Ammonia Removal Rate Research Articles

Performance of an immobilized microalgae-based process for wastewater treatment and biomass production: Nutrients removal, lipid induction, microalgae harvesting and dewatering

Immobilized microalgae are good for wastewater treatment and biomass production. This study investigated treatment efficiency of a continuously operated system employing immobilized microalgae for secondary effluent of wastewater treatment plants, as well as the effectiveness on induction of valuable products, harvesting and dewatering of microalgae biomass. Under semi-continuous operation condition, microalgal dry weight increased 4.75 times within 2 d, associated with the highest removal rate of ammonia and phosphate at 28.95 mg/L·d and 4.83 mg/L·d, respectively. An immobilized microalgae membrane bioreactor (iMBR) was continuously operated for a month. The harvested immobilized microalgae beads were transferred to induction stage to obtain 4.5 times increase of lipid content per cell within 2 d. Immobilized microalgae performed 1.9 cm/s settling velocity and 97% water removal efficiency around 40 °C. A prospective integrated process on resource recovery and carbon neutrality was proposed for wastewater treatment, induction, harvesting and dewatering of immobilized microalgae cells.

Effect of peracetic acid solution on a nitrifying culture: Kinetics, inhibition, cellular and transcriptional responses

Peracetic acid (PAA) has been widely used as a disinfectant in many industries. However, information related to the potential inhibitory effect of PAA solutions (PAA and H2O2) on biological wastewater treatment processes is very limited. The work reported here assessed the effect of PAA and H2O2 solutions on nitrification kinetics and inhibition, cellular level responses and gene expression of a suspended-growth nitrifying culture. The initial ammonia removal and nitrate production rates significantly decreased at 1/0.14 to 3/0.42 mg/L PAA/H2O2. H2O2 up to 3 mg/L did not impact nitrification, cell viability or related respiratory activities; thus, the impact of the PAA solution is attributed to PAA alone or in some combination with H2O2. Nitrification inhibition by PAA was predominantly related to enzyme inhibition, rather than to loss of cell viability and/or cell lysis. PAA and H2O2 negatively affected Nitrosomonas but resulted in Nitrosospira enrichment. Most nitrogen metabolism-related genes (e.g., hydroxylamine oxidoreductase and nitrite oxidoreductase genes) as well as oxidase genes (e.g., cytochrome c oxidase, catalase-peroxidase, and peroxidase genes) were upregulated in PAA- and H2O2-amended cultures. Major ATPase genes were downregulated while ATP synthase genes upregulated under the effect of PAA and/or H2O2. Upregulation of ATP-dependent protease genes indicates protein damage predominantly caused by PAA rather than H2O2. The transcriptional level of genes related to cell division and DNA repair did not show a particular pattern; thus, cell division functionality and DNA integrity were not significantly affected by PAA or H2O2. The results of this study have significant implications in the design and operation of effective biological nitrogen removal systems for the treatment of PAA-bearing wastewater.

Oxygen vacancies enhancing performance of Mg-Co-Ce oxide composite for the selective catalytic ozonation of ammonia in water

Catalytic ozonation based on heterogeneous metal oxides is a promising approach to removing ammonia as gaseous nitrogen from water. Herein, MgO/Co3O4/CeO2 was prepared for catalytic ozonation of ammonia in an aqueous solution. The influence of various reaction conditions was systematically investigated and optimized, in which the reaction kinetics was also analyzed. After doping Ce, the catalyst with Mg-Co-Ce molar ratio of 4:1:1 and calcined at 700 °C for 3 h, has abundant surface oxygen vacancies and exhibited excellent performance for the selective catalytic oxidation of ammonia to gaseous nitrogen by ozone. It was found that the catalytic activity of catalysts was positively related to oxygen vacancies concentration on the composites surface, which might play a vital role in selective catalytic ozonation. Under the optimal conditions, the ammonia removal rate in MgO/Co3O4/CeO2 catalytic system was 0.03328 min−1 (R2 = 0.99942), about 2.1 times greater than that of MgO/Co3O4 (0.01597 min−1, R2 = 0.99813), and the selectivity was further enhanced from 73.57% to 86.94%. Moreover, the evolution of nitrogen and chlorine species was determined to discuss the mechanism of selective oxidation of ammonia in the low chlorine-containing solution. This study might promote the understanding of catalytic ozonation of ammonia to gaseous nitrogen selectively.

Efficient nitrogen removal from onsite wastewater by a novel continuous flow biofilter

Soil-based passive biofiltration system is an economically feasible technology for nitrogen removal from onsite wastewater. However, the conventional design requires a large system footprint with limited treatment capacity. In this study, a novel continuous flow biofilter (CFB) with adjustable recirculation and continuous flow pattern was developed for onsite wastewater treatment with a small footprint. Efficient total nitrogen removal (80.1–97.5%) was observed at various hydraulic loadings (0.03–0.12 m3 m−2 d−1), nitrogen loadings (1.1–8.6 g N m−2 d−1) and recycle ratios (2–3) when treating septic tank effluent (STE), with low effluent TN (0.7–13.6 mg N L−1). Nitrous oxide was observed in the denitrification effluent indicating incomplete denitrification at elevated dissolved oxygen levels (3.3–5.8 mg L−1). Nitrogen removal rate (2.9–7.0 g N m−2 d−1) and ammonium removal rate (2.4–7.2 g N m−2 d−1) were positively correlated with nitrogen loadings increase (1.1–8.6 g N m−2 d−1) but were not significantly impacted by the hydraulic loading rate change (0.08–0.12 m3 m−2 d−1). The total biomass abundance and nitrifying microorganisms decreased significantly as the nitrification columns depth increased, while homogeneous microbial distribution was observed in the denitrification columns. The abundance of ammonium oxidizing archaea (AOA) increased significantly at increased hydraulic and nitrogen loading rate, while the ammonium oxidizing bacteria (AOB) abundance remained steady. The abundance of functional genes involved in denitrification process (nirS, nirK and nosZ) responded differently when hydraulic and nitrogen loading rate changes. Collectively, this study suggested the CFB could efficiently remove nitrogen from onsite wastewater with fluctuating influent compositions and various hydraulic loadings.

Influence of ammonia and NaCl on nitrifying community and activity: Implications for formulating nitrifying culture augmentation

Bioaugmentation of nitrifying cultures can accelerate nitrification during startup and transition periods of recirculating aquaculture system (RAS) operations. To formulate nitrifying cultures for RASs, impacts of ammonia and salinity (NaCl) on culturing nitrifying microorganisms were comprehensively investigated by including currently known groups of nitrifying microorganisms (ammonia oxidizing bacteria (AOB), ammonia-oxidizing archaea (AOA), comammox, Nitrospira, and Nitrobacter). By varying ammonia loading rate (ALRs of 1.6, 8, 20, 40, 60 and 150 mgN/L/d) of continuous-flow bioreactors fed with inorganic medium experimented for culture preparation, cultures containing distinct patterns of nitrifying communities were produced. Operating the reactors at the ALRs of ≤40 mgN/L/d, resulting in the effluent total ammonia nitrogen (TAN) and nitrite concentrations of ≤2.64 and ≤0.53 mgN/L, respectively, delivered the consortia consisting of a broad spectrum of substrate affinity nitrifying microorganisms. At the lower ranges of these ALRs (≤8 mgN/L/d), the most desirable consortia comprising comparable numbers of AOB, AOA, and comammox could be produced (the effluent TAN concentrations of ≤0.20 mgN/L), which would be resilient for applying in various RAS types. Enriching the cultures at the ALRs of ≥60 mgN/L/d allowed only the nitrifying microorganisms with low substrate affinity to dominate, incongruent with the consortia found in actual RASs. AOB were adaptable at all salinity studied (2, 15, and 30 g/L), while AOA and comammox were sensitive to elevated salinity (15 and 30 g/L, respectively). The ammonia removal rate of a culture prepared at 2 g/L salinity decreased largely when applied at 15 and 30 g/L. In contrast, those prepared at 15 and 30 g/L were more robust to different salinity. Separately preparing the cultures at different salinity for uses in freshwater-low salinity and brackish-marine RASs is recommended. The findings of this work enhance our understanding on how to formulate nitrifying culture augmentation for used in different RAS types.

Ammonium removal by erythrocyte-bioreactors based on glutamate dehydrogenase from Proteus sp. jointly with porcine heart alanine aminotransferase

Excessive ammonium blood concentration causes many serious neurological complications. The medications currently used are not very effective. To remove ammonium from the blood, erythrocyte-bioreactors containing enzymes that processing ammonium have been proposed. The most promising bioreactor contained co-encapsulated glutamate dehydrogenase (GDH) and alanine aminotransferase (ALT). However, a low encapsulation of a commonly used bovine liver GDH (due to high aggregation), makes clinical use of such bioreactors impossible. In this study, new bioreactors containing ALT and non-aggregating GDH at higher loading were first produced using the flow dialysis method and the new bacterial GDH enzyme from Proteus sp. The efficacy of these erythrocyte-bioreactors and their properties (hemolysis, osmotic fragility, intracellular and extracellular activity of included enzymes, erythrocyte indices, and filterability) were studied and compared with native cells during 1-week storage. The ammonium removal rate in vitro by such erythrocyte-bioreactors increased linearly with an increase in encapsulated GDH activity. Alanine in vitro increased in accordance with ammonium consumption, which indicated the joint functioning of both included enzymes. Thus, novel bioreactors for ammonium removal containing GDH from Proteus sp. are promising for clinical use, since they have a more efficient GDH encapsulation and their properties are not inferior to previously obtained erythrocyte-bioreactors.

Metagenomic insights into responses of microbial population and key functional genes to fulvic acid during partial nitritation

The long-term impact of fulvic acid (FA) on partial nitritation (PN) system was initially examined in this study. The obtained results revealed that the FA lower than 50 mg/L had negligible effect on the nitrite accumulation rate (NAR nearly 100%) and ammonium removal rate (ARR 56.85%), while FA over 50 mg/L decreased ARR from 56.85% to 0.7%. Sludge characteristics analysis found that appropriate FA (<50 mg/L) exposure promoted the settling performance and granulation of PN sludge by removing Bacteroidetes and accumulating Chloroflexi. The analysis of metagenomics suggested that the presence of limited FA (0-50 mg/L) stimulated the generation of NADH, which favors the denitrification and nitrite reduction. The negative impact of FA on the PN system could be divided into two stages. Initially, limited FA (50-120 mg/L) was decomposed by Anaerolineae to stimulate the growth and propagation of heterotrophic bacteria (Thauera). Increasing heterotrophs competed with AOB (Nitrosomonas) for dissolved oxygen, causing AOB to be eliminated and ARR to declined. Subsequently, when FA dosage was over 120 mg/L, Anaerolineae were inhibited and heterotrophic bacteria reduced, resulting in the abundance of AOB recovered. Nevertheless, the ammonium transformation pathway was suppressed because genes amoABC and hao were obviously reduced, leading to the deterioration of reactor performance. Overall, these results provide theoretical guidance for the practical application of PN for the treatment of FA-containing sewage.

Symbiotic treatment of ammonia-nitrogen wastewater by algae and activated sludge: effects of algae and sludge inoculation rates

