BACKGROUND: Hydroponic greenhouse effluent has high concentrations of total phosphorus (30100 mg PO4-P L1) and nitrates (200300 mg NO3-N L1). Current technologies for effluent treatment have limitations of performance and high maintenance costs. The goals of this study were to investigate strategies which combine alkali treatment and microalgae cultivation for removal of nutrients from hydroponic greenhouse effluent. RESULTS: Treatment with strong alkali was found to effectively remove 97% of total phophorous especially in the form of phosphate, without affecting the nitrate ion concentration in the greenhouse effluent. After alkali treatment, marine algae Dunaliella salina (UTEX 1644) cultivation on treated hydroponic effluent (pH 7.5) showed > 80% decrease in nitrate content in the effluent within 4 days of cultivation. In the same period, the carotene content of the micro-algal system was in the range 0.5 +/- 0.02 mu g mg1 (dry cell weight) which was 1.5 times higher than in the control. CONCLUSION: This study demonstrated that combination of a conventional alkali precipitation method with a microalgae treatment system is a highly efficient approach for the removal of excess nutrients from hydroponic greenhouse effluent in a short treatment time. The microalgae can provide a source of value in the form of carotene. (c) 2012 Society of Chemical Industry