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Odour prevention

What causes odour?

Slow moving effluent, especially in long rising (pressure) mains, becomes anaerobic as the latent bacteria use up all the oxygen dissolved in the water. As a result, sewage odour is produced by sulphide-generating bacteria that thrive…

  1. On fatty compounds under anaerobic conditions;
  2. In the absence of sufficient aerobic bacteria, which outperform anaerobic strains, capable of degrading complex fatty compounds.
Formation of fat ring on pump station wet-well

Typical pump station wet-well
showing formation of fat rings on walls

Natural evolutionary processes that adapt the human body over generations have not had time to increase the production of sufficient quantities of the type of bacteria necessary to degrade complex fats found in our modern diet (e.g. 'lite' bread spreads, mayonnaises and cooking oils etc.). Click on Changes in modern effluent for a detailed explanation of this phenomenon.

In a nutshell, the combined effect of medicines, alcohol, biocides and fatty foods is responsible for the reduced population of benign bacteria passing from the human body into the sewers. It is upon the efficacy of this ‘good’ bacteria that the operation of a wastewater treatment system relies.

Common odour problems

It’s important to note that sewage flowing in a gravity line moves quite fast as a combined factor of volume flushed to degree of inclination (slope). Upon entering the wet-well of the pump station the fluid slows down and stops. This allows buoyant solids and emulsified fats to float to the surface forming a FOG (fats, oils and greases) ‘scum'.

Over time, the scum becomes increasingly thick and causes anaerobic conditions in the wet-well as the rising and falling scum layer effectively seals out air from contacting the surface; and therefore being beneficially absorbed. If untreated, this becomes a fat raft and/or ring of fat that will collect at the ‘high tide’ mark on walls and suspension gear. Sulphide-generating bacteria thrive in the putrefying FOG, generating sewer gasses that accumulate beneath the chamber covers. When a gout of waterborne waste is dumped into the wet-well, the scum is disturbed and a quantity of sewer gas escapes, forced out under pressure by the incoming liquid waste.

Being warmer than the ambient air (outside), the sewer gas escapes and – in the cooler external environment to the sewer - rapidly expands. Light breezes propel the warmer (but cooling) gas cloud laterally and the sulphide gas drops to street level where the nuisance is forcibly noticed. As an example of the pungency of this gas, a jam-jarful released in your Town Hall, would clear the room in seconds – remember those marble-sized ‘stink bombs’ from your school days?

The BIO-SYSTEMS solution

Prevention is better than cure! The equipment comprising the pump station must be well maintained and fully operational – a prerequisite to odour control.

To redress the numerical imbalance of good bacteria and the build up of odour-causing contaminants, it is necessary to introduce these organisms to the system via the process of 'bioaugmentation' – which is like introducing crack storm troopers to help a tired army. Ideally this would take place in the human body (we would all eat a pinch of a pinch per week), but this is impractical. The next best thing is to inoculate directly into the wet-well of the pump station.

BIO-SYSTEMS B220R is a microbial blend that has been specifically designed to address the problems found in pump stations in the following ways:

