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Renewable energy production using microorganisms is one of the challenging issues for environmental sustainability. Algal hydrogen (H2) production has often been achieved by sulfur (S) and chloride ion (Cl−) deprivation in a growth medium; however, it may not be realistic to control S or Cl− concentrations in natural sources (e.g., wastewater). In this study, two different green algal species, Chlamydomonas reinhardtii and Chlorella sorokiniana were selected and their photosynthetic activities were compared with different acetate/Cl− ratios both in batch and continuous modes. At 150 of acetate/Cl− ratio, the H2 production rates were 0.25–0.33 μmol L−1 min−1 for C. sorokiniana and 0.20–0.38 μmol L−1 min−1 for C. reinhardtii, respectively. The hydrogenase (HydA) reactivation and photosystem II (PSII) inhibitor test revealed that biohydrogen production by algae is due to photosynthetic activity. It was found that maintaining acetate/Cl− ratios greater than 60–100 leads to continuous O2 depletion and thus renewable H2 production for both algal species. Molecular dynamics (MD) simulations of hydrogen bonding between Yz and His190 in PSII supported O2 inhibition using acetate. Using fermenter effluents, C. sorokiniana and C. reinhardtii showed a successful continuous H2 production of ~80 μmol L−1 and ~95 μmol L−1, respectively, for 15 days.

A novel As(III) sensor was developed by co-electrodepositing a Fe-Chitosan composite to a screen-printed carbon electrode sensor. The newly developed Fe-Chitosan-coated carbon electrode sensor exhibited successful As(III) detection in mining wastewater and soil leachate using square wave anodic stripping voltammetry (SWASV). A noticeable peak was observed at +0.15 V associated with stripping current of As(III) for both real wastewater samples. The calibration curves showed strong correlations with respect to As(III) with the limit of detection (LOD) of 1.12 ppb for mining wastewater and 1.01 ppb for soil leachate, respectively. Lower relative standard deviations (RSD) were obtained with 2.91% for mining wastewater and 4.54% for soil leachate during repeated measurements (n = 8), respectively, indicating enhanced stability for As(III) detection in the real wastewater application. The interference from copper and other metal ions (e.g., Zn(II), Pb(II) and Cd(II)) was found negligible for As(III) detection using the polymer modified Fe-coated electrode sensor, which suggests that the Fe-chitosan composite imparted the selectivity in the presence of other metal ions to As(III) detection in complex water matrix. These results demonstrate the applicability of a novel Fe-Chitosan-coated carbon electrode sensor to real wastewater As(III) pollution monitoring with the acceptable range of characteristics.

A novel Au nanoparticle (AuNP)-biopolymer coated carbon screen-printed electrode (SPE) sensor was developed through the co-electrodeposition of Au and chitosan for mercury (Hg) ion detection. This new sensor showed successful Hg2+ detection in landfill leachate using square wave anodic stripping voltammetry (SWASV) with an optimized condition: a deposition potential of −0.6 V, deposition time of 200 s, amplitude of 25 mV, frequency of 60 Hz, and square wave step voltage of 4 mV. A noticeable peak was observed at +0.58 V associated with the stripping current of the Hg ion. The sensor exhibited a good sensitivity of ~0.09 μA/μg (~0.02 μA/nM) and a linear response over the concentration range of 10 to 100 ppb (50–500 nM). The limit of detection (LOD) was 1.69 ppb, which is significantly lower than the safety limit defined by the United States Environmental Protection Agency (USEPA). The sensor had an excellent selective response to Hg2+ in landfill leachate against other interfering cations (e.g., Zn2+, Pb2+, Cd2+, and Cu2+). Fifteen successive measurements with a stable peak current and a lower relative standard deviation (RSD = 5.1%) were recorded continuously using the AuNP-biopolymer-coated carbon SPE sensor, which showed excellent stability, sensitivity and reproducibility and consistent performance in detecting the Hg2+ ion. It also exhibited a good reliability and performance in measuring heavy metals in landfill leachate.

A novel modified nanoporous bismuth electrode (modified-NPBiE) sensor was prepared by consecutive procedures which consist of bismuth (Bi) and tin (Sn) electroplating, thermal treatment for alloying Bi-Sn film, and selective chemical dealloying of Sn. The newly prepared modified-NPBiE sensor exhibited improved lifetime (2.7 times longer than a conventional nanoporous Bi-filmed electrode with over 40 repeated measurements) sensor with lower relative standard deviation (RSD), indicating enhanced stability and reproducibility for heavy metal detection. Using square wave anodic stripping voltammetry (SWASV), two noticeable peaks were observed at −0.65 V and −0.45 V associated with stripping currents of Cd2+ and Pb2+ in 0.1 M acetate buffer solution at pH 4.6, respectively. The calibration curves showed strong correlations with respect to various concentrations of Cd2+ and Pb2+ with the limit of detection (LOD) of 1.3 ppb for Cd2+ and 1.5 ppb for Pb2+. The newly modified-NPBiE sensor was then successfully applied for detecting Cd2+ and Pb2+ in a tap water environment and exhibited an acceptable performance for measuring heavy metals with a good reliability.

