Articles & Case Studies


Posted: Monday 7th September 2009

The Client and Background

Rural Sewage Treatment Works inNorth Yorkshire

The sewage treatment plant was designed to treat standard municipal effluent to a discharge quality of 30, 60, 10 ppm biological oxygen demand (BOD), suspended solids and ammonia respectively. However following installation, the plant rarely achieved its consented treated effluent quality, particularly in relation to ammonia.

At times the ammonia concentration in the treated effluent reached levels of 60 ppm (almost equivalent to the inlet concentration), indicating no significant biological ammonia removal was achieved.

From a mechanical & electrical point of view the plant was operating satisfactorily and although carbonaceous degradation processes were still operative, nitrification inhibition testing revealed an almost complete inhibition of the nitrifying biomass.

This meant the bacteria needed to remove ammonia (nitrifying bacteria) were not present in the treatment plant i.e. the resident bacterial population was not able to reduce ammonia levels appropriately and a change needed to be made.

The Solution

Nitrifiers, responsible for ammonia removal, are recognised as being very slow growing organisms. More importantly however, compared with organic degraders, nitrifiers are very sensitive to a range of growth inhibitors, which may have little if any negative impact on the more robust organic degraders.

In situations where such inhibitors are present, if they are organic in nature, by bio-augmenting the treatment plant with specifically selected bacteria designed to degrade the offending carbonaceous inhibitors, nitrification processes recover and proliferate naturally. As a result consented discharge ammonia levels would be again achieved.

The Product – The Baccelerator®.

Cleveland Biotech developed The Baccelerator in conjunction with a leading UK Water Company almost three years ago.

The mobile bioreactor works with all aerobic waste water treatment plants and is an inexpensive alternative to building a new effluent treatment plant. It can be used to resolve temporary or persistent discharge consent issues with ammonia, COD or suspended solids.

Cleveland Biotech’s microbiologists work with the plant owners to ensure the correct bacterial mix is identified and dosed for any given situation. Following this the Baccelerator operates unattended with monthly service and replenishment visits by the biotechnology company’s team of engineers.

The Baccelerator, which has won a prestigious industry award, can be adapted to break down hydrocarbons in the waste stream, can provide rapid recovery from toxic shock and also rapid start-ups for new or seasonal plants. It will also overcome and prevent the onset of filamentous growths.

The product is available for sale or hire, is easy to transport as it can be trailer mounted and is CE marked.

At this sewage treatment plant as investigations of organic inhibitors revealed the presence of oils and a number of other possible negative effectors the bacterial product chosen to grow up in the Baccelerator and bio-augment the plant with was a mixture of a standard organic degrader plus a petroleum-type hydrocarbon degrader.

The Biological Solution Process

When bio-augmenting a biological treatment plant with specifically tailored bacteria it is important to maximise the effect from the smallest quantity of base bacteria in order make the process of bio augmentation viable on cost grounds.

In the past Cleveland Biotech has achieved this by growing up bacteria prior to use in its Mark I Activation unit. Although this amplifies the bacteria prior to addition it relies on BATCH CULUTRE and therefore is subject to the non-bacterial yielding lag phase, the time it takes for the bacteria to germinate and start to grow and also the daily inconvenience of operator involvement to empty the bacterial inoculum into the plant. These factors restrict the amount of bacteria that can be produced in any 24hr period. Due to the fact a synthetic substrate is used (not the effluent stream in question) the bacteria, once they are produced, are not acclimatised to the effluent and on application to the treatment plant there is a further lag in their growth.

As described above in batch culture the growth conditions undergo continual changes; the bacterial concentration rises as the substrate concentration diminishes. For many applications however it is desirable to grow the bacteria over extended periods during which the substrate concentration and other conditions remain constant and the cells grow at a constant, fully acclimatised XXXXXXXXXX rate on the effluent in question.

Such a situation can be achieved by frequent transfer of the growing bacteria from a base inoculum to a fresh growth medium. In practice this is achieved by constant addition of fresh effluent to the growing bacteria and concomitant withdrawal of equal volumes of the growing bacterial culture. This type of bacterial growth is referred to as CONTINUOUS CULTURE.

Under such growth conditions the rate of bacterial growth (or doubling of bacterial numbers) increases in direct proportion to the rate at which fresh nutrient (effluent) is added to the system. At the same time the yield of bacteria in unit time increases similarly up to the maximum growth rate of the bacteria.

Thus in continuous culture, a bacterial species with a doubling time of two hours, if fed with a complete volume change of fresh effluent (nutrients) every two hours, will produce 12 times the amount of maximally growing bacteria compared with a similar batch growth system over the same period of time.

The Mark II Activation Unit was developed to exploit the latter type of microbial growth. By the automatic daily addition of site specifically selected bacteria, into the aerated growth chamber containing continuously fed influent waste water and a special biological accelerant, large, daily quantities of highly active, fully-acclimatised bacteria are produced and fed continuously into the inlet feed to the plant.

The effect of this continuous feed of bacteria is to boost the resident microbial activity of the effluent treatment plant and / or overcome any transient biological shocks, which may have impeded the natural microbial degradation processes within the plant.


The graph of Water Authority data from the bio-augmented plant showed the Baccelerator was installed on the 15th of the month at which time the treated chemical oxygen demand and ammonia levels recorded were 1200 and 40 ppm respectively. After one day of batch growth, the Baccelerator was switched to continuous feed mode, delivering 6000L/d of actively growing, fully acclimatised, specifically tailored bacteria.

After 48 hours a dramatic reduction in both COD and ammonia levels was measured in the treated effluent. After 10 days this had fallen to less than 100 and 2.0 ppm respectively. At this point the effluent treatment plant was within consent for all parameters for the first time in 15 months.

By day 18 the ammonia level in the treated effluent had fallen to less than one ppm.

On the 7th of the following month, the Baccelerator was switched off to allow assessment to place to test the impact on the plant if a cessation of bio-augmentation took place. Seven days after this event, the ammonia level rapidly increased, once again taking the treatment plant out of Consent.

This demonstrated the consistent need of the Baccelerator unit to enhance organic degradation leading to a re-instatement of nitrification at a biologically compromised treatment plant.

Shortly afterward this, at the request of the Water Company, the Baccelerator unit was re-commissioned and was an integral part of the effluent treatment plant for a further 12 months until it was fully up-graded.

Dr Tony Brooke is the Development Director at Cleveland Biotech, one of Europe’s leaders in environmental biotechnology, which specialises in providing innovative natural solutions to the growing problems of pollution and those arising from the discharge of effluents and wastes into the environment.

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August 2021

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