Lime treatment process

Much work has been carried out on the nutritional benefits derived from the lime treatment of com (7,8). Although this aspect is very important, an understanding of the overall physical-chemical changes occurring in the com, which determine the mechanical and sensory properties of the resultant food products, is also essential. Such information can lead to modification of the traditional lime treatment process to... 

An advantage of the lime treatment process is that it can precipitate dissolved metals (see section 28.3.3) and remove them at the clarification stage. Increasingly, however, industry is required to treat its waste-water before discharge to sewer and this includes the removal of heavy metals. 

In the typical lime treatment process, lime reacts with the weak acid bleed as follow ... 

Figure 10.9 Schematic process flow diagram of a lime treatment process to precipitate and coagulate CMP wastewater.

Sodium alumiaate is used ia the treatment of iadustrial and municipal water suppHes and the use of sodium alumiaate is approved ia the clarification of drinking water. The FDA approves the use of sodium alumiaate ia steam generation systems where the steam contacts food. One early use of sodium alumiaate was ia lime softening processes, where it iacreases the precipitation of ions contributing to hardness and improves suspended soHds removal from the treated water (17). Sodium alumiaate reacts with siHca to leave very low residual concentrations of siHca ia hot process water softeners. Sodium alumiaate is often used with other chemicals such as alum, ferric salts, clays, and polyelectrolytes, as a coagulant aid (18,19). 

Lime and Lime-Soda Processes. The first softening plant in the early 1900s used the lime softening process with fill and draw units. Later, continuous-treatment units, which greatiy increased the amount of water that could be treated in a faciUty of given size, were developed. More than 1000 municipahties soften water. Most are in the Midwest and in Florida. However, concern for the adverse effect of soft water on cardiovascular disease (CVD) may limit the number of plants that introduce softening. 

The chemical concenirations, hath temperature and process limes noted above are only indicative and for general reference They may vary with the type of chemicals, the manufacturer and the condition of the surface to be treated. Details may be obtained from the chemical manufacturer to formulate the internal sheet treatment process guidelines. 

While the emphasis here has been on the reduction of the amount of waste sludges, it is also equally important to address the problem of regulating the effluents and emissions. In this context, special mention may be made of ammonia which must be carefully regulated. The procedure for processing ammonium fluoride or ammonium sulfate containing solutions begins with lime treatment. The filtrates are fed continuously into a column and stripped with live steam and upgraded. In this way it is possible (with improved equipment and carefully controlled operation) to attain ammonia contents of less than 50 ppm in the effluent. 

Ion exchange as well as lime treatment is another method that can be applied in this process to reduce some of the toxic trace metals in the wastewater from the plant. 

It is not known whether this process would be competitive with the lime/soda precipitation process for primary treatment. For new plants, the main issue is capital cost. The lime/soda process is relatively inexpensive for large-scale plants. For small plants, the BDFI system may be competitive, particularly for packaged turn-key plants, if installation and start-up costs are taken into consideration. The BDH system is very compact and can be quickly started and easily operated with minimal labour requirements. 

Heavy metals such as copper, zinc, lead, nickel, silver, arsenic, selenium, cadmium and chromium may originate from many sources within a rehnery and may, in specihc cases, require end-of-pipe treatment. Some agencies have set discharge limits that are beyond the capability of common metals removal processes such as lime precipitahon and clarihcation to achieve. Other treatment processes such as iron coprecipitation and adsorption, ion exchange, and reverse osmosis may be required to achieve these low effluent concentrations [52]. 

Low-volume waste sources include water treatment processes that prevent scale formation such as clarification, filtration, lime/lime soda softening, ion exchange, reverse osmosis, and evaporation. Also included are drains and spills from floor and yard drains and laboratory streams. 

The costs associated with S/S technologies have generally been considered low compared with those for other treatment techniques. The reasons for this are the availability of rather cheap raw products (e.g., fly ash, cements, lime), simple processing requirements, and the use of readily available equipment from the concrete and related construction industries (D150141, p. 7.99). 

According to the vendor, the setup of all systems in a KB-1 plant typically costs 150,00 to 250,000. A lime treatment plant can cost 4 to 6 million. Average costs of the KB-1 system are 3.00 to 5.00 per 1000 gal. The vendor claims the KB-1 process can cost below one cent per gallon for treatment of acid mine drainage. Costs depend upon metal load and the cleanup... 

Primary treatment processes, such as clarification, lime-soda softening, ion-exchange, and RO... 

Lime-soda process. Combination of the use of slaked lime for the removal of temporary hardness and sodium carbonate for the removal of permanent hardness constitutes the lime-soda process for softening natural waters. This method is commonly used in municipal water-treatment plants and is a cheap and yet fairly effective process. If sufficient time can be allowed, the insoluble carbonates may be permitted to settle out in settling basins, or they may be more rapidly removed by means of filters. Frequently, iron or aluminum salts are added, and these hydrolyze to form gelatinous precipitates of ferric or aluminum hydroxides. As these precipitates slowly settle, they carry with them the insoluble normal carbonates, as well as any other suspended matter such as sand, clay, or organic matter which is sometimes slow in settling otherwise. 

This metaphosphate is used in water treatment in the form of sodium hexametaphosphate [(NaP03)s], which is known by the trade name Calgon, to prevent the precipitation of small quantities of calcium and magnesium salts not removed in the lime-soda process and to dissolve scale that has formed in boilers, water pipes, and so forth. 

There has been some concern about the effect of alkaline conditions on the formation of toxic amino acids in corn, particularly lysinoalanine (13). However, since lysinoalanine was found in very small amounts in foods prepared under more rigorous conditions than those applied traditionally, and since the lime treatment of corn has been a processing... 

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