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In line with the recent promotion of biocementation as an environmentally friendly ground improvement method, this study presents an investigation into microbially induced calcite precipitation (MICP) as a method of improving the engineering properties of soft clay. Bacillus pasteurii bacterium in vegetative cell and bacterial spore forms were used to induce MICP in clay specimens. Untreated and treated clay specimens were tested for their mechanical properties and microstructures through unconfined compression (UC) tests, free–free resonance (FFR) tests, X-ray diffraction (XRD) tests, and scanning electron microscopy with energy dispersive X-ray (SEM/EDX) tests. Results showed that both vegetative cells and bacterial spores can effectively enhance the strength and modulus of clays by inducing MICP to generate calcite crystals. Clays treated with vegetative cells exhibited earlier improvements in their strength than clays treated with bacterial spores due to earlier activity availability; however, the clays treated with bacterial spores exhibited greater strength improvements in the long term. Bacterial spores may also prove more convenient to use in geotechnical engineering practice.

This study presents the feasibility of using bacterial cells to repair of the existing cracks within the cement mortar. Bacillus sphaericus (LMG 22257) has been used to produce microbially induced calcium carbonate precipitation (MICP) for crack closing. The healing agent were externally applied to the cracked mortar specimens by dropping the bacteria and urea solutions daily. After 20 days of treatment, the MICP-treated sample showed 43% higher compressive strength than that of cracked sample. In addition, it is comparable in terms of water tightness to control mortar made without artificial crack.

In this research, hydrodynamic behaviour in a novel fluidized bed reactor (FBR) was studied by using a residence time distribution (RTD) experiment. The RTD experimental result showed that the liquid flow pattern closed to plug flow behaviour. Moreover, the novel FBR was performed under low hydraulic retention time (HRT) operation (without internal recirculation), and its performance should be further investigated. There are two experimental approaches for wastewater treatment application. The first approach, a novel FBR, was performed for treating nitrate with a denitrification process at COD : NO3- - N of 1 : 1, 2 : 1, 3 : 1, 5 : 1 and 10 : 1. The highest nitrate removal efficiency was obtained at 99 ± 1%, with a ratio of COD:NO3- - N of 3 : 1. In the second approach, a novel FBR was evaluated in low strength anaerobic wastewater treatment. The novel FBR achieved 86 ± 6% of COD removal efficiency at an organic loading rate (OLR) of 5.6 g COD L-1 d-1.

A dissimilatory nitrate reduction to ammonium (DNRA) microbial community was developed under a high organic carbon to nitrate (C/NO3-) ratio in an anoxic semi-continuous sequencing batch reactor (SBR) fed with glucose as the source of carbon and NO3- as the electron acceptor. Activated sludge collected from a municipal wastewater treatment plant with good denitrification efficiency was used as the inoculum to start the system. The aim of this study was to examine the microbial populations in a high C/NO3- ecosystem for potential DNRA microorganisms, which are the microbial group with the ability to reduce NO3- to ammonium (NH4+). A low C/NO3- reactor was operated in parallel for direct comparisons of the microbial communities that developed under different C/NO3- values. The occurrence of DNRA in the high C/NO3- SBR was evidenced by stable isotope-labeled nitrate and nitrite (15NO3- and 15NO2-), which proved the formation of NH4+ from dissimilatory NO3-/NO2- reduction, in which both nitrogen oxides induced DNRA activity in a similar manner. An analysis of sludge samples with Illumina MiSeq 16S rRNA sequencing showed that the predominant microorganisms in the high C/NO3- SBR were related to Sulfurospirillum and the family Lachnospiraceae, which were barely present in the low C/NO3- system. A comparison of the populations and activities of the two reactors indicated that these major taxa play important roles as DNRA microorganisms under the high C/NO3- condition. Additionally, a beta-diversity analysis revealed distinct microbial compositions between the low and high C/NO3- SBRs, which reflected the activities observed in the two systems.

