Definitions of Waste Characteristics

Ammonia-Nitrogen

Nitrogen exists in several compounds and molecules. The main ones are ammonia, organic nitrogen, nitrite and nitrate - each representing a different stage of waste decomposition.

Nitrogen is an important element in the biological process of sewage treatment, and also has an effect on the receiving watercourse.

Within the biological process, nitrogen is essential to the growth of microorganisms involved in the decomposition of the organic matter.

Sewage normally contains an excess of both nitrogen and phosphorus.

If such an excess is discharged in the final effluent, it may act as an undesirable fertiliser and promote the growth of algae in watercourses.

Ammonia is increasingly becoming a concern to the Water Companies and the Environment Agency.

COD

Chemical oxygen demand is a measure of the oxygen that certain chemicals will take from the environment.

It requires only about two hours to complete the tests.

Microorganisms do not degrade some of the chemicals measured by this test.

The COD result is used in the Mogden formula and has major influence on the trade effluent charge: higher strength = higher charge.

Flammable or Explosive

Photographic processing chemicals are usually water-based and are not flammable or explosive.

Some film cleaners can be considered flammable.

Because these solutions evaporate as they are used, there is no waste material left which requires disposal.

Heavy Metals

Included are metals such as cadmium, chromium, cobalt, copper, gold, iron, lead, manganese, mercury, molybdenum, nickel, silver and zinc.

Heavy metals are restricted in sewer discharges since at certain concentrations, some of these metals can be highly toxic to the microorganisms in the sewage treatment plant.

Some heavy metals may pass through the plant and be toxic in the final bodies of water.

Where sludge from the plant is sent for recycling to land, heavy metals remaining in the sludge may restrict that disposal route.

Photo effluent would normally only contain silver.

Hydroquinone/Phenols

Hydroquinone is currently used in some photographic chemicals (commonly in developers for black and white and Ilfochrome processes).

Some manufacturers incorporate trace amounts of phenols into photographic film and paper, to act as a stabilising agent against the growth of microorganisms in the gelatine.

The water companies have some concern with phenols since, in high concentrations, they may inhibit the sewage treatment process.

The amount of phenols in photo effluent is very small.

The simple chemical test for phenols also detects hydroquinone (as two phenols) and hence it is difficult to distinguish between them.

Iron

Iron complexes contain iron that has bonded with another chemical, for example, iron EDTA (ethylenediamine tetraacetic acid).

EDTA is safe to handle and is used in food products such as bread and baked goods.

Iron EDTA complexes are key components of many photographic bleaches and bleach-fixes.

Iron is also contained in steel wool silver recovery cartridges and will be present in the discharge from a cartridge.

Some iron is useful at the sewage treatment works to assist in the removal of phosphorus from the effluent.

Too much iron can affect both the appearance and the taste of water.  Consequently, iron is often regulated.  These regulations do not differentiate between stable iron complexes found in photographic solution and undesirable forms.

pH

pH is a measure of the acid or alkaline nature of the effluent.

Acid solutions have a pH between 0 and 7.

Alkaline solutions have a pH between 7 and 14.

Water has a pH of 7 and is considered neutral.

Phosphorous

This is not commonly used in photographic chemical products but may be present in small quantities in some film developers.

Phosphorus, like nitrogen, is a nutrient that acts as an undesirable fertiliser. This promotes the growth of algae in receiving waters.

Silver

Silver is not a component of the processing chemicals; it comes from photographic films and papers.
In the colour process, the silver in the film and paper becomes soluble in the fixer and bleach-fixer solutions. It is removed completely by complexing with the thiosulphate found in the solutions.  The silver stays in solution in the form of silver thiosulphate. 

In the black/white process, the final image is silver, and the silver that is not used in the image area is removed in the fixer.

Photofinishers must recover silver from fixer and stabiliser/rinse in the film process and bleach-fixer and stabiliser/rinse in the paper process if these solutions are to be discharged to a sewer system.

As a non-renewable natural resource and a precious metal, silver should not be wasted.

Even with efficient silver recovery, however, small amounts of silver thiosulphate will reach the sewage treatment works.

During secondary treatment, the microorganisms convert most of the silver thiosulphate into insoluble silver sulphide, which precipitates in the sludge.

Silver sulphide is an immobile form of silver meaning that it is unlikely to be converted to another form. Thus, sludge containing silver sulphide could be used on agricultural lands with no adverse effects. In addition, when silver sulphide is present in discharges from a sewage works, to a receiving watercourse, there should be no effect on fish and aquatic life.

Silver Ion

Free silver ion (Ag+) is at least 15,000 times more toxic than silver thiosulphate and silver sulphide.

Free silver ion is the form of silver for which regulations are designed since it can readily destroy the microorganisms in the sewage treatment works and is toxic to aquatic life.

There is no analytical test procedure reliable enough to be accepted by regulators, that can differentiate free silver ion from the other less toxic forms of silver.

The accepted test measures total silver, thus grouping the harmless silver sulphide and silver thiosulphate with the free silver ion.

TDS and TSS

These stand for Total Dissolved Solids and Total Suspended Solids respectively.

Dissolved solids include salts such as sulphates, carbonates, and chlorides.

Suspended solids are undissolved matter in the effluent and used in the Mogden Formula.

Minimal levels of suspended solids would be expected in photo effluent.