High Nitrate Concentrations Research Articles

Direct and specific analysis of nitrite and nitrate in biological and non-biological samples by capillary ion analysis for the rapid identification of fatal intoxications with sodium nitrite

In recent years, a significant increase of reports about suicidal cases due to intentional sodium nitrite intake has been described. In the forensic pathology context, the strategy to approach intoxication cases by sodium nitrite, without any preliminary information or hint, is not straightforward. Indeed, in a number of cases the lack of crime scene data and/or specific pathological signs makes difficult the identification of nitrite poisoning. Moreover, the analytical determination of nitrite in blood is challenging, due to its rapid oxidization to nitrate by hemoglobin. Although several methods have been proposed for the clinical analysis of nitrate and/or nitrite in biological samples, none of these is specifically focused on the determination of these ions in cadaveric samples. Consequently, the diagnosis of nitrite fatal intoxication is still based on methemoglobin analysis. The present paper reports the optimization and validation of an analytical method of capillary ion analysis (CIA) with UV detection, for the determination of nitrite and nitrate in biological fluids and its application to two authentic cases of death by nitrite intake. The analyses were carried out in a bare fused-silica capillary (75 µm inner diameter) using 100 mM sodium tetraborate (pH 9.24) as background electrolyte and applying a voltage of − 15 kV between the capillary ends. The detection was obtained by direct UV absorption recorded at 214 nm wavelength. Bromide was used as the internal standard. Linearity was established in the range of 0.25–5 mmol/L). Reproducibility (intraday and day-to-day) was characterized by relative standard deviations (RSDs) 14.7% for peak areas. The method was applied to the determination of nitrite and nitrate in two real forensic cases, where high concentrations of nitrate were found in cadaveric blood samples (6.5 and 4.4 mmol/L, respectively). Nitrite was found only in trace amounts, due to the instability of this ion in cadaveric blood where it is oxidized to nitrate. The present method represents a new tool for the direct and rapid determination of nitrite and nitrate in cases of forensic interest, and thus offers a diagnostic tool more sensitive and precise than the need methemoglobin analysis.

Effect of Light-Emitting Diodes (LEDs) on Some Physical and Bioactive Compounds of ‘Iceberg’ Lettuce (Lactuca Sativa L.)

Abstract The use of light-emitting diodes (LEDs) is a recent concerned application in the indoor crop system of the modern plant production. In our research, we evaluated the influence of four monochromic LED lights including 100% White (W), Yellow (Y), Red (R) and Blue (B) in comparison to solar lightening condition (GR) as a control. In this regard, some morphological characteristics and biochemical content of the common outdoor ‘Iceberg’ lettuce (Lactuca sativa L.) was measured. The results show that leaf length, leaf area and total head weight were significantly greater in the plants grown under B LED, while all the other physical parameters were significantly higher in the plants grown under GR environmental conditions. On the other hand, chlorophyll (Chl), carotenoids (Car), and nitrate content were also influenced by different light treatments. Plants grown under LED light treatment resulted in significantly higher chlorophyll content compared to the control. However, significantly greater carotenoid content was in the plants grown under GR condition. The highest total chlorophyll content was recorded under B and R LED, whereas the lowest was in the GR condition. The lowest nitrate content in the blade and petiole was recorded in the plants grown under Y LED, while the highest nitrate content was recorded in the GR. Based on our result, it is possible to grow and improve some quality parameters of common outdoor ‘iceberg’ lettuce under LED where the solar light is limited or unavailable. Thus, plants performed better under GR light conditions than monochromic LEDs; however, some LED lights could improve some quality parameters and biochemical contents in the ‘iceberg’ lettuce variety.

Degradation of High-Concentration Nitrate Nitrogen in Groundwater: A Laboratory Study

To investigate effective and reasonable methods for the remediation of nitrate nitrogen pollution in groundwater, two groups of laboratory denitrification experiments were conducted: one on the effect of native denitrifying microbes in groundwater and another on the effect of artificially added denitrifying microbes. The water used in the experiment was typical groundwater with a high concentration of nitrate nitrogen. The temperature was controlled at 15°C. Both groups of experiments established four types of culture environments: anaerobic, anaerobic with an added carbon source (glucose), aerobic, and aerobic with an added carbon source (glucose). The results indicated that native denitrifying microbes in the groundwater have almost no ability to remove high concentrations of nitrate nitrogen. However, artificially added denitrifying microbes can effectively promote denitrification. Artificially added denitrifying microbes had the highest activity in an anaerobic environment in which a carbon source had been added, and the rate removal of a high concentration of nitrate nitrogen in groundwater was the highest and reached as high as 89.52%.