ABSTRACT A symbiotic microalgal-bacterial system may be an optional technology for wastewater treatment. It was composed of microalgae and activated sludge and established in the SBR to explore the effect of different dosing ratios of algae and sludge on the removal of nitrogen and phosphorus from simulated wastewater containing ammonium. It can be seen from the result that varied algae–sludge dosing ratios had a higher removal effect on COD removal, but the difference was not significant. The algal-bacterial symbiosis system had a 100% removal rate for ammonium removal on the 8th day. Relatively speaking, the removal of nutrients and related mechanisms vary with environmental conditions (inoculation rate). In general, when the additive ratio was 5:1 (algae: AS), the removal rate of TN and TP was the highest, reaching 53.85% and 85.13% in the shortest time (14 days), among them, the removal rate of ammonium and COD was 100%, and the reduction rates of Nitrite nitrogen and Nitrate nitrogen were 362.99% and 73.42%, respectively. In addition, 16S rDNA gene analysis results demonstrated that the microbial community in the reactor with algal sludge inoculation ratio of 5:1 had differences in three stages of the initial reaction, the middle reaction and the end of the reaction. Comamonadaceae, Flavobacterium, Paenarthrobacter, Mesorhizobium, Nitrobacter were enriched during the reaction operation.

Fine powders from dyed waste wool as odor adsorbent and coloration pigment

Herein, waste dyed wool was transferred into wool powder (WP) using a mechanical pulverization process. This powder benefits from the rich exposed functional groups and porous structures, which endow WP with capacities to adsorb odor molecules. WP milled for 6 h exhibited improved properties including homogeneous surfaces, small mean particle size (3.63 μm) and increased surface area, contributing to its highest odor ammonia adsorption capacity (2.65 mg g−1) and removal rate (91%) among all tested samples. Loading with WP endows cotton fabrics (CF) with greatly improved deodorizing properties and vivid color. WP-coated CF displayed improved ammonia removal properties compared to pristine CF, achieving 65.71% adsorption rate. The K/S value of WP-coated CF reached 1.844 at o.w.f.% of 15. Coated fabrics also showed stable color fastness to washing. This study paves the way for using powders from waste as both odor adsorbent and coloring pigment for fabric functionalization.

Impact of influent strengths on nitrous oxide emission and its molecular mechanism in constructed wetlands treating swine wastewater

Constructed wetlands (CWs) can remove nitrogen (N) through plant assimilation and microbial nitrification and denitrification, while it also releases large greenhouse gas nitrous oxide (N2O) into the atmosphere. However, N2O emissions and the underlying microbial mechanisms of CWs when treating high-strength wastewater have not been systematically surveyed. Here, the effect of three influent strengths on N2O emissions in a pilot-scale CW treatment of swine wastewater was determined and the underlying microbial mechanisms were explored. The results showed that the removal rates of ammonium (NH4+) and total nitrogen (TN) increased significantly with the increasing influent strengths, however, the ratio of N2O emission/TN removal rose by 1.5 times at the same time. Quantitation of microorganisms responsible for N-cycle in the sediment indicated that the abundance of ammonia-oxidizing bacteria (AOB) in high influent strengths (COD, 962.38 ± 3.05 mg/L; NH4+, 317.89 ± 4.24 mg/L) was 51.6-fold compared with that in low influent strengths (COD, 516.94 ± 4.18 mg/L; NH4+, 100.65 ± 2.65), and AOB gradually replaced ammonia-oxidizing archaea (AOA) to dominate ammonia oxidizers. Structural equation models demonstrated that NO2− accumulations promoted the ratio of AOB/AOA, which further led to an increase in the ratio of N2O emission/TN removal. It is worth noting both the N removal rates and N2O emissions increased with the increasing influent strength. To obtain reduced N2O emissions, pretreatment technology for strength reduction should be supplemented before high-strength wastewater enters the CWs. This study may shed new light on the sustainable operation and application of CWs.

