Scale problems

 
WC's, and more importantly urinals, can be particularly prone to the build up of scale deposits on the bowl surfaces, around the rim, and in pipe work. These deposits can be unsightly and can lead to an accumulation of bacteria, and can potentially lead to pipe blockages and flooding in the washroom.

What is scale?

There are two types of scale that can form in the washroom and these are commonly termed "hard" and "soft" scale.
Hard scale is lime scale - calcium carbonate, or chalk - identical to that, which can accumulate, in domestic kettles, central heating systems, and washing machines. Hard scale deposits in urinals are generally a solid porous layer, which is extremely hard.
Soft scale is very different, being a softer deposit consisting of uric acid salts and phosphates, mainly calcium phosphate.
Untreated urinals can often have a combination of both types of scale, the exact composition of which will vary with the mineral content of the flush water, flush frequency and volume, and the frequency and volume of usage of the urinals.

How Does Scale Form?
Soft Scale
Forms as a result of the deposition of nitrogenous compounds in urine. Human urine contains uric acid and other nitrogenous waste compounds, which are only sparingly soluble at low concentrations. Therefore as urine passes through a urinal and evaporation occurs, these uric compounds rapidly come out of solution and accumulate on surfaces and in traps and pipe work.

Bacteria in the urinal can then begin to digest these nitrogenous compounds, releasing by products including ammonia - with its characteristic malodour - and other waste compounds, which can reduce the acidity of the urine/water mixture.
Hard Scale
The deposition of lime scale is directly related to the mineral content of the water (water hardness) and this will vary geographically according to the geology of the area from which the water is sourced. As a rule, water which has come from a surface source such as a reservoir will be low in mineral content, whilst groundwater which has percolated through the ground, dissolving minerals en route, and then pumped up from underground aquifers will have a high mineral content.

Under normal circumstances the water contains dissolved calcium and magnesium carbonates. However certain chemical changes can lead to these carbonates becoming insoluble and forming solid lime scale deposits.
For example, if the acidity of the water is reduced, or if the water is heated or evaporates, scale can form - this is demonstrated where scale forms on the heating element of a kettle.
In a urinal, the flush water will mix with urine, which contains uric acid, and other dissolved nitrogenous compounds. Many of these nitrogenous compounds are only slightly soluble and rapidly form soft scale (uric acid) deposits. Bacteria in the urinal digest these nitrogenous compounds and the by-products of this digestion process reduce the acidity of the water/urine mixture.
As a consequence of this drop in acidity the calcium and magnesium carbonate becomes insoluble and solid lime scale deposition is the result.

Malodour

Malodour in washrooms is generally caused either by malodours produced by the users of the washroom, or by the degradation of nitrogenous waste compounds by bacteria.
The presences of scale deposits can exacerbate malodour problems by providing a porous substrate, which is ideal for the proliferation of bacteria. A porous layer of scale on an enamel bowl surface allows millions of bacteria to live in a protected environment, breaking down the components of urine and releasing ammonia and ammonia-related compounds which give characteristic malodours.

Blockages
A more serious and costly consequence of scale accumulation in urinals is blockages. Scale accumulation in the waste outlet pipes of urinals can be so severe that it can reduce the internal diameter of the pipe to virtually nothing, obstructing the flow of urine and flush water. This will result in the 'backing-up' of water and urine in the urinal bowl and can lead to flooding in the washroom.
Therefore an effective method of scale removal is required. Many mechanical methods of scale removal are available involving a rotating flexible bore, which is inserted down the waste pipe, or high pressure jets to loosen and remove the blockages. However these methods are costly, require specialist equipment and training, and are extremely disruptive to washroom users.
Alternative methods involve the prevention of the scale deposition rather than its removal. Various chemical treatments are available on the market, ranging in sophistication from simple channel-blocks which are thrown into urinals and slowly dissolve, having limited effect, through to automatic dispensing systems such as the Auto Sanitizer system which can detect when each flush occurs and dose a chemical treatment accordingly.
Systems such as this vary in the exact way in which they attempt to control scale deposition. Some simply contain a dilute acid, which can, under certain circumstances, inhibit scale deposition by maintaining acidic conditions and keeping the calcium and magnesium soluble. Others - like the Healthguard system - utilise sequestrates which will actively attach to the dissolved calcium and magnesium preventing them from depositing as scale.