Nitrate-rich Wastewater Research Articles

Ammonia recovery from nitrate-rich wastewater using a membrane-free electrochemical system

Ammonia recovery from nitrate-rich wastewater using a membrane-free electrochemical system

Enhanced Charge Carrier Dynamics on Sb2 Se3 Photocathodes for Efficient Photoelectrochemical Nitrate Reduction to Ammonia.

Ammonia (NH3 ) is recognized as a transportable carrier for renewable energy fuels. Photoelectrochemical nitrate reduction reaction (PEC NO3 RR) offers a sustainable solution for nitrate-rich wastewater treatment by directly converting solar energy to ammonia. In this study, we demonstrate the highly selective PEC ammonia production from NO3 RR by constructing a CoCu/TiO2 /Sb2 Se3 photocathode. The constructed CoCu/TiO2 /Sb2 Se3 photocathode achieves an ammonia Faraday efficiency (FE) of 88.01 % at -0.2 VRHE and an ammonia yield as high as 15.91 μmol h-1 cm-2 at -0.3 VRHE with an excellent onset potential of 0.43 VRHE . Dynamics experiments and theoretical calculations have demonstrated that the CoCu/TiO2 /Sb2 Se3 photocathode possesses high light absorption capacity, excellent carrier transfer capability, and high charge separation and transfer efficiencies. The photocathode can effectively adsorb the reactant NO3 - and intermediate, and the CoCu co-catalyst increases the maximum Gibbs free energy difference between NO3 RR and HER. Meanwhile, the Co species enhances the spin density of Cu, and increases the density of states near the Fermi level in pdos, which results in a high PEC NO3 RR activity on CoCu/TiO2 /Sb2 Se3 . This work provides a new avenue for the feasibility of efficient PEC ammonia synthesis from nitrate-rich wastewater.

Municipal wastewater driven partial-denitrification (PD) aggravated nitrous oxide (N2O) production

Partial Denitrification (PD) provides a new route for nitrate-rich wastewater treatment by combining with energy-efficient anammox. This process was reported to hardly produce N2O despite high nitrite accumulation using acetate as carbon source. This study, however, demonstrated significant N2O would be produced when feeding with real municipal wastewater, the NTR-N2O (NO3−-to-N2O transformation ratio) reached as high as 10%. The supply of feed with a high COD/NO3−-N ratio was unable to alleviate N2O production but was severely aggravated after nitrate was depleted. Excess carbon source resulted in accumulated nitrite further being reduced with NTR-N2O largely improved to 63.4%. Besides, it was observed that acid pH inhibited PD activity and resulted in N2O production significantly increased with the NTR-N2O of 39.9% at an initial pH of 5.5. The increase of pH to alkaline conditions cannot mitigate N2O production. A low feeding proportion of real municipal wastewater for low nitrate wastewater treatment can drastically lower N2O production. The NTR-N2O was only 0.1% at a nitrate concentration of 10 mgN/L (10%), much lower than that at 30 mgN/L with a 30% feeding proportion of municipal wastewater (9.4%). Complex organics and ammonium present in municipal wastewater were supposed to be the primary reasons for the high N2O production. Overall, this work offered a new insight into N2O production during the PD process using the complex organics from wastewater itself.

Inducement mechanism and control of self-acidification in elemental sulfur fluidizing bioreactor

The sulfur fluidizing bioreactor (S0FB) has significant superiorities in treating nitrate-rich wastewater. However, substantial self-acidification has been observed in engineering applications, resulting in frequent start-up failures. In this study, self-acidification was reproduced in a lab-scale S0FB. It was demonstrated that self-acidification was mainly induced by sulfur disproportionation process, accounting for 93.4 % of proton generation. Supplying sufficient alkalinity to both the influent (3000 mg/L) and the bulk (2000 mg/L) of S0FB was essential for achieving a successful start-up. Furthermore, the S0FB reached 10.3 kg-N/m3/d of nitrogen removal rate and 0.13 kg-PO43-/m3/d of phosphate removal rate, respectively, surpassing those of the documented sulfur packing bioreactors by 7–129 times and 26–65 times. This study offers a feasible and practical method to avoid self-acidification during restart of S0FB and highlights the considerable potential of S0FB in the treatment of nitrate-rich wastewater.