New insight into the nitrogen removal capacity and mechanism of Streptomyces mediolani EM-B2

The utilization of actinomycetes as the bioresources for heterotrophic nitrification and aerobic denitrification is rarely reported due to the lack of work to explore their nitrogen biodegradation capabilities. Streptomyces mediolani EM-B2 belonging to actinomycetes could effectively remove high concentration of multiple nitrogen forms, and the maximum removal rates of ammonium, nitrate and nitrite reached 3.46 mg/(L·h), 1.71 mg/(L·h) and 1.73 mg/(L·h), respectively. Nitrite was preferentially consumed from the simultaneous nitrification and denitrification reaction system. Nitrogen balance analysis uncovered that more than 37% of the initial total nitrogen was converted to nitrogenous gas by aerobic denitrification. Experiments with specific inhibitors of nitrification and denitrification revealed that strain EM-B2 contained ammonia monooxygenase, hydroxylamine oxidoreductase, nitrate reductase and nitrite oxidoreductase, which were successfully expressed and detected as 0.43, 0.59, 0.12 and 0.005 U/mg proteins, respectively. These findings may provide new insights into the actinomycetes for bioremediation of nitrogen pollution wastewater.

Unveiling microbial electricity driven anoxic ammonium removal

Microbial electricity-driven anoxic ammonium removal could remove ammonium from wastewater without the presence of oxygen (aeration) using electricity. This study aims at unveiling the potential biologic pathways for the bioelectrochemical oxidation of ammonium to dinitrogen gas in an anaerobic bioelectrochemical system (BES). Known intermediate metabolites of this process (hydroxylamine, nitrite and nitrate) were monitored in two BES replicates. Ammonium was fully oxidized to dinitrogen gas without intermediates accumulation in the anodic chamber. Achromobacter sp. was the most abundant microorganism (up to 60%, according to sequence reads) in the mixed community. Hydroxylamine and nitrite oxidation were electroactive processes, reinforcing the role of the anodic electrode as the electron acceptor for ammonium oxidation. Taking it all together, ammonium can be removed in BES by a combination of different bio/electrochemical processes. A deeper understanding on how the different metabolisms are coupled together is required for increasing the current ammonium removal rates.

Influence of diet and feeding strategy on the performance of nitrifying trickling filter, oxygen consumption and ammonia excretion of gilthead sea bream (Sparus aurata) raised in recirculating aquaculture systems

Gilthead sea bream (Sparus aurata) was raised in six individual recirculating aquaculture systems (RAS) whose biofilters’ performance was analyzed. Fish were fed with three different diets (a control diet, a fishmeal-based diet (FM), and a plant meal-based diet (VM)) and with three different feeding strategies (manual feeding to apparent satiation, automatic feeding with restricted ration, and auto-demand feeding). For every combination of diet and feeding strategy, the mean oxygen consumption, ammonia excretion, and ammonia removal rate were determined. Fish fed with the VM diet consumed the most oxygen (20.06 ± 1.80 gO2 consumed kg−1 day−1). There were significant differences in ammonia excretion depending on the protein content and protein efficiency of the diet, as well as depending on feeding strategy, which in turn affected ammonia removal rates. Fish fed by auto-demand feeders led to the highest mean ammonia removal rate (0.10 gN-TAN removed m−2 biofiltration area day−1), while not leading to peaks of high ammonia concentration in water, which preserve fish welfare and growth.

Ammonium Removal from Ammonium Rich Solution by Bio Char

When biochar made from waste pallet was added to treated livestock wastewater, the total nitrogen and ammonium ion concentrations decreased, with removal rates over 10 days of about 60% and 30%, respectively. Bacteria were isolated with high ammonium removal ability and they were identified based on their 16S rRNA gene sequences. Anaerobic denitrifying Cronobacter spp. was isolated from the biochar used for water purification. When each strain was cultured in a liquid medium containing ammonium sulfate (initial ammonium concentration 30 mg/L), the highest ammonium removal rates were 83.8% - 96.5%. Organic acids were more effective than carbohydrates as sole carbon sources for nitrogen removal from wastewater. The absorbance at 660 nm increased with nitrogen removal, indicating that cells proliferated, so it was presumed that ammonium was taken up by assimilation.

