Determination of purification ratio of Lake Maninjau in epilimnion zone

This study aims to determine the purification ratio (reaeration and deoxygenation ratio) in the epilimnion layer of Lake Maninjau. The parameters studied were BOD, COD, and environmental parameters such as temperature, pH, DO, wind speed and water velocity. Sampling was taken at three sampling station at east- and west side of the lake at 0, 2, 4, 6 m depth, and at 10 m depth of the center of the lake in the rain and not rain condition. The water quality of Lake Maninjau showed that the organics parameters had exceeded the quality standard. The organic substances measured as BOD ranged in average 12 mg/L and COD ranged in average 193 mg/L in rain conditions, whereas under dry conditions the BOD were higher i.e. in range of 22 mg/L and COD 218 mg/L. The deoxygenation rate (K1) during rain and dry were ranged in 0.047-0.371/day and 0.038-0.967/day respectively, whereas the reaeration rate (K2) of those were in the range of 0.117-0.647/day and 0.161-0.691/day respectively. The overall value of the purification ratio (K2/K1) of Lake Maninjau was in the range of 1.282-5.048 in rain condition and 1.107-7.230 in dry condition. It indicated, that Lake Maninjau in the epilimnion zone still has self-purification ability to assimilate the organic pollutants.