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Four plant–sediment microbial fuel cells (plant-SMFCs) with four plant species, Oryza sativa, Acorus calamus, Spathiphyllum petite and Chamaedorea elegans, were built to investigate sulfide concentrations, pH and oxidation–reduction potential (ORP) in the sediment as well as plant growth. Sulfide concentrations at 1 and 2 cm depth of sediment in plant-SMFCs and their control reactors were 1.66 ± 0.30, 9.29 ± 3.46, 2.38 ± 0.10 and 24.20 ± 1.02 μmol g−1, respectively. The ORP in water and sediment of 1 and 2 cm depth in plant-SMFCs was 106.0 ± 7.7, − 142 ± 30 and − 209 ± 9 mV, respectively. The ORP in the three control reactors was 119.0 ± 11.5, − 209 ± 9 and − 386 ± 2 mV, respectively. Harvest of O. sativa, A. calamus, Spathiphyllum petite and C. elegans was 0.218 ± 0.009, 0.136 ± 0.007, 0.127 ± 0.007 and 0.340 ± 0.007 gDW g−1GW in the plant-SMFCs, while that of their control reactors was 0.179 ± 0.011, 0.127 ± 0.008, 0.102 ± 0.007 and 0.318 ± 0.006 gDW g−1GW, respectively. The results showed that sulfide concentrations decreased in sediments of plant-SMFCs, while the ORPs in both the overlying water and sediments increased. Moreover, plant growth due to operating plant-SMFCs was promoted. Running plant-SMFCs abates the toxicity of sulfide to the emerged plants as well as decreases the sulfide emission in water–plant–sediment systems.

Current risk assessment models for metals such as the biotic ligand model (BLM) are usually applied to individual metals, yet toxic metals are rarely found singly in the environment. In the present research, the toxicity of Cu and Zn alone and together were studied in wheat (Triticum aestivum L.) using different Ca2+ and Mg2+ concentrations, pH levels and Zn:Cu concentration ratios. The aim of the study was to better understand the toxicity effects of these two metals using BLMs and toxic units (TUs) from single and combined metal toxicity data. The results of single-metal toxicity tests showed that toxicity of Cu and Zn tended to decrease with increasing Ca2+ or Mg2+ concentrations, and that the effects of pH on Cu and Zn toxicity were related not only to free Cu2+ and Zn2+ activity, respectively, but also to other inorganic metal complex species. For the metal mixture, Cu–Zn interactions based on free ion activities were primarily additive for the different Ca2+ and Mg2+ concentrations and levels of pH. The toxicity data of individual metals derived by the BLM, which incorporated Ca2+ and Mg2+ competition and toxicity of inorganic metal complexes in a single-metal toxicity assessment, could predict the combined toxicity as a function of TU. There was good performance between the predicted and observed effects (root mean square error [RMSE] = 7.15, R2 = 0.97) compared to that using a TU method with a model based on free ion activity (RMSE = 14.29, R2 = 0.86). The overall findings indicated that bioavailability models that include those biochemistry processes may accurately predict the toxicity of metal mixtures.

In search of a cost effective cathode material for microbial fuel cells (MFCs), graphite was chemically treated with H3PO4, HNO3, ZnCl2, urea or melamine, and the effect of chemical activations on the oxygen reduction reaction (ORR) was examined. The performance of MFCs with activated graphite as the catalyst-free cathodes was then compared to those with untreated graphite. Results suggested that H3PO4 and HNO3 activations could improved ORR, showing the highest ORR activity in graphite treated with 14.62 M H3PO4 for 12 h at 30–50 °C. MFCs with H3PO4 and HNO3 activated graphite cathodes generated maximum power densities (7.9 W/m³ and 6.5 W/m³, respectively) 2.4 and 1.8 times higher than that of the untreated control. The chemical activation process involves just a simple immersion step, and it does not require heating, electrochemical process or expensive chemicals. Therefore, it is a highly cost-effective approach to improve the performance of MFCs. We recommend an in-situ modification of graphite cathodes in scale-up MFCs with either H3PO4 or HNO3 to optimize MFCs' various industrial applications.

Bioelectrochemical systems (BESs) have been focused on by many researchers to treat wastewater and recover energy or valuable chemicals from wastes. In BESs, metal ions play an important role in the conductivity of solution, reactors' internal resistance, power generation, chemical production and activity of microorganisms. Additionally, the metal ions are also involved in anodic or cathodic reaction processes directly or indirectly in BESs. This paper reviews the behavior of metal ions in BESs, including (1) increase of the conductivity of electrolyte and decrease of internal resistance, (2) transfer for desalination, (3) enhancement or inhibition of the biocatalysis in anode, (4) improvement of cathodic performance by metal ions through electron acceptance or catalysis in cathodic process and (5) behavior of metal ions on membranes. Moreover, the perspectives of BESs removing heavy metal ions in wastewater or solid waste are discussed to realize recovery, reduction and detoxification simultaneously.