Oxygen (O2) is a strong inhibitor of hydrogenase (HydA) activity and expression and altering the sulfur (S) oxidizing transitions in photosystem II (PSII) often allows algal photohydrogen production; however, this may not be practical in a wastewater environment. To counteract natural mechanisms of oxygen evolution in PSII, we utilized acetic acid and butyric acid, which are main volatile fatty acids (VFAs) found in anaerobic bacterial digestion in wastewater treatment, as oxygen regulators for photosynthetic biohydrogen production using Chlorella vulgaris. It was found that a VFA-containing synthetic wastewater promotes oxygen depletion in a photobioreactor (PBR), producing maximum hydrogen yield of 65.4 ± 0.3 μmoL H2 L−1 mM−1 acetate without artificial sulfur or chloride deprivation. Butyric acids showed no significant effect on oxygen depletion and biohydrogen production in the PBR. The measurements of both relative expression level of mRNA and specific activities of reactivate HydA revealed that repetitive algal H2 photo-evolution was possible by HydA synthesis in C. vulgaris followed by complete oxygen depletion controlled by acetic acid levels in the PBR. This emerging understanding of the role of VFAs on oxygen regulation in PSII in natural environments is expected to lead algal-driven bioenergy production technologies to the next level.

In this work, a novel copper-chitosan (Cu-chitosan) nanocomposite-based flexible electrochemical sensor with an integrated Ag/AgCl reference electrode is fabricated. The electrochemical sensor is fabricated using low-cost screen-printing technology on a flexible substrate, followed by the electrochlorination of silver to form an integrated Ag/AgCl reference electrode and electrochemical deposition of a Cu-chitosan nanocomposite film to produce a working electrode. The surface chemical analysis of the working and reference electrodes using XPS (X-ray photoelectron spectroscopy) shows the formation of functional layers. The fabricated Cu-chitosan nanocomposite-based sensors are used to determine the trace level lead (Pb2+) ions in real-world water samples (i.e., tap water, mining wastewater, and soil leachate) using square wave anodic stripping voltammetry (SWSAV). A noticeable peak for lead ions is observed at ∼0.46 V vs. integrated Ag/AgCl reference electrode. The limit of detection (LOD) of the developed flexible electrochemical sensor in tap water is 0.72 ppb with the relative standard deviations (n = 10) of 0.65 %. The fabricated electrochemical sensor exhibits a higher response to lead ions (Pb2+) than the previously reported copper-based electrochemical sensor. These results show that chitosan's presence on the composite material enhances the sensitivity and mechanical flexibility.

A novel bismuth (Bi)-biopolymer (chitosan) nanocomposite screen-printed carbon electrode was developed using a Bi and chitosan co-electrodepositing technique for detecting multiple heavy metal ions. The developed sensor was fabricated with environmentally benign materials and processes. In real wastewater, heavy metal detection was evaluated by the developed sensor using square wave anodic stripping voltammetry (SWASV). The nanocomposite sensor showed the detection limit of 0.1 ppb Zn2+, 0.1 ppb Cd2+ and 0.2 ppb Pb2+ in stock solutions. The improved sensitivity of the Bi-chitosan nanocomposite sensor over previously reported Bi nanocomposite sensors was attributed to the role of chitosan. When used for real wastewater samples collected from a mining site and soil leachate, similar detection limit values with 0.4 ppb Cd2+ and 0.3 ppb Pb2+ were obtained with relative standard deviations (RSD) ranging from 1.3% to 5.6% (n = 8). Temperature changes (4 and 23 &deg, C) showed no significant impact on sensor performance. Although Zn2+ in stock solutions was well measured by the sensor, the interference observed while detecting Zn2+ in the presence of Cu2+ was possibly due to the presence of Cu-Zn intermetallic species in mining wastewater. Overall, the developed sensor has the capability of monitoring multiple heavy metals in contaminated water samples without the need for complicated sample preparation or transportation of samples to a laboratory.

Microalgal (Micractinium reisseri YSW05) photo-heterotrophic hydrogen production was investigated with using volatile fatty acids (acetate and butyrate) from dark-fermentation effluent. Dilution ratio (effluent: deionized water) of 1:0 at pH 8.0 supported the maximum hydrogen and biomass production, and the highest acetate and butyrate consumption. Microalgal hydrogen production was higher with continuous light condition compared to alternating dark/light cycle. Hydrogen production correlated with both, biomass production and hydrogenase activity under all experimental conditions. Hydrogenase activity and apparent hydrogen production decreased significantly with increasing headspace oxygen. Interestingly substantial hydrogenase activity was observed at almost atmospheric partial pressure of oxygen (19%), indicating that the enzyme could be oxygen tolerant. The present study demonstrated the application of conventional microbial fermentation effluent for microalgae cultivation and hydrogen production, and showed the presence of oxygen tolerant hydrogenase in M. reisseri which might help to establish a novel strategy for biohydrogen technology in atmospheric condition.

