Total Ammonia Nitrogen Removal Research Articles

Electrical stimulation improves the efficiency of treating typical reclaimed water in biofilters

ABSTRACT To conduct advanced treatment on reclaimed water with a low C/N ratio and a low content of biodegradable organic matter, this paper established an electrically coupled biological filter system (biofilter-microbial electrolysis cell, BF-MEC). Through two-stage influent, the influence of electrical stimulation and electrochemical structure on the nitrogen and carbon removal of the system was explored, and the following results were obtained. The optimal externally applied voltage for the BF-MEC system is 0.55 V. The optimal structure of the BF-MEC system is an electrode spacing of 100 mm, and the optimal electrode position is when the electrode is located at the bottom of the system. Compared with the BF system, in the first stage, the removal rates of chemical oxygen demand, total ammonia nitrogen (TAN), and total nitrogen (TN) in the optimal structure BF-MEC system are increased by 13.4, 118.1, and 273.65%, respectively. In the second stage, COD, TAN, and TN removal rates are increased by up to 277.98, 115, and 722.98, respectively. The optimal electrode position is when the electrode is located at the lower part of the system. At this time, the microbial community is more abundant, the microbial activity and lifespan are longer, and the system efficiency is optimal. optimal.

Investigation of cockleshell waste as a natural biocarrier and its performance efficiency for blackwater treatment in a free-floating plant-constructed wetland

ABSTRACT This study investigated the potential of using waste cockleshell (CS) as a natural biocarrier for blackwater treatment. The CS were analysed for surface porosity, area, volume, elements, and crystal structure. Then, the pilot-scale study confirmed biofilm growth on the CS surface after 29 days, using a crystal violet assay and scanning electron microscopy (SEM) analysis. The free-floating plant-constructed wetland (FFP-CW) was optimally designed with a redox gradient: an aerobic-aquatic zone for nitrification and an anoxic gravel-filled zone for denitrification. The effect of integrating CS biocarriers and active aeration in FFP-CW (aquatic zone) treatment efficiency was investigated. The FFP-CW treatment efficiency for nitrate, chemical oxygen demand (COD), and total ammonia nitrogen (TAN) increased by 9.62%, 6.8%, and 4.83%, respectively, after integrating CS biocarriers of 0.55% filling ratio. Furthermore, the optimal dosage of 192.51 mol of oxygen in FFP-CW increased in TAN and COD removal by 31.11% and 16.54%, respectively. The X-ray diffractometry of CS unravelled aragonite and calcite crystalline forms at 2θ range from 10 to 70°C. The stability of CS biocarriers during 427 days of treatment was monitored using SEM-energy-dispersive X-ray spectroscopy to assess the physical and chemical changes. Thus, CS holds the potential to be a sustainable biocarrier.

Response and recovery of nitrifying moving bed biofilm reactor systems exposed to 1°C with varying levels of ammonia starvation

This study investigated the impact of varying total ammonia nitrogen (TAN) feed levels along with water temperature decreases on the performance of nitrifying moving bed biofilm reactor (MBBR) at 1 °C and its recovery at 3 °C. Five MBBR reactors were operated with different TAN concentrations as water temperature decreased from 20 to 3 °C: reactor R1 at 30 mg N/L, reactor R2 at 20 mg N/L, reactor R3 at 15 mg N/L, reactor R4 at 10 mg N/L and reactor R5 at 0 mg N/L. The corresponding biofilm characteristics were also analyzed to understand further nitrifying MBBR under different TAN feeding scenarios. The findings revealed that the higher TAN levels were before reaching 1 °C, the better nitrification performance and the more biomass grew. However, the highest TAN concentration (30 mg N/L) might negatively affect the nitrification performance, the activity of nitrifiers, and the growth of biofilms at 1 °C because of the toxic effects of un-ionized or free ammonia (FA). It was observed that the activities of ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) were affected by FA concentrations ranging from 0.2 to 0.7 mg N/L at 1 °C, but they could gradually be adapted to such inhibitory environment, with NOB recovering more quickly and robustly than AOB. The study identified 20 mg N/L (67 % of maximum influent TAN at 1 °C in R2 as the optimal TAN feeding concentration, achieving over 90 % TAN removal and a surface area removal rate (SARR) of 0.78 ± 0.02 g N/m2·d at 1 °C. Meanwhile, R2 also exhibited the highest biofilm mass, with total solids at 13.3 mg/carrier and volatile solids at 11.3 mg/carrier. As TAN was removed, nitrite accumulation was observed at 1 °C, and higher influent TAN concentrations prior to 1 °C appeared to delay the accumulation. When water temperature increased from 1 °C to 3 °C, nitrification performance improved significantly in all reactors without nitrite accumulation, and the higher TAN feeding in the previous stage led to faster recovery. Compared with 20 °C, biofilm became thinner and denser at 1 °C and 3 °C. Furthermore, this study revealed significant shifts in microbial community composition and nitrifier abundances in response to changes in water temperature and influent TAN levels. The dominant nitrifiers were identified as Nitrosomonadaceae (AOB) and Nitrospiraceae (NOB). At 1 °C, the nitrifier abundances were significantly correlated with SARRs, FA, and biofilm density. R2, which exhibited the best nitrification performance, maintained higher nitrifier abundances at 1 °C.