Hydrogen sulfide emission in sewer systems is associated with toxicity, corrosion, odour nuisance and high costs treatment. In this study, a novel method to inhibit sulfide generation from sewage by means of glutaraldehyde supplementation has been suggested and evaluated under anaerobic conditions. Different concentrations of glutaraldehyde at 10, 15, 20, 30 and 40 mg·L−1 have been investigated. Besides, the possible impacts of glutaraldehyde supplementation on an activated sludge system and an appraisal of the economic aspects are presented as well. As observed from the experimental results, a dosage of 20 mg·L−1 glutaraldehyde resulted in a significant decrease of the sulfide production by 70%–80% in the simulated sewage. Moreover, the impacts of additional glutaraldehyde at 20 mg·L−1 on activated sludge, in terms of chemical oxygen demand removal and oxygen uptake rates, were negligible. From an economical point of view, the cost of the commercial glutaraldehyde products required in the operation, which was calculated on the basis of activated sulfide removal avoidance, was around €3.7–4.6 S·kg−1. Therefore it is suggested that glutaraldehyde supplementation is a feasible technique to abate the sulfide problems in sewer systems. Yet further research is required to elucidate the optimum “booster” dosage and the dosing frequency in situ accordingly.

The overall process enhancement by different electrical current application on the biological phosphorus release and uptake have been investigated. Five reactors were constructed for three experiments and activated sludge was used as inoculums. In Exp.1 by comparing the control and the bio-electrochemical reactors, it was found that the overall phosphorus removal efficiency could be enhanced at lower electrical current applications of 5mA and 10mA, but were restrained at higher than 20mA, although 20mA could be a sensitive turning point. Moreover, the electrochemical effects of the cathodic and the anodic reactions on the phosphorus release and uptake, respectively, have been further evaluated separately under an electrical current application of 10mA in Exp.2 and Exp.3, respectively. As observed, both of the biological release and uptake were improved by the cathodic reactions in the cathode reactor, but not by the anodic reactions in the anode reactor, and thus indicated that the cathodic reactions play an important role in the improvement of the biological phosphorus release and uptake.

A rotating disk electrode (RDE) was used to investigate the concentration loss and impedance characteristics of anodic biofilms in microbial fuel cells (MFCs). Amperometric time-current analysis revealed that at the rotation rate of 480 rpm, a maximum current density of 168 µA cm(-2) can be achieved, which was 22.2 % higher than when there was no rotation. Linear sweep voltammetry and electrochemical impedance spectroscopy tests showed that when the anodic potential was set to -300 mV vs. Ag/AgCl reference, the power densities could increase by 59.0 %, reaching 1385 mW m(-2), the anodic resistance could reduce by 19 %, and the anodic capacitance could increase by 36 %. These results concur with a more than 85 % decrease of the diffusion layer thickness. Data indicated that concentration loss, diffusion layer thickness, and the mixing velocity play important roles in anodic resistance reduction and power output of MFCs. These findings could be helpful to the design of future industrial-scale MFCs with mixed bacteria biofilms.

Five different pre-treatments were investigated to enhance the solubilisation and anaerobic biodegradability of kitchen waste (KW) in thermophilic batch and continuous tests. In the batch solubilisation tests, the highest and the lowest solubilisation efficiency were achieved with the thermo-acid and the pressure–depressure pre-treatments, respectively. However, in the batch biodegradability tests, the highest cumulative biogas production was obtained with the pressure–depressure method. In the continuous tests, the best performance in terms of an acceptable biogas production efficiency of 60% and stable in-reactor COD s and VFA concentrations corresponded to the pressure–depressure reactor, followed by freeze–thaw, acid, thermo-acid, thermo and control. The maximum OLR (5 g COD L −1 d −1 ) applied in the pressure–depressure and freeze–thaw reactors almost doubled the control reactor. From the overall analysis, the freeze–thaw pre-treatment was the most profitable process with a net potential profit of around 11.5 € ton −1 KW.

Full-scale anaerobic single-phase digesters can be confronted with process instabilities, which often result in the accumulation of propionic acid (HPr). As a solution, an enhanced propionic acid degradation (EPAD) system has been conceptually designed and experimentally tested at lab-scale. The system consisted of two components: a liquid/solid separator containing a microfiltration membrane and an up-flow anaerobic sludge bed (UASB) reactor specialized in HPr degradation. Two lab-scale continuous stirred tank reactors (CSTR) were used, i.e. the CSTR(control) and the CSTR(treatment). Firstly, the CSTRs were stressed by organic overloading to obtain high HPr levels. During the recovery period, besides stop feeding, no actions were taken to decrease the residual HPr concentration in the CSTR(control), while the CSTR(treatment) was connected to EPAD system in order to accelerate its recovery. By the end of the experiment, the CSTR(treatment) completely recovered from HPr accumulation, while no significant decrease of the HPr level in the CSTR(control) was observed. Based on the experimental results, the up-scaling of EPAD system was evaluated and it would only account for about 2% of the volume of the full-scale digester, thus suggesting that the implementation of a mobile EPAD system in full-scale practice should be feasible.

