Nitrate-rich agricultural runoff treatment by Vallisneria-sulfur based mixotrophic denitrification process

Sulfur-based mixotrophic denitrification: A promising approach for nitrogen removal from low C/N ratio wastewater

Sulfur-based mixotrophic denitrification has significant potential as a promising denitrification technology for treating low ratio of carbon-to‑nitrogen (C/N) wastewater. This paper provided an in-depth and comprehensive overview of the sulfur-based mixotrophic denitrification process and discussed the underlying mechanisms and functional microorganisms. Possible electron transfer pathways involved in the sulfur-based mixotrophic denitrification process are also analyzed in detail. This review focused on the various sulfur-based electron donors used in the sulfur-based mixotrophic denitrification process, including S0, S2-, S2O32-, and pyrite (FeS2), and their performances when combined with various carbon sources (such as methanol, ethanol, glucose, and woodchips) were also explored. The analysis of the contribution proportion between autotrophic and heterotrophic denitrification suggested an appropriate C/N ratio can emphasize the dominance of autotrophs, thus exerting synergistic effects and reducing the consumption of carbon sources. Additionally, three strategies, including developing new composites, new bioreactors, and new sulfur sources, were proposed to improve the performance and stability of the sulfur-based mixotrophic denitrification process. Finally, the applications (such as secondary effluent, groundwater, and agricultural/urban storm water runoff), challenges, and perspectives of the sulfur-based mixotrophic denitrification were highlighted. This review provided an in-depth insight into the coupling mechanism of sulfur-based autotrophic and heterotrophic denitrification and guidance for the future implementation of the sulfur-based mixotrophic denitrification process.

Towards nutrient neutrality: A review of agricultural runoff mitigation strategies and the development of a decision-making framework

Nutrient runoff from agriculture practices poses a significant risk to waterway health and can have long-lasting and complex implications for the environment, ecosystems, and the human population. Consequently, a systematic quantitative literature review (SQLR) was conducted to identify different nutrient runoff mitigation strategies (NRMS) that are currently used globally to prevent or remediate environmental damage from excessive agricultural fertilisation. Empirical data on the outcomes from various NRMS from the reviewed studies were used to evaluate the strategies based on environmental benefit, implementation cost, and practicality perspectives. An overall assessment of the feasibility of NRMS was determined, and a macro-level assessment of the reported barriers preventing the widespread implementation of NRMS was provided. Identified research gaps and issues included a dearth of literature covering nutrient runoff mitigation, scepticism from agricultural landowners to voluntarily adopt policy without substantial incentives, and a general lack of cost/benefit analyses, including an understanding of the uncertainty associated with NRMS that can inform decision-makers about effective and efficient strategies for different site situations. Synthesis of SQLR data facilitated the development of a comprehensive nutrient runoff decision-making framework which addresses present limitations and provides site-specific NRMS recommendations for policymakers to implement.

A comprehensive review on mixotrophic denitrification processes for biological nitrogen removal

Biological denitrification is the most widely used method for nitrogen removal in water treatment. Compared with heterotrophic and autotrophic denitrification, mixotrophic denitrification is later studied and used. Because mixotrophic denitrification can overcome some shortcomings of heterotrophic and autotrophic denitrification, such as a high carbon source demand for heterotrophic denitrification and a long start-up time for autotrophic denitrification. It has attracted extensive attention of researchers and is increasingly used in biological nitrogen removal processes. However, so far, a comprehensive review is lacking. This paper aims to review the current research status of mixotrophic denitrification and provide guidance for future research in this field. It is shown that mixotrophic denitrification processes can be divided into three main kinds based on different kinds of electron donors, mainly including sulfur-, hydrogen-, and iron-based reducing substances. Among them, sulfur-based mixotrophic denitrification is the most widely studied. The most concerned influencing factors of mixotrophic denitrification processes are hydraulic retention times (HRT) and ratio of chemical oxygen demand (COD) to total inorganic nitrogen (C/N). The dominant functional bacteria of sulfur-based mixotrophic denitrification system are Thiobacillus, Azoarcus, Pseudomonas, and Thauera. At present, mixotrophic denitrification processes are mainly applied for nitrogen removal in drinking water, groundwater, and wastewater treatment. Finally, challenges and future research directions are discussed.