Disease suppression is an essential aspect of shrimp farming. To control water quality, a recirculating aquaculture system (RAS) is employed in worldwide. In RAS, water quality is achieved by nitrification biofilter treatment, whereas disease prevention is achieved by the application of an oxidizing agent such as ozone (O3). This study investigates the proper residual ozone concentration (ROC) dosage for controlling pathogenic bacteria Vibrio parahaemolyticus (VP) and minimizing mal-effects on nitrifying bacteria activity in the biofilter media inside an RAS. Juvenile Pacific white shrimp, Litopenaeus vammanei, were cultured for 4 months in a lab-scale brackish RAS integrated with ozonation. Results showed that although the system biofilter's nitrification activity was influenced by ROC, the 0.3 mg L−1 ROC dosage provided an optimum condition which effectively eliminated VP in the biofilter but did not inhibit ammonia removal. At a higher ROC (approximately 0.4 mg L−1) ozonation dosage, the biofilter's ammonia oxidation rate significantly reduced. Over a 40-day shrimp-rearing operational period, the viable VP count in an aerated (non-ozonated RAS) gradually increased, but the viable VP counts in both biofilm and water in a 0.3 mg L−1 ROC treated RAS significantly reduced down to undetectable levels. As such, the conclusion was drawn that a 0.3 mg L−1 ROC ozonation treatment in the biofilter tank of a RAS can effectively control VP pathogens without influencing the activity of the nitrification biofilter, thus providing a balanced control between water quality and safety to the shrimp.

This study compares the crack healing performances of biological self-healing concretes using cell/nutrient dropping and immobilization methods to produce microbially induced calcium carbonate precipitation (MICP). Vegetative cells and microencapsulated bacterial spores of Bacillus sphaericus (LMG 22257) were used to heal pre-cracked mortars. Mortar specimens were cured for 7 and 28 days before pre-cracking, and then repaired under wet-dry cycles for 7 days. Comparisons were made in terms of crack-width and crack-area healing and load recovery after repairing. Results showed that the vegetative cell dropping method was more effective in closing cracks and recovering ultimate load after repair than the method of using immobilized microencapsulated bacterial spores for mortar repair. In fact, specimens mixed with microencapsulated bacterial spores exhibited lower ultimate loads than comparable control specimens.

The aim of this study was to evaluate the effect of salinities on the nitrogen removal performance of a pilot-scale down-flow hanging sponge (DHS) reactor and an up-flow sludge blanket (USB) reactor which was installed in a closed recirculating aquaculture system for the purpose to maintain the water quality in the aquaculture tank. In this study, water quality and the growth of the Longtooth grouper, Epinephelus bruneus, were investigated at 30‰, 22.5‰, and 15‰ salinity for over 1000 days. The tested DHS reactor has successfully maintained total ammonium nitrogen in aquaculture tank at less than 1.0 mg-N·L−1 at various salinities. The abundance of nitrifying bacteria detected in the DHS reactor was higher at salinities of 15‰ and 22.5‰ than at 30‰. The USB reactors achieved a nitrate removal efficiency of over 60%. All fish survived all salinity conditions, exhibiting the highest daily weight gain of 2.0 ± 3.4 g-fish·day−1 at 15‰ salinity, which was 1.6 times higher than that at 30‰. The DHS-USB system could exert nitrogen removal under changing salinity conditions.

Issues associated with accumulating microplastic (MP) in sewage sludge during wastewater treatment in a membrane bioreactor (MBR) system have not been studied in detail. Here, we investigated the microplastic's effects on floc characteristics, microbial community compositions, and fouling behavior inside sequencing-batch MBRs. MBRs were operated with 0, 7, 15, and 75 MPs/L of feed for 124-days. Results indicated that MP presence decreased sludge floc size, floc hydrophobicity, and extracellular polymeric substance (EPS) molecular size, and increased EPS concentration and the floc's negative zeta potential. These results were attributed to the facilitation of divalent cation (Ca2+ and Mg2+) uptake by MPs that weakened ion-bridging interactions within the sludge flocs. MPs accumulation slightly affected microbial structure and diversity. Relative abundances of dominant phyla, Actinobacteria, also decreased substantially. MPs also acted like a scouring material on membrane surfaces, inducing transformation of matured biofilm structures where protein content was substantially lower than nucleic acid content, in contrast to the control. Overall, MPs' negative effects on sludge flocs were counteracted by their scouring effect; consequently, SB-MBRs operated up to 4 months did not suffer from severe cake fouling, compared to control.

