Lagoon

Soil. Composting of soils contaminated by high explosives is being carried out at the Umatilla Army Depot near Hermiston, Oregon (70). Soil from munitions washout lagoons is being treated iadoors ia compost rows of 2,000 m, and the estimated cost is less than one-third the estimated cost of iaciaeration. If this is successful, there are 30 similar sites on the National Priority List that could be treated ia a similar way. 

Static tube aerators are economically attractive and have a high transfer efficiency. They are weU-suited for lagoon appHcations. On the other hand, they are poor mixers and are not recommended for use when the sludge concentration is over 3000 mg/L. 

Residue Disposal. The major environmental problem in the Bayer process is disposal of bauxite residue which is effected by marine disposal, lagooning, use of underdrain lakes, or semidry disposal. Marine disposal in oceans or rivers, diluting the alkaline residue by large quantities of water, is environmentally unacceptable. Lagooning behind retaining dikes built around clay-sealed ground is commonly used, but there have been isolated leaks into aquifers. This has motivated installation of underdrains between the residue and clay-sealed, plastic-lined, lake bottom. This design removes the hydraulic head from the lake bottom and improves consoHdation of the residue. 

Lagoons. Where large land areas are available, lagooning provides a simple and economical treatment for nontoxic or nonhazardous wastewaters. There are several lagoon alternatives. 

The impounding and absorption lagoon has no overflow or there may be an intermittent discharge during periods of high stream flow. These lagoons are particularly suitable to short seasonal operations in arid regions. 

Anaerobic ponds are loaded such that anaerobic conditions prevail throughout the Hquid volume. One of the major problems with anaerobic ponds is the generation of odors. The odor problem can frequentiy be eliminated by the addition of sodium nitrate at a dosage equal to 20% of the appHed oxygen demand. An alternative is the use of a stratified facultative lagoon, in which aerators are suspended 3 meters below the Hquid surface in order to maintain aerobic surface conditions, with anaerobic digestion occurring at the lower depths. 

Fig. 15. Aerated lagoon types (a) aerobic (b) facultative (c) settling.

Aerated lagoons are employed for the treatment of nontoxic or nonha2ardous wastewaters such as food processing and pulp and paper. Retention time varies from 3 to 12 d, so a large land area is usually required. 

Sludge Disposal. Land disposal of wet sludges can be accomplished ia a number of ways Lagooniag or the application of liquid sludge to land by tmck or spray system, or by pipeline to a remote agricultural or lagoon site. 

The BPT is defined as the level of treatment that has been proven to be successful for a specific industrial category and that is currendy in fuU-scale operation. Sufficient data exist for this level of treatment so that it can be designed and operated to achieve a level of treatment consistendy and with rehabUity. For example, in the pulp and paper industry, BPT has been defined as biological treatment using the aerated lagoon or the activated sludge process with appropriate pretreatment. 

The goethite process precipitates crystalline aFeO-OH (goethite) as well as PFeO-OH, aFe202, and amorphous phases. The reaction is carried out at 90°C and pH 3.0, for 4—6 h in either batch or continuous fashion, and the iron(III) ion must be kept <1 g/L. Both jarosite and goethite soHds are usually lagooned. 

Sedimentation. This is the traditional method of treating wastewater in lagoons and uses the force of gravity to remove settable soHds (50,51). These soHds are separated out as a watery sludge which is removed mechanically. 

The four most common aerobic biological treatment processes are stabilization ponds, aerated lagoons, trickling filters, and activated sludge (see... 

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