Phosphorus optimization for simultaneous nitrate-contaminated groundwater treatment and algae biomass production using Ettlia sp

Nitrate reductase enzymes in alga Chattonella subsalsa are regulated by environmental cues at the translational and post-translational levels

Nitrate reductase (NR) catalyzes the rate-limiting step in nitrate assimilation. Plant and algal NRs have a highly conserved domain architecture but differ in regulation. In plants, NR activity is regulated by reversible phosphorylation and subsequent binding of 14-3-3 proteins at a conserved serine residue. Algal NRs typically lack 14-3-3 binding motifs, which have only recently been identified in a few algal species. Previous research indicates that the alga, Chattonella subsalsa, possesses a novel NR, NR2-2/2HbN (NR2), which incorporates a 2/2 hemoglobin domain. A second NR (NR3) in C. subsalsa lacks the cytochrome b5 (heme-Fe) domain but includes a putative binding motif for 14-3-3 proteins. The expression of NR2 and NR3 genes indicates that NR2 transcript abundance was regulated by light, nitrogen source, and temperature, while NR3 transcript levels were only regulated by light. Here, we measured total NR activity in C. subsalsa and the potential for regulation of NR activity by putative 14-3-3 binding proteins. Results indicate that NR activity in C. subsalsa was regulated by light, nitrogen source, and temperature at the translational level. NR activity was also regulated by endogenous rhythm and temperature at the post-translational level, supporting the hypothesis that NR3 is regulated by 14-3-3 binding proteins. Together with a previous report describing the regulation of NR gene expression in C. subsalsa, results suggest that C. subsalsa responds to environmental conditions by differential regulation of NRs at transcriptional, translational, and post-translational levels. This flexibility may provide a competitive advantage for this species in the environment. To date, this is the first report which provides evidence for the potential post-translational regulation of NR by 14-3-3 proteins in algal species and suggests that regulatory mechanisms for NR activity may be shared between plants and some algal species.

Recent advances in the source identification and remediation techniques of nitrate contaminated groundwater: A review

Researchers have long been committed to identify nitrate sources in groundwater and to develop an advanced technique for its remediation because better apply remediation solution and management of water quality is highly dependent on the identification of the NO₃^- sources contamination in water. In this review, we systematically introduce nitrate source tracking tools used over the past ten years including dual isotope and multi isotope techniques, water chemistry profile, Bayesian mixing model, microbial tracers and land use/cover data. These techniques can be combined and exploited to track the source of NO₃^- as mineral or organic fertilizer, sewage, or atmospheric deposition. These available data have significant implications for making an appropriate measures and decisions by water managers. A continuous remediation strategy of groundwater was among the main management strategies that need to be applied in the contaminated area. Nitrate removal from groundwater can be accomplished using either separation or reduction based process. The application of these processes to nitrate removal is discussed in this review and some novel methods were presented for the first time. Moreover, the advantages and limitations of each approach are critically summarized and based on our own understanding of the subject some solutions to overcomes their drawbacks are recommended. Advanced techniques are capable to attain significantly higher nitrate and other co-contaminants removal from groundwater. However, the challenges of by-products generation and high energy consumption need to be addressed in implementing these technologies for groundwater remediation for potable use.

Assessment of a novel microalgae-cork based technology for removing antibiotics, pesticides and nitrates from groundwater

Groundwater pollution has increased in recent years due to the intensification of agricultural and livestock activities. This results in a significant reduction in available freshwater resources. Here, we have studied the long term assessment of a green technology (1-4 L/day) based on a photobioreactor (PBR) containing immobilised microalgae-bacteria in polyurethane foam (PF) followed by a cork filter (CF) for removing nitrates, pesticides (atrazine and bromacil), and antibiotics (sulfamethoxazole and sulfacetamide) from groundwater. The prototype was moderately effective for removing nitrates (58%) at an HRT of 8 days, while its efficiency decreased at a HRT of 4 and 2 days (<20% removal). The combined use of PBR-CF enabled antibiotics and pesticides to be attenuated by up to 95% at an HRT of 8 days, but their attenuation decreased with shorter HRT, with pesticides being the compounds most affected (reducing from 97 to 98% at an HRT of 8 days to 23-45% at an HRT of 2 days). Pesticide transformation products were identified after the CF, supporting biodegradation as the main attenuation process. A gene-based metataxonomic assessment linked the attenuation of micropollutants to the presence of specific pesticide biodegradation species (e.g. genus Phenylobacterium, Sphingomonadaceae, and Caulobacteraceae). Therefore, the results highlighted the potential use of microalgae and cork to treat polluted groundwater.

Nitrification of anaerobic digestate using a consortium of microalgae and nitrifiers in an open photobioreactor with moving bed carriers

A consortium of microalgae and nitrifiers has attracted attention as an alternative to the expensive traditional nitrification process. A possible obstacle to achieving this is the inhibition of nitrifiers under strong light irradiation. This study evaluated the effect of moving bed carriers on anaerobic digestate nitrification in an open photobioreactor inoculated with microalgae and nitrifiers under an incident light intensity of 1000 μmol photons m^-2 s^-1. The results showed higher specific nitrification activity in the carrier-added photobioreactor (103.6 mg-N g-TSS day^-1) than in one in which no carrier was added (11.7 mg-N g-TSS day^-1). The empirical equations for determining the light intensity at different depths in the photobioreactor showed a significant contribution by carriers in attenuating the incident light intensity. This is due to the large light attenuation caused by the carrier (1.09 cm^-1). The average light intensity inside of the photobioreactor decreased considerably in the carrier-added photobioreactor (342 μmol photons m^-2 s^-1), whereas it did not decrease in the one with no added carrier. It was found that specific nitrification activity was significantly negatively affected by average light intensity inside of the reactor, and not by incident light intensity, by combining the results from different studies including ours. This study demonstrated, for the first time, the effectiveness of adding moving bed carriers in photobioreactors to mitigate light inhibition of nitrifiers in a consortium of microalgae and nitrifiers.