Hydrochemical Assessment of Groundwater around Lapite Dumpsite for Irrigation Water Quality in Ibadan, Southwestern Nigeria

Due to the increase in population and industrialization growth, most countries in the world depend on groundwater to meet agriculture demands for food production. The increase in water contamination due to indiscriminate solid wastes has necessitated the assessment of water quality and its suitability for agricultural usage. Twenty four groundwater and ten stream water samples were randomly collected from the downslope and upslope side of the dumpsite for all the major physio-chemical parameters. The pH of water samples indicates slightly acidic to alkaline in nature. High concentrations of nitrate, total dissolved solids and electrical conductivity suggest the impact of the waste on the water resource. Assessment of irrigation water quality based on Sodium Adsorption Ratio (SAR), Soluble Sodium Percentage (SSP), Permeability Index (PI) and Magnesium content (MC) indicated that most of the water samples fall within the permissible standard for irrigation water. Thus, the water should be used with caution on crops for long time agricultural sustainability.

Nitrate content of spring leafy vegetables from different outlets

The issue of nitrate contamination has become increasingly acute, with the awareness of their toxicity on the human body and the identification of increasing sources of contamination. Human intervention in the natural nitrogen cycle has serious repercussions that are manifested by its accumulation at one or more levels. The use of fertilizers in agriculture is crucial to ensure food security, but their unreasonable use causes accumulations of nitrogen in the form of nitrate ions in plants, and from here they reach human intake, over a certain amount becoming harmful. The aim of this paper is to quantify the amount of nitrates present in certain vegetables intensively consumed during spring, sources of food which if does not conform with the current recommendations of EFSA and EU, can become major factors of risk to public health. The studied material consists of 5 types of vegetables products intensively consumed in spring: lettuce (Lactuca sativa), curly lettuce (or Lollo - Lactuca sativa var Crispa), Iceberg lettuce (Lactuca sativa lime Iceberg), spinach (Spinacia oleracea) and wild garlic (Allium ursinum). The samples were collected from different commercial locations (outlets): hypermarkets (H), open markets (OM), street trade (ST) and house gate trade (HGT). The highest nitrate concentrations were found in lettuce in ST (4306 mg kg-1) and HGT (4175.5 mg kg-1), in Lollo salad in ST (4306.5 mg kg-1) and HGT (4602.75 mg kg-1) and spinach in OM (3469.25 mg kg-1). The study findings suggest that ST and HGT are commercial points that may constitute a danger to public health, the ADI value exceedingly even by 107.21% in the case of Lollo salad purchased from HGT. The issue calls for more drastic controls by the authorities.

Impact of Nutrients and Water Quality in some Khors of Lake Nasser, Egypt

The present study has been carried out with the goal to assess the seasonal variation as well as water quality status based on some physic-chemical characteristics of four main khors in lake Nasser, water samples were collected from many sites for each khor as shown on the map. Seasonally changes in physic-chemical parameters such as temperature, pH, dissolved oxygen to study their effect on the concentration of nutrients (NH3, NO , NO ,PO and SiO ) in 2013, where high concentration of nitrate or phosphate is indicative of eutrophication. Temperature play important role in plankton’s distribution and lake stratification. Where minimum valus were recorded during winter, but maximum values were observed during summer, pH values were in slightly alkaline side, fluctuated between 7.21-9.37. High mean value 12.1mgl-1 was detected in khor Kalabsha during winter, then in khor Toushka 7.7 mgl-1 during autumn. The concentration of NH3 ranged between 1.86 to 810 µg NH3l-1, for NO2 showed variations from zero to 76.35 µgl-1. The concentrations of NO , PO and SiO were measured and fluctuated between 21-3838.8, ND-312 µgl-1 and 1.7-8.9 mgl-1 respectively. Accordingly, the mean values of different parameters from four different sites were used for the calculation of ANOVA (analysis of variance different seasons). The results of the study pointed out an excellent opportunity to characterize the quality of the water of the four major khors in different seasons and can be used for drinking water, pisclculture irrigation, domestic and in many other uses.

Stability-limited ion-exchange of calcium with zinc in biomimetic hydroxyapatite

The exchange of Ca2+ ions in hydroxyapatite (HAp) with Zn2+ ions into Zn-HAp is of interest for applications ranging from bone tissue engineering to the use as a precursor in subsequent ion-exchange reactions. Previous studies, using direct synthesis, showed that ~ 20 mol% Zn2+ ions can be incorporated into HAp, before byproducts are observed. However, this is realized at the cost of a loss in crystallinity and control over crystal size and shape with increasing amounts of Zn2+ ion incorporation. In this work a simple post-synthetic ion-exchange strategy for the formation of Zn-HAp has been investigated. By merely exposing HAp to high concentrations of zinc nitrate in water, up to 22 mol% of the Ca2+ ions can displaced by Zn2+ ions without any measured loss in crystallinity and preservation of crystallite size and shape. It was found that the incorporation of Zn2+ ions destabilizes the HAp crystals resulting in their gradual dissolution and reprecipitation. Consequently, promoting the exchange of Ca2+ with Zn2+ions using increased reaction times, sonication and increased temperature results in an increased dissolution of HAp and precipitation of hopeite crystals, thereby preventing the formation of more zinc rich Zn-HAp.

A pressurized hydrogenotrophic denitrification reactor system for removal of nitrates at high concentrations

A pressurized hydrogenotrophic denitrification reactor to remove nitrate from groundwater was recently presented. To enable treatment of nitrate-concentrated brines, we demonstrate here the removal of high nitrate concentrations without nitrogen gas accumulation in the reactor’s headspace over time. In order to eliminate nitrogen gas build up in the pressurized reactor’s headspace, the main unsaturated flow pressurized reactor was connected to an external degassing unit via liquid recirculation. Pressurized liquid from the main reactor was intermittently discharged to the degassing unit where dissolved N2 gas effervesced and escaped to the atmosphere. The degassed effluent water was continuously recirculated back to the main reactor to maintain steady-state nitrogen and hydrogen gas partial pressures. Denitrifying rates of up to 6 g N/L-reactor/d were achieved in the reactor system under freshwater and brine conditions. Nitrate removal was over 97 %, with nitrate effluent concentrations lower than 10 mg N/L for influent concentrations of about 400 mg N/L. The reactor system maintained steady-state nitrogen and hydrogen gas partial pressures using low external recirculation rates at low reactor total pressures (< 5 atm). At high denitrification rates, dissolved nitrogen concentrations in the reactor were super saturated (125–150%) while on the other hand, dissolved hydrogen was undersaturated (30–60%) due to intense bacteria uptake from the water. These dynamic conditions reduced the external recirculation flow requirement for degassing and resulted in much better hydrogen utilization than expected (greater than 93 %).

Application of central composite design approach for optimization nitrate removal from aqueous solution by immobilized Pseudomonas putida.

High nitrate concentration is a dangerous pollutant in the environment. Immobilization for the optimum denitrifying bacterial strain isolated from collected wastewater samples was suggested for bioremediation of excessive nitrate concentration from aqueous solutions and its denitrification activity under different pH, nitrate concentration, bacterial beads, temperature and sodium alginate concentration conditions was explored. The active isolate was identified as Pseudomonas putida MT364822.1 by 16S rRNA analysis. Nitrate bioremediation process was optimized by applying response surface methodology based on central composite design approach. Nitrate uptake was significantly affected by variables of study (P-value <0.05). Maximum removal of nitrate (91.1%) was achieved at pH 7, nitrate concentration 400 mg/L, immobilized bacterial beads 3.0 g/L, temperature 35 °C and sodium alginate concentration 2.5% as optimal variable values. For application, immobilized P. putida MT364822.1 removed 82.2% of nitrate from raw fish farm effluent. Storage and reusability experiments showed that the immobilized strain stronger and more stable than the pure strain. The results suggested that immobilized P. putida MT364822.1 is a highly promising and suitable microorganism for use in the bio-removal of nitrate, and the central composite design was more effective in optimizing variables to achieve the best nitrate removal efficiency.

