This paper presents the recent attention in scientific studies and development of electrochemical processes. Electrochemical technology has contributed significantly to the purification of water for better human health and aquatic life forms. In this study, we emphasize the developmental trends of electrochemical technologies, their applications, and recent developments in the context of water and wastewater treatments. Recent studies have made great advances in investigating and optimizing advanced electrochemical oxidation processes in treatment of various organic pollutants, reduction of halogenated contaminants, and disinfection of microorganisms. Besides, electrochemical oxidation processes have been combined with other treatment methods to enable their practical application. Excellent electro-catalytic treatment of contaminant and their by-products was achieved through the application of mixed metal oxides (PbO2, SnO2, Ti/RuO2, etc.), Pt, and boron-doped diamond (BDD) electrodes. Several studies have focused on selective removal of trace pollutants in a complex matrix. These studies have shown the possibility of removing target pollutants with relatively low energy consumption. It can be concluded that enhancement of treatment performance of the present technologies will contribute to a wider application of electrochemical processes in water and wastewater treatment.
This study aimed to estimate the sanitization effectiveness of compost by solar heating. Compost produced from composting toilet was inoculated with Escherichia coli, Enterococcus faecalis and Ascaris eggs and subjected to solar heating. The heating was performed by direct exposure of compost to sun and in a solar box. From treated compost, the number of isolated bacteria was determined by plating method and the number of Ascaris eggs was determined by microscopy counting. The inactivation kinetics of microorganisms were modeled using nonlinear regression software tool. The result showed that the temperature regime produced by direct sunlight and solar box during heating were categorized as mesophilic (> 30°C) and pasteurization (> 70°C), respectively. The log reduction of microorganisms in heated compost by solar box was significantly higher than that of direct sunlight. The inactivation rate was slow in compost heated by the sun but fast in compost heated by solar box. Escherichia coli appears to be the most sensitive to destruction temperatures achieved by solar heating. The thermal decimal decay occurred rapidly in solar box while it was prolonged with the direct sunlight. The high and uniform temperature distribution obtained with solar box during heating proved to be an efficient option for safe use of compost.
Reclamation of nutrients from human urine for agricultural purposes is an alternative for chemical fertilizers. By reacting with formaldehyde, urea in human urine precipitates as slow-release fertilizer. However, the recovery of nitrogen decreases as formaldehyde is added and all of the nitrogen cannot be recovered. The aim of this paper was to find out the reason of this decrease. We assumed that some by-products of nitrogen might be created during the reaction and then limiting the polymerization process. Three levels of formaldehyde/urea (F/U) ratio have been investigated and the presence of undefined nitrogen compounds was found. These compounds were assumed to be low molecular weight polymers and by-products of nitrogen. Elution time of liquid chromatography with organic carbon detector (LC-OCD) corresponded to compounds of 350 Da and the degree of polymerization of the low molecular weight polymers was lower than 5. Mass spectrometry (MS) allows clear identification of by-products. They were essentially constituted by molecules with incomplete sequences of polymers. The reaction model proposes possible pathways that could lead to these by-products.
Groundwater management is a significant task to have sustainable groundwater sources in Afghanistan especially in Kabul Basin. In this study, the groundwater level fluctuation simulation and forecast by a traditional tank model, snow tank + traditional tank model (S + traditional tank), combined tank model and snow combined tank model (SC-tank model) were compared. The variables (precipitation, groundwater level, temperature and evaporation) were utilized to simulate and forecast groundwater level fluctuations at a representative observation well (CKB1-W) in Kabul Basin from 2005 to 2013. Shuffled Complex Evolution-University of Arizona (SCE-UA) algorithm was utilized to find the best parameter for the models. Accuracy of model estimation was evaluated by coefficient of determination, Nash-Sutcliffe efficiency (NSE) coefficient and root-mean-square error (RMSE). Consequently, the SC-tank model provided the most accurate result in simulation and forecast of groundwater level fluctuations at the representative observation well in Kabul Basin. The result indicated that the SC-tank model constructed in this study could be applied for groundwater management in Kabul Basin, Afghanistan.
The factors of eutrophication in lakes are dependent on external loads of nutrients carried from inflowing rivers and internal loads of nutrients leached from bottom sediment. In this study, dissolution tests were conducted using the sediment obtained before and after a large-scale flood to understand the impact that floods have on sediment and water quality. In addition, microbial communities in the sediment were analyzed using new generation sequencer to determine the behavior of in situ materials and the condition of environment. The dissolution tests showed that the NH4-N dissolution rate under anaerobic condition had increased at the sampling site near the mouth of inflowing river after the flood. In contrast, the PO4-P dissolution rate had decreased. Microbial community analysis results at the sampling site showed no large difference between surface and deep layer of bottom sediment. This suggests that the bottom sediment was disturbed by high wind.
