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Physical Processes
Published in Ralph L. Stephenson, James B. Blackburn, The Industrial Wastewater Systems Handbook, 2018
Ralph L. Stephenson, James B. Blackburn
Steam stripping consists of treating the contaminated stream of water in a packed vessel where the water is trickled down through the packing and steam is countercurrently forced up through the packing, or is generated by heating the VOC contaminated water. This system has been used in a number of cases for at source treatment of VOC contaminated industrial waste water and is also commonly used for sour water treatment. Since the process raises the water temperature to above the boiling point of most VOCs, effectively boiling them off, the process works very well, removing VOCs to extremely low levels in the water. In fact, the levels to which this process can remove VOCs are used as the basis of many regulatory requirements. The process generates a stream of VOC contaminated condensed steam, which must be properly disposed of. This can be accomplished by fractional condensation or by distilling the VOCs from the condensed steam or by burning the steam and VOCs in a boiler or furnace. Since the entire stream of water must be heated to steam temperatures, this process is usually used only for low volumes of contaminated wastewater, although the heat is usually recovered. VOCs can also be recovered from the fractional condensation or distillation process with carbon columns or with low temperature condensers, but again, the cost effectiveness of these methods is generally limited to smaller streams.
Wastewater Stripping
Published in Gaetano Joseph Celenza, Specialized Treatment Systems, 2020
Design assumptions of either adiabatic or isothermal conditions should be understood. These include The validity of simplifying assumptions that the equilibrium is a straight line function, or that the molar flows are relatively constant, depends on a small tower temperature gradient.If heat losses from a system are large, the tower operating temperature will change.Temperature losses in an air stripper are primarily from evaporative cooling, which could be reduced if the air stream were saturated prior to entering the tower. This is not a common practice, but not difficult to accomplish using a simple spray section. Other tower losses from relatively low bulk fluid temperatures are negligible, except in extreme winter conditions. Where severe conditions are expected, losses can be minimized by insulating.In steam stripping the first consideration is the feed concentration and its boiling point, since the temperature can range from 212°F at the hot end to the feed boiling point. For low concentrations the temperature span is low since the feed boiling point is close to water. As the volatile feed concentration increases the resulting boiling point defines the tower operating temperature range, and a significant temperature difference can occur between the inlet and outlet conditions. In such cases a simple Henry’s law constant may not define the entire tower conditions and more complex design procedures will have to be employed. In addition, constant molar flow rates are an important design assumption, based on using a straight line to define operating conditions. Adiabatic conditions must be assured to obtain these conditions.
Nutrient removal and recovery from digestate: a review of the technology
Published in Biofuels, 2018
Evelyne Monfet, Geneviève Aubry, Antonio Avalos Ramirez
The removal of ammonia from liquid effluents can be performed using air or steam stripping. The latter is more expensive, but it can be applied when the end product obtained from ammonia recovery is economically attractive. The ammonia released from stripping units is easily absorbed into sulfuric acid solutions, which results in ammonium sulfate, a marketable platform chemical for the production of base fertilizers and other chemical products [19]. In order to increase the release of nitrogen as ammonia gas, it is necessary to increase the pH of the liquid to about 10.8–11.5 by adding lime or another alkaline compound. In the liquid phase, the ammonium hydroxide is in chemical equilibrium with the ammonia. This equilibrium is a function of the pH and temperature; at a fixed temperature, the increase in pH moves the equilibrium toward ammonia production [27]. Ammonia stripping is performed in desorption columns, the performance of which is a function of pH, temperature, packing characteristics and size, and operating parameters [8].