Abstract:
The literature relating to nitrification in wastewater treatment and bioaugmentation
as a method to enhance wastewater treatment processes is reviewed.
The use of a commercially available bioaugmentation product (based on a
Nitrosomonas culture), which claimed to enhance nitrification in biological
wastewater treatment was investigated.The product was tested in full scale trials,
in shake flask experiments and its efficacy modelled using a simple activated
sludge simulation.
At full scale trickling filter plants a bioaugmentation product designed to enhance
BOO removal was also tested. This product increased BOO removal by up to 7%
in the recovery period following low temperature. The Nitrosomonas culture
improved percentage ammonia removal by nearly 10% in trickling filters even at
low temperatures of 6.5°C. A maximum improvement of 20% occurred at one
trickling filter site at higher temperatures.
At activated sludge sites the Njtrosomonas culture improved the nitrifying ability of
the activated sludge, as assessed by the laboratory standard method, and at one
site noticeably improved percentage ammonia removal during periods of high
dosing. At one site the maximum improvement was an increase of 22% in
percentage ammonia removal during high dosing. However the operational
parameters, loads, hydraulic retention time, mixed liquor suspended solids,
sludge age and temperature had a great effect on nitrification. If better process
control was applied at one of the works the plant would have had little trouble
nitrifying i.e. lower loads, higher HRT, MLSS and sludge age during low
temperatures. Sludge wastage regimes contributed greatly to the failure to nitrify.
It was found that the activity of the Nitrosomonas culture increased with
temperature and acclimatisation and decreased on inoculation into activated
sludge. The product facilitated nitrification when inoculated into non-nitrifying
activated sludge. Ammonia removal increased with size of inoculum.
The simple dynamic model described showed the development of a
Njtrosomonas population from inoculation with the Nitrosomonas culture. The
model showed that the effectiveness of a bioaugmentation product in activated
sludge would depend on the amount of nitrifiers returned to the aeration basin
more than other operational factors. The model predicted full nitrification at one of
the full scale sites within three days.
Bioaugmentation did enhance nitrification at full scale works. However, dosage
rates required for improvement meant that conventional methods such as better
process control or retrofitting would be economically more feasible.