| Abstract | The concentration of Ammonium-nitrogen (NH4 T -N) in some groundwater is very
high. The presence of it causes human health effects, corrosion of pipelines and problem in
disinfection by chlorine, hence removal of NH"+ -N from water is essential. Some times the
source of water supply to a particular city or town is both, groundwater and surface water. In
this research it has been assumed the similar situation where groundwater contains high NH4 + -
N and surface water contains negligible amount of NH4 + -N and it has been tried to see how
the percentage removal efficiency is like when both sources are mixed together in different
proportions. Out of various existing treatment facilities for NH4 + -N, biological treatment
process with formation of biofilm, was chosen for this research.
Although the title does not mention any thing about the situation in Kathmandu
valley, some data about the problem of main contaminants like ammonia-nitrogen and iron in
groundwater and the performance of existing treatment plants etc. are tried to explain briefly.
The experimental research of this thesis has been divided into two parts. In the first part, the
specific growth rate of microorganisms in case of mixed condition was foundout. Five batch
reactors containing surface water to groundwater ratios (P:G) of 10:90, 20:80, 30:70, 40:60
and 50:50 was conducted for the experiment and the reactor containing 50:50 proportion
gave the maximum value of specific growth rate (0.37/wk). This proportion has been
recommended to be the most applicable in the removal of NH/-N in mixed condition
biologically.
In the second part, the removal of NH4 • -N from groundwater in a mixed condition
with surface water was carried out with different operating conditions totaling 8 runs. Two
types of reactors, vertical column type and plug flow type with two types of media, pumice
stone and synthetic fiber respectively were chosen for the experiment. In run 1 to run 4,
concentration of NH/ -N was fixed to 3mg/I, P:G ratio 10:90 and flow varied from
45m3
/m2
.day to 350m3
/m2
.day. In all four runs, the percentage removal was found more than
99% in both type of reactors. In run 5, the concentration of NH/ -N doubled to 6mg/l, flow
changed to 240m3
/m2
, P:G ratio same 10:90, the maximum removal of 95% was obtained. In
run 6, the NH/-N concentration and flow rate was kept same as run 5 and P:G ratio changed
to 30:70, the% removal of more than 99% was obtained. In run 7, with all conditions same as
run 6, P:G ratio was changed to 50:50, the removal rate of more than 99% and faster steady
state condition was obtained. The nutrient like NaH2P04 and Na2HP04 was supplied at the
rate of 2mg/l in run 1 to run 7. However, in run 8, with all conditions same as run 7, the
experiment was tried without nutrient, still the removal rate was more than 99% in both type
of reactors.
With the performance during run I to run 8, it can be concluded that pumice stone is
better than synthetic fiber as media in the removal of NH/-N. It could remove 99.44% of
3mg/l ofNH4 + _N with flow rate of 350m3
/m2 in a contact time of only 2.66min. In conclusion,
it can be said that biological treatment process is the best fitted for removal of NH4 + -N
concentration not exceeding 6mg/I in water. |