Self-powered photoelectrochemical aptasensor based on hollow tubular g-C3N4/Bi/BiVO4 for tobramycin detection.

A highly sensitive photoelectrochemical aptasensor based on phosphorus-doped hollow tubular g-C3N4/Bi/BiVO4 (PT-C3N4/Bi/BiVO4) for tobramycin (TOB) detecting was developed. This aptasensor is a self-powered sensing system which could generate the electrical output under visible light irradiation with no external voltage supply. Based on the surface plasmon resonance (SPR) effect and unique hollow tubular structure of PT-C3N4/Bi/BiVO4, the PEC aptasensor exhibited an enhanced photocurrent and favorably specific response to TOB. Under the optimized conditions, the sensitive aptasensor presented a wider linearity to TOB in the range of 0.01-50 ng mL-1 with a low detection limit of 4.27 pg mL-1. This sensor also displayed a satisfying photoelectrochemical performance with optimistic selectivity and stability. In addition, the proposed aptasensor was successfully applied to the detection of TOB in river water and milk samples.

Exploration on the role of different iron species in the remediation of As and Cd co-contamination by sewage sludge biochar.

Numerous studies have explored the adsorption of cadmium (Cd) and arsenic (As) by iron (Fe)-modified biochar, but few studies have examined in-depth the similarities and differences in the adsorption behavior of different iron types on Cd and As. In this study, sewage sludge biochar (BC) was co-pyrolyzed with self-made Fe minerals (magnetite, hematite, ferrihydrite, goethite, and schwertmannite) to treat Cd and As co-contaminated water. The adsorption of Cd and As on the Fe-modified biochar was further analyzed by adsorption kinetics, adsorption isotherms, and adsorption thermodynamics combined with a series of characterization experiments. Both SEM-EDX and XRD results confirmed the successful loading of iron minerals onto BC. Both adsorption kinetics and adsorption isotherms experiments showed that the adsorption of Cd and As by BC and the other five Fe-modified biochar was mainly controlled by chemical interactions. The results also indