Key Parameters for Purification of Pickled Mustard Wastewater with a Domestic Microbial Community Containing the Diatom <i>Halamphora coffeaeformis</i>

Abstract

The utilization of nutrients in pickled mustard wastewater (PMW) was carried out with co-treatment of bacteria and microalgae system. The orthogonal experiment method was used to identify the best processing parameters for PMW purification. The results showed all treatments had a significant removal efficiency of total organic carbon (TOC) in PMW, with a reduction of 90% by day 6. Approximately 97% of NH4+-N was removed in treatments 1, 3, and 5, and 90% of total nitrogen (TN) was removed in treatments 3 and 5 by day 12. Overall, treatment 5 with algae of 2 mg·L−1, 12% PMW, and a nitrogen/phosphorus (N/P) ratio of 15∶1, demonstrated the highest removal rate of both NH4+-N and TN by day 12, with rates up to 15.0 mg·L−1·day−1 and 14.3 mg·L−1·day−1, respectively. About 95% of TP was reduced in treatment 3 by day 9. Furthermore, Halamphora coffeaeformis grew well in PMW with an initial density of 2 mg·L−1, and the chlorophyll a grew to 6.7 mg·L−1. The N/P ratio of 15∶1 resulted in higher reduction percentages of TN and NH4+-N in 8% PMW and more protein accumulation in the microalgae by day 6. The condition treatments 3 and 6 might be more favorable to accumulate proteins and lipids, respectively. The relative abundance of species of Marinobacter, Methylophaga, Algoriphagus, Coraliomargarita, Winogradskyella, and other advantageous bacteria increased, which promoted the utilization of nutrients. In addition, the diatom (H. coffeaeformis)-bacteria system strengthened the expression of functional genes for the carbon, nitrogen, and phosphorus metabolic pathways. The proposed procedure offers a green and sustainable method for resource utilization of high-salt PMW.