Test of Membrane Aerated Biofilm Reactors for Nitrogen Removal in Wastewater Treatment

Membrane aerated biofilm reactor, as a biological wastewater treatment technology, has been nearly mature on a commercial scale. It uses bubble-free aeration to provide oxygen for biological nitrification and wastewater degradation. A novel oxygen-permeable hollow fiber membrane (Zeelung cord) specifically designed for use in a membrane aerated biofilm reactors (MABR). These fibers are organized into bundles, which are wrapped around the reinforcing core to increase strength. This permeable membrane allows oxygen to diffuse into the attached biofilm, which directly leads to the biological oxidation of pollutants in the wastewater. This study aimed to determine the nitrification and oxygen transfer capacity of Zeelung fibers used in the MABR system. The effects of various C/N ratios (in the range of 1.0 to 3.0) on the membrane modules were studied using three laboratory-scale reactors over the course of 165 days. In this test, the average removal efficiency of COD can reach 74% under selected conditions, up to 90%. Meanwhile, the average nitrification rate is 3.9 g/d/m2, the average ammonia removal rate is 90%, and the maximum value can reach 99%. In addition, the oxygen transfer rate of the fiber in the liquid phase was 19.65 g/d/m2. The experiment also indicated that the nitrification rate is directly proportional to the transfer flux of oxygen and is related to the content of dissolved oxygen in the water. The nitrification rate can be controlled by controlling the concentration of dissolved oxygen in water, thus affecting the removal rate of ammonia nitrogen.

Evaluating fixed-film nitrification systems in autotrophic mode: enhanced biomass retention does not improve bioreactor performance during alkalinity induced stress

Fixed-film bioreactors with different biomass loads operated in parallel. Similar ammonia removal rates indicated a lack of biomass-concentration dependent mechanisms to overcome alkalinity induced stress.

NOB suppression strategies in a mainstream membrane aerated biofilm reactor under exceptionally low lumen pressure

Integrating the aeration-efficient membrane aerated biofilm reactor (MABR) with anaerobic ammonium oxidation (anammox) could yield further reduction in energy in wastewater treatment facilities. However, nitrite oxidizing bacteria (NOB) suppression remained challenging due to the absence of intrinsic inhibition factors in mainstream conditions. This study investigated selective NOB suppression strategies in MABR under <5 kPa lumen pressure. Three MABRs were seeded from different seeding sludge, and operated under various ammonium loading rates, aeration pressure, and temporary inhibitory shock conditions. The three reactors were operated for 170–456 days depending on studied parameters. The results showed that higher ammonium loading could create a substrate-oxygen imbalance and quickly contain emergent NOB activity when aeration pressure was not excessive. In addition, lowering of aeration pressure reversed nitrite oxidizing activities without affecting ammonium oxidizing bacteria (AOB). Cultivating partial nitritation biofilm under zero positive aeration pressure slowed down the growth of NOB yet resulted in self-induced anammox activities. With the aid of temporary free ammonia (FA)/free nitrous acid (FNA) treatment, full-nitrifying biofilm could be transformed to stable partial nitritation biofilm. More than 84% nitrite accumulation ratio (NAR) was sustained during stable operation in each reactor together with an ammonium removal rate of more than 100 mg-N/L/d. Microbial analysis revealed that Nitrosomonas was the main AOB taxon in the three reactors while K-strategist Nitrospira showed presence despite low nitrite oxidizing activities. Under zero positive pressure, proliferation of Nitrospira was much slower while Candidatus Brocadia was self-induced. Furthermore, Nitrospira showed downturn after temporary inhibition treatment.

The Odor Release Regularity of Livestock and Poultry Manure and the Screening of Deodorizing Strains.