Optimal design and modelling of sustainable bio-catalytic enzyme for wastewater treatment using response surface methodology and artificial neural network

ABSTRACT The accessibility of various wastewater treatment systems has become increasingly prominent in current times, coinciding with a rising concern regarding the substantial content of food waste that poses a significant challenge in waste management. In this context, ecoenzymes have emerged as a promising technique for water treatment due to their remarkable efficiency in pollutant removal and cost-effectiveness. Nevertheless, many experts encounter difficulties in determining the optimal combination of ecoenzyme variables to maximize pollutant removal. The objective of this study is to apply a comprehensive approach utilizing Response Surface Methodology (RSM), Artificial Neural Networks (ANN), and Multi-objective Genetic Algorithm (MOGA) methods for the modeling and optimization of ecoenzyme-based water treatment processes. The research outcomes demonstrate a noteworthy alignment between the actual removal rates of Total Suspended Solids (TSS), Volatile Suspended Solids (VSS), and Total Ammonia Nitrogen (TAN) with the values predicted by both RSM and ANN models, validating the robustness of the regression analysis (R2 >0.95). From the optimization results, it is elucidated that to attain the maximum removal of TSS, VSS, and TAN, the treatment process should be conducted over a period of 3.5 days, employing specific enzyme concentrations of 0.07 units/ml for protease, 0.027 units/ml for amylase, and 0.36 units/ml for lipase. This study employed machine learning approaches and MOGA optimization to predict the optimum ecoenzyme properties for maximum wastewater removal utilizing the concept of a low-cost, sustainable purification technology.

Growth, productivity and nutrient removal rates of sea lettuce (Ulva lactuca) in a land-based IMTA system with white seabass (Atractoscion nobilis) in Southern California

Three consecutive 3-week trials were conducted to assess the growth, productivity, and nutrient removal rates of sea lettuce (Ulva lactuca) cultured in effluents from white seabass (Atractoscion nobilis) raceways. All U. lactuca cultivation trials were conducted in 175 L tanks with a surface area of 0.89 m2 run in triplicate, with water quality and growth measurements taken weekly. For the shading trial, U. lactuca was stocked at 0.56 kg/m2 with either 0%, 30%, or 60% shade and seawater supplied at 63 tank volumes per day (vol./day) water exchange (7.6 L/min) for each tank. The removal rate of total ammonia nitrogen (TAN) decreased with increasing shade levels, and the peak exceeded 80% removal at 0% shading. Growth rate and productivity of U. lactuca under 0% shading was 12.09 ± 3.13%/d and 13.28 ± 4.66 g DW/m2/d, which were both significantly higher than other shading levels. For the stocking density and water exchange rate trial, the stocking density of U. lactuca was 0.56 or 1.12 kg/m2, and seawater exchange rates were 4, 12, or 63 vol./day in a 2-factor design. In this trial, TAN removal rates were 100% across all treatment combinations. Growth rate of U. lactuca was highest (20.36 ± 2.36%/d) at 0.56 kg/m2 under the exchange rate of 63 vol./day, and the productivity reached up to 30.89 ± 6.53 g DW/m2/d, which was not different than that of U. lactuca stocked with 1.12 kg/m2 at the same exchange rate (p = 0.47). In a trial comparing sand-filtered seawater (RAW seawater) with seawater effluent from a raceway containing A. nobilis (FISH seawater), TAN removal rate by U. lactuca was consistently nearly 100% when supplied with FISH seawater with a TAN concentration ranging from 0.11 to 0.18 mg/L. Growth rate and productivity of U. lactuca supplied with FISH seawater were 21.36 ± 2.25%/d and 33.83 ± 7.29 g DW/m2/d, respectively, which was not different than that for U. lactuca supplied with RAW seawater. However, the protein content of U. lactuca cultured with FISH seawater was significantly higher and C/N ratio significantly lower than those cultured with RAW seawater (p < 0.01), which indicated that U. lactuca was in a nitrogen-limited situation when cultured with RAW seawater. In light of the better understanding of U. lactuca performance achieved in our study, the optimum U. lactuca and A. nobilis density combinations will be confirmed in future studies based on nitrogen balance to maximize the nutrient removal rates and diversity of seafood production.