Diversity and functional annotation of microorganisms in anaerobic chamber treating nitrate-rich wastewater.

The vertical flow constructed wetlands (VFCW) for the treatment of domestic wastewater has become a conventional and cost effective treatment system with one of the major disadvantage of elevated nitrate concentrations. The present study makes an effort in providing a new design of anaerobic denitrification unit termed as anaerobic chamber (AC) whichwas introduced after two-stage VFCW to remove nitrates from the treated wastewater (WW). The AC provided all the essential conditions of effective denitrification such as anaerobic environment with enough carbon and nitrogen source. To understand the pollutant removal mechanism in AC, microbial diversity and functional annotation was studied by metagenomic analysis of sequences obtained from biofilm formed in AC. The efficiency of AC was measured with respect to physicochemical wastewater quality parameters. The removal efficiencies were 88, 65, 43 and 27% for total nitrogen, nitrate (NO3), ammoniacal-nitrogen (NH4) andortho-phosphate respectively. The microbial flora was much more diverse and unique pertaining to anaerobic microbes in AC compared to WW with total of 954 and 1191 genuses respectively with minimum abundance of 10 hits. The metagenomes exhibited 188% more Archaea in the AC than WW where Crenarchaeota, Euryarchaeota, Korarchaeota, Nanoarchaeota and Thaumarchaeota were major phyla with 60 genuses. The nitrogen metabolism was reported in terms of assimilatory nitrate reductase. As the class, Proteobacteria, Actinobacteria were prominent in WW, whereas Proteobacteria, Chloroflexi in AC were abundant. From functional annotation of sequences, the microbial flora in AC has the potential of removal of pollutants present in the form of carbon, nitrogen, and phosphorus.

Low-carbon nitrogen removal from power plants circulating cooling water and municipal wastewater by partial denitrification-anammox

As a reclaimed water reuse strategy, using treated municipal wastewater as power plants circulating cooling water (PPCCW) generates nitrate-rich wastewater due to evaporation requiring retreatment. An innovative low-carbon nitrogen removal process, partial denitrification-anammox (PD-A), was used in this study. The PPCCW and municipal wastewater pre-treated with 10 mg/L Fe3+ were simultaneously subjected to the PD-A process. The results showed that the total nitrogen of effluent less than 10 mg/L, and a removal efficiency of 79.67 ± 3.48% was attained. Unclassified_f_Brocadiaceae was the dominant anammox genus, with an increasing percentage (from 0.42 to 1.27%), laterally indicating the reactor stability. Furthermore, the hydrolytic acidifying bacteria SBR1031 and Bacillus increased substantially after feeding with actual wastewater, and the removal efficiencies of organic material and nitrogen increased, indicating that hydrolytic acidifying bacteria have a synergistic effect with PD-A bacteria. Finally, a novel wastewater treatment process that fully recovers carbon, phosphorus, and water was proposed.

Evaluating Molecular Catalyst-Mediated Nitrate Reduction for Reactive Separation and Recovery of Ammonia