High nitrate inhibited adventitious roots formation in apple rootstock by altering hormonal contents and miRNAs expression profiles

The adventitious roots (ARs) formation is a major setback for the mass proliferation of apple rootstocks. Nitrate is a vital signaling molecule for the regulation of root architecture. However, the inhibitory effect of nitrate at a high dose is missing. In this study, the physiological and molecular mechanism underlying ARs inhibition was tested. The B9 stem cuttings were grown on low and high nitrate concentrations, namely T1 and T2, respectively, and the T2 appeared as ARs inhibiting dose, where the rooting percentage was only 28% that was 130% less than T1 cuttings. Moreover, the average root numbers of T2 were only 31, which was 78% lower than T1 cuttings. At most time points, the endogenous hormones: JA, BR, ABA, CTK, GA, and AUX were exhibited at higher levels in response to T2, leading to hormonal imbalance in the plant and led to ARs inhibition. In addition, 205 known miRNAs belonging to 42 families and 438 novel miRNA were observed differentially expressed by the nitrate treatments. Where miR160a, miR390a, miR167, miR394, and miR169a were found to be related to auxin and ABA signaling, and miR171, miR166, miR156, miR319, and miR396 were related with cell fate transformation, proliferation, and enlargement. Our results propose that ARs formation is a complicated biological process, which was influenced by multiple hormone signaling pathways. This work is a pioneer giving knowledge on the inhibitory effects of high nitrate concentration on AR formation for future studies in woody plants.

Rotifers stimulate the specific uptake rate in lotic phototrophic biofilms

Abstract Stream biofilms can improve water quality (e.g. excessive nitrogen loads) because their microorganisms such as microphytobenthos and bacteria, are involved in self‐depuration processes in the biofilm. In marine sediments, meiofauna can influence primary productivity of phototrophic biofilms, stimulate bacterial growth, and exert a significant role on nitrogen cycling. We hypothesised that in rivers biofilms, increased meiofauna abundance in combination with nutrient enrichment can lead to improve biofilm nutrient uptake ability. River biofilms (from the Garonne River, France) were incubated in flumes supplied with natural river water. The uptake rates of the biofilms as well as the response of microorganisms were studied under different conditions of meiofaunal density and concentration over a 10‐day experiment. Rotifers dominated the meiofauna community in all biofilms. Under high nitrate conditions, the biofilm uptake rate was significantly higher in meiofauna‐enriched than non‐enriched biofilms over the first 2 days. This suggests that under high nitrate concentration conditions, high densities of rotifers enhanced the nitrogen uptake capacity of phototrophic biofilm despite a lower biomass. Densities of rotifers and bacteria in biofilms were positively correlated under enriched conditions suggesting that these two communities interacted over the experimental period. Signature pigment concentrations show that, under low concentrations of , biomasses of diatoms and green microalgae were higher in meiofaunal‐enriched than non‐enriched biofilms, indicating that rotifer activity favoured biomass accumulation of these algae. This study demonstrates that meiofauna inhabiting biofilms may contribute to the limitation of nitrogen loads in stream water and supports the thesis that the potential interactions between faunal groups and microbial communities of biofilms merits further investigation to improve our understanding of processes which regulate interactions between biofilms and the overlying water in rivers.

