Synergistic Effects of Micro-electrolysis-Photocatalysis on Water Treatment and Fish Performance in Saline Recirculating Aquaculture System

Zhangying Ye,Weishan Gao,Songming Zhu,Shuo Wang,Mingwei Shen,Luowei Pei,Haijun Li

doi:10.1038/srep45066

Zhangying Ye, Weishan Gao + Show 5 more

Open Access

https://doi.org/10.1038/srep45066

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Abstract

A new physico-chemical process for TAN (total ammonia nitrogen) removal and disinfection is introduced in saline recirculating aquaculture system (RAS), in which the biofilter is replaced with an integrated electrolysis cell and an activated carbon filter. The electrolysis cell which is based on micro current electrolysis combined with UV-light was self-designed. After the fundamental research, a small pilot scale RAS was operated for 30 days to verify the technical feasibility. The system was stocked by 42 GIFT tilapia (Oreochromis niloticus) fish with the rearing density of 13 kg/m3. During the experiments, the TAN concentration remained below 1.0 mg/L. The nitrite concentration was lower than 0.2 mg/L and the nitrate concentration had increased continuously to 12.79 mg/L at the end. Furthermore, the concentration of residual chlorine in culture ponds remained below 0.3 mg/L, ORP maintained slight fluctuations in the range of 190~240 mV, and pH of the water showed the downtrend. Tilapia weight increased constantly to 339.3 ± 10 g. For disinfection, the active chlorine generated by electrochemical treatment caused Escherichia coli inactivation. Enzyme activity assay indicated that the activity of glutamate dehydrogenase, carbonic anhydrase and glutamic pyruvic transaminase increased within the normal range. The preliminary feasibility was verified by using this physico-chemical technology in the RAS.

Highlights

In recirculating aquaculture system(RAS), the metabolites, food remnants, biological body and other proteins of cultured species can not be decomposed in time, leading to a rising ammonia, nitrite nitrogen and other harmful substances in water bodies, which will pollute the water environment and produce toxic effects on cultured species, causing a large number of animal death[1,2,3]
This study addresses the effect of electrochemical oxidation technology combined with low-power and low-pressure mercury lamp for treating low concentration of ammonia in aquaculture water, so as to explore cooperative technology between micro electrolysis and UV-light for practical aquaculture water treatment
When the effluent of electrolysis cell flowed into buffer pool, due to the mixture of two parts pH remained at around 7.15

Summary

Introduction

In recirculating aquaculture system(RAS), the metabolites, food remnants, biological body and other proteins of cultured species can not be decomposed in time, leading to a rising ammonia, nitrite nitrogen and other harmful substances in water bodies, which will pollute the water environment and produce toxic effects on cultured species, causing a large number of animal death[1,2,3]. In this regard, during the process of industrial aquaculture, the traditional way of water treatment is the application of biological purification technology. The overall electrochemical reaction of ammonia to nitrogen is generally considered to be a three-electron exchange reaction (Equation (1))[18,19,20]: NH3

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