The current state of centralized nitrogen (N) management has destabilized global environmental cycles via Haber-Bosch (HB) ammonia-N manufacturing which contributes 1.2% of global anthropogenic CO2-eq emissions.1 The majority of this N that is discharged to wastewaters goes untreated, leading to harmful algal blooms that threaten coastal and river ecosystems, which already costs the U.S. an estimated $210 billion per year in health and environmental damages.2 Furthermore, the production of HB ammonia, and the subsequent discharge of wastewater nitrogen, is expected to substantially increase in the next three decades as the human population climbs to 9 billion people.3 Simultaneously removing nitrogen pollutants and recovering value-added products can preserve national water quality and supplement supply chains of nitrogen consumables with renewably sourced electricity. The electrochemical nitrate reduction reaction (NO3RR) can be leveraged in reactive separation processes to convert wastewater nitrates to commodity products, such as ammonia. Engineering catalytic NO3RR processes that operate at feasible rates and faradaic efficiencies is challenging because the majority of nitrate-rich wastewaters (e.g., fertilizer runoff) are dilute in nitrate concentration (< 5 mM).4 Molecular catalysts are uniquely suited to reduce nitrate at low concentrations in real wastewaters due to their strong substrate recognition (reactant selectivity) and product selectivity. In this study, we benchmarked the performance of the molecular catalyst Co-DIM (a Co-N4 macrocycle complex and the only known molecular NO3RR catalyst selective for ammonia5) in a reactive separations process for the treatment of real, nitrate-rich wastewaters.We first demonstrated by cyclic voltammetry (CV) and controlled-potential electrolysis (CPE) that selective Co-DIM-mediated NO3RR is feasible in nitrate-rich secondary effluent (municipal wastewater after biological nitrification). We then employed Co-DIM in electrochemical stripping (ECS): a membrane-separated cell that facilitates reactive separation of produced ammonia.6,7 From real secondary effluent (28 mg NO3-N/L), we achieved greater than 60% nitrate removal with a faradaic efficiency of 25% and ammonia selectivity of 98%. However, the energy consumed for ECS per unit mass of N is 16 times the combined energy requirement for conventional wastewater N removal and HB ammonia synthesis. By introducing a mixed feed of ammonia- and nitrate-rich wastewater and performing electrodialysis (ED) to concentrate the reactant nitrate before ECS, the energy requirement for N removal and ammonia recovery was decreased by three times while the ED process became the dominant energy consumer in the overall process. Additionally, the increase in nitrate removal could not be explained by an increase in nitrate concentration alone. The ED process changes the concentrations and relative ratios of competing anions and buffering species, which can inhibit or promote the molecular electrocatalytic activity. We therefore explored a matrix of anion identities and concentrations by rotating-disk voltammetry and CPE to elucidate plausible inhibition and promotion mechanisms associated with catalyst activation and NO3RR catalysis. This study therefore (1) benchmarks current and future efforts to reactively separate ammonia from real nitrate-rich wastewater with a molecular catalyst and (2) highlights molecular and process-level improvements to realize a circular nitrogen economy.References1 C. Smith, A. K. Hill and L. Torrente-Murciano, Energy Environ. Sci., 2020, 13, 331–344.2 D. J. Sobota, J. E. Compton, M. L. McCrackin and S. Singh, Environ. Res. Lett., 2015, 10, 025006.3 J. W. Erisman, M. A. Sutton, J. Galloway, Z. Klimont and W. Winiwarter, Nature Geoscience, 2008, 1, 636–639.4 Unesco, Ed., Wastewater: the untapped resource, UNESCO, Paris, 2017.5 S. Xu, D. C. Ashley, H.-Y. Kwon, G. R. Ware, C.-H. Chen, Y. Losovyj, X. Gao, E. Jakubikova and J. M. Smith, Chem. Sci., 2018, 9, 4950–4958.6 W. A. Tarpeh, J. M. Barazesh, T. Y. Cath and K. L. Nelson, Environ. Sci. Technol., 2018, 52, 1453–1460.7 M. J. Liu, B. S. Neo and W. A. Tarpeh, Water Research, 2020, 169, 115226.

Engineering a Kesterite‐Based Photocathode for Photoelectrochemical Ammonia Synthesis from NOx Reduction

Ammonia is a key chemical feedstock for industry as well as future carbon-free fuel and transportable vector for renewable energy. Photoelectrochemical (PEC) ammonia synthesis from NOx reduction reaction (NOx RR) provides not only a promising alternative to the energy-intensive Haber-Bosch process through direct solar-to-ammonia conversion, but a sustainable solution for balancing the global nitrogen cycle by restoring ammonia from wastewater. In this work, selective ammonia synthesis from PEC NOx RR by a kesterite (Cu2 ZnSnS4 [CZTS]) photocathode through loading defect-engineered TiOx cocatalyst on a CdS/CZTS photocathode (TiOx /CdS/CZTS) is demonstrated. The uniquely designed photocathode enables selective ammonia production from NOx RR, yielding up to 89.1% Faradaic efficiency (FE) (0.1V vs reversible hydrogen electrode (RHE)) with a remarkable positive onset potential (0.38V vs RHE). By tailoring the amount of surface defective Ti3+ species, the adsorption of reactant NO3 - and * NO2 intermediate is significantly promoted while the full coverage of TiOx also suppresses NO2 - liberation as a by-product, contributing to high ammonia selectivity. Further attempts on PEC ammonia synthesis from simulated wastewater show good FE of 64.9%, unveiling the potential of using the kesterite-based photocathode for sustainably restoring ammonia from nitrate-rich wastewater.

