Abstract
Caprolactam wastewater (WCP), which is generated during the production of caprolactam, contains high contents of NO3− and inorganic P and is considered to be difficult to treat. In this study, Arthrospira platensis was used to remove N and P from WCP. Culture conditions and wastewater addition were optimized to relieve the inhibition effects of WCP. The results show that A. platensis growth and photosynthetic activity were inhibited depending on WCP concentrations. The inhibition rates were enhanced as the culture time increased under batch mode. However, the fed-batch mode significantly minimized the negative impact on A. platensis, which is beneficial for removing N and P from WCP by Arthrospira. After 10 d of cultivation of A. platensis in a 25 L circular photobioreactor in fed-batch addition of WCP (1.25% mixed WCP (v/v) each day), the average biomass productivity reached 17.48 g/(m2·d), the maximum protein content was 69.93%, and the N and P removal ratios were 100%. The accumulation effect of WCP inhibition on algal growth was not observed under this culture condition. Fed-batch cultivation of A. platensis is a promising way for bioremediation of WCP with high N and P removal efficiencies and high value-added biomass production.
Highlights
Microalgae are photosynthetic organisms that convert C, N, P, and light energy into biomass and can be applied in biofuels, food, feed, and biofertilizer industries [1]
After 6 d of cultivation, the final biomass concentrations varied between different WCP concentrations (Figure 2B), with the highest dry weight (DW) of 2.57 g/L observed in the culture without WCP addition and the lowest DW of 1.86 g/L observed in the culture with 50% WCP addition
It is important to investigate other possible inhibitory factors to improve the performance of N and P removal from WCP by A. platensis
Summary
Microalgae are photosynthetic organisms that convert C, N, P, and light energy into biomass and can be applied in biofuels, food, feed, and biofertilizer industries [1]. The main factors limiting the commercial mass culture of microalgae are the high production costs and water resource consumption [2]. To alleviate this issue, wastewater has been considered as a medium for microalgae cultivation [3]. Caprolactam wastewater (WCP) is generated during the production of caprolactam (CPL). It is estimated that approximately 4.2 t to 4.7 t of wastewater will be generated for each ton of CPL production [9]. WCP discharge may lead to a risk of environmental pollution
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