Solution Carryover and Replenishment

If each of the above steps could be carried out under ideal, pristine conditions, there would be few unwanted reactions or byproducts and therefore waste would be minimal. Unfortunately, in actual practice this is not the case.

Oxygen from the air is the primary cause of unwanted reactions. It slowly oxidizes components such as the developing agent and fixer upon long-term standing or solution agitation, both of which tend to promote dissolving of air, and during attempts to reuse solutions or recover silver. As previously mentioned, this oxidation necessitates adding preservatives such as sulfite and other ingredients needed to counter the effects of oxidation. These preservatives are also eventually consumed by oxidation, thereby forming byproducts of their own.

Solution carryover is the second major cause of chemical loss, since a solution is carried on the surface and within the saturated emulsion from one tank to the next, thereby losing the solution from the first tank and contaminating the second. To protect against the undesirable effects of contamination, each succeeding solution must be chemically bolstered to contain more of the active ingredient than might be needed strictly to react with components in the film or paper, if carryover did not occur.

Squeegees are important devices for minimizing carryout on the surfaces of photographic materials, and extra washes can be important means of reducing the carry over of unwanted contaminants. However, the fact remains that some unwanted material, even if it is water, will always be trapped within an emulsion and taken into the next processing tank. In addition, small amounts of some chemicals that were originally incorporated into the film or paper, including gelatin, will leach out into the solutions during processing. As previously stated, some chemicals produce byproducts by reacting with oxygen from the air. Finally, some portion of the processing chemicals will always have reacted with the emulsion, producing reaction byproducts (e.g., halides) that are released in one processing tank or another. The total effect of releasing chemicals from all of these sources into the solutions during processing, as well as partial oxidation by air, is known as "seasoning."

Therefore, some means of replenishing the lost components and removing the unwanted components or neutralizing their effects is necessary to operate a continuous process. This means that some waste will always be generated and needs to be treated in some fashion.

6.2 PHOTOPROCESSING EFFLUENT CHARACTERISTICS 6.2.1 Introduction

The photoprocessing industry is very diverse. It includes photofinishing laboratories, x-ray processing at medical and dental facilities and industrial sites, professional photographic operations, motion picture laboratories, processing systems for scientific uses such as astronomy and geology, aerial mapmaking and satellite photography, microfilm processors, graphic arts operations, and others.

Photographic effluents vary in composition because there are many different types of photographic processes and no two processing laboratories operate in the same manner. Processing laboratories vary greatly in size, wash water usage, daily operating time, volume of effluent, and the use of chemical recovery systems.

The actual effluent characteristics [2,7-10] for any photographic processing laboratory can best be determined by collecting a representative sample of the photoprocessing wastewater and having it analyzed by a certified analytical laboratory. However, although concentrations will vary, the effluent from most photoprocessing laboratories will generally be quite similar in chemical composition.

It is not within the scope of this section to provide the actual processing effluent characteristics of every photographic process. Tables 1 through 3 represent typical effluent concentration ranges for conventional color processes, plumbingless color processes, and black and white processes. The chemical concentrations (and other environmental parameters) of plumbingless processes (i.e., systems that do not utilize a conventional wash cycle) are usually quite high, but the loading of these ingredients in pounds or kilograms per day per unit of product processed will be similar to photographic processes using a conventional wash cycle. The plumbingless process is designed for use by relatively small processing operations; consequently, the total daily loading from these operations will likewise be small.

6.2.2 Environmental Parameters

The following sections discuss parameters that might be expected to occur in typical municipal sewer codes.

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