Electrochemical enrichment of marine denitrifying bacteria to enhance nitrate metabolization in seawater

High concentrations of nitrate from industrial discharges to coastal marine environments are a matter of concern owing to their ecological consequences. In the last years, Bioelectrochemical Denitrification Systems (BEDS) have emerged as a promising nitrate removal technology. However, they still have limitations, such as the enrichment strategy for specific microbial communities in the electrodes under natural conditions. In this study, three-electrode electrochemical cells were used to test microbial enrichment from natural seawater by applying three reported potentials associated with the dissimilatory denitrification process (−130, −260, and −570 mV vs. Ag/AgCl). The microbial community analysis showed that by applying −260 mV (vs. Ag/AgCl) to the working electrode, it was possible to significantly enrich denitrifying microorganisms, specifically Marinobacter, in comparison with the control. Furthermore, −260 mV (vs. Ag/AgCl) led to a significantly higher nitrate removal than other conditions, which, combined with cyclic voltammetry analysis, suggested that the polarized electrodes worked as external electron donors for nitrate reduction. Hence, this work demonstrates for the first time that it is possible to enrich marine denitrifying microorganisms by applying an overpotential of −260 mV (vs. Ag/AgCl) without the need for a culture medium, the addition of an exogenous electron donor (i.e., organic matter) or a previously enriched inoculum.

Water, Health, and Environmental Justice in California: Geospatial Analysis of Nitrate Contamination and Thyroid Cancer.

Environmental health hazards are known to disproportionately burden marginalized communities. Agriculture, wastewater, and industrial waste contaminate surface and groundwater, used for drinking, with nitrates. High nitrate concentrations in drinking water have been linked to methemoglobinemia and, recently, thyroid cancer. With a large proportion of the nation's agriculture grown in California, thyroid cancer linked to nitrate water contamination is of concern. This research entailed geographic and statistical analysis of water, nitrate, health, and disadvantaged communities (DACs) in California. DACs are Californian defined areas that experience a combination of hardships from socioeconomic, health, and environmental fields. Our analysis of the California Cancer Registry and California Water Board's well data shows statistically significant correlation (p < 0.05) between nitrate contamination (wells >5 and 10 ppm NO3-N per square mile and percentage of total wells) and thyroid cancer incidence. DACs had twice the rate of thyroid cancer compared with non-DACs, and higher numbers of nitrate-contaminated wells and hot spots compared with the state averages. Almost half (47%) of the Central Valley's area contained DACs and 27% of wells >10 ppm NO3-N contaminants. Our study provides a method for other states and countries to conduct preliminary geospatial analysis between water contamination and health with open data. Maps and analysis from this research can inform the public, advocacy groups, and policy leaders of health-related concerns in relation to nitrate water contamination and environmental justice in California. DACs should be provided cost-effective drinking water monitoring and treatment, and governments should incentivize nitrate loading reductions in agriculture, industry, and wastewater. Future research is recommended with more localized, private health data on thyroid cancer incidence.

Assessment of Groundwater Quality for Drinking and Domestic Purposes through Local Survey and Water Quality Index in Vietnam

The quality of groundwater resources is increasingly declining, significantly affecting people’s life and health. The study aims to assess public perception on existing groundwater quality and scheme over conventionally used free groundwater. The contemporaneous analytical procedures applied to determine the concentration of physical parameters: total dissolved solids and total solids and chemical parameters: pH, nitrite (N-NO2-), nitrate (N- NO3-), ammonium (N-NH4+/ NH3), iron (FeII + III) and total hardness were collected for 30 drinking water well samples located in 5 Quarters (An Hoa, An Loi, Ben Don, Phu Hoa, and Phu Nghi) to calculate the water quality index. The results show that up to 96% of people still use groundwater as their main source of drinking, domestic purposes, although groundwater quality is showing a serious decline in quality. The low pH index ranges from 3.0 ÷ 4.5. On average, 3.5 ÷ 4.0 pH of groundwater samples are outside the permissible limit according to VN standards 09: 2015 (5.5 - 8.5), which makes the water acidic, which harmful to human health. Besides, 10% of groundwater samples had high nitrate content, and 6.67% of water samples had ammonium content that did not meet VN standards 09: 2015. The current state of groundwater quality is not good for cooking and drinking. The results will benefit future groundwater exploitation to support more evidence of water quality and deteriorate the water quality soon, ultimately proving to be disastrous for all living beings in the region.