Removal of nitrate from agricultural runoff in biochar electrode based biofilm reactor: Performance and enhancement mechanisms

A biochar electrode based biofilm reactor was developed for advanced removal of nitrate from agricultural runoff. The corn-straw (Zea mays L.) biochar formed at 500 °C has an adsorption capacity of NO₃^--N up to 2.659 mg g^-1. After 45-day start-up phase, the removal efficiency of nitrate reached 93.4% when impressed current was 20 mA, hydraulic retention time was 12 h and chemical oxygen demand/total nitrogen (C/N) ratio was 0.56 without additional carbon source. In comparison, neither electrochemical reduction alone nor microbial denitrification alone could obtain the ideal nitrate removal efficiency. The results implied that bio-electrochemical reduction was the main way of nitrate removal in the biofilm electrode reactor (BER). The denitrification efficiency of 88.9% could still be obtained when C/N = 0. It is because biochar can significantly promote the utilization efficiency of cathode electrons by microorganisms. Thus, biochar is a promising electrode material, which provides a new idea for the optimization of BER.

Denitrification performance of sulfur-based autotrophic denitrification and biomass‑sulfur-based mixotrophic denitrification in solid-phase denitrifying reactors using novel composite filters

Both the elemental sulfur-based autotrophic denitrification (ESAD) and the biomass‑sulfur-based mixotrophic (simultaneous autotrophic and heterotrophic) denitrification processes (BSMD) are efficient methods for removing nitrate from wastewater. However, a comparative analysis of the denitrification capacity of the BSMD and ESAD in the packed bed reactors is still lacking. In this paper, corncob powder was selected as the biomass source to prepare biomass‑sulfur-based composite filter (BSCF) for the BSMD process. The denitrification performances of the three identical lab-scale bioreactors packed with varying elemental sulfur-based composite filters (ESCFs) were compared under varying loading conditions, and the optimal ESCF of the ESAD system was 2:1 by weight ratio of sulfur powder to shell powder. In pilot-scale experiments, the results showed that BSCF could decrease the sulfate productivity and gave better denitrification performance than the ESCF with the optimal nitrate removal rate (NRR) of 504 ± 12.3 mg NO₃^--N·L^-1·d^-1. In addition, the two-stage flushing strategy (for the removal of aged sludge) can effectively improve the denitrification capacity, while the denitrification will be inhibited when the influent dissolved oxygen concentration was higher than 4.5 mg L^-1. Moreover, the heterotrophs and autotrophs were abundant in the reactors. Over time, the abundance of autotrophs increased while that of heterotrophs decreased. Overall, BSCF could be a promising and economic technology to improve the effluent quality.

Microbial induced calcium precipitation based anaerobic immobilized biofilm reactor for fluoride, calcium, and nitrate removal from groundwater

In this study, the anaerobic quartz sand fixed biofilm reactor containing Cupriavidus sp. W12 was established to simultaneously remove calcium (Ca²⁺), fluoride (F^-) and nitrate (NO₃^-N) from groundwater. After 84 days of continuous operation, the optimum operating parameters and defluoridation mechanism were explored, and the microbial community structure under different pH environments were compared and analyzed. Under the optimal operation conditions (HRT of 6 h, initial Ca²⁺ concentration of 180 mg L^-1, and pH of 7.0), the removal efficiencies of Ca²⁺, F^-, and NO₃^-N were 58.97%, 91.93%, and 100%, respectively. Gas chromatography (GC) results indicate that N₂ is the main gas produced by the bioreactor. Three-dimension excitation emission matrix fluorescence spectroscopy (3D-EEM) showed that extracellular polymers (EPS) are produced during bacterial growth and metabolism. The results of Scanning electron microscopy-energy dispersive spectrometer (SEM-EDS), X-ray diffraction (XRD), and Fourier transform infrared spectrometer (FTIR) demonstrated that the defluoridation mechanism is attributed to the synergetic effects of ion exchange, co-precipitation, and chemisorption. The comparative analysis of the microbial community structure under different pH conditions show that Cupriavidus is the dominant bacteria in the bioreactor throughout the experiment, and it shows a prominent advantage at pH of 7.0. This research provides an application foundation for anaerobic microbial induced calcium precipitation (MICP) bioremediation of Ca²⁺, F^-, and NO₃^-N from groundwater.

