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Artificial wetland, representing an important natural
process, has been used successfully in treating wastewater with
low concentrations of organic matters. This study, however, is
intended to evaluate the treatment capability of such a system
under conditions of high organic and nutrient loads. Two types
of wetland, i.e., subsurface flow and free surface systems were
constructed in field and in laboratory scales. With hydraulic
retention time (HRT) as a master process parameter, these
constructed wetla In the field-scale experiment with
subsurface flow wetland, three HRTs of 4.3, 8.5 , and 14.7 days
have been performed. The results showed that treatment
efficiencies of COD, BOD5, and SS were above 70%; except for
COD, two other parameters were able to meet the discharge
standard of the year 1998 . Removal mechanisms for those
pollutants primarily consisted of sedimentation, filtration ,
adsorption, and microbial oxidation. Indicated by the DO and
ORP, the wetland was in anaerobic conditions, which ren of 14.1
and 66.5 days were conducted for free surface wetlands. Results
showed that effluent quality was poorer than that in subsurface
system. From lab-scale wetland experiments, results indicated
that water hyacinth has better capability of transporting oxygen
and uptaking nutrients than brachiaria mutica . However, such
superiority was not obvious while the wetlands were subjected to
high loads such as swine wastewater. In conclusion, when
the wetlands are under heavy loads of organics and nutrients,
physical separations would be the most important mechanism for
removing pollutants, microbial metabolisms the next and plants
the least. Since rate of solids accumulation exceeds that of
solids hydrolysis, the wetlands should be cleaned once for about
4 to 5 years. As far as microbial metabolisms are concerned,
methanogenisis of organics is predominated while ammonia
nitrification has been inhibited on account of deficien
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