Autotrophic granulation of hydrogen consumer denitrifiers and microalgae for nitrate removal from drinking water resources at different hydraulic retention times

To avoid hydrogen injection and to enhance the settleability of microbial biomass in biological treatment of nitrate-contaminated drinking water resources, a new method based on granulation of a mixture of hydrogen consumer denitrifiers (HCD) and microalgae is introduced. Decreasing hydraulic retention time (HRT) was applied as the selection pressure in an up-flow photobioreactor to increase the speed of granulation and nitrate removal under autotrophic condition during a 50-day operation. Formation of granules occurred at three phases including granule nucleation, growth of granule, and mature granule, with decreasing the values of ζ-potential from -19 mV to -4 mV. Enhancement of microbial attachment within granule formation could reduce the presence of total suspended solids in the effluent. Developed granules of HCD and microalgae could settle down with velocity of 40 ± 0.6 m/h when reaching the average size of 1.2 mm at day 40. Complete NO₃^--N removal from drinking water was achieved from the initial stage of granulation until the end of operation at all HRTs of 3 days-5 h. The clear treated water was obtained at the growth phase when the chemical oxygen demand and phosphate were undetectable. Therefore, the application of HCD-microalgae granule is a promising way for nitrate removal from water.

Attenuation of nitrates, antibiotics and pesticides from groundwater using immobilised microalgae-based systems

Groundwater pollution by nitrates and organic microcontaminants (OMCs) such as pesticides and antibiotics has increased in recent years due to the intensification of agriculture and livestock activities. Here we demonstrate, for the first time, the suitability of using microalgae immobilised in different materials (luffa sponge and polyurethane foam) to attenuate nitrates, antibiotics (sulfacetamide, sulfamethazine, and sulfamethoxazole), pesticides (bromacil, atrazine, diuron, bentazone, and mecoprop) from groundwater in two operational modes (batch and continuous-feeding). The results from the batch experiments show that OMC kinetic removal rates ranged from 0.01 to 0.18 d^-1, with half-lives from 4 to 69 days. Immobilised microalgae in luffa and foam materials in the batch study was found to enhance the attenuation of selected OMCs from 36% to 51%, on average, after 10 operational days. Microalgae reactors in continuous-feeding operational mode out performed batch mode in terms of OMC removal (65% vs. 50%, on average) at a hydraulic residence time (HRT) of 8 days, whereas nitrate removal was greater in the batch experiments (81 vs. 48%, on average). OMC attenuation showed a high HRT dependence, but immobilised reactors were more resilient to the decrease in HRT. Further studies are needed, including the assessment of transformation products as well as the scale-up of the system to check the feasibility of the technology. Nevertheless, we expect our assay to be the starting point for the applicability of immobilised-microalgae-based systems for the treatment of polluted groundwater.

Dataset on non-carcinogenic risk via nitrate and nitrite in the groundwater of Divandarreh County, Kurdistan province, Iran: A potential concern for drinking

The presence of elevated nitrate (NO_3-) and nitrite (NO_2-) concentration in drinking water higher than the standard limits could endanger the health of consumers. For this data article, concentration of NO_3- and NO_2- was measured in 118 samples collected from 59 active rural wells in Divandarreh County and the non-carcinogenic risk in the adults and children was estimated by Monte Carlo simulation (MCS). The obtained data showed that the average concentration of NO_3- and NO_2- was ranges from 31.37 ± 18.87 mg/L and 1.45 ± 0.90 mg/L respectively. Based on acquired data, NO_3- concentrations were 37 times higher than NO_2- with significant p value of < 0.05. The average concentration of NO_3- and NO_2- was lower than the national standard with p value < 0.05. However, the concentration of NO_3- and NO_2- in 23.7% and 13.5% of wells was higher than the national standard of Iran. Total target hazard quotient (TTHQ) in the adults and children was 1.78 and 1.54, respectively. Although, the average concentration of NO_3- and NO_2- in drinking water was lower than the national standard limits, but the non-carcinogenic risk assessment showed that the children and adults are at a significant risk via nitrate and nitrite in the rural Divandarreh County (TTHQ > 1).

Optimal strategies for bioremediation of nitrate-contaminated groundwater and microalgae biomass production

Optimizing the mono-cultivation and mixed cultivation of Chlamydomonas reinhardtii, Chlorella vulgaris, and an Ettlia sp. was evaluated for treating nitrate-contaminated groundwater and biomass production. Ettlia sp. showed the highest nutrient assimilation and growth rate among the three microalgae during bioremediation. Light-dark cycle was the effective condition for nutrient removal and COD mitigation by microalgae. Mixed microalgae with a larger presence of the Ettlia sp. exhibited the highest biomass productivity, nitrate-nitrogen, and phosphate-phosphorus removal rates of 0.21 g/L/d, 16.6, and 3.06 mg/L/d, respectively. An N:P mass ratio of 5 was necessary to increase the mixed-microalgal performance. The settling efficiency of the mixed microalgae increased up to 0.55 when using pH modulation during 30 min. Therefore, applying an Ettlia sp.-dominant consortium was the optimum strategy for the bioremediation of nitrate-contaminated groundwater in 3 days.