Microbially-induced calcite precipitation (MICP) is a promising technique to improve the engineering properties of soft soil in a sustainable, environmentally friendly, and energy saving manner. This study determined the suitable chemical condition to induce MICP activity from alkaliphilic urease-producing Sporosarcina pasteurii bacterium, and to explore the MICP activity’s effectiveness in improving the mechanical properties of three types of natural fine-grained soils (Kaolin clay, Laterite, and Bangkok clay). Untreated and treated clays were evaluated by the free-free resonant frequency test, unconfined compression test, and their microstructures and chemical compositions. The results showed that a urea-Ca2+ input rate of 7.5 mmol/h efficiently promoted the precipitation of calcite by bacteria, as indicated by the highest degree of media clogging in sand column tests. A higher urea-Ca2+ input rate created soil samples that exhibited a high degree of supersaturation, which impacted the precipitation pattern at the microscale, resulting in less contact between soil particles; this was caused by the increase in salinity of the solution to a level that inhibited bacterial activity and retarded calcite precipitation. Once the optimal urea-Ca2+ input rate was determined, bacterial cultures were introduced into samples of each clay, and fed with the optimal chemical mixture while being maintained at room temperature (25–30 °C) for 7 d. Increases in the samples’ stiffness and shear strength coincided with increased amounts of precipitated calcite. Enhancements to each clay type’s strength parameters were dependent on the natural characteristics of clay. Specifically, liquid media carrying the necessary nutrients for MICP activity could not efficiently permeate through the clayey soil with a high plasticity, resulting in a lower observable degree of MICP activity to improve the soil’s characteristics.

A novel configured fluidized bed reactor (FBR) with granular rubber as the fluidized media was operated without internal recirculation to achieve denitrification. This FBR could operate under a low hydraulic retention time (HRT) of 50 min due to the low rubber media density and absence of recirculation. Synthetic nitrate-rich wastewater with a fixed nitrate (NO 3 − -N) concentration and varying COD concentrations was fed into the FBR. The nitrate removal profile showed a rapid nitrate reduction at the bottom of the reactor with a high performance under the low HRT. Different microbial communities were identified using Illumina Miseq sequencing. The dominant microorganisms belonged to the Beta- and Gamma-proteobacteria classes and played important roles in nitrate reduction. Acidovorax was abundant at low COD: NO 3 − -N ratios, while Rhizobium and Zoogloea were dominant at high COD: NO 3 − -N ratios. The COD: NO 3 − -N ratio strongly influenced the composition of the microbial community including the dominant species.

Concrete cracks must be repaired promptly in order to prevent structural damage and to prolong the structural life of the building (or other such construction). Biological self-healing concrete is a recent alternative technology involving the biochemical reaction of microbial induced calcium carbonate precipitation (MICP). This study determined the most appropriate technique to encapsulate spores of Bacillus sphaericus LMG 22257 with sodium alginate so as to protect the bacterial spores during the concrete mixing and hardening period. Three techniques (extrusion, spray drying and freeze drying) to encapsulate the bacterial spores with sodium alginate were evaluated. The freeze-drying process provided the highest bacterial spore survival rate (100%), while the extruded and spray-dried processes had a lower spore survival rate of 93.8% and 79.9%, respectively. To investigate the viability of microencapsulated spores after being mixed with mortar, the decomposed urea analysis was conducted. The results revealed that the freeze-dried spores also showed the highest level of urea decomposition (metabolic activity assay used as a surrogate marker of spore germination and vegetative cell viability). Thus, the self-healing performance of concrete mixed with freeze-dried spores was evaluated. The results showed that the crack healing ratio observed from the mortar specimens with freeze-dried microencapsulated spores were significantly higher than those without bacteria. This study revealed that freeze drying has a high potential as a microencapsulation technique for application to self-healing concrete technology.

A high-rate nitrogen removal process is required to maintain the water quality in aquaculture tanks used to produce high-density fish populations in recirculating aquaculture systems. In this study, a combined pilot-scale system of down-flow hanging sponge (DHS) reactors and upflow sludge blanket (USB) reactors was applied as a nitrogen removal system for a longtooth grouper Epinephelus bruneus recirculating aquaculture system. The DHS reactors demonstrated high total ammonium nitrogen (TAN) removal efficiencies and the TAN concentration in the aquaculture tank was maintained at 0.32 ± 0.12 mg-N·L−1. The USB reactor fed with sodium acetate acted as a denitrification unit and adjusted the pH through denitrification reaction. All E. bruneus survived the entire experimental period and the daily weight gain rate of 0.6%·day−1 was comparable to that in marine aquaculture. This result shows that the DHS-USB system to be a novel applicable system for nitrogen removal processes in recirculating aquaculture systems and further study at a large scale should be recommended.

