Ammonium and phosphate ions present in wastewater sampled from the Puerto Colombia oxidation lagoon effluent were removed by immobilized microalgae Chlorella sp. The wastewater was filtered and sterilized to ensure the elimination of suspended solids and micro-organisms prior to biological post-treatment. Two different initial pH levels were tried in experiments. The biological nutrient removal at the lagoon was poor, compared to the limit of technology, i.e. 3 mg L−1 for total nitrogen and 0.1 mg L−1 for total phosphorus. After a 32 h contact period, 68% ammonium and 65% phosphate were uptaken by the immobilized biomass. Initial pH values of 6.5 or 7.5 slightly affected the biomass ability to remove these nutrients. These results indicate that immobilized microalgae can be a suitable alternative for nutrient removal.