Exploration and verification of the feasibility of the sulfur-based autotrophic denitrification integrated biomass-based heterotrophic denitrification systems for wastewater treatment: From feasibility to application

The sulfur-based autotrophic denitrification (SAD) and the solid organic carbon-based denitrification processes are both efficient techniques to remove nitrate from wastewater, and the hydrogen ions generated by the SAD process would be consumed in the heterotrophic denitrification process. Therefore, it is possible to improve the denitrification capacity when the solid organic carbon was added into a SAD reactor. In this study, corncob powder and sawdust powder were selected as solid organic carbon sources, and the sulfur-based autotrophic denitrification integrated biomass-based heterotrophic denitrification system was formed (SBD). The laboratory and field experiments showed that SBD could shorten the start-up period, decrease the sulfate productivity, and maintain a good denitrification performance when treated wastewater. According to the field experiment results, when the HRT was 1 h, the effluent total nitrogen (TN) concentration was always lower than 15 mg L^-1. In addition, nitrite inhibition was observed when the concentration of nitrite in the reactors reached above 30 mg L^-1. The mixture of elemental sulfur powder, shell powder, corncob powder, and sawdust powder with a mass ratio of 6:2:1:1 was the optimal filter for the SBD system, with an average nitrate reduction rate (NAR) of 420 mg NO₃^-N·L^-1·d^-1 obtained at the end of the study. During the whole operation, the major autotrophs in the SBD systems were Thermomonas, Ferritrophicum, and Thiobacillus, while the major heterotrophs were Saprospiraceae, Ferruginibacter, Dokdonella, and Simplicispira. Overall, the SBD system was a feasible and practically favorable way to remove nitrate from wastewater.

Sulfur-based Mixotrophic Vanadium (V) Bio-reduction towards Lower Organic Requirement and Sulfate Accumulation

Although remediation of toxic vanadium (V) [V(V)] pollution can be achieved through either heterotrophic or sulfur-based autotrophic microbial reduction, these processes would require a large amount of organic carbons or generate excessive sulfate. This study reported that by using mixotrophic V(V) bio-reduction with acetate and elemental sulfur [S(0)] as joint electron donors, V(V) removal performance was enhanced due to cooccurrence of heterotrophic and autotrophic activities. Deposited vanadium (IV) was identified as the main reduction product by scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction and X-ray photoelectron spectroscopy. Based on 16S rRNA gene amplicon sequencing, qPCR and genus-specific reverse transcription qPCR, it was observed that V(V) was likely detoxified by heterotrophic V(V) reducers (e.g., Syntrophobacter, Spirochaeta and Geobacter). Cytochrome c, intracellular nicotinamide adenine dinucleotide and extracellular polymeric substances were involved in V(V) reduction and binding. Organic metabolites synthesized by autotrophs (e.g., Thioclava) with energy from S(0) oxidation might compensate electron donors for heterotrophic V(V) and sulfate reducers. Less sulfate was accumulated presumably due to activities of sulfur-respiring genera (e.g., Desulfurella). This study demonstrates mixotrophic microbial V(V) reduction can save organic dosage and avoid excessive sulfate accumulation, which will be beneficial to bioremediation of V(V) contamination.

Release Mechanism, Secondary Pollutants and Denitrification Performance Comparison of Six Kinds of Agricultural Wastes as Solid Carbon Sources for Nitrate Removal

Agricultural wastes used as denitrification carbon sources have some drawbacks such as excessive organic carbon release and unclear release characteristics of nitrogen, phosphorus, and chromatic substances, which can cause adverse effects on the effluent quality during the denitrification process. The composition and surface characteristics, carbon release mechanisms, and secondary pollutant release properties of six kinds of agricultural wastes, i.e., rice straw (RS), wheat straw (WS), corn stalk (CS), corncob (CC), soybean stalk (SS), and soybean hull (SH) were studied and analyzed in this research. The denitrification performance of these agricultural wastes was also investigated extensively by batch experiments. The results showed that the carbon release basically followed the second-order reaction kinetic equation and Ritger-Peppas equation in the 120 h reaction, and it was mainly controlled by the diffusion process. The kinetic equation fitting results and bioavailability test suggested that the potential risk of excessive effluent COD of CC was the lowest due to the appropriate amount and degradability of its released carbon. The NH₄⁺-N, TN, and TP in the leachate of RS were higher than those of the other five agriculture wastes, and the chroma in the leachate of WS and CS was heavier than that of the others. CC released the lowest pollutants, which resulted in slight fluctuations of effluent quality in the start-up period (1-11 d), and it had the best nitrogen removal capacity in the denitrification experiment. The average NO₃^--N removal of CC was 5.12 mg for each batch in the stable period (11-27 d), which was higher than that of others, and less NO₂^--N, NH₄⁺-N, and COD were accumulated in the CC effluent during the whole denitrification process.