This research investigated the efficiency of a pumice stone biofilter tank for nitrogen removal from a recirculating aquaculture system. The pumice bottom substrate nitrification-denitrification tank was a glass tank packed with a 5 cm depth of pumice stone (approximately 3 mm in diameter) at the bottom. It was found that the pumice stone could perform as a nitrification biofilter under aerobic conditions. When applying methanol as the external carbon source at a COD:N ratio of 5:1 and then covering the tank with a plastic sheet to reduce gas exchange, pumice stone could remove nitrate through denitrification. Thereafter, nitrification and denitrification treatments using the pumice tank were applied to a 100 L moderate density (10 kg m −3 ) recirculating aquaculture system (RAS) under laboratory conditions. The RAS consisted of a 100 L tilapia culture tank connected to a 100 L pumice tank packed with a 5 cm layer of pumice stone. It was found that the nitrification treatment performed by the pumice tank could control ammonia and nitrite concentrations within the required safety range throughout the 121-day culture period. When nitrate accumulated to approximately 50 mg-N L −1 in water, water recirculation was paused, after which batch denitrification treatment was performed by adding methanol at COD:N of 5:1 in the pumice tank. With nitrification-denitrification treatment, ammonia and nitrite concentrations were below 1 mg-N L −1 and nitrate was kept below 50 mg-N L −1 while nitrate in the control tank was as high as 352.47 ± 9.67 mg-N L −1 . Moreover, the pumice bottom substrate tank with methanol supplement had no negative effect on growth and survival of fish in the recirculating system.

Aquaponic systems (APSs) are based upon the sustainable utilization of nitrogen and phosphorus from a recirculating aquaculture system (RAS) as the nutrient source for plant production. Since the proper management of nitrogen and suspended solids are important for nutrient utilization efficiency, their optimization was evaluated. The RAS integrated with filtration unit and nitrifying biofilter provided complete nitrification without solid accumulation. Under the optimal treatment condition for 16 d, the treated water was low in ammonia (0 mg-N/L) and high in nitrate (> 6 mg-N/L) concentrations, which was appropriate for use in the cultivation of lettuce (Lactuca sativa). The RAS was then incorporated with hydroponics at a 5:1 fish: plant weight ratio. Moreover, the simplified APS was compared with a typical APS system that incorporated filtration unit and nitrifying biofilter. The natural growth of nitrifying microorganisms in the simplified APS could perform complete nitrification after 20 d of operation giving low ammonia and nitrite concentrations. The nutrient removal efficiency of the simplified APS resembled the typical system. During the aquaponics, the hydroponic unit in the aquaculture system was sufficient to control the nutrient concentrations within the appropriate levels for fish cultivation, i.e. nitrate (< 20 mg-N/L) and phosphate (< 3 mg-P/L).

This research focused on the solid and nitrate removal efficiency in a solid digestion-denitrification column. The 20 L up-flow column consisted of 18 L acrylic column with 2 L down-comer inlet tube located in the middle. In the first part, the wastewater with high suspended solids from the Tilapia fish tank was applied into the sedimentation unit at 5 variable flow rates i.e., 11.25, 25.71, 60, 105.88 and 360 L/h. The results indicated that the flow rate of 11.25 L/h (0.57 m/h) gave the highest solid removal efficiency of 72.72% ± 8.24%. However, the total suspended solids removal was highest at 360 L/h (18.13 m/h). In the second part, methanol was added as an external organic carbon source for denitrification process in a hybrid column containing settled solids. The COD:N ratios of 0.5:1, 1:1, 2:1, 3:1, 4:1, 5:1 and 6:1 were investigated and compared with control without methanol addition. This experiment was operated at the HRT of 1 h with 450 L wastewater from recirculating aquaculture pond containing 100 mg-N/L sodium nitrate. The results indicated that the COD:N ratio of 3:1 gave the highest nitrate removal efficiency of 33.32% ± 21.18% with the denitrification rate of 5,102.88 mg-N/day.

