calcium carbonate. This calcium carbonate reacts with the acids to form harmless neutral salts, carbon dioxide and water. The use of proper types of limestone chips is the most corrimon, least expensive, safest, and easiest way to neutralize acids and sometimes caustics. Engineers and contractors have been known to specify or install ali kinds of rocks or marble chips in a neutralizing basin. Unfortunately, they are often in error when they cali for marble chips or stones in aneutralizing basin. Marble is only one form of limestone, and the marble or stones may not contain the proper content of calcium carbonate. The proper limestone is one that is a random mixture of 1 to 3 inches in size and contains a minimum calcium carbonate content (neutralizing agent) of 90 percent. it the stones are too small, they will dissolve too quicly and cause clogging of the drainage system. it the stones are too large, they will not have enough surtace area to react with the incoming chemicals. it the limestone contains less than 90 percent calcium carbonate, there will not be enough neutralizing agent to react with the chemicals, and other minerals in the limestone could precipitate out and cause blockages and build up sludge in the drain pipes. Many engineers are not aware that battery acid wastes, and other wastes that are primarily sulfuric acid, must be neutralized with a special random mixture of 1- to 3-inch size dolomitic limestone chips. These chips contain high percentages of calcium carbonate and magnesium carbonate (approximately 60 and 35 percent, respectively) as the effective ingredients. in many cases, the limestone chips will neutralize the waste within acceptable limits (usually to within pH values of 5 to 9). However, sometimes tanks are undersized, which means some wastes go through the system untreated. Sizing procedures Many codes and manufacturers size tanks according to the number of sinks UYGULAMA or drains located within a building. This is not always the best way to size atank. For example, ita neutralization/dilution tank is needed tor one photographic sink, a tank much larger than codes specify or most manufacturers supply may be needed. Normally, anominal 5gallon tank can be instalied tor one sink. However, tora photographic sink, the flow rate of the proccessing unit may vary, and the tank should be sized according to flow rates. Also be aware that some photo processing units are using less aggressive chemicals in the development process. Check with the photo processor manufacturer tor the chemicals used in the process. Finally, the biggest complaint about limestone chips in neutralization basins is that many maintenance departments do not check or replace the limestone. No matter what system is installed, it must be maintained. Make sure that the building owner sets up a routine maintenance schedule tor the system. lf necessary, check with the manufacturer tor recommendations. Engineers should specify posted operation and maintenance instructions on the wall near the neutralization bas in. Monitoring There is a growing demand tor waste effluent monitoring. in some cases, insurance companies want the waste monitored tor liability reasons, or the owner's environmental department could require monitoring asa company safety standard. Most of the time, a loca! authority with the environmental department or sewage treatment facility wili require the monitoring of acid wastes. There are various methods of monitoring acid wastes. These include continuous monitoring, intremittent monitoring, and monitorig using stations or manholes that allow samples to be taken from the waste stream for evalutrative authority a look at what is being discharged into the public sewer. The information gathered can allow the owner to make adjustments to the treatment process if needed. Treatment More sophisticated industrial waste treatment systems use multiple waste treatment tanks. The first tank usually has limestone chips. The second tank will have a pH probe, an agitator/mixer and an acid or caustic injection line. The agitator mixes the waste in the second tank and the pH probe takes readings to determine it the mixture is neutral ized. lf the mixture gets too alkaline, the acid injection pump adds small amounts of acid or caustic solution to the mixing tank to bring the solution closer to a neutral pH level. Sometimes athird and final tank or manhole is provided tor final sampling or pH monitoring. The material of these tanks are usually highdensity polypropylene, polypropylene, fiber-glass or ceramics. Tablc 1 - lntcnsity ofpH Valııcs pl-1 pH Vnlucs lntcııs ity Dcscription o 10 000.000 acidic (ınost e~treıne erosion ofsoıne pipe ıneterials) 1.000.000 acidic 2 100.000 acidic .) 10000 acidic 4 1.000 acidic (ınild erosion ofsome piping ınaterials noticeable) 5 100 acidic 6 10 acidic (NOTE: pH is the negative ofıhe log ıo 7 neuıral thc base 10 ofa so lutio ıı's hydrogen ion 8 10 alkaline concentration, expressed in gram 9 100 alkaline moles/liter, or-log,o(HJ! 10 1.000 alkaline (ınild dcposits ofscale can be noticed) il 10.000 alkaline 12 100.000 alkaline 13 1.000000 alkaline 14 10.000.000 alkaline (deposits ofscale most severe) 95
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