The maximum propionic acid (HPr) removal rate (R(HPr)) was investigated in two lab-scale Upflow Anaerobic Sludge Bed (UASB) reactors. Two feeding strategies were applied by modifying the hydraulic retention time (HRT) in the UASB(HRT) and the influent HPr concentration in the UASB(HPr), respectively. The experiment was divided into three main phases: phase 1, influent with only HPr; phase 2, HPr with macro-nutrients supplementation and phase 3, HPr with macro- and micro-nutrients supplementation. During phase 1, the maximum R(HPr) achieved was less than 3 g HPr-CODL(-1)d(-1) in both reactors. However, the subsequent supplementation of macro- and micro-nutrients during phases 2 and 3 allowed to increase the R(HPr) up to 18.1 and 32.8 g HPr-CODL(-1)d(-1), respectively, corresponding with an HRT of 0.5h in the UASB(HRT) and an influent HPr concentration of 10.5 g HPr-CODL(-1) in the UASB(HPr). Therefore, the high operational capacity of these reactor systems, specifically converting HPr with high throughput and high influent HPr level, was demonstrated. Moreover, the presence of macro- and micro-nutrients is clearly essential for stable and high HPr removal in anaerobic digestion.

The effect of three different types of glycerol on the performance of up-flow anaerobic sludge blanket (UASB) reactors treating potato processing wastewater was investigated. High COD removal efficiencies were obtained in both control and supplemented UASB reactors (around 85%). By adding 2 ml glycerol product per liter of raw wastewater, the biogas production could be increased by 0.74 l biogas ml(-1) glycerol product, which leads to energy values in the range of 810-1270 kWh(electric) per m(3) product. Moreover, a better in-reactor biomass yield was observed for the supplemented UASB reactor (0.012 g VSS g(-1) COD(removed)) compared to the UASB control (0.002 g VSS g(-1) COD(removed)), which suggests a positive effect of glycerol on the sludge blanket growth.

Protons (H(+)) as well as different major and trace elements may inhibit cadmium (Cd) uptake in aquatic organisms and thus alleviate Cd toxicity. However, little is known about such interactions in soil organisms. In this study, the independent effects of the cations calcium (Ca(2+)), magnesium (Mg(2+)), potassium (K(+)), H(+) and zinc (Zn(2+)) on Cd toxicity were investigated with 5-day long barley root elongation tests in nutrient solutions. The tested concentrations of selected cations and trace metal ions were based on the ranges that occur naturally in soil pore water. The toxicity of Cd decreased with increasing activity of Ca(2+), Mg(2+), H(+) and Zn(2+), but not K(+). Accordingly, conditional binding constants were obtained for the binding of Cd(2+), Ca(2+), Mg(2+), H(+), and Zn(2+) with the binding ligand: logK(CdBL) 5.19, logK(CaBL) 2.87, logK(MgBL) 2.98, logK(HBL) 5.13 and logK(ZnBL) 5.42, respectively. Furthermore, it was calculated that on average 29% of the biotic ligand sites needed to be occupied by Cd to induce a 50% decrease in root elongation. Using the estimated constants, a biotic ligand model was successfully developed to predict the Cd toxicity to barley root elongation as a function of solution characteristics. The feasibility and accuracy of its application for predicting Cd toxicity in soils were discussed.

This work focused on studying the effect of the chemical oxidation demand to sulfide ratio (COD/S) on power generation and sulfide oxidation in microbial fuel cells treating sulfide-rich wastewater containing organic contaminants. The maximum power density achieved was 20 +/- 1 W m(-3) V(Anode) and the C(oulombic) yield was 20 +/- 2%. The COD/S ofinfluent played an important role in elemental sulfur and sulfate production because of competition between acetate oxidation and element sulfur oxidation to sulfate in the anode. When the COD/S was 12.50/1, more than 74.0% of sulfide was converted into elemental sulfur after 24 hours of operation. The effect of the COD/S on power generation was negligible when the COD/S ranged between 4.85/l and 18.53/l. After 24 hours, the COD removals were 110 +/- 6, 213 +/- 9, 375 +/- 8 and 410 +/- 10 mgl(-1) when the COD/S was 4.85/1, 8.9/1, 12.5/1 and 18.53/1, respectively. The COD removal increased with the increasing COD of the influent, which fitted to the model of first-order reaction kinetics.

Digital holographic microscopy under partially coherent source allows to identify intracellular morphologic features of parasitic protozoan (oo)cysts. A new rationale for the unambiguous detection of Giardia lamblia contamination risks is proposed.