The disposal of dairy
effluent in Hawaii is a current concern because of possible contamination of
ground water and coastal water. The objective of this study was to quantify the
effectiveness of MSL systems in removing nitrogen (N), phosphorus (P), and fecal
indicator organisms (Fecal coliform) from the dairy effluent and to explore
ways to increase MSL efficiency. Four MSL units were constructed in two treatments with two replications. The two
materials for the aerobic layer were commercial Perlite and Leilehua soil (Oxisol). The
anaerobic layer was based on the Honouliuli soil (Vertisol). Untreated dairy effluent was applied to the MSL
systems during a 12 month period at a rate varying from 272 to 545 L m-2 d-1.
The percentage removal of total N (TN) for the first 10 months in both systems
averaged to 47% (13-96%) whereas during the last two months, it decreased to 9%
and 21% for two-soil and soil-perlite system, respectively. This drop may due
to a pause in the effluent delivery or an inefficient denitrification process.
The percentage removal of dissolved reactive P (DRP) was greatest in the system
with Oxisol in the aerobic zone, an average of 81% (42-98%) in contrast to the
soil-perlite system, 39% (3-97%). High P adsorption capacity of the Leilehua soil
probably caused greater removal of P in the two-soil system than in the
soil-perlite system. The soil-perlite MSL was more effective in reducing fecal
coliform bacteria (63%) versus the two-soil system (58%), which may due to the
tropical soil, which are known to contain large amount of coliform bacteria. The results indicate that
MSL units can be effective in removing N, P, and fecal coliform from dairy
effluent with low cost materials while occupying a small amount of space.