Integrated approach for wastewater remediation and biofertilizer development using Chlorella vulgaris in raceway ponds

Abstract

Wastewater is quite complex and requires a series of different processes for its treatment. Vermifilters are one such strategy that significantly reduces pollutants but with limited ability to remove phosphorus and nitrogen. To address this, the effluent from the vermifilters can be further processed by microalgae, which can enhance water quality. In this study, microalgae were cultivated in an outdoor raceway pond, using treated wastewater as medium, and the resulting biomass was used as a biofertilizer for Cherry tomato (Solanum lycopersicum var. cerasiforme) cultivation. The microalgae treatment led to significant reductions of 78 % in COD, 86 % in phosphorus, and 45 % in nitrogen (p < 0.05). A microalgae concentration of 1.45 g/L was achieved, with a productivity rate of 0.43 g/L/day. The microalgae biomass contained 56.17 % protein, 30.73 % carbohydrates, and 18 % lipids. After 90 days of growth, cherry tomato plants fertilized with the microalgae-based biofertilizer produced a total weight of 622.4 g, compared to 756.5 g with chemical NPK fertilizer (20-20-20) and 285.4 g with no fertilizer (the control). In terms of other growth metrics such as average height, dry biomass, and number of leaves; the plants treated with commercial fertilizer reached the best results, following by the microalgae biofertilizer and finally, the control showed the least growth. These results suggest that microalgae-based biofertilizer can be a promising alternative, particularly for sandy loam soils, which are usually employed for tomato cultivation.