Piggery effluent is one of the most highly produced wastewaters throughout the world, containing high levels of inorganic nutrient species. In this study, a microalga Scenedesmus obliquus YSW-14 (S. obliquus) was employed not only for nutrient removal from piggery wastewater effluent but also for lipid accumulation in the algal biomass as a feedstock for biofuel production. The piggery wastewater effluent was diluted up to fivefold with synthetic media to reduce the toxicity of (in)organic components, which resulted in improved microalgal growth, nutrient removal, and lipid productivity. Among the examined culture conditions, a 40% concentration of wastewater effluent was found to be most effective for microalga lipid productivity (0.13 mg L−1). S. obliquus removed 155 mg total nitrogen and 4 mg total phosphate per gram of dried algae for growth at the same dilution condition. These results demonstrate the feasibility of using microalgae for advanced wastewater treatment and subsequent production...

The quantitative relationship between sulfate reducing bacteria (SRB) and hydrogen (H2) production from sulfate (SO42−) and ferrous [Fe(II)] enriched wastewater was investigated. Both Fe(II) (0–11,600 mg/L) and SO42− (0–20,000 mg/L) improved the H2 production efficiency from wastewater. The H2 yields were increased up to 1.9 mol H2/mol glucose in 580–1750 mg Fe(II)/L and 1000–3000 mg SO42−/L enriched wastewater at pH 5.8–6.2. Quantitative Fluorescence In Situ Hybridization (FISH) analyses revealed that the specific sulfate reducing activities (SSRA) were increased from 0.08 and 0.06 to 0.16 and 0.21 g TS/g SRB h in response to variations in sulfate concentration from 300–20,000 mg/L at pH 5.8 and 6.2, respectively. H2 production was not influenced by low SSRA (≤0.1 g TS/g SRB h), which was independent of pH variation. The results demonstrated that the SSRA and Fe(II) concentration can significantly influence on the biological H2 production from SO42− and Fe(II) containing wastewater.

The effects of varying sulfate concentrations with pH on continuous fermentative hydrogen production were studied using anaerobic mixed cultures growing on a glucose substrate in a chemostat reactor. The maximum hydrogen production rate was 2.8 L/day at pH 5.5 and sulfate concentration of 3000 mg/L. Hydrogen production and residual sulfate level decreased with increasing the pH from 5.5 to 6.2. The volatile fatty acids (VFAs) and ethanol fractions in the effluent were in the order of butyric acid (HBu) > acetic acid (HAc) > ethanol > propionic acid (HPr). Fluorescence In Situ Hybridization (FISH) analysis revealed the presence of hydrogen producing bacteria (HPB) under all pH ranges while sulfate reducing bacteria (SRB) were present at pH 5.8 and 6.2. The inhibition in hydrogen production by SRB at pH 6.2 diminished entirely by lowering to pH 5.5, at which activity of SRB is substantially suppressed.

The effect of chemical oxygen demand/sulfate (COD/SO(4)(2-)) ratio on fermentative hydrogen production using enriched mixed microflora has been studied. The chemostat system maintained with a substrate (glucose) concentration of 15 g COD L(-1) exhibited stable H(2) production at inlet sulfate concentrations of 0-20 g L(-1) during 282 days. The tested COD/SO(4)(2-) ratios ranged from 150 to 0.75 (with control) at pH 5.5 with hydraulic retention time (HRT) of 24, 12 and 6h. The hydrogen production at HRT 6h and pH 5.5 was not influenced by decreasing the COD/SO(4)(2-) ratio from 150 to 15 (with control) followed by noticeable increase at COD/SO(4)(2-) ratios of 5 and 3, but it was slightly decreased when the COD/SO(4)(2-) ratio further decreased to 1.5 and 0.75. These results indicate that high sulfate concentrations (up to 20,000 mg L(-1)) would not interfere with hydrogen production under the investigated experimental conditions. Maximum hydrogen production was 2.95, 4.60 and 9.40 L day(-1) with hydrogen yields of 2.0, 1.8 and 1.6 mol H(2) mol(-1) glucose at HRTs of 24, 12 and 6h, respectively. The volatile fatty acid (VFA) fraction produced during the reaction was in the order of butyrateacetateethanolpropionate in all experiments. Fluorescence In Situ Hybridization (FISH) analysis indicated the presence of Clostridium spp., Clostridium butyricum, Clostridium perfringens and Ruminococcus flavefaciens as hydrogen producing bacteria (HPB) and absence of sulfate reducing bacteria (SRB) in our study.