Advances in Bioreactor Technologies for Sustainable Aquaculture Water Treatment

The recirculating aquaculture system (RAS) has been rapidly adopted worldwide in recent years due to its high productivity, good stability, and good environmental controllability (and therefore friendliness to environment and ecology). Nevertheless, the effluent from seawater RAS contains a high level of ammonia nitrogen which is toxic to fish, so it is necessary to overcome the salinity conditions to achieve rapid and efficient nitrification for recycling. The moving bed biofilm reactor (MBBR) has been widely applied often by using PE fillers for efficient wastewater treatment. However, the start-up of MBBR in seawater environments has remained a challenge due to salinity stress and harsh inoculation conditions. This study investigated a new PE-filler surface modification method towards the enhanced start-up of mariculture MBBR by combining liquid-phase oxidation and maifanstone powder. The aim was to obtain a higher porous surface and roughness and a strong adsorption and alkalinity adjustment for the MBBR PE filler. The hydrophilic properties, surface morphology, and chemical structure of a raw polyethylene filler (an unmodified PE filler), liquid-phase oxidation modified filler (LO-PE), and liquid-phase oxidation combined with a coating of a maifanstone-powder-surface-modified filler (LO-SCPE) were first investigated and compared. The results showed that the contact angle was reduced to 45.5° after the optimal liquid-phase oxidation modification for LO-PE, 49.8% lower than that before modification, while SEM showed increased roughness and surface area by modification. Moreover, EDS presented the relative content of carbon (22.75%) and oxygen (42.36%) on the LO-SCPE surface with an O/C ratio of 186.10%, which is 177.7% higher than that of the unmodified filler. The start-up experiment on MBBRs treating simulated marine RAS wastewater (HRT = 24 h) showed that the start-up period was shortened by 10 days for LO-SCPE compared to the PE reactor, with better ammonia nitrogen removal observed for LO-SCPE (95.8%) than the PE reactor (91.7%). Meanwhile, the bacterial community composition showed that the LO-SCPE reactor had a more diverse and abundant AOB and NOB. The Nitrospira has a more significant impact on nitrification because it would directly oxidize NH4⁺-N to NO3⁻-N (comammox pathway) as mediated by AOB and NOB. Further, the LO-SCPE reactor showed a higher NH4+-N removal rate (>99%), less NO2−-N accumulation, and a shorter adaption period than the PE reactor. Eventually, the NH4+-N concentrations of the three reactors (R1, R2, and R3) reached <0.1 mg/L within 3 days, and their NH4+-N removal efficiencies achieved 99.53%, 99.61%, and 99.69%, respectively, under ammonia shock load. Hence, the LO-SCPE media have a higher marine wastewater treatment efficiency.

Onsite research indicates that activated sludge membrane biological reactors (MBRs) are an effective waste treatment technology for aquaculture effluents. MBRs produce a filtered permeate that is nearly free of dissolved nutrients, organics, and solids; therefore, this technology could be well-suited for integration within the process control loop of recirculation aquaculture systems (RAS). A four-month study was carried out to evaluate the feasibility of incorporating single-vessel MBRs within freshwater RAS while culturing rainbow trout Oncorhynchus mykiss. Triplicate RAS with and without MBRs (controls) were evaluated; mRAS and cRAS, respectively. System backwash water of mRAS was processed and retained within MBRs which allowed increased water recycling, while cRAS utilized standard dilution rates to limit nitrate accumulation. On average, mRAS required six and a half times less makeup water. Mean daily water replacement of the RAS volume for mRAS and cRAS was 1.2 ± 0.4 and 7.8 ± 0.5%, respectively (P < 0.05). A range of water quality concentrations were significantly greater in mRAS including chloride, carbon dioxide, heterotrophic bacteria count, pH, nitrate-nitrogen, total ammonia-nitrogen, total phosphorous, and true color, as well as dissolved concentrations of calcium, copper, magnesium, and sulfur. Alkalinity and ultraviolet transmittance levels were significantly lower in mRAS. These culture environment differences did not affect rainbow trout growth, feed conversion, or survival (P > 0.05). In addition, concentrations of common off-flavor compounds (geosmin and 2-methylisoborneol) in water and fish flesh were not affected by MBR presence. Improvements for future MBR integration with RAS were realized including optimization of MBR permeate rates, increased RAS water exchange through the MBRs, and infrequent supplementation of a carbon source to enhance denitrification efficiency and alkalinity recovery. Overall, incorporating MBRs within RAS resulted in substantial water savings and was biologically feasible for rainbow trout production.

This study examined the performance of three independently operated denitrifying moving bed biofilm reactors (MBBRs) in a zero-exchange marine recirculating aquaculture system (RAS) stocked with European seabass (Dicentrarchus labrax). A semi-automated control strategy was applied to foster spontaneous denitrification. Process automation consisted of a pulsed carbon supply and an inflow of nitrate-rich, aerated process water controlled by the oxidation-reduction potential (ORP) in the MBBR. Carbon dosing frequency was adjusted manually if the process produced unwanted products (i.e., nitrite or ammonia). OPR-controlled inflow stimulated bacterial activities in the MBBRs until inflow reached the pre-set maximum at a hydraulic retention time (HRT) of 0.75 h. This allowed for a quick start-up of the denitrification processes in spite of high initial variability of process water inflow and of nitrate removal efficiency (NRE). A start-up with glycerol did not induce a stable denitrification process; however, after the process had been established with acetate, glycerol promoted efficient denitrification with NRE close to one. The successive application of the two carbon sources resulted in a high nitrate removal rate (NRR) of 2 kg nitrate-N m−3 day−1 in the biofilters. This diminished the concentration of nitrate-nitrogen (nitrate-N) in the RAS (volume 9 m3) from 176 to 36 g m−3 in 42 days with biofilters comprising only 1% of the RAS volume. The implications for the development of an automated denitrification process are discussed.

Traditional aquaculture systems appear challenged by the high levels of total ammoniacal nitrogen (TAN) produced, which can harm aquatic life. As demand for global fish production continues to increase, farmers should adopt recirculating aquaculture systems (RAS) equipped with biofilters to improve the water quality of the culture. The biofilter plays a crucial role in ammonia removal. Therefore, a biofilter such as a moving bed biofilm reactor (MBBR) biofilter is usually used in the RAS to reduce ammonia. However, the disadvantage of biofilter operation is that it requires an automatic system with a water quality monitoring and control system to ensure optimal performance. Therefore, this study focuses on developing an Internet of Things (IoT) system to monitor and control water quality to achieve optimal biofilm performance in laboratory-scale MBBR. From 35 days into the experiment, water quality was maintained by an aerator’s on/off control to provide oxygen levels suitable for the aquatic environment while monitoring the pH, temperature, and total dissolved solids (TDS). When the amount of dissolved oxygen (DO) in the MBBR was optimal, the highest TAN removal efficiency was 50%, with the biofilm thickness reaching 119.88 μm. The forthcoming applications of the IoT water quality monitoring and control system in MBBR enable farmers to set up a system in RAS that can perform real-time measurements, alerts, and adjustments of critical water quality parameters such as TAN levels.

Effect of seeding biofloc on the nitrification establishment in moving bed biofilm reactor (MBBR)

Membrane bioreactor (MBR) technology has attracted great attention over the last 3 decades and achieved rapid growth in an increasing number of practical small‐ and large‐scale applications worldwide. However, its application in Sub-Saharan Africa as well as in aquaculture was so far limited. The installation and operation of a pilot membrane bioreactor (MBR) in Kisumu, Kenya, adopts an integrated approach by providing an integral, sustainable, cost‐effective, and robust solution for water sanitation, which also meets the demand for clean water in the fish processing industry, aquaculture, and irrigation. The innovative system comprises a pilot MBR coupled with a recirculating aquaculture system (RAS) which is linked to a 14.3 kW photovoltaic (PV) system, including a 30 kWh Li battery storage to supply sustainable energy. The RAS is able to recirculate 90–95% of its water volume; only the water loss through evaporation and drum filter back flushing has to be replaced. To compensate for this water deficit, the MBR treats domestic wastewater for further reuse. Additionally, excess MBR treated water was used for irrigating a variety of local vegetables and could be also used in fish processing plants. The pilot‐scale MBR plant with around 6 m2 submerged commercial UF polyethersulfone (PES) membranes provides treated water in basic agreement with Food and Agriculture Organization (FAO) standards for irrigation and aquaculture, showing no adverse effects on tilapia fingerlings production. A novel membrane module with a low‐fouling coating technology is operating stably but has not yet shown improved performance compared to the commercial one.KeywordsMembrane bioreactorWater reuseRecirculation aquaculturePhotovoltaicIrrigation

Genotype by environment interaction for growth of sole (Solea solea) reared in an intensive aquaculture system and in a semi-natural environment

A systematic review of moving bed biofilm reactor, membrane bioreactor, and moving bed membrane bioreactor for wastewater treatment: Comparison of research trends, removal mechanisms, and performance

Comparison of MBR and MBBR followed by UV or electrochemical disinfection for decentralized greywater treatment

High operational cost due to membrane fouling propensity remains a major drawback for the widespread application of membrane bioreactor (MBR) technology. As a result, studies on membrane fouling mitigation through the application of integrated processes have been widely explored. In this work, the combined application of electrochemical processes and moving bed biofilm reactor (MBBR) technology within an MBR at laboratory scale was performed by applying an intermittent voltage of 3 V/cm to a reactor filled with 30% carriers. The treatment efficiency of the electro moving bed membrane bioreactor (eMB-MBR) technology in terms of ammonium nitrogen (NH4-N) and orthophosphate (PO4-P) removal significantly improved from 49.8% and 76.7% in the moving bed membrane bioreactor (MB-MBR) control system to 55% and 98.7% in the eMB-MBR, respectively. Additionally, concentrations of known fouling precursors and membrane fouling rate were noticeably lower in the eMB-MBR system as compared to the control system. Hence, this study successfully demonstrated an innovative and effective technology (i.e., eMB-MBR) to improve MBR performance in terms of both conventional contaminant removal and fouling mitigation.

