Removal of nutrients from hydroponic greenhouse effluent by alkali precipitation and algae cultivation method

Abstract

BACKGROUND: Hydroponic greenhouse effluent has high concentrations of total phosphorus (30–100 mg PO4‐P L−1) and nitrates (200–300 mg NO3‐N L−1). 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 µg mg−1 (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. © 2012 Society of Chemical Industry

Removal of phosphate from greenhouse wastewater using hydrated lime

“…These concentrations were chosen to represent the common P concentration range in greenhouse wastewater, as reported in the literature. [4,9,10,20,21] The solutions also contained all required plant micro and macro nutrients ( Table 2) at concentrations representing the typical greenhouse vegetable feeding nutrient solution. Solutions were made by dissolving KH 2 PO 4 (for P) and Plantex® 14-0-14 Cal Mag Fertilizer (for other nutrients; Plant Products Co. Ltd., Brampton, Ontario, Canada) in deionized water.…”

“…[4,[9][10][11]21] Three Erlenmeyer flasks were filled with 1 L of solution and 280 mg of lime was added to each, to give three replicates. This was the minimum amount of lime required to obtain PRE of 95%, as determined by Equation (1).…”

“…[20] P precipitation from greenhouse wastewater has been investigated using NaOH addition to raise pH with no supplementary Ca addition. [11,21] However, NaOH is expensive and fluctuating Ca and P concentrations throughout the year may affect PRE. [16] Hydrated lime (Ca(OH) 2 , or a combination of Ca(OH) 2 and Mg(OH) 2 ) is < 1/3 the price of NaOH, [22] would allow for simultaneous pH increase and calcium addition, and has been shown to be effective for P precipitation from other wastewaters.…”

“…[16,[24][25][26] P precipitation would ideally be implemented in conjunction with a constructed wetland to provide total nutrient contaminant removal, so the contribution of the P precipitation process to removal of other nutrient contaminants such as Mg 2+ , NH + 4 , and micronutrients is of interest. [11,21] This paper is aimed at determining lime addition and pH requirements for a lime-based P-precipitation reactor treating greenhouse wastewater of varying [P] using batch experiments. For situations diverging from those investigated in batch experiments, the potential to use chemical equilibrium modelling to predict the effects of changes in various lime-wastewater system parameters on PRE was evaluated.…”

Mixotrophic Algae Cultivation for Energy Production and Other Applications

“…While the claims may be exaggerated and even though many scale-up and commercialization strategies are unproven or unrealized, the production of bio-fuels from microalgae does seem to offer a potentially attractive alternative. The study of microalgae systems for energy production possibly began in 1955, when the production of methane from microalgae biomass was proposed by Meier (DOE 2010;Saxena and Bassi 2012). Since that time, especially in last decade, intensive research has been carried out on microalgae cultivation and down streaming processing.…”