Elsevier

Aquacultural Engineering

Volume 52, January 2013, Pages 80-86
Aquacultural Engineering

Performance of sequencing microbead biofilters in a recirculating aquaculture system

https://doi.org/10.1016/j.aquaeng.2012.10.002Get rights and content

Abstract

Biological filtration, or biofiltration, is the key technology in recirculating aquaculture systems. Sequencing microbead biofilters, in which the media maintains a continuous up-and-down movement, are based on traditional microbead filters but offer superior filtration properties. The performance characteristics of a sequencing microbead biofilter installed in a recirculating aquaculture system for rearing Barcoo perch at 29 ± 1 °C were examined. The total ammonia-nitrogen (TAN) concentrations and the nitrite-nitrogen concentrations during a 52-day culture period were maintained blow 1.6 mg/L and 0.9 mg/L. In order to ensure efficient biofiltration, the optimal actual application of hydraulic retention time was determined to be approximately 3–5 min. The water flow produced by the reciprocating motion of the media served to wash away suspended solids, ensuring the occurrence of optimal nitrification processes. Additionally, the reciprocating motion of the media enhanced ammonia treatment efficiency significantly by improving the transport of nutrients and nitrification activity. Compared to a static situation the ammonia removal rate increased by 27% based on the application of up-and-down reciprocating movement. The biofilm on the microbead forms as a compact, complex, and homogeneous structure, consisting of numerous microscopic thin sheets. Additionally, a multitude of pores, interstitial voids, and vertical channels were widely observed to convey obviously advantageous properties in support of fluid passage, thus enhancing mass transfer and ultimately contributing to biofiltration effectiveness. The optimum biofilm thickness for providing efficient biofiltration was determined to be approximately 70 μm for this filter.

Highlights

► A new kind of self-clean biofilter was proposed, which can be used for RAS. ► The TAN removal rate of the biofilter was about 600 g/(m3 day). ► The movement of the media could increase the treatment efficiency significantly. ► IThe biofilter can be working under high TSS concentration properly.

Introduction

Recirculating aquaculture systems (RAS) are focused on treatment of nitrogenous wastes, optimization of oxygenation, removal of suspended solids, and control of organic compound accumulation (Brian, 2006). A biological filter is the key technology in the RAS system. Ammonia accumulation in RAS systems is controlled through water exchange and biofilters (Brian, 2006). The system is dependent upon efficient biofilters (nitrifying bacteria) capable of oxidizing the toxic ammonia produced by aquatic organisms into nitrates, which is relatively non-toxic. Microbead biofilters employ a combination of trickling and granular biological filters. Microbead filters use an expanded polystyrene bead that ranges in diameter from 1.0 to 3.0 mm. These biofilters have great potential for use in recirculating aquaculture systems because of their high efficiency, low cost, and stable performance (Timmons et al., 2006).

Conventional microbead biofilters are operated in a down flow configuration. In this configuration, influent water is distributed over the top of the media bed, and the water subsequently trickles down through the media. Gravity flow then conducts it out of the reactor vessel. Wu et al. (2008) reported a biological filtration method using 2.0 to 3.0 mm diameter beads, each with a volume of 0.2 m3, that had an average total ammonia-nitrogen (TAN) removal rate of 172 g TAN/(m3 day) with influent ammonia-nitrogen levels of 3.0 mg/L. In the Greiner and Timmons (1998) study, the proposed microbead filter possessed nitrification rates ranging from 512 to 2244 g TAN/(m3 day) for influent TAN concentrations between 0.81 and 4.63 mg/L in an intensive recirculating tilapia production facility. Timmons et al. (2006) suggested that microbead filters had a safe nitrify value for designs up to approximately 1200 g TAN/(m3 day) for warm water systems with influent ammonia-nitrogen levels from 2 to 3 mg/L. These filters are simple and reliable in form, but they possess certain limitations due to the thickness of the filter. Excessive filter thickness can cause channeling along the wall and even moderate to severe blockage. The low hydraulic retention time within the bead bed volume will, however, lead to reduced nitrification efficiencies in microbead biofiltration systems (Timmons et al., 2006). If the height of the microbead in the filtration system is too great, or if the width of the chamber is too great, the essentially free flow of water through the center region of the filter tends to initiate water channeling. Water channeling detrimentally decreases the residing time of the reactants passing through the biofilm, thus leading to decreased nitrification activity. The force that prevents water channeling through the media forms the limiting factor for the height as well as diameter of microbead beds. Timmons et al. (2006) considered bead filters to be limited to a depth of approximately 50 cm.

The sequencing microbead biofilter is a successful design modification based on the conventional microbead biofilter concept that was patented by Holder Timmons Engineering, LLC (United States Patent Number US 2007/0056890 “Water filtration system and its use,” awarded March 15, 2007). In this modified system, the microbead maintains a continuous up-and-down movement. The breaker bars are positioned in the bead bed volume in order to generate a relative displacement between microbeads, which enable the biofilter obtain the effect of self-cleaning. Microbead biofilter treatment technology is a new recirculating aquaculture water treatment method with potential for use in many commercial systems; however, information on the performance and optimization of sequencing microbead biofiltration in RAS systems is rare. This study seeks to characterize the performance of a sequencing microbead biofilter installed in RAS system, providing a useful case and operation parameter with wide potential applications.

Section snippets

Equipment

The experimental sequencing microbead biofilter, as shown in Fig. 1, was set up in the Key Laboratory of Fishery Equipment and Engineering, Fishery Machinery and Instrument Research Institute, Chinese Academy of Fishery Sciences. The biofilter was divided into two chambers, designated A-chamber and B-chamber. The water flow through the filtration system was proceed by the electric control valve and water level switch in an alternating fashion, regularly switching between the vessels to enter

Biofilter startup and operation

The biofilter was able to establish nitrification functions ranging from 10 to 20 days in freshwater systems (Carmignani and Bennett, 1977, Yang and Yan, 1988). Based on the experimental results shown in Fig. 3, which details the sequencing microbead biofilter startup and operation in this experiment, the cultivation of nitrification function required 8 days, spending less time compared with previous studies of 11 days (Carmignani and Bennett, 1977), 15 days (Yang and Yan, 1988) and 17 days (

Conclusions

To investigate ammonia removal performance of sequencing microbead biofilter a pilot scale recirculating aquaculture system was developed. At the startup period of the filter, Barcoo perch was reared in the culture tanks. When the water temperature was 29 ± 1.2 °C and the culturing load was 7 kg fish/m3, the establishment of nitrification function of the experimental filter was about 8 days, spending less time compared with previous studies. The shorter activation period results from the low

Acknowledgments

This study was supported by the National Key Technology Research and Development Program of the Ministry of Science and Technology of China (Grant Nos. 2011BAD13B04, 2012BAD38B04), the Technology Development and Research Special Projects of Research Institutes of China (Grant No. 2010EG134287). We would like to thank Dr. Michael B. Timmons for his enormous assistance in the process of filter design and experimental implementation. Special appreciation is extended to Dr. Shulin Chen for his help

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