Human living environments and health are seriously affected by the odor produced from fermentation of livestock and poultry manure. In order to reduce the odor pollution caused by livestock and poultry manure, efficient strains were screened and two methods were tried in this study. The orthogonal test design was used to analyze the gas produced by pig manure under different conditions of temperature, time, wheat straw doping amount and calcium carbonate doping amount. Then, according to ammonia, hydrogen sulfide and comprehensive odor removal effects, the high efficiency of deodorizing strains were screened. The results showed that pig manure produced the least odor when the temperature was 20 °C, added 0% calcium carbonate, 20% wheat straw and waited for 48 h. Three strains were screened to inhibit the odor production of pig manure: Paracoccus denitrificans, Bacillus licheniformis and Saccharomyces cerevisiae, showed that their highest removal rate of ammonia and hydrogen sulfide gas could reach 96.58% and 99.74% among them; while for three strains of end-control pig manure stench: Pichia kudriavzevii, P. denitrificans and Bacillus subtilis, the highest removal rate of ammonia and hydrogen sulfide gas reached 85.91% and 90.80% among them. This research provides bacteria resources as the high-efficiency deodorizing function for the source suppression and the end treatment of the odor gas of pig manure, which has high application value for the control of odor pollution.

Enhancement of ammonium removal from landfill leachate using microalgae by an integrated strategy of nutrient balance and trophic mode conversion

Landfill leachate is heavily-polluted wastewater generated from municipal solid wastes, which generally includes amounts of ammonium that are highly toxic to living organisms and the environment. The locally isolated microalgae have great potential in removing ammonium and producing value-added biomass from leachate. In this study, we determined the most robust algal strain, which was isolated and screened from a local landfill, and identified using the 18 s RNA gene sequences analysis. Subsequently, the integrated strategy of nutrient balance and trophic mode conversion was employed to make the leachate suitable for ammonium removal and algal growth. The results showed that a most robust, locally isolated strain NCU-9 (Nanchang University-9), was a promising strain and was selected out of four candidates and identified as Chlorella pyrenoidosa. This strain had a high tolerance to ammonium and leachate-borne bacteria when grown in unsterilized leachate. An optimal strategy was used, which included the nutrient balancing of nitrogen (N) to phosphorus (P) ratio (N/P) at 30:1 along with trophic mode conversion of N deprivation, to enhance the ammonium removal rate to as high as 95% in leachate remediation. The protein analysis of the cell composition was used to confirm this optimum strategy for ammonium removal, while the potential of NCU-9 was also considered as a value-added feedstock for animal feed in the downstream industry. Based on these results, we can conclude that microalgae-based leachate remediation has practical potential for nutrient recovery and biomass utilization.

Evaluation of modified biofloc system with filtration unit in controlling suspended solids and inorganic nitrogen concentrations in a recirculating aquaculture system

AbstractBACKGROUNDBiofloc technology systems (BFT) often encounter difficulties in controlling suspended solid levels in tanks. The oxygen consumption rates and ammonia removal rates of bioflocs as the BFT system shifts from assimilation towards nitrification have rarely been reported. Thus, the performance of the BFT system with a filtration unit was evaluated.RESULTSPreliminary work found that the optimal screen pore size and recirculating flow rate were 100 μm and 3000 L day−1, respectively. The BFT system with the filtration unit could maintain suspended solids in the fish tank below 50 mg‐SS L−1 while retaining significantly higher suspended solids in the biofloc reactor (509 ± 44.6 mg‐SS L−1). The daily starch addition at a C:N mass ratio of 10:1 in phase I (day 1–38) induced the biofloc formation that kept TAN and nitrite levels below 1.0 mg‐N L−1. The fraction of inorganic nitrogen compounds increased from 2.5% in phase I to 27.6% in phase III (day 56–70). TAN removal rates increased from 3.0 mg‐N g‐SS−1 day−1 during phase I to 10.34 ± 0.392 mg‐N g‐SS−1 day−1 after complete nitrification occurred. Relatively constant oxygen consumption rates of the bioflocs (149.1 ± 9.53 mg‐ O2 g‐SS−1 day−1) were observed for the entire experiment.CONCLUSIONThe BFT system with a filtration unit was effective in controlling suspended solid and inorganic nitrogen concentrations. Nitrogen treatment pathway of BFT system was assimilation during startup period but gradually shifted to nitrification. Oxygen consumption rates of the bioflocs are relatively constant regardless of the pathways responsible for nitrogen treatment. © 2021 Society of Chemical Industry (SCI).