Cultivation of recently identified Gluconobacter nephelii to produce 1,3-dihydroxyacetone (DHA) was conducted using the growth medium containing the external nitrogen source from agro-industrial wastes. Cell cultivation in 250 mL glass flasks using 80 g/L glycerol and corn steep liquor as nitrogen source yielded the highest biomass (1.75 ± 0.23 g/L) and DHA (49.5 ± 3.14 g/L) concentrations as compared to other nitrogen sources (i.e., glutamic mother liquor and soybean meal hydrolysate). Subsequent cultivation in larger bioreactors (32 L) with corn steep liquor as the preferred nitrogen source indicated that internal-loop airlift bioreactor yielded significantly higher biomass and DHA concentrations than flat-panel airlift and bubble column bioreactors. Further optimization of internal-loop airlift photobioreactor revealed that DHA production in G. nephelii depended on the aeration rates, with the maximum DHA concentrations (46.09 ± 1.01 g/L) obtained when maintaining the aeration rates at 0.64 vvm.

A bottom substrate denitrification tank for a recirculating aquaculture system was developed. The laboratory scale denitrification tank was an 8 L tank (0.04 m 2 tank surface area), packed to a depth of 5 cm with a bottom substrate for natural denitrifying bacteria. An aquarium pump was used for gentle water mixing in the tank; the dissolved oxygen in the water was maintained in aerobic conditions (e.g. > 2 mg/L) while anoxic conditions predominated only at the bottom substrate layer. The results showed that, among the four substrates tested (soil, sand, pumice stone and vermiculite), pumice was the most preferable material. Comparing carbon supplementation using methanol and molasses, methanol was chosen as the carbon source because it provided a higher denitrification rate than molasses. When methanol was applied at the optimal COD:N ratio of 5:1, a nitrate removal rate of 4591 ± 133 mg-N/m 2 tank bottom area/day was achieved. Finally, nitrate removal using an 80 L denitrification tank was evaluated with a 610 L recirculating tilapia culture system. Nitrate treatment was performed by batch transferring high nitrate water from the nitrification tank into the denitrification tank and mixing with methanol at a COD:N ratio of 5:1. The results from five batches of nitrate treatment revealed that nitrate was successfully removed from water without the accumulation of nitrite and ammonia. The average nitrate removal efficiency was 85.17% and the average denitrification rate of the denitrification tank was 6311 ± 945 mg-N/m 2 tank bottom area/day or 126 ± 18 mg-N/L of pumice packing volume/day.

The objective of this research is to propose the suitable suspended solid (SS) treatment process for the wastewater of the actual aquaculture systems (tilapia ponds). Sedimentation, coagulation, and depth filtration were chosen and applied in this study. Sand and anthracite were used as media in the depth filtration; while alum was used as a coagulant in jar tests. The results showed that, at the optimal operating condition, sedimentation (overflow rate of 0.8 m/hr) and coagulation (alum concentration of 15 mg/L) can provide treatment efficiencies of 90% and 99.25%, respectively. However, several drawbacks (high detention time, decrease of pH value, sludge generation) were observed. Therefore, the depth filtration processes with single and dual media were applied at different media configurations. The highest treatment efficiency (92%) and moderate filtration performance (80 minutes operating time and 12 m/hr filtration rate) can be obtained with the combination of media between anthracite (2 mm effective size and 0.15 m in depth) and sand (0.8 mm effective size and 0.55 m in depth). Finally, sedimentation as pretreatment and aeration in batch mode along the media depth were proven to significantly enhance the overall filtration performance.

This study investigates the effects of sulfate on biological azo dye decolorization in anaerobic baffled reactors (ABRs) using Acid Red 18 as a model azo dye. The ABRs supplemented with sulfate at chemical oxygen demand (COD):sulfate ratios of 2.5 and 0.6 had the decolorization efficiencies of (89.4 ± 3.62)% and (89.9 ± 5.50)%, respectively. These were significantly greater than the decolorization efficiency of the ABR without sulfate supplements that had the decolorization efficiency of (76.7 ± 5.14)%. The primary decolorization mechanisms in the ABR with no sulfate added and the ABR with the COD:sulfate ratio of 2.5 were biological and required the presence of cells. By contrast, the azo dye decolorization in the ABR with the COD:sulfate ratio of 0.6 can occur to a great extent in the absence of cells, suggesting the role of extracellular mechanisms on azo dye decolorization under this condition. © 2012 American Institute of Chemical Engineers Environ Prog, 32: 1045–1054, 2013

The effects of chitosan characteristics including the degree of deacetylation, molecular weight, particle size, pH pretreatment and immobilization time on the immobilization of nitrite-oxidizing bacteria (NOB) on biopolymeric chitosan were investigated. Nitrite removal efficiency of immobilized NOB depended on the degree of deacetylation, particle size, pH pretreatment on the surface of chitosan and immobilization time. Scanning electron microscope characterization illustrated that the number of NOB cells attached to the surface of chitosan increased with an increment of immobilization time. The optimal condition for NOB immobilization on chitosan was achieved during a 24-hr immobilization period using chitosan with the degree of deacetylation larger than 80% and various particle size ranges between 1-5 mm at pH 6.5. In general, the NOB immobilized on chitosan flakes has a high potential to remove excess nitrite from wastewater and aquaculture systems.

