In addition, silver ions form salts with chloride, bromide and, in particular, sulphide ions which are very difficult to dissolve. This chemical compound has considerably less toxic properties than the free silver ion. The silver is present in the rinsing water is in the form of a thiosulphate complex. However, given that adequate precautions and sensible processing conditions prevail, the chance that silver will cause problems in the wastewater is small. Therefore when processing NDT film attention must be paid in particular to the recovery of silver.Īs Ag+-ion, it is toxic for most micro organisms and fish. TOXIC COMPONENTS that are present in photographic processing include METALS, being various metal ions in fairly small concentrations, but because of the risk of disturbing the biological balance in biochemical treatment units, they may not be discharged in too high a concentration into sewers connected to a water treatment plant. Nutrients which are not toxic and which do not use up oxygen but which upset the biological balance in the water.With too high concentration of these substances an oxygen deficiency occurs, an indirect result of which all life becomes impossible. The biochemically oxidisable substances which are broken down by organisms, a process which, however uses oxygen.the toxic substances, which directly kill the living organisms in water.However CHEMICAL POLLUTION FACTORS do come into play and the three important classes of pollutants should be distinguished between OILS, FATS and INFLAMMABLE products may not be present in wastewater but as it is in a diluted form and neither explosive or flammable where NDT is concerned we need not take any action. I will elaborate on this aspect later in the presentation. It is easy to check and although the pH VALUE of individual baths can deviate from the regulations (between 6 and 9), the pH value will almost always lie within the limits with a normal combined discharge from a processor as a result of mutual neutralisation of the various baths. The acidity of the discharged water however is an important parameter which may affect us. MECHANICAL POLLUTION FACTORS are affected by various legislations which impose restrictions concerning the amount of solid components that may be suspended in waste water but NDT waste contains only a negligible amount of solids so we can almost completely disregard this factor. However, the temperature of NDT waste water does not normally exceed 35oC, nor is abnormal hindrance to be expected from the smell or colour of the water. In addition to the colour, smell and lack of clarity of wastewater, the temperature is penalised in particular. But this is no reason to be complacent when PHYSICAL POLLUTION FACTORS are present in our everyday work activities. It is important to note that whilst we should be aware of responsible waste disposal, NDT is regarded as only a very small polluter in the overall scheme of things. Urban sewers often depend on the type and capacity of the municipal treatment plant, if you have the luxury of working in this type of civilised environment compared to that of a pipeline in remote circumstances or even offshore. Generally speaking the regulations for urban sewers are usually less stringent than those for surface or ground water. Depending on the outlets into which the wastewater is drained, we encounter various regulations. With NDT film processing, we can more or less exclude air pollution and ground pollution by solids and concern ourselves only with water pollution. They have to ensure that the load on the environment is minimised at the source, and that their products or packaging can either be recycled after use or be destroyed without any further burden on the environment.ĭuring this presentation I will attempt to address issues directly affecting NDT in terms of film and chemistry technologies and these will include īroadly speaking, legislation relating to environmental pollution can be divided into three areas Government, industrial companies and private citizens are daily confronted with the many aspects of this complex problem. Care for the environment is one of the greatest concerns of our modern society.
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