Novel Denitrification Fuel Cell for Energy Recovery of Nitrate-N and TN Removal Based on NH4+ Generation on a CNW@CF Cathode.

NO3- is an undesirable environmental pollutant that causes eutrophication in aquatic ecosystems, and its pollution is difficult to eliminate because it is easily converted into NH4+ instead of N2. Additionally, it is a high-energy substance. Herein, we propose a novel denitrification fuel cell to realize the chemical energy recovery of NO3- and simultaneous conversion of total nitrogen (TN) into N2 based on the outstanding ability of NH4+ generation on a three-dimensional copper nanowire (CNW)-modified copper foam (CF) cathode (CNW@CF). The basic steps are as follows: direct and highly selective reduction of NO3- to NH4+ rather than to N2 on the CNW@CF cathode, on which negative NO3- ions can be easily adsorbed due to their double-electron layer structure and active hydrogen ([H]) can be generated due to a large number of catalytic active sites exposed on CNWs. Then, NH4+ is selectively oxidized to N2 by the strong oxidation of chlorine free radicals (Cl•), which originate from the reaction of chlorine ions (Cl-) by photogenerated holes (h+) and hydroxyl radicals (OH•) under irradiation. Then, the electrons from the oxidation on the photoanode is transferred to the cathode to form a closed loop for external power generation. Owing to the continuous redox loop, NO3- completely reduces to N2, and the released chemical energy is converted into electrical energy. The results indicate that 99.9% of NO3- can be removed in 90 min, and the highest yield of electrical power density reaches 0.973 mW cm-2, of which the nitrate reduction rates on the CNW@CF cathode is 79 and 71 times higher than those on the Pt and CF cathodes, respectively. This study presents a novel and robust energy recycling concept for treating nitrate-rich wastewater.

Nitrate-rich wastewater discharged from a bio-trickling filter can be reused as a moisture conditioning agent for organic waste composting

Biotrickling filter (BF) is an effective ammonia-contain odour purification device for organic waste composting. However, proper disposal of nitrogen-rich trickling liquid (TL) discharged from the BF is consider ‘the last-mile problem’ for the application of this coupled system. Although our previous study demonstrated that reusing a TL as moisture conditioning agent for a composting system could promote compost maturity and nitrogen content, the exploration of the intrinsic promotion mechanism was obscured by the complexity (i.e., multiple forms of nitrogen contained) of the TL. Thus, a simulated TL (STL, pH =7.18) containing exclusively nitrate nitrogen was reused to condition the moisture of composting in this study. Effects of STL addition phase [adding STL in mesophilic (days 0–9),​ thermophilic (days 4–13), and cooling period (days 13–22)] on the performance of composting were explored. Results revealed that the organic degradation was partly promoted by adding STL in thermophilic or cooling period, but mightily inhibited in mesophilic period. Furthermore, adding STL in thermophilic period stimulates the denitrification of nitrate-N into dinitrogen at high temperature, whereas most of added nitrate-N was retained in compost product when adding STL in cooling period. Eventually, STL addition effectively increased total nitrogen (TN) by 2%–9%, especially the nitrate nitrogen by 10–11 times. Notably, adding STL rarely affected nitrous oxide and greenhouse gas emission. Therefore, STL can be reused to condition the moisture of compost in a proper composting phase (i.e., thermophilic period) as defined in term of the enhancement of TN and nitrate content of compost product.

Acclimation to a broad range of nitrate strength on a euryhaline marine microalga Tetraselmis subcordiformis for photosynthetic nitrate removal and high-quality biomass production