Autotrophic denitrification in constructed wetlands: Achievements and challenges

The use of constructed wetlands for wastewater treatment is rapidly increasing worldwide due to their advantages of low operating and maintenance costs. Denitrification in constructed wetlands is dependent on the presence of organic carbon sources, and the shortage of organic carbon is the primary hurdle for nitrate removal. Therefore, the use of inorganic electronic donors has emerged as an alternative. This paper provides a comprehensive review of nitrate removal pathways using various inorganic electron donors and the performance and development of autotrophic denitrification in constructed wetlands. The main environmental parameters and operating conditions for nitrate removal in wetlands are discussed, and the challenges currently faced in the application of enhanced autotrophic denitrification wetlands are emphasized. Overall, this review illustrates the need for a deep understanding of the complex interrelationships among environmental and operational parameters and wetland substrates for improving the wastewater treatment performance of constructed wetlands.

A sulfur-based cyclic denitrification filter for marine recirculating aquaculture systems

Nitrogen removal from saline wastewater is challenging due to adverse effects of salinity on biological processes. A novel sulfur-autotrophic cyclic denitrification filter (CDF) was tested for marine recirculating aquaculture systems (RAS) under varying conditions. Low ammonia, nitrite and sulfide concentrations were maintained at residence times between 4 and 12 h. After introduction of Poecilia sphenops, concentrations of NH₄⁺-N, NO₂^--N, NO₃^--N were maintained below 1, 1, and 60 mg/L, respectively. Fish waste inputs to the CDF contributed to mixotrophic denitrification and low sulfate production. A mass balance showed that 7% of the feed nitrogen was assimilated by fish, 6% was removed by passive denitrification (e.g., in anoxic zones in filters), 60% in the CDF and 27% was discharged during sampling and solids removal. Daily fresh water addition was <2% of fish tank volumes. The results are promising as a low cost alternative for saline wastewater denitrification.

Comparative Study of Denitrifying-MBBRs with Different Polyethylene Carriers for Advanced Nitrogen Removal of Real Reverse Osmosis Concentrate

Nitrogen (N) remains a great challenge in wastewater treatment while attempts to remove N has continuously been a research point for decades. In this study, the long-term performance of four identical-shape denitrification MBBRs (moving bed biofilm reactors) with four different configurations of cylindrical polyethylene as carriers (Φ25 × 12, Φ25 × 4, Φ15 × 15, and Φ10 × 7 mm) for advanced N removal of real reverse osmosis concentrate was investigated in great detail. The N of the real concentrate can be effectively removed by denitrification MBBRs when the pH, temperature, hydraulic retention time (HRT), C/N ratio, and filling rate are 7.50–8.10, 24~26 °C, 12 hours, 6.6, and 50%, respectively. The results showed that the MBBR with the Φ15 × 15 poly-carrier had the best removal efficiency on NO₃^-–N (78.0 ± 15.8%), NO₂^-–N (43.79 ± 9.30%), NH₄⁺–N (55.56 ± 22.28%), and TN (68.9 ± 12.4%). The highest biomass of 2.13 mg/g-carrier was in the Φ15 × 15 poly-carrier was compared with the other three carriers, while the genes of the Φ15 × 15 poly-carrier reactor were also the most abundant. Proteobacteria was the most abundant phylum in the system followed by Bacteroidetes and then Firmicutes. The entire experiment with various parameter examination supported that Φ15 × 15 poly-carrier MBBR was a promising system for N removal in high strength concentrate. Despite the lab-scale trial, the successful treatment of high strength real reverse osmosis concentrate demonstrated the reality of the treated effluent as possible reclaimed water, thus providing a good showcase of N-rich reverse osmosis concentrate purification in practical application.

Hydrilla verticillata-Sulfur-Based Heterotrophic and Autotrophic Denitrification Process for Nitrate-Rich Agricultural Runoff Treatment

