ABSTRACT
Nutrient recovery from wastewater treatment plants (WWTPs) for hydroponic cultivation holds promise for closing the nutrient loop and meeting rising food demands. However, most studies focus on solid products for soil-based agriculture, thus raising questions about their suitability for hydroponics. In this study, we address these questions by performing the first in-depth assessment of the extent to which state-of-the-art nutrient recovery processes can generate useful products for hydroponic application. Our results indicate that less than 11.5% of the required nutrients for crops grown hydroponically can currently be recovered. Potassium nitrate (KNO3), calcium nitrate (Ca(NO3)2), and magnesium sulfate (MgSO4), constituting over 75% of the total nutrient demand for hydroponics, cannot be recovered in appropriate form due to their high solubility, hindering their separated recovery from wastewater. To overcome this challenge, we outline a novel nutrient recovery approach that emphasizes the generation of multi-nutrient concentrates specifically designed to meet the requirements of hydroponic cultivation. Based on a theoretical assessment of nutrient and contaminant flows in a typical municipal WWTP, utilizing a steady-state model, we estimated that this novel approach could potentially supply up to 56% of the nutrient requirements of hydroponic systems. Finally, we outline fundamental design requirements for nutrient recovery systems based on this new approach. Achieving these nutrient recovery potentials could be technically feasible through a combination of activated sludge processes for nitrification, membrane-based desalination processes, and selective removal of interfering NaCl. However, given the limited investigation into such treatment trains, further research is essential to explore viable system designs for effective nutrient recovery for hydroponics.
Subject(s)
Wastewater , Water Purification , Hydroponics , Fertilizers , Nutrients , Water Purification/methodsABSTRACT
RESUMO Grande parte do lodo gerado em estações de tratamento de água (ETAs) no Brasil ainda é disposta em rios ou em aterros sanitários. Contudo, principalmente em grandes centros urbanos, legislações ambientais restritivas e custos logísticos crescentes têm levantado interesse em usos benéficos para esse resíduo. Para uma avaliação dos possíveis usos, além do conhecimento das características qualitativas do lodo, operadores e projetistas de ETAs devem ser capazes de prever, com algum grau de confiabilidade, sua massa e volume. Os objetivos deste trabalho são: comparar o desempenho de dois dos principais métodos quantitativos de estimativa de produção de lodo - o método de fórmulas empíricas e o de balanço de massa; investigar a prática disseminada de se estimar a concentração de sólidos em suspensão totais na água bruta por meio de modelos de regressão linear com a turbidez como variável independente e delinear condições para a aplicação dessa correlação.
ABSTRACT Most of the water treatment plant (WTP) residuals generated in Brazil are still discharged into water bodies, or disposed in landfills. However, especially in large urban areas, ever-stringent environmental legislation and rising logistical costs have put focus into beneficial uses for those residuals. To evaluate the possible beneficial uses, beyond the knowledge of qualitative characteristics of the residuals, operators and designers should be able to predict, with some degree of certainty, its mass and volume. The objectives of this work are: to compare the performance of two of the main quantitative estimation methods for residuals production - the empirical formulas and the mass balance; to investigate the widespread practice of estimating the concentration of total suspended solids using turbidity as a surrogate; and to identify the conditions under which such procedure is acceptable.
