposed. Multivariable steady state methods such as relative gain array, Niederlinski stability criterion, singular value decomposition and Morari integral controllability are employed. Several dynamic analyses such as biggest log-modulus tuning, robustness analysis and Tyreus load rejection criterion are carried out. Steady state analysis results are used for variable pairing. The results of multivariable analysis show that thermophilic anaerobic digestion is more favourable in terms of speed of response and disinfection capability. It also maintains dynamic and steady state stability if controlled properly.

KeyWords Plus:
SYSTEMS