Industrial wastewaters usually possess a wide range of nitrate strength. Microalgae-based nitrate-rich wastewater treatment could realize nitrate recovery along with CO2 sequestration for sustainable biomass production, but the low tolerance of the microalgal strains to high-strength nitrate restricted the treatment process. The present study comprehensively evaluated a euryhaline marine microalga Tetraselmis subcordiformis for photosynthetic nitrate removal and biomass production in synthetic wastewater with a broad range of nitrate strength (0.24–7.0 g NO3−-N/L). This alga could acclimate to high nitrate strength up to 3.5 g NO3−-N/L (HN) without compromising biomass production. Nitrate could be completely removed within four days when low nitrate (0.24 g NO3−-N/L, LN) was loaded. The maximum nitrate removal rate of 331 mg N/L/day and specific nitrate removal rate of 360 mg N/day/g cell was obtained under medium nitrate condition (1.8 g NO3−-N/L, MN). High-nitrate stress under 7.0 g NO3−-N/L (SHN) caused an increased light energy dissipation while decreased the density of photosystem II active reaction center, which partially protect the cells from photodamage and contributed to their acclimation to SHN. The algae also enhanced amino acid/fatty acid proportions essential for maintaining intracellular redox states to cope with the stress caused by LN or SHN. HN and SHN was in favor of protein accumulation and maintenance with enhanced proportion of essential amino acids, which entitled the algal biomass to be of high quality for animal feed applied in livestock graziery and aquaculture. LN facilitated productive starch and lipid accumulation with good quality for biofuels production. The nitrate removal rate and biomass productivity exceeded most of the microalgae reported in literature under similar conditions, which highlighted Tetraselmis subcordiformis as a potent strain for flexible nitrate-rich wastewater remediation coupled with fast CO2 bio-mitigation and high-quality biomass production for sustainable algal biorefinery.

Bioaugmentation and quorum sensing disruption as solutions to increase nitrate removal in sequencing batch reactors treating nitrate-rich wastewater

Bioaugmentation of denitrifying bacteria can serve as a promising technique to improve nutrient removal during wastewater treatment. While denitrification inhibition by bacterial quorum sensing (QS) in Pseudomonas aeruginosa has been indicated, the application of bacterial QS disruption to improve nitrate removal from wastewater has not been investigated. In this study, the effect of bioaugmentation of P. aeruginosa SD-1 on nitrate removal in sequencing batch reactors that treat nitrate rich wastewater was assessed. Additionally, the potential of a quorum sensing inhibitor (QSI) to improve denitrification following bacterial bioaugmentation was evaluated. Curcumin, a natural plant extract, was used as a QSI. The chemical oxygen demand (COD) and initial nitrate concentration of the influent were 700±20 mg/L and 200±10 mg/L respectively, and their respective concentrations in the effluent were 56.9±3.2 mg/L and 9.0±3.2 mg/L. Thus, the results revealed that bioaugmentation of P. aeruginosa SD-1 resulted in an increased nitrate removal to 82%±1%. Further, nitrate was almost completely removed following the addition of the QSI, and activities of nitrate reductase and nitrite reductase increased by 88%±2% and 74%±2% respectively. The nitrogen mass balance indicated that aerobic denitrification was employed as the main pathway for nitrogen removal in the reactors. The results imply that bioaugmentation and modulation of QS in denitrifying bacteria, through the use of a QSI, can enhance nitrate removal during wastewater treatment.

Performance of branched polyethyleneimine grafted porous rice husk silica in treating nitrate-rich wastewater via adsorption

Excessive nitrate discharge into aquatic environment is a serious concern as it gives huge impacts on aquatic life as well as corrupts ecosystem and water sources. The effective treatment of nitrate-containing wastewater is essential for the sake of health and environmental protection. In this study, the adsorption of nitrate was carried out using porous rice husk silica functionalized with branched polyethyleneimine (RSi-bPEI). A series of experiments were conducted to measure several adsorption conditions, adsorption isotherms, kinetics, selectivity and reusability. Experimental results demonstrated that the functionalization with branched PEI (bPEI) has significantly improved the adsorption about 40% higher. The ideal conditions for the nitrate adsorption onto RSi-bPEI is at pH = 4, 0.5 g L−1 dose, 50 mg L−1 concentration and about 120 min adsorption time. The pseudo-second-order and Langmuir equations were the most suitable models to describe the nitrate sorption from aqueous solution with high correlation coefficient (0.99). The monolayer adsorption capacity was found to be 94.49 mg g−1 for RSi-bPEI and 47.46 mg g-1 for RSi. The reusability test manifested RSi-bPEI has good regeneration capacity, hence can be an ideal adsorbent for practical wastewater treatment.