Investigating the root cause of N-nitrosodimethylamine formation in metformin pharmaceutical products

ABSTRACT Background FDA limited N-nitrosodimethylamine (NDMA) – a carcinogenic impurity formed during metformin (MET) tablets manufacturing – level to 96 ng/day; a step which led to recall of MET products. This work aims to investigate the root cause of NDMA formation during MET tablets manufacturing. Research design and methods We focused on three main contributing causes: use of water and heat during intra-granulation, and the nitrite/nitrate quantities in excipients. Thirteen MET tablet formulations (immediate or sustained-release) were manufactured, on batch level. Each batch was manufactured using one excipient and excluding one cause at a time and NDMA level was assayed. Results NDMA traces were undetectable in MET tablets manufactured using polyvinyl pyrrolidone or hydroxypropyl cellulose SSL, even when water and/or heat were employed during intra-granulation. Levels of NDMA in MET tablets with hydroxypropyl methyl cellulose (HPMC) E5 or carboxymethyl cellulose sodium 4000 were 67.08 ± 2.3 and 66.21 ± 2.5 ng/day, in the presence of water and/or heat. No impact of employing extra-granular PolyoxTM, HPMC E5 or HPMC K15 on NDMA formation, despite the high nitrite and nitrate content in these excipients. Conclusions Water, heat, and excipients’ nitrite and nitrate levels are the key players, which should collectively exist, to cause NDMA formation during MET tablets manufacturing.

Assessment of ground water pollution through metal index analysis and its source identification along the Delhi-Haryana boarder, India

An integrated study of health risk assessment, pollution indices, and factor analysis was carried out to assess the pollution and heavy metal sources in groundwater of the Delhi-Haryana boarder, India. A total of 25 groundwater samples were analyzed for major ions, and 13 samples were analyzed for 6 elements (Mn, Cu, Cd, Zn, Fe, and Pb). Most of the samples show a high concentration of nitrate, fluoride, and EC and indicate the influence of anthropogenic activities. Out of the elements analyzed, the elements like Cd, Pb, and Fe exceed the prescribed limits of WHO standard for drinking water. Health risk index (HRI) values reveal risk of toxicity through oral pathways is less, as all trace elements are < 1. Six locations (Sl. No. 2, 7, 8, 10, 11, and 13) are considered as the most polluted based upon their heavy metal pollution index (HPI). The distribution pattern of these locations indicates that the pollution is due to anthropogenic activities. Sources of the pollution were determined by statistical analysis. There are three major factors like mining and agriculture, geogenic source, and crusher zone activities and domestic activities that are mainly responsible for the heavy metal pollution in the study area.

Variation of salinity and nitrogen concentration affects the pentacyclic triterpenoid inventory of the haloalkaliphilic aerobic methanotrophic bacterium Methylotuvimicrobium alcaliphilum

The occurrence and activity of aerobic methanotrophs are influenced by environmental conditions, including pH, temperature, salinity, methane and oxygen concentrations, and nutrient availability. Aerobic methanotrophs synthesize a variety of lipids important for cell functions. However, culture-based experiments studying the influence of environmental parameters on lipid production by aerobic methanotrophs are scarce. Such information is crucial to interpret lipid patterns of methanotrophic bacteria in the environment. In this study, the alkaliphilic strain Methylotuvimicrobium alcaliphilum was cultivated under different salinities and different nitrate concentrations to assess the effect of changing conditions on the inventory of pentacyclic triterpenoids. The results indicate that hopanoid abundance is enhanced at lower salinity and higher nitrate concentration. The production of most pentacyclic triterpenoids was favored at low salinity, especially for aminotriol. Interestingly, 3-methyl-aminotetrol and tetrahymanol were favored at higher salinity. Bacteriohopanepolyols (BHPs), particularly aminotriol and 3-methyl-aminotriol, increased considerably at higher nitrate concentrations. Four novel N-containing BHPs—aminodiol, 3-methyl-aminodiol, and isomers of aminotriol and 3-methyl-aminotriol—were identified. This study highlights the significance of environmental factors for bacterial lipid production and documents the need for cultivation studies under variable conditions to utilize the full potential of the biomarker concept.