Hydrilla verticillata-sulfur-based heterotrophic and autotrophic denitrification (HSHAD) process was developed in free water surface constructed wetland mesocosms for the treatment of nitrate-rich agricultural runoff with low chemical oxygen demand/total nitrogen (C/N) ratio, whose feasibility and mechanism were extensively studied and compared with those of H. verticillata heterotrophic denitrification (HHD) mesocosms through a 273-day operation. The results showed that the heterotrophic and autotrophic denitrification can be combined successfully in HSHAD mesocosms, and achieve satisfactory nitrate removal performance. The average NO₃^--N removal efficiency and denitrification rate of HSHAD were 94.4% and 1.3 g NO₃^--N m^-3·d^-1 in steady phase II (7-118 d). Most nitrate was reduced by heterotrophic denitrification with sufficient organic carbon in phase I (0-6 d) and II, i.e., the C/N ratio exceeded 4.0, and no significant difference of nitrate removal capacity was observed between HSHAD and HHD mesocosms. During phase III (119-273 d), sulfur autotrophic denitrification gradually dominated the HSHAD process with the C/N ratio less than 4.0, and HSHAD mesocosms obtained higher NO₃^--N removal efficiency and denitrification rate (79.1% and 1.1 g NO₃^--N m^-3·d^-1) than HHD mesocosms (65.3% and 1.0 g NO₃^--N m^-3·d^-1). As a whole, HSHAD mesocosms removed 58.8 mg NO₃^--N more than HHD mesocosms. pH fluctuated between 6.9-9.0 without any pH buffer. In general, HSHAD mesocosms were more stable and efficient than HHD mesocosms for NO₃^--N removal from agricultural runoff during long-term operation. The denitrificans containing narG (1.67 × 10⁸ ± 1.28 × 10⁷ copies g^-1 mixture-soil^-1), nirS (8.25 × 10⁷ ± 8.95 × 10⁶ copies g^-1 mixture-soil^-1), and nosZ (1.56 × 10⁶ ± 1.60 × 10⁵ copies g^-1 mixture-soil^-1) of litter bags and bottoms in HSHAD were higher than those in HHD, which indicated that the combined heterotrophic and autotrophic denitrification can increase the abundance of denitrificans containing narG, nirS, and nosZ, thus leading to better denitrification performance.

Glyphosate and nutrients removal from simulated agricultural runoff in a pilot pyrrhotite constructed wetland

Pyrrhotite is often considered as a gangue mineral, and discarded in mine wastes and tailings. Glyphosate and fertilizer, often excessively used in agriculture, flow into water bodies with agriculture runoff, and cause pollution of water bodies. In this study, the pyrrhotite was used as a substrate in a pilot constructed wetland (CW) to remove the glyphosate and nutrients from simulated agriculture runoff. In nearly one year, the pilot pyrrhotite constructed wetland (Pyrr-CW) removed 90.3 ± 6.1% of glyphosate, 88.2 ± 5.1 of total phosphorus (TP) and 60.40 ± 5.60% of total nitrogen (TN) on average, much higher than the control CW. The abundances of sulfur-oxidizing bacteria, such as Sulfurifustis, Sulfuriferula and Thiobacillus, were much higher in the Pyrr-CW than those in the control CW. In the Pyrr-CW goethite was produced by pyrrhotite aerobic oxidation (PAO) and pyrrhotite autotrophic denitrification (PAD) continuously and spontaneously. Higher glyphosate and TP removals were resulted from adsorption on the goethite produced, and higher TN removal was attributed to the PAD. High glyphosate and nutrients removal could keep a long term until the pyrrhotite in the Pyrr-CW was used up. The phosphorus (P) sequestered in the Pyrr-CW existed mainly in organic P, (Fe + Al)P and (Ca + Mg)P, and their order was (Fe + Al)P > organic P > (Ca + Mg)P. No heavy metal ions released from the Pyrr-CW. With higher and lasting removal rate, and lower cost, the Pyrr-CW is a promising technology for simultaneous glyphosate and nutrients removal from agricultural runoff and wastewater.

Denitrification and microbial community in MBBR using A. donax as carbon source and biofilm carriers for reverse osmosis concentrate treatment

In this study, raw Arundo donax (A. donax) pieces were applied as carbon source and biofilm carriers for denitrification in a lab-scale moving bed biofilm reactor (MBBR) for the treatment of reverse osmosis concentrate gathered from local wastewater reuse plant. At stable phase (about 60 days), efficient denitrification performance was obtained with 73.2% ± 19.5% NO₃^--N average removal and 8.10 ± 3.45 g N/(m³·day) NO₃^--N average volumetric removal rate. Mass balance analysis showed that 4.84 g A. donax was required to remove 1 g TN. Quantitative real-time PCR analysis results showed that the copy numbers of 16S r-RNA, narG, nirS, nosZ and anammox gene of carrier biofilm and suspended activated sludge in the declination phase (BF2 and AS2) were lower than those of samples in the stable phase (BF1 and AS1), and relatively higher copy numbers of nirS and nirK genes with lower abundance of narG and nosZ genes were observed. High-throughput sequencing analysis was conducted for BF2 and AS2, and similar dominant phyla and classes with different abundance were obtained. The class Gammaproteobacteria affiliated with the phylum Proteobacteria was the most dominant microbial community in both BF2 (52.6%) and AS2 (41.7%). The PICRUSt prediction results indicated that 33 predictive specific genes were related to denitrification process, and the relative abundance of 18 predictive specific genes in BF2 were higher than those in AS2.