Relevance of N-nitrosation reactions for secondary amines in nitrate-rich wastewater under UV-C treatment

This study investigated the transformation of secondary amine pharmaceuticals in UV-C/NO3− and in nitrate-rich wastewater at 254 nm by taking diclofenac, diphenylamine, mefenamic acid and furosemide as probe compounds. The degradation of targeted compounds were positively related to nitrate concentration and mainly caused by the formation of peroxynitrite and related reactive nitrogen species (e.g., nitrogen oxide and nitrogen dioxide radicals). Major transformation products were identified to provide fundamental understanding of the selective oxidation of secondary amine with reactive nitrogen species. UV photolysis, hydroxyl radical oxidation, nitration and nitrosation processes were found to be the most significant transformation pathways. In case of diphenylamine, for which most of the identified intermediates were available as standard, the relative significance of each transformation route could be established, highlighting for the first time the important role of N-nitrosation processes in UV/NO3− treatment followed by the decomposition of the resulting N-nitroso compounds by an alpha hydroxylation mechanism. This specific transformation pathway was of concern because it constitutes the molecular basis of N-nitrosamine carcinogenicity and may contribute to the increase in effluent genotoxicity under UV-C treatment in addition to the formation of nitrophenols. Hydrogenocarbonate ions at concentration values higher than 300 mg/L appeared to be a protective specie against nitrosation processes due to the formation of carbamate adducts but H2O2 in UV-C/H2O2 could be responsible for an exacerbation of the N-nitrosation pathway due to an addition source of hydroxyl radical in the system. The occurrence of major transformation products of diclofenac was confirmed in nitrate-rich wastewater under UV-C treatment at pilot-scale operation.

Evaluating the effects of Zn(II) on high-rate biogranule-based denitrification: Performance, microbial community and sludge characteristics

High-rate denitrification is a popular and efficient process for treatment of nitrate-rich wastewater. Knowing the effect of heavy metals on denitrification is essential for industrial development. In the present study, the long-term impacts of Zn(II) on denitrifying granular sludge were investigated. The suppression threshold of Zn(II) on denitrifying bacteria was 10 mg L−1 for long-term exposure. The nitrogen removal rate was decreased by long-term addition of 10 mg L−1 Zn(II). Castellaniella and Klebsiella were the two dominant genera under Zn(II) stress. The relative abundance of Klebsiella sharply decreased to 4.64% after the addition of 10 mg L−1 Zn(II), whereas Castellaniella was susceptible to 2 mg L−1 Zn(II), revealing that Castellaniella mainly was devoted to denitrification under no or low Zn(II) stress conditions, whereas Klebsiella was effective under high Zn(II) stress.

Temperature dependence of denitrification microbial communities and functional genes in an expanded granular sludge bed reactor treating nitrate-rich wastewater.

The temperature dependence of denitrification was investigated for high nitrate nitrogen denitrification in an expanded granular sludge bed (EGSB) reactor. The optimal reaction temperatures were 15–35 °C in which nearly complete denitrification was achieved with the removal of COD maintained over 80%. Nitrite accumulation was observed at 10 °C indicating the incomplete denitrification at low temperature. However, almost complete denitrification was even accomplished as high as 52 °C. High-throughput sequencing detected a total of 84 bacterial genera and 7 phyla, and temperature variation resulted in the shift of microbial community structure and diversity. Proteobacteria thrived while Firmicutes and Bacteroidetes were inhibited by temperature stress. The predominance of Halomonas and the significant decrease of Azoarcus at low temperature indicated a more important role of these two genera in denitrification in an EGSB reactor. The results of qPCR indicated that temperature exerted effects on the abundance of denitrification function genes, nirK, nirS, narG, and nosZ, due to the shift of the bacterial community. This study provided a comprehensive understanding of temperature effects on the denitrification process in an EGSB reactor treating high concentration nitrate wastewater.

Microbial community analysis using MiSeq sequencing in a novel configuration fluidized bed reactor for effective denitrification

A novel configured fluidized bed reactor (FBR) with granular rubber as the fluidized media was operated without internal recirculation to achieve denitrification. This FBR could operate under a low hydraulic retention time (HRT) of 50min due to the low rubber media density and absence of recirculation. Synthetic nitrate-rich wastewater with a fixed nitrate (NO3−-N) concentration and varying COD concentrations was fed into the FBR. The nitrate removal profile showed a rapid nitrate reduction at the bottom of the reactor with a high performance under the low HRT. Different microbial communities were identified using Illumina Miseq sequencing. The dominant microorganisms belonged to the Beta- and Gamma-proteobacteria classes and played important roles in nitrate reduction. Acidovorax was abundant at low COD: NO3−-N ratios, while Rhizobium and Zoogloea were dominant at high COD: NO3−-N ratios. The COD: NO3−-N ratio strongly influenced the composition of the microbial community including the dominant species.