A bacterial strain, WL(T), which was isolated from an activated sludge, was able to degrade alkylphenols. 16S rDNA sequence analysis indicated that strain WL(T) belonged to the genus Pseudomonas (sensu stricto) and formed a monophyletic clade with the type strain of Pseudomonas graminis and other members in the Pseudomonas putida subcluster with sequence similarity values higher than 97%. Genomic relatedness based on DNA-DNA hybridization of strain WL(T) to these strains is 2-41%. Strain WL(T) contained ubiquinone-9 as the main respiratory quinone, and the G+C content of DNA was 66 mol%. The organism contained hexadecanoic acid (16:0), hexadecenoic acid (16:1) and octadecenoic acid (18:1) as major cellular fatty acids. The hydroxy fatty acids detected were 3-hydroxydecanoic acid (3-OH 10:0), 3-hydroxydodecanoic acid (3-OH 12:0) and 2-hydroxydodecanoic acid (2-OH 12:0). These results, as well as physiological and biochemical characteristics clearly indicate that the strain WL(T) represents a new Pseudomonas species, for which the name Pseudomonas japonica is proposed. The type strain is strain WL(T) (=IAM 15071T=TISTR 1526T).

This research aims to describe the nitrogen and phosphorus removal in Recirculating Aquaculture System (RAS) by crop plants biomass production. The 3 experiment systems consisted of 1 treatment (fish tank + baked clay beads + Chinese cabbage) and 2 controls as control-1 (fish tank only) and control-2 (fish tank + baked clay beads), were performed. With all experimental RAS, Nile tilapia (Oreochromis niloticus) was cultured at 2 kg/m3 density. The baked clay beads (8-16 mm in diameter) were filled as a layer of 10 cm in the water treatment tank of control-2. While in the treatment tank, Chinese cabbage (Brassica pekinensis) was planted at 334 plants/m2 in baked clay beads layer. During 35 days of experiment, the average fish wet-weight in control-1, control-2 and treatment systems increased from 16.31±1.49, 15.18±1.28 and 11.31±1.49 g to 29.43±7.06, 28.65±3.12 and 27.20±6.56 g, respectively. It was found that the growth rate of 0.45±0.15 g-wet weight/day in a treatment tank was higher than in those 2 controls, which were rather similar at 0.37±0.16 and 0.38±0.05 g-wet weight/day, respectively. The fish survival rate of all experimental units was 100%. The average Chinese cabbage wet-weight in treatment system increased from 0.15±0.02 g to 1.00±0.38 g. For water quality, all parameters were within the acceptable range for aquaculture. The assimilation inorganic nitrogen in a treatment tank showed a slower rate and lower nitrite accumulation relative to those in control tanks. The nitrogen and phosphorus balance analysis illustrated that most of the nitrogen and phosphorus input in all systems was from feed (82-87% and 21-87%) while at the final day of experiments, nitrogen and phosphorus in tilapia culture revealed at 15-19% and 4-13%. The accumulation of nitrogen and phosphorus in the water, up to 56% and 70%, was found in control-1 while water in the tank with baked clay beads had substantial lower nitrogen and phosphorus concentration. The most important part was unaccounted nitrogen and phosphorus as high as 60% and 17% in treatment and 53% and 10% in control-2 systems. Nitrogen and phosphorus incorporated in plant (treatment) was only 1.31% and 0.11%, respectively. It can be implied from the results that the assimilation in plant was a minor process for nutrient removal in this RAS. On the other hand, the nitrification and denitrification occurred in the sediment layer of baked clay beads tank were the major treatment processes to maintain water quality in the recirculating system. Without baked clay bead, nitrogen waste was accumulated as nitrate in the water while in treatment tank with backed clay beads, nitrogen was significantly removed by denitrification process.