External carbon addition for enhancing denitrification modifies bacterial community composition and affects CH4 and N2O production in sub-arctic mining pond sediments

Explosives used in mining operations release reactive nitrogen (N) that discharge into surrounding waters. Existing pond systems at mine sites could be used for N removal through denitrification and we investigated capacity in tailings and clarification pond sediments at an iron-ore mine site. Despite differences in microbial community structure in the two ponds, the potential denitrification rates were similar, although carbon limited. Therefore, a microcosm experiment in which we amended sediment from the clarification pond with acetate, cellulose or green algae as possible carbon sources was conducted during 10 weeks under denitrifying conditions. Algae and acetate treatments showed efficient nitrate removal and increased potential denitrification rates, whereas cellulose was not different from the control. Denitrifiers were overall more abundant than bacteria performing dissimilatory nitrate reduction to ammonium (DNRA) or anaerobic ammonium oxidation, although DNRA bacteria increased in the algae treatment and this coincided with accumulation of ammonium. The algae addition also caused higher emissions of methane (CH₄) and nitrous oxide (N₂O). The bacterial community in this treatment had a large proportion of Bacteroidia, sulfate reducing taxa and bacteria known as fermenters. Functional gene abundances indicated an imbalance between organisms that produce N₂O in relation to those that can reduce it, with the algae treatment showing the lowest relative capacity for N₂O reduction. These findings show that pond sediments have the potential to contribute to mitigating nitrate levels in water from mining industry, but it is important to consider the type of carbon supply as it affects the community composition, which in turn can lead to unwanted processes and increased greenhouse gas emissions.

Characterization of the Cd(II) and nitrate removal by bacterium Acinetobacter sp. SZ28 under different electron donor conditions

In this study, zero-valent iron (ZVI), nanoscale zero-valent iron (nZVI), Fe(II), and Mn(II) were investigated for their effects on mixotrophic denitrification coupled with cadmium (Cd(II)) adsorption process by Acinetobacter sp. SZ28. The removal rates of nitrate were 0.228 mg L^-1 h^-1 (ZVI), 0.133 mg L^-1 h^-1 (nZVI), 0.309 mg L^-1 h^-1 (Fe(II)) and 0.234 mg L^-1 h^-1 (Mn(II)), respectively. The Cd(II) removal efficiencies were 97.23% (ZVI), 95.79% (nZVI), 80.63% (Fe(II)), and 84.58% (Mn(II)), respectively. Meteorological chromatography analysis indicated that the characteristics of gas composition were different under different electron donor conditions. Moreover, characterization of bacterial metabolites produced by strain SZ28 under different conditions was analyzed. Sequence amplification identified the presence of the nitrate reductase gene (napA) and Mn(II)-oxide gene (cumA) in strain SZ28. The results of XRD and SEM indicated that ZVI, nZVI, Fe(II), and Mn(II) were oxidized into corresponding oxides. XPS spectra indicated that the Cd(II) was adsorbed onto biogenic precipitation.

Biological denitrification in marine aquaculture systems: A multiple electron donor microcosm study

There is a lack of information on denitrification of saline wastewaters, such as those from marine recirculating aquaculture systems (RAS), ion exchange brines and wastewater in areas where sea water is used for toilet flushing. In this study, side-by-side microcosms were used to compare methanol, fish waste (FW), wood chips, elemental sulfur (S⁰) and a combination of wood chips and sulfur for saline wastewater denitrification. The highest denitrification rate was obtained with methanol (23.4 g N/(m³·d)), followed by FW (4.5 g N/(m³·d)), S⁰ (3.5 g N/(m³·d)), eucalyptus mulch (2.6 g N/(m³·d)), and eucalyptus mulch with sulfur (2.2 g N/(m³·d)). Significant differences were observed in denitrification rate for different wood species (pine > oak ≫ eucalyptus) due to differences in readily biodegradable organic carbon released. A pine wood-sulfur heterotrophic-autotrophic denitrification (P-WSHAD) process provided a high denitrification rate (7.2-11.9 g N/(m³·d)), with lower alkalinity consumption and sulfate generation than sulfur alone.