  1. Scum control
    B220R bacteria live in the top 300mm of effluent in the wet-well, this enables them to feed off the fats that have floated to or near the surface. Scum is controlled, being degraded from the underside, and the water surface remains clear. As a result, oxygen transfer is improved, promoting healthy aerobic conditions.
  2. Gas suppression
    Aerobic bacteria out-compete the anaerobic ones for the fatty substrate (food). As a result, the formation of sulphide gass is greatly reduced, ultimately to nothing.
  3. Cleansing action
    B220R has a bacterial cell count in excess of 6 billion per dry gram. These ‘bugs’ have the ability to penetrate fat slimes which they progressively degrade to harmless natural gasses (CH4, CO2) and water. In so doing, they leave surfaces free of cloying hydrocarbons that would otherwise have putrefied giving rise to odour. See How ‘bugs’ actually work for more info.
  4. Seed life
    Being living organisms (unlike commercial enzymes) the bacteria reproduce themselves approximately every 20 minutes, and will continue to do so for as long as there is food upon which they can thrive.
  5. Drought resistance
    The bacteria selected have a high resistance to desiccation (drying out). Typically, pump stations are most active from 6am–9am and again from 4:30pm–11pm with a rest period overnight. Under normal circumstances, living organisms removed from their natural aquatic environment would perish. With B220R, we have overcome that problem.
  6. Corrosion control
    Sewage is highly corrosive. B220R counters the formation of sulphide gases (by preventing the anaerobic conditions under which they are produced) thereby preventing the formation of corrosive sulphuric acid. Left untreated over time, sulphuric acid build-up will lead to structural damage of metal, masonry and electrical switchgear, causing expensive failures.
  7. Pumping cycle and rising (pressure) main
    Although B220R lives in the top 300mm of the wet-well, sub-surface disturbance in the last half of the pump-down cycle permits the 'bleeding' of a small percentage of the biomass into the pump and rising main when the unit draws down. By degrading FOG on the pump impeller/s and chambers during the rest period, B220R purges the internal walls of the casing and rising main, which in turn allows the pump to perform at its peak.
  8. Effluent quality
    B220R microbes remain active for as long as there is FOG upon which they can thrive. Biocides and weakening factors will slowly reduce the population, which is why their numbers need to be replenished by regular maintenance dosing. This need is normally indicated either by scum formation, odour, or both. Should the ingress of fats cease, the established B220R biomass will recess and form spores awaiting better times – a surfeit of fats – ahead. 

Before using B220R  Before using B220R

After using B220R  After using B220R

Financial implications

Bioaugmentation treatment with B220R overcomes problems in pump stations in various ways:

  1. COD removal

    This is the pre-treatment of high organic loadings (from restaurant grease traps, for example) and has the following effects...
    a. Control of fats, greases and slimes on pipe walls and especially at junctions;
    b. By removing COD the substrate for latent anaerobic bacteria is reduced, thus reducing the prevalence of sulphide     odours;
    c. By preventing the generation of sulphide odours, the consequent formation of corrosive agents (sulphuric acid) is     inhibited;
    d. The organic load on the ultimate destination (Wastewater Treatment Works) is reduced.

  2. Reduction of organic load down-line
    Apart from the above reasons, any reduction in COD reduces the health risks in the event of accidental spillage or electrical and/or mechanical malfunction (which can lead to spillage). The next pump station down-line will receive a better quality effluent and the gravity lines will be cleaner, reducing the opportunity for alien solids to ‘snag’ in the fatty deposits and form potential blockage nodes.

  3. Control of odour
    B220R will control odour in wet-wells within 12 hours. Within 48 hours the odour will generally be gone, unless there is an incoming main that has an odour problem up-line. It is standard practice to treat the preceding pump station wet-well where there may not be an odour problem. However, as is generally the case, the odour may be being generated in the rising main and gravity line between this and the pump station where the odour is apparent.

  4. Reduction of corrosion
    This is directly related to anaerobic conditions, which lead to sulphide (sewer odour) generation and the ultimate formation of sulphurous acids that cause corrosion. Although not immediately apparent, insidious damage is done over extended time to metal fittings (look at the underside of most inspection man-hole covers), catwalks, landings and stages, concrete and masonry. Severe corrosion can occur on electrical switch gear where panels are housed in the same building structure (usually above the wet-well). This can lead to malfunctions and prove very expensive after a short time.

  5. Reduction in maintenance
    Pre-treatment of COD will reduce and/or prevent the formation of ‘fat rafts’, which take time to manually break up, remove, transport and dispose. Fat rafts hinder (by coagulating together) the removal of ‘rags’ and the growing quantities of plastic refuse, which under untreated circumstances come out as greasy, slimy rubbish that is noxious and needs to be sanitized and handled carefully. A pump station treated with B220R is much quicker to service and clean than one that hasn’t been treated with B220R.

  6. Reduction in capex
    It follows that the routine replacement of (ferrous) fittings etc. will be much extended.

  7. Labour considerations
    Working conditions within the confined space of the pump station wet-well will be greatly improved due to resultant cleanliness and lack of odour (toxic fumes) created as a result of the B220R treatment. Read more on Confined spaces.

    Click on the BIO-SYSTEMS Product table for a complete list of products. Also see our Odour prevention case histories.

    Go to Effluent streams, Grease traps and interceptors, Oil spills, Drain dos and don’ts, and Industrial catering effluent for more on the industrial effluent disposal system.

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