Biopolishing sanitary landfill leachate via cultivation of lipid-rich Scenedesmus microalgae

Sanitary landfill leachate is a toxic effluent with a composition that can vary widely and biological treatment using microalgae represents a promising for bioremediation alternative. In this study, treated sanitary landfill leachate (TSLL) collected after undergoing secondary treatment (biological stabilization pond) was used for the cultivation of Scenedesmus sp. (Chlorophyceae). The TSLL was mixed with tap water to obtain different concentrations (0, 20, 40, 60, 80 and 100% TSLL) before microalgal cultivation aimed at maximizing the production of biomass and lipids. The best concentration for Scenedesmus sp. growth was 80% TSLL, resulting in biomass and lipid productivities of 420 and 36 mg L−1 d−1, respectively, high concentrations of oleic (C18:1) and palmitic (C16:0) fatty acids, and effective removal of nitrogen (NO3−, ∼69%) and phosphorus (PO3−1, 87%). In addition, Scenedesmus sp. removed metals (Al, Cd, Cu, Fe, Ni, Rb and Zn) from the 80% TSLL through biosorption, suggesting that microalga can be used to remediate wastewater that has high polluting capacity. The ability of Scenedesmus sp. to grow in TSLL with high nitrate and heavy metal contents, allows the simultaneously purification of wastewater and the production of a lipid-rich biomass. The proportion of C16-C18 fatty acids in this biomass makes it suitable for biodiesel production.

Effects of Nutrient Content and Nitrogen to Phosphorous Ratio on the Growth, Nutrient Removal and Desalination Properties of the Green Alga Coelastrum morus on a Laboratory Scale

In wastewater, nutrient concentrations and salinity vary substantially, however, the optimal N:P ratio for the treatment using microalgae is not well described. In this study, the effects of higher and lower nitrate and phosphate contents and N:P ratios on growth, nutrient removal ability and halotolerance of the common green alga Coelastrum morus were investigated in model solutions. The results suggest that high nitrate content (above 100 mg L−1) with a similarly high phosphate concentration (resulting low N:P ratio) is not favorable for growth. The studied isolate can be considered as a halotolerant species, showing remarkable growth up to 1000 mg L−1 NaCl and it seems that despite the negative effects on growth, higher nutrient content contributes to higher halotolerance. A significant amount of nitrate removal was observed in media with different nutrient contents and N:P ratios with different salt concentrations. High N:P ratios favor phosphate removal, which is more inhibited by increasing NaCl concentration than nitrate uptake. Overall, with a relatively higher nutrient content and a favorable (5 or higher) N:P ratio, a common green algal species such as C. morus could be a promising candidate next to species from the Chlorellaceae and Scenedesmaceae families.

Woodchip bioreactors provide sustained denitrification of brine from groundwater desalination plants

Woodchip bioreactors are widely known as a best management practice to reduce excess nitrate loads that are discharged with agricultural leachates. The aim of this study was to evaluate the performance of citrus woodchip bioreactors for denitrification of brine (electrical conductivity ≈ 17 mS cm−1) from groundwater desalination plants with high nitrate content (NO3−-N ≈ 48 mg L−1) in the Campo de Cartagena agricultural watershed, one of the main providers of horticultural products in Europe. The performance was evaluated relative to seasonal changes in temperature, dissolved organic carbon (DOC) provided by woodchips, hydraulic residence time (HRT) and woodchip aging. Bioreactors (capacity 1 m3) operated for 2.5 years (121 weeks) in batch mode (24 h HRT) with three batches per week. Denitrification efficiency was modulated by DOC concentration, temperature, hydraulic residence time and the drying-rewetting cycles. High salinity of brine did not prevent nitrate removal from occurring. The high DOC availability (>25 mg C L−1) during the first ≈48 weeks resulted in high nitrate removal rate (>75%) and nitrate removal efficiency (until ≈ 25 g N m−3 d−1) regardless of temperature. Moreover, the high DOC contents in the effluents during this period may present environmental drawbacks. Denitrification was still high after 2.5 years (reaching ≈9.3 g N m−3 d−1 in week 121), but dependence on warm temperature became more apparent with woodchips aging from week ≈49 onwards. Nitrate removal efficiency was highest on the first weekly batch, immediately after woodchips had been unsaturated for four days. It was attributable to a flush of DOC produced by aerobic microbial metabolism during drying that stimulated denitrification following re-saturation. Hence, alternance of drying-rewetting cycles is an operation practice that increase bioreactors nitrate removal performance.