The treatment of saline wastewater containing oil and organic matter of different biodegradability was examined for 35 days using a laboratory-scale membrane bioreactor (MBR) at a thermophilic condition (50°C). The performances were compared with those of a room-temperature reactor. The removal of COD was comparable for the two reactors. The half-life of mineral oil (C15 − C22 alkanes) was around 3 hours in the reactor. However, the operation at high temperature condition decreased the removal of dark brown (melanoidin) color from 58% to 44%. The fouling of the membrane was more severe for the thermophilic reactor. The room-temperature reactor maintained a volume flux of 0.22 m/day, while keeping the volume flux at the same level was difficult for the thermophilic reactor. It was suggested that lower flux operation of the membrane and worse effluent quality have to be considered, if high-temperature operation is required.
Synchrotron-based X-ray absorption near edge structure (XANES) spectroscopy was applied to study sulfur species in the sediments of Lake Biwa. Samples were collected at Nagahama Port where muddy substances were deposited all year around. The XANES analysis revealed the presence of reduced inorganic S (e.g. FeS, FeS2, and element S), reduced organic S (e.g. methionine), intermediate S (e.g. sulfonate), and oxidized S (e.g. sulfate). By storing the sediments under aerobic condition, the most reduced inorganic S nearly faded out after seven months, and oxidized S increased extremely. On the contrary, under anaerobic condition, the population of each species remained unchanged, except a slight decrease of the most reduced inorganic S in the first week, which might be due to biological oxidization. It is proved that XANES is not only a non-invasive method to determine the chemical states of S species in the sediments, but also to trace the oxidation state of the sediment consisting of solid and liquid.
Laboratory-scale reactor experiments for the treatment of lipid-rich wastewater were conducted using a combination system consisting of an anaerobic baffled reactor (ABR) and an aerobic trickling filter (ATF). Lipid-rich wastewater was collected from the school cafeteria at the National Institute of Technology, Kure College. A water bath was installed to heat the bottom portion of the ABR to 35°C to help separate the lipids from the wastewater. The chemical oxygen demand (COD), total suspended solids, and lipid concentration of the wastewater were 88.6, 23.9 and 11.2 g/L, respectively. The ABR removed 94.4% of the COD during the continuous experiment at a maximum organic loading rate of 9.2 kgCOD/(m3·d). Finally, 96.8% of the COD was removed by the whole system. Next, 57.8% of inlet COD was converted to methane in the ABR. In contrast, 16.3% of the COD removed had accumulated as scum at the top of each compartment of the ABR and the accumulated scum was found to self-combust. Therefore, the ABR can achieve a high-rate treatment of lipid-rich wastewater with energy recovery by converting degradable substances to methane and persistent substances to scum.
A novel magnetic nanoadsorbent (magnetic chitosan modified by N,N-bis (carboxymethyl) glutamic acid, G-MCTS for short) was prepared by covalent binding of tetrasodium of N,N-bis (carboxymethyl) glutamic acid onto the surface of chitosan-coated Fe3O4 nanoparticles. The adsorbent was characterized by scanning electron microscopy, infrared spectrum, vibrating sample magnetometer and X-ray powder diffractometer. It was found that G-MCTS had a spherical structure with a particle size ranging from 100 − 150 nm and a saturation magnetization value of 21 emu/g. Meanwhile, the adsorption performances of G-MCTS were tested with adsorption of methylene blue. Correspondingly, the adsorption effect factors (initial concentration, solution pH, contact time and temperature), adsorption kinetics, isotherms and adsorption thermodynamics were investigated in detail. Results showed that the adsorption could reach equilibrium within 30 min, besides, the adsorption kinetics accepted the pseudo-second-order kinetic model, and the adsorption isotherm data fit with Freundlich model as well as Langmuir model. More importantly, the maximum adsorption capacity was 3.3 g/g obtained by Langmuir model and the adsorption capacity was more than 90% of the initial saturation adsorption capacity after being used for four times. All of these results indicated that, G-MCTS can serve as an effective adsorbent for the adsorption of methylene blue.
The potential of the use of zirconium, an abundant and less expensive element, as a non-platinum catalyst of the cathode in microbial fuel cells (MFCs) was studied. The oxygen reduction reaction (ORR) activity of various cathodes made from three kinds of zirconium-based materials (ZrO2, ZrCN, and ZrCNO) was evaluated under the operating conditions of MFC. Only ZrCNO catalyst exhibited ORR. Manipulation of parameters of the preparation conditions of the ZrCNO cathode (proportion of Ketjenblack, amount of Nafion, and coating amount of catalyst ink) improved the ORR activity about seven- to twenty-twofold, which was equivalent to about 26 − 29% of the activity of a platinum cathode. The ZrCNO cathode having the highest ORR activity was built into a MFC, which was then used in treating synthetic wastewater. The maximum current density attained was 0.58 W/m2, which is more than two fifths of the density achieved by a platinum cathode. Stable current density maintained by the MFC over about four weeks has made ZrCNO a promising non-platinum material for a cathode catalyst of MFCs.