d) Nutrients
Nutrients, especially nitrogen and phosphorus, have been recognized as the pollutants
that contribute to algal bloom or eutrophication in
lakes and slowly flowing water. The Effluent
Standards of Thailand specified nitrogen as TKN
should be less than 35 mg/l in effluent. Even though
nitrogen was found to be at low concentration, a
problem with high amount of algae in the effluent
of the Hat Yai Municipality Central Wastewater
Treatment Plant has occurred. As seen in Table 2
and Figure 5, nitrogen removal efficiency among
lotus, hydrilla and control units was not different
and ranged from 49 to 63 percent. Aquatic plants,
themselves, can assimilate nitrogen for their
growth and provide a good habitat for bacteria to
enhance nitrification and denitrification which
should result in higher nitrogen removal efficiency
than in the control unit. In contrast, the decay of
plant biomass could reduce this removal efficiency.
For phosphorus removal, the lotus unit showed
higher efficiency than hydrilla and control units,
respectively in RUN No.1 but there was no
difference in RUN No.2. Phosphorus removal
mechanisms are plant uptake, and chemical adsorption and precipitation in the soil (Crites and
Tchobanoglous, 1998). In general, chemical