Background: Recirculatory aquaculture system (RAS) is an intensive and sustainable aquaculture system that involves the reuse of water within a closed loop system minimizing water usage and reduces environmental impact. This study compares the growth performance of Climbing Perch (Anabas testudineus) in a low-cost recirculatory aquaculture system (RAS) versus an advanced RAS. The low-cost RAS aims to reduce economic burdens on fish farmers while maintaining sustainability through efficient water reuse. Methods: Climbing perch fingerlings were cultured under Advance RAS, Low cost designed RAS and fiberglass reinforced plastic (FRP) (control) tanks in triplicate with meticulous monitoring of various growth parameters and water quality assessments following standard methods. Result: The study reveals that A. testudineus grew better in advanced RAS, with higher weight and length compared to low-cost RAS and FRP tanks. However, the survival rate was highest in the low-cost RAS (100%) versus advanced RAS (97.61%) and FRP tanks (86.77%). Weight gain, specific growth rate, PER and FCR were statistically similar in both RAS systems. Advanced RAS had a higher temperature (29.02oC) and lower pH (7.56) than the low-cost RAS (28.66oC, 7.82) and FRP tanks (28.46oC, 8.25). The low-cost RAS outperformed in dissolved oxygen levels, lower ammonia, nitrite and nitrate content Low-cost RAS demonstrated superior efficiency in controlling total suspended solids (20.00 mg/l) compared to advanced RAS (58.21 mg/l) and FRP tanks (158.74 mg/l) and superior control of total suspended solids. The low-cost RAS offers comparable performance to advanced RAS, with proper filtration maintenance enhancing fish survival and quality.

Biofilm, the aggregates of microbial layers that are attached on the surface of biofilter carriers, plays a central role in the removal and conversion of nutrients in recirculating aquaculture systems (RAS). The bacterial activity in biofilm involves autotrophic and heterotrophic processes. These biological processes are crucial for the water quality in RAS but are difficult to monitor. In this study, we demonstrate a new method based on intermittent respirometry to selectively estimate bacterial activity in biofilm following a spike in substrate concentration. The method was tested with three different biofilter carriers (extruded polypropylene, injection molded polypropylene and polymeric foam) from moving bed biofilm reactors in a common freshwater RAS. Oxygen consumption rates of biofilm-associated bacteria were measured in closed metabolic chambers under standard conditions. The protocol included sequential flushes of either pure tap water, or tap water spiked with nitrite, ammonium or acetate. The results showed consistent carrier-specific metabolic activities of endogenous respiration, nitrite-oxidizing bacteria (NOB), ammonia-oxidizing bacteria (AOB) and heterotrophic bacteria (HB) in biofilm. The highest activities normalized to volumetric oxygen consumption rates, were found in polymeric foam with values of 677 ± 125, 764 ± 156 and 166 ± 36 g O2·m−3·d−1 for NOB, AOB and HB, respectively. The biofilter performance evaluation based on respirometric data showed satisfactory accordance with the values from substrate degradation batch kinetic tests for all three tested carriers, confirming the feasibility and robustness of the method as a means to assessing biofilter performance. Our study provides an on-site tool in biofilter performance tests and leads to a better understanding of dynamic and relationship between biofiltration and water quality.

Microbiota differences of giant river prawn (Macrobrachium rosenbergii) cultured in a recirculating aquaculture system (RAS) – A prototype vertical farming and traditional pond cultured system and their impact on autolysis rate and textural characteristics

The current study evaluated the effects of thermal stress and hypoxia on skin mucus immune and stress responses in an ornamental fish, blue gourami (Trichogaster trichopterus), reared in intensive recirculation aquaculture system (RAS) and semi-intensive traditional pond system (TPS). Fish were derived from RAS and TPS and exposed to thermal (T1: 32 ± 2°C; T2: 12 ± 1°C) and hypoxia (DO: 3–3.5 mg L-1, over 0, 4, 8, 12 and 24 h) stresses. The results showed that the lysozyme and alkaline phosphatase (ALP) activities and the soluble protein contents of skin mucus were significantly higher in fish cultured in RAS than those of TPS, while the lactate dehydrogenase (LDH) and lactate were significantly lower in RAS compared with those of TPS (p < 0.05). Lysozyme activity and the amount of soluble protein showed a significant decrease after exposure to low temperature in both RAS- and TPS-reared fish, while the skin mucus complement activity revealed a significant increase (p < 0.05) at low temperature. Hypoxia condition significantly increased the LDH activity, and the lactate content of fish reared in both RAS and TPS 12–24 h after exposure (p < 0.05). Glucose levels significantly increased after 4 h of exposure to hypoxia (p < 0.05) and then returned to the initial level at 8–24 h after exposure. The results of this study demonstrate that both RAS condition and environmental challenges can affect mucosal immune and stress responses in blue gourami.

Periodic bacterial control with peracetic acid in a recirculating aquaculture system and its long-term beneficial effect on fish health