Low-cost production of green microalga Botryococcus braunii biomass with high lipid content through mixotrophic and photoautotrophic cultivation.

Botryococcus braunii is a microalga that is regarded as a potential source of renewable fuel because of its ability to produce large amounts of lipid that can be converted into biodiesel. Agro-industrial by-products and wastes are of great interest as cultivation medium for microorganisms because of their low cost, renewable nature, and abundance. In this study, two strategies for low-cost production of B. braunii biomass with high lipid content were performed: (i) the mixotrophic cultivation using molasses, a cheap by-product from the sugar cane plant as a carbon source, and (ii) the photoautotrophic cultivation using nitrate-rich wastewater supplemented with CO2 as a carbon source. The mixotrophic cultivation added with 15 g L(-1) molasses produced a high amount of biomass of 3.05 g L(-1) with a high lipid content of 36.9 %. The photoautotrophic cultivation in nitrate-rich wastewater supplemented with 2.0 % CO2 produced a biomass of 2.26 g L(-1) and a lipid content of 30.3 %. The benefits of this photoautotrophic cultivation are that this cultivation would help to reduce accumulation of atmospheric carbon dioxide and more than 90 % of the nitrate could be removed from the wastewater. When this cultivation was scaled up in a stirred tank photobioreactor and run with semi-continuous cultivation regime, the highest microalgal biomass of 5.16 g L(-1) with a comparable lipid content of 32.2 % was achieved. These two strategies could be promising ways for producing cheap lipid-rich microalgal biomass that can be used as biofuel feedstocks and animal feeds.

Biological nitrate removal using waste-derived extracts as sole carbon source

Waste-derived multicomponent extracts were investigated as carbon source for biological nitrate removal. Aerobic and anaerobic sludge from a municipal wastewater treatment plant and leachate from an anaerobic digester treating food waste were studied. Alkaline-heat treatment was used for sludge solubilisation. More than 90% carbon was recovered at pH 10–11. The extracts contain very high volatile fatty acids (VFAs), protein and carbohydrate. The protein/carbohydrate ratio was 2/1 for both aerobic and anaerobic sludge extracts and 9/1 for leachate. Of the total chemical oxygen demand (COD), 60% was solubilised in both the aerobic and anaerobic sludge extracts, while 80% was solubilised in the leachate. The extracts were successfully tested in batch experiments for different time intervals as a sole carbon source for biological nitrate removal in synthetic wastewater. More than 95% nitrate removal was achieved in 24 h batch studies at carbon-to-nitrate (C/N) ratio of 8 and at 35oC. The nitrate removal performance was comparable to that obtained with glucose as the external carbon source. Further, the nitrate removal efficiency of all the three extracts is similar. Thus, the result of this study shows the potential of these waste derived materials for the low-cost treatment of nitrate rich wastewaters characterised by low C/N ratio that are generated from many industries.

Nitrogen Removal in Constructed Wetlands Using Nitritation/Anammox and Nitrification/ Denitrification: Effects of Influent Nitrogen Concentration

Simultaneous nitritation/anammox and nitrification/denitrification (SNAND) is a promising method to increase nitrogen removal from ammonium- and nitrate-rich wastewater. This study examined the effects of influent nitrogen concentrations on plant assimilation and microbial nitrogen removal via SNAND in three free water surface wetlands. Anammox and denitrification contributed 78 and 22%, respectively, of microbial removal of total inorganic nitrogen (TIN). Nitrogen removal rates increased with influent concentrations in the low ranges of 17 to 105 mg N/L ammonium and 51 to 179 mg N/L TIN. However, nitrogen removal rates appeared to decrease with influent concentrations in the high ranges of 248 to 293 mg N/L ammonium and 348 to 391 mg N/L TIN. Plant growth was negatively affected when influent ammonium concentration exceeded 46 to 76 mg N/L. Plant assimilation contributed 11 to 47% toward TIN removal at low influent ammonium concentrations (42 to 76 mg N/L) and 4% at high influent ammonium concentrations (mean 264 mg N/L).