Rural Treatment Works Brought Within Consent
A rural sewage treatment works is designed to treat effluent to a discharge quality of 30, 60, 10 ppm BOD, s/s and ammonia respectively. However following installation, the plant rarely achieved its consented treated effluent quality, particularly with respect 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 across the process.
From an M&E point of view the plant was operating satisfactorily.
Although carbonaceous degradation processes were still operative, nitrification inhibition testing revealed an almost complete inhibition of the nitrifying biomass.
The bacterial population responsible for ammonia removal comprises very slow growing organisms, with a low biomass yield. Most importantly however, compared with organic degraders, nitrifiers are very sensitive to a range of growth inhibitors, which 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.
Investigations of organic inhibitors feeding the treatment plant revealed the presence of oils and a number of other possible negative effectors. Consequently 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 graph of Water Authority data shows the Baccelerator was installed on the 15th of the month at which time the treated COD and ammonia levels recorded were 1200 and 40 ppm respectively. After 1 days batch growth, the Baccelerator was switched to continuous feed mode, delivering 6000L / d of actively growing, fully acclimatised, specifically tailored bacteria.
After 48h a dramatic reduction in both COD and ammonia levels was measured in the treated effluent, which after 10 days 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 for 15 months.
By day 18 the ammonia level in the treated effluent had fallen to less than 1 ppm.
On the 7th of the following month, the Baccelerator was switched off in order to assess the impact on the plant of a cessation of bio-augmentation. 7 days after this event, the ammonia level rapidly increased, once again taking the treatment plant out of Consent.
These events unequivocally demonstrate the ability of the Baccelerator unit to enhance organic degradation leading to a re-instatement of nitrification at a biologically compromised treatment plant.
Shortly afterwards, at the request of the Water Authority, the Baccelerator unit was re-commissioned and has now become an integral part of the effluent treatment plant at this location.