INFLUENCE OF SUBCRITICAL WATER PRETREATMENT TEMPERATURE ON PINEAPPLE WASTE BIOGAS EFFICIENCY: EXPERIMENTAL AND KINETIC STUDY

Anaerobic digestion of pineapple waste appears to be an effective method for non-renewable energy substitution through biogas production. The potential power generation from the exploitation of pineapple waste as fuel is estimated to be roughly 20.8 MW. Nevertheless, the intricate composition of pineapple waste, characterized by the complex arrangement of its structure, poses a significant challenge in attaining a substantial amount of biogas production. This study pretreated pineapple waste with subcritical water to increase biogas production. Two temperature settings (120⁰C and 200⁰C) were used for pretreatment. Combined pre-treatment at low temperatures and short time (120⁰C, 5 minutes, 10 water to solid ratio) resulted in 31.6% higher biogas production than untreated. However, pretreatment at high temperatures and longer reaction time (200⁰C,25 min) reduced the biogas production by 9% as compared to untreated. Using the Modified Gompertz kinetic model, pretreatment improved the lag phase and increased biogas production to 14.41 mL/day. The lignocellulosic composition of pre-treated pineapple waste decreased, while process parameters such as total ammonia nitrogen removal and pH improved after the pretreatment. Subcritical water pretreatment, particularly when conducted at high temperatures, did not yield any enhancements in the anaerobic digestion of pineapple waste. As a result, it is not advisable to employ this method for these purposes.

Treatment of sludge from intensive whiteleg shrimp farming using a sequencing batch reactor

The wastewater/sludge generated from the shrimp aquaculture industry contains high levels of nitrogen (N), phosphorous (P), and carbon (C). This study aimed to evaluate the efficacy of N, P, and C removal and recovery from sludge obtained during the siphoning process of intensive white leg shrimp farming by using a sequencing batch reactor (SBR) with two trials. In the first trial, reactors were operated aerobically (3 - 5 days) and anaerobically (4 - 6 days) in sequence, resulting in a total cycle time of 9 days. In trial 2, the reactors were run aerobically for the first 3, 4, &amp; 5 days, respectively, succeeded by anoxic conditions until the end of the experiment on day 14. The results showed that the removal of total ammonia nitrogen and chemical oxygen demand was about 60 - 70%, but the treatment efficiencies of total N and P were extremely low. Moreover, the anaerobic mode improved the mineralization of P, while aerobic condition promoted nitrate production. Further studies are needed to improve the nutrient and organic removal performance of the SBR.

Wood biochar enhances methanogenesis in the anaerobic digestion of chicken manure under ammonia inhibition conditions

The process of breaking down chicken manure through anaerobic digestion is an effective waste management technology. However, chicken manure can be a challenging feedstock, causing ammonia stress and digester instability. This study examined the impacts of adding wood biochar and acid-alkali-treated wood biochar to anaerobically digest chicken manure under conditions of ammonia inhibition. The results highlighted that only the addition of 5 % acid-alkali-treated wood biochar by volume can achieve cumulative methane production close to the typical methane potential range of chicken manure. The treated wood biochar also exhibited highest total ammonia nitrogen removal compared to the Control treatment. Scanning Electron Microscope revealed growing interactions between biochar and methanogens over time. Real-time polymerase chain reaction showed that treated wood biochar produced the highest number of bacterial biomass. In addition, 16S amplicon-based sequencing identified a more robust archaeal community from treated biochar addition. Overall, the acid-alkali treatment of biochar represents an effective method of modifying biochar to improve its performance in anaerobic digestion.

Electrochemically Mediated Ammonia Removal and Recovery from Wastewater Using Functional Membranes

Wastewater treatment plants (WWTPs) typically use anaerobic digestion (AD) to treat sludge, but ammonia produced during AD process returns to the headworks of WWTPs. The amount of ammonia in the liquid stream produced after dewatering the stabilized sludge, commonly referred to as dewatering sidestream, could contribute as high as 20% of the overall ammonia loading to WWTPs. Several sidestream treatment technologies are being developed not only to prevent additional ammonia inputs to WWTPs, but also to valorize ammonia for fertilizer production. Electrochemically mediated processes can achieve this goal in two simultaneous steps: (1) ammonium separation from wastewater through a cation-exchange membrane and (2) ammonium-to-ammonia conversion for its recovery by membrane stripping. Although electrochemical reactions in electrodialysis or flow-electrode capacitive deionization have been shown to drive the separation and increase the solution pH, an acid solution must be externally fed in the subsequent stripping process. Here, we demonstrated the use of bipolar membrane electrodialysis (BMED) to separate ammonium while simultaneously producing acid and base streams. Using a three-compartment BMED cell (effective repeating unit area = 29.2 cm2) with a synthetic sidestream containing 50 mM total ammonia nitrogen (TAN), we achieved TAN removal up to 80% with energy consumption less than 10 kWh kg−1 N at a productivity of 34.2 L m−2-repeating unit membrane area h−1 (LMH). The separated ammonia was recovered (>90%) in a subsequent membrane contactor that was fed with acid and base streams produced from the BMED cell. We specifically focused on increasing TAN concentration in the final product stream by changing relative flow rate of acid/base streams, which allowed for concentrating TAN nearly 8 times greater than the feed. These results show the use of BMED coupled with membrane stripping enables ammonia recovery without the need for chemical inputs, representing a promising sidestream treatment technology.

Total ammonia nitrogen removal and microbial community dynamics in an outdoor HDPE-lined shrimp pond with no water discharge

This study assessed the characteristics of a zero-discharge outdoor high-density polyethylene (HDPE)-lined demonstration aquaculture pond (400 m2) in terms of water quality variables, total ammonia nitrogen (TAN) removal and oxygen net primary production (NPP) indices, and photosynthetic microbiome over a 76-day crop cycle. The shrimp harvest yield was 4.1 t/ha/crop with an average daily gain (ADG) of 0.15 g/day and a feed conversion ratio (FCR) of 1.49. During shrimp cultivation with a semi-intensive stocking density (40 shrimp/m2), there were low levels of TAN (<1.01 mg-N/L), nitrite (<0.21 mg-N/L), and nitrate (<2.79 mg-N/L). Ammonia removal was mainly mediated by photoautotrophic uptake, as evidenced by the consistent estimated TAN uptake rate of 0.05 ± 0.02 g-N/m3 h, which was calculated based on photosynthesis. The overall TAN removal rate of 0.10 ± 0.08 g-N/m3 h was maintained by suspended microorganisms in water, which exceeded that of microorganisms attached to the HDPE liner surface. A positive oxygen NPP of 0.24–1.16 g-O2/m3 h during light availability indicated prevailing autotrophic conditions. The bacterial community in the water was dominated by Phyla Pseudomonadota (Proteobacteria; 16–32%), Bacteroidota (Bacteroidetes; 15–29%), Cyanobacteria (7–35%), and Actinomycetota (Actinobacteria; 3–39%). The chloroplast amplicon sequence variants (ASVs) indicated abundances of Bacillariophyta (27–97%) and Chlorophyta (0.4–67%). High centric diatom populations (Bacillariophyta) were detected throughout cultivation, while the proportion of green algae (Chlorophyta) was positively correlated with increased TAN availability when feeding was increased. The findings enabled estimations of TAN removal and oxygen NPP rates and provided an understanding of correlations between environmental variables and bacterial and phytoplankton populations in the outdoor lined shrimp pond.

Sustainable practice for a zero-discharge outdoor earthen shrimp pond based on biological nitrogen waste carrying capacity

In this study, we proposed a sustainable practice for managing an environmentally friendly outdoor earthen ponds for shrimp biomass production based on biological nitrogen treatment processes. A 26-day bottom soil acclimation was operated under appropriate oxygen (> 5 mg/L) and alkalinity (100–150 mg-CaCO3) concentrations, followed by a 76-day Penaeus vannamei cultivation in small (0.04 ha; pond I) and large (0.16 ha; pond II) ponds without water exchange and the addition of probiotic bacteria. With the proper pond preparation, the nitrification process was promoted during the pond acclimation period, as demonstrated by the conversion pattern of total ammonia nitrogen (TAN) oxidation to nitrite. During shrimp cultivation, the acclimated ponds were able to control TAN and nitrite concentrations below acceptable limits (< 0.2 mg-N/L) while the TAN build-up was reported when the feeding rate exceeded 220 kg-feed/ha/day, indicating the limitation of the nitrogen waste carrying capacity. Additionally, pond acclimation encouraged bacterial activities, especially assimilation and nitrification processes, with higher rate indices of TAN removal (0.048–0.069 g-N/m2/h) compared to photoautotrophic uptake (0.014–0.028 g-N/m2/h). The overall TAN carrying capacity was extrapolated to be 1.31–2.00 g-N/m2/day. Biological treatment processes all contributed to low dissolved inorganic nitrogen (DIN) accumulation (4.8–6.0%) and high unidentified nitrogen loss (54.7–59.3%). The pond ecological balance also promoted phytoplankton growth at chlorophyll-a concentration of 122.34–169.66 mg/m3. Oxygen evolution index by photosynthesis (2.65–2.98 g-O2/m2/h) was sufficient for the consumption of both water (1.85–1.96 g-O2/m2/h) and bottom soil (0.09–0.12 g-O2/m2/h); however, mechanical aeration was necessary during a light absence period due to lower rate of extrapolated daily photosynthesis (31.81–35.81 g-O2/m2/day) compared to the respiration rate indices of water and bottom soil (45.88–47.57 g-O2/m2/day). High shrimp production of 7.9–9.2 t/ha/crop was achieved with the average daily gain (ADG) of 0.29–0.31 g/day and the feed conversion ratio (FCR) of 1.13–1.28. These findings contributed to the strategic development of pond acclimation and the sustainability of outdoor earthen shrimp ponds in terms of both ecosystem balance and the profitability of high biomass production.

Effects of dissolved organic carbon and total ammonia nitrogen concentrations with the same DOC/TAN on biofloc performance

The regulation of the carbon-to‑nitrogen ratio (C/N) is at the core of biofloc technology. This study compared the performance of bioflocs under different dissolved organic carbon (DOC) and total ammonia nitrogen (TAN) concentrations but the same DOC/TAN ratio. Dissolved organic carbon and total ammonium nitrogen were set at 200 mg/L and 10 mg/L (Group 200/10), 100 mg/L and 5 mg/L (Group 100/5), and 50 mg/L and 2.5 mg/L (Group 50/2.5), respectively. The TAN removal rates of groups A, B, and C were 1.89 ± 0.02 mg N/g TSS·h, 1.63 ± 0.03 mg N/g TSS·h, and 1.32 ± 0.02 mg N/g TSS·h, respectively, and the differences were significant (P < 0.05). At the phylum level, the microbial community structure was dominated by Proteobacteria, Bacteroidetes, Actinobacteria, Verrucomicrobia, and Planctomycetes. At the genus level, Gemmobacter, Hydrogenophaga, and Microbacterium were the dominant genera. Most of bacteria community differed significantly among the three groups. As the concentration of carbon and nitrogen sources increased, the Shannon index showed a decrease in bacterial diversity, and the number of heterotrophic bacteria significantly increased. The crude protein content of flocs in group A ((29.22 ± 0.20)%) was significantly lower than that in groups B ((30.56 ± 0.32)%) and C ((30.83 ± 0.20)%). In groups A and B with higher carbon and nitrogen concentrations, the copy numbers of genes related to nitrification were relatively low, but the copy numbers of genes related to denitrification were relatively high. Therefore, it can be concluded that with a ratio of 20 of DOC/TAN, increasing DOC and TAN concentrations led to a significant increase in TAN removal capacity, heterotrophic bacteria count, denitrification function gene copies, and crude protein content of bioflocs, and a decrease in bacterial diversity, nitrification function gene copies, and C/N of bioflocs (P < 0.05). These results suggest that the influence of DOC and TAN concentrations on bioflocs performance may be more significant than that of DOC/TAN, and should be fully considered in practical bioflocs technology systems.

Rhizofiltration potential of floating aquatic macrophytes (FAMs) in Nile Tilapia (Oreochromis niloticus L.) tanks

Currently additional sustainable ways to mitigate the degradation of water quality are being researched all over the world. Phytoremediation is one of the serious efforts towards sustainability. The main objective of this study was to assess the rhizofiltration potential of water lettuce (Pistia stratiotes), common duckweed (Lemna minor) and mosquito fern (Azolla pinnata) on the removal of total ammonia-nitrogen (TAN) in circular outdoor tanks. Physico-chemical water quality parameters such as dissolved oxygen (DO), temperature and pH were also monitored. It was observed that the mean initial TAN concentration in all treatments were statistically comparable. In the final TAN concentration, tank with L. minor had the highest TAN concentration which was significantly different to tanks with P. stratiotes and A. pinnata. Likewise, tanks with L. minor had the lowest removal efficiency. For the DO concentration, it was observed that DO in all treatments was depleted in the first one week of the study. However, on the ninth day of the study, DO started to rise. Tanks with P. stratiotes had shown the highest trend among treatments. Mean temperature and pH in all treatments were statistically comparable. For the relationship of root length and TAN removal efficiency of floating aquatic macrophytes, it was observed that there was a strong positive correlation. These results show that the utilization of these floating aquatic macrophytes as bioremediator in small-scale tilapia production are feasible. In addition, other physico-chemical water quality parameters such as phosphorus, total dissolved solids, alkalinity, hardness, nitrate, and nitrite can be conducted.

Evaluation of the main pollutants present in Brazilian landfill leachates using ecotoxicity assays

The present study investigated the acute toxic effects caused by the main pollutants found in landfill leachates: total ammonia nitrogen (TAN), alkalinity, and humic substances (HS) for the test organisms Vibrio fischeri, Danio rerio, Daphnia similis, and Artemia sp. The leachates were obtained from two Brazilian landfills with different ages and operating modes. Air stripping and membrane filtration treatability experiments were performed to remove pollutants from the leachate. The results showed high toxicity of the raw leachate from both landfills for the studied organisms. In the individual treatments, air stripping achieved TAN and alkalinity removal efficiencies > 99%, and the membrane filtration treatment achieved HS removal efficiencies > 98%. Compared to the individual treatments, the combination of treatments resulted in the most significant reductions in leachate toxicity from both landfills for all test organisms studied. The principal component analysis showed a strong correlation between COD or HS parameters and the toxicity of V. fischeri and strong correlations between TAN and the toxicity of D. rerio, D. similis, and Artemia sp. Finally, this study highlights the application of a treatment route to remove acute toxicity from complex effluents, such as landfill leachate, to avoid potential environmental hazards to the aquatic ecosystem.

Chlorine vs. Sodium Chloride Regeneration of Zeolite Column for Ammonium Removal from an Explosives Impacted Mining Wastewater

There has only been limited research on ammonium removal by zeolites followed by chlorine regeneration; these studies used batch tests and, in many cases, only dealt with single solute solutions as opposed to multi-component ones. To better simulate full-scale applications, this study used a continuous-flow ion exchange (IE) column system to assess the feasibility of chlorine regeneration of a zeolite IE column used for the removal of ammonium from synthetic explosives impacted mining wastewater (EIMWW). Multi-cycle column loading-regeneration tests were used to evaluate and compare the performance of a NaOCl (1000 ppm as free Cl2) solution with that of a standard salt regeneration solution (5% NaCl). In addition, the impact of two loading cycle durations was evaluated. After three operational cycles with 6 h loading phases, the TAN (total ammonia nitrogen) uptake after NaOCl regeneration was almost the same as that obtained with salt regeneration (0.21 meq/g vs. 0.21 meq/g). The zeolite with NaOCl regeneration showed a higher preference for TAN than with NaCl regeneration (Ca:TAN:K = 2.8:2.3:1 vs. 2.5:1.9:1 for the 6 h loading phase); however, the NaOCl regeneration took longer to complete. It was also found that effluent pH, total chlorine level, and free chlorine level during the chlorine regeneration were positively related, seemingly confirming that the ammonium is oxidized to nitrogen gas and producing hydrogen ions. Regardless of the regeneration solution, if one uses a two-column system, with one column online and the other offline, the shorter loading cycles (6 h) yield a substantially higher daily TAN removal rate.

Effect of biocarrier material on nitrification performance during start-up in freshwater RAS

Biofilters are key components in recirculating aquaculture systems (RAS). For ensuring cost-efficient function of biofilters, characteristics of biocarriers such as shape, material, surface area, density, longevity, and price needs to be evaluated. In this study, we compared otherwise identical biocarriers made of polyethylene (PE) against ones made of polypropylene (PP) and PP biocarriers with three different levels of pigment (carbon black) addition (without added pigment, semi-pigmented, fully-pigmented). The four types of biocarriers were tested in 12 parallel moving bed bioreactors under identical conditions receiving water from a semi-commercial freshwater RAS with rainbow trout. Measurements of total ammonium nitrogen (TAN) and nitrite-nitrogen (NO2--N) removal rates and nitrification kinetics were carried out by spiking events with NH4Cl or NaNO2 two, four, and six weeks after start-up. The results showed all biofilters removed TAN only after two weeks of operation, and that biofilters with PP biocarriers had a shorter maturation time, reaching their maximum TAN removal rate at week 4, while PE biofilters reached equal maximum at week 6. Biofilters with PE had generally lower NO2--N removal rates and first-order reaction constants than PP biofilters. Pigmentation level had a minor effect on TAN and NO2--N removal rates and kinetics, as fully pigmented biocarriers initially were found to have lower removal rates and first order constants for TAN and NO2--N than semi-pigmented or biocarriers without added pigment. Overall, the results suggest that PE is inferior biocarrier material than PP, due to the longer start-up period and nitrite accumulation, which might be related to the differences in the surface characteristics between these two materials. Furthermore, the results indicate that pigment addition does not provide any extra benefit for nitrification.

Mathematical modelling of an intermittent anoxic/aerobic MBBR: Estimation of nitrification rates and energy savings

This study aimed at modelling the performance of a novel MBBR configuration, named A/O-MBBR, comprised of a pre-anoxic reactor, with an HRT of 4.5 h, coupled with an intermittent anoxic/aerobic MBBR (HRT = 6.8 h). The lab-scale system was fed with municipal wastewater with an average influent Total Ammonia Nitrogen (TAN) and total COD (TCOD) concentrations of 46 mg of TAN-N L−1 and 310 mg TCOD L−1. During the whole experimental period, TAN removal efficiency was always higher than 96%; denitrification was also very effective, achieving nitrate and nitrite concentrations in the effluent both lower than 5 mg NOx-N L−1 on average. Moreover, TCOD average removal efficiency was equal to 85%. Modelling was performed to investigate the nitrification efficacy enhancement; to this aim, a biofilm model was developed, adopting the equations for mixed-culture biofilms and the Activated Model Sludge n°1 (ASM1) for the biological processes rates. The model allowed to determine the maximum uptake rate for autotrophic growth (μA was 2.5 d−1) and the semisaturation constant (KOA was 0.2 mg O2 L−1), suggesting that the nitrification process was 3-fold faster than average and very effective at low oxygen concentrations. The model estimated that about 85% of TAN was removed by the biofilm and only the remaining part by suspended biomass in the bulk liquid. Finally, it was assessed that the A/O-MBBR configuration allowed for a 45–60% savings of the energy requirement compared to a Benchmark WWTP layout.

Robust non-toxic macroscale beads with antibacterial and contaminant scavenging properties for aquaculture

Non-toxic macroscale (few millimeters in diameter) cationic antibacterial beads were made for suppression of bacteria in fish culture. The beads were formed by the diffusion-driven layer by layer (dd-LBL) process using graphene oxide substrate and branched polyethyleneimine and were stabilized by post-assembly crosslinking process in which carboxyl groups on the graphene oxide were crosslinked with amine groups on the branched polyethyleneimine using 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride/N-hydroxysuccinimide (EDC/NHS) chemistry. The crosslinked beads have negligible in vitro toxicity to 3T3 cells and zebrafish embryos. Further, the crosslinked beads exhibit excellent antibacterial activity, which can reach over 99.9% inactivation against Escherichia coli (E. coli) in 30 min even with ultrahigh (~ 108 CFU/mL) E. coli concentration. The antibacterial activity of the crosslinked beads can be regenerated with a simple procedure and remains high in the 10th cycle of regeneration. The crosslinked beads have much improved mechanical stability compared to the raw (uncrosslinked) beads. The highly porous structure and abundant functional groups of the crosslinked beads give them high adsorption capacity towards various forms of organic matter such as fish waste. Addition of zeolite nanoparticles during the bead formation process and subsequent chemical crosslinking with hyaluronic acid makes these beads suitable for removal of total ammonia nitrogen (TAN) while preserving the antibacterial activity and biocompatibility.

An Eco-Friendly Conversion of Aquaculture Suspended Solid Wastes Into High-Quality Fish Food by Improving Poly-β-Hydroxybutyrate Production

The aquaculture industry is vital in providing a valuable protein food source for humans, but generates a huge amount of solid and dissolved wastes that pose great risks to the environment and aquaculture sustainability. Suspended solids (in short SS), one of the aquaculture wastes, are very difficult to be treated due to their high organic contents. The bioconversion from wastewater, food effluents, and activated sludge into poly-β-hydroxybutyrate (PHB) is a sustainable alternative to generate an additional income and could be highly attractive to the agricultural and environmental management firms. However, little is known about its potential application in aquaculture wastes. In the present study, we first determined that 7.2% of SS was PHB. Then, the production of PHB was increased two-fold by the optimal fermentation conditions of wheat bran and microbial cocktails at a C/N ratio of 12. Also, the PHB-enriched SS showed a higher total ammonia nitrogen removal rate. Importantly, we further demonstrated that the PHB-enriched SS as a feed could promote fish growth and up-regulate the expression of the immune-related genes. Our study developed an eco-friendly and simple approach to transforming problematic SS wastes into PHB-enriched high-quality food for omnivorous fish, which will increase the usage efficiency of SS and provide a cheaper diet for aquatic animals.

Wood Biochar Enhances the Valorisation of the Anaerobic Digestion of Chicken Manure

In this study, the efficacy of biochar to mitigate ammonia stress and improve methane production is investigated. Chicken manure (CM) was subjected to high-solid mesophilic anaerobic digestion (15% total solid content) with wood biochar (BC). Wood biochar was further treated using HNO3 and NaOH to produce acid–alkali-treated wood biochar (TBC), with an improvement in its overall ammonium adsorption capacity and porosity. Three treatments were loaded in triplicate into the digesters, without biochar, with biochar and with acid–alkali-treated biochar and maintained at 37 °C for 110 days. The study found a significant improvement in CH4 formation kinetics via enhanced substrate degradation, leading to CH4 production of 74.7 mL g−1 VS and 70.1 mL g−1 VS by BC and TBC treatments, compared to 39.5 mL g−1 VS by control treatments on the 28th day, respectively. However, only the use of TBC was able to prolong methane production during the semi-inhibition phase. The use of TBC also resulted in the highest removal of total ammonia nitrogen (TAN) of 86.3%. In addition, the treatment with TBC preserved the highest microbial biomass at day 110. The presence of TBC also resulted in an increase in electrical conductivity, possibly promoting DIET-mediated methanogenesis. Overall, the acid–alkali treatment of biochar can be a novel approach to improve biochar’s existing characteristics for its utilisation as an additive in anaerobic digestion.