Bioremediation of Aquaculture Wastewater with Algal-Bacterial Biofilm Combined with the Production of Selenium Rich Biofertilizer

Wei Han,Xu Zhou,Yunpeng Wei,Yufeng Mao,Peng Shang

doi:10.3390/w12072071

Wei Han, Xu Zhou + Show 3 more

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https://doi.org/10.3390/w12072071

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Abstract

The discharge of aquaculture wastewater and the excessive selenium in aquaculture effluent caused by selenium addition to aquatic feed are posing a serious risk for the marine environment. In this study, batch tests were carried out to investigate the feasibility of utilizing algal–bacterial biofilm for the treatment of selenium-rich aquaculture wastewater. The effects of four different types of commercial biofilm carriers on the attached growth of biofilms and the contaminant removal capacity were examined. The braided cotton biofilm carrier had the best performance on biofilm growth, while in an exponential growth period the dry weight density of the biofilm was above 2.0 g L−1. By utilizing the braided cotton carrier with a hydraulic retention time (HRT) of 6 days, the removal rate of N and P from the raw aquaculture wastewater was 88.5 ± 6.2% and 99.8 ± 0.2%, respectively. After that, the effects of different initial wastewater load ratios (IWLR) and HRT on the effluent quality of the treatment process were studied. The decrease in IWLR and the extension of HRT could improve the treatment performance. The effluent N, P and Se concentrations in the group with 50% IWLR and 6-day HRT were 0.75 ± 0.10 mg L−1, 0.015 ± 0.02 mg L−1, 35.2 ± 3.2 μg L−1, respectively, indicating an effective removal of the main contaminants. The algal–bacterial biofilm harvested from the batch test was rich in N, P and Se, where the Se content was 21.8 ± 3.4 mg kg−1, which has the potential to be used as an Se-rich biofertilizer.

Highlights

Global aquaculture has undergone tremendous growth since the middle of the 20th century, providing approximately half of all food fish consumption, which is currently over 80 million tons [1]
The present study explores the removal of conventional contaminants, and excessive selenium from aquaculture effluent, utilizing an algal–bacterial biofilm batch reactor (ABBR) as a bioremediation strategy
The results show that the exponential growth phase of the biofilm was from Day 6 to 18, and after Day 24, the biofilm growth curve entered a stable phase

Summary

Introduction

Global aquaculture has undergone tremendous growth since the middle of the 20th century, providing approximately half of all food fish consumption, which is currently over 80 million tons [1]. China is the world’s largest producer of aquaculture products, but the enormous quantity of wastewater discharged from the intensive development of the aquaculture industry has caused severe environmental impacts [2]. The nutrient-rich effluent usually results in eutrophication events such as green tides, which could block vast areas of marine channels and cause great economic losses [3]. More than 70% of antibiotics added to aquaculture systems are released into the water and accumulate in the sediment, while the public health risk of selective pressure posed on the aquatic microbial community remains unclear [4,5]. The widespread use of copper sulfate to prevent infections and algal overgrowth in aquaculture has resulted in heavy metal accumulation in the effluent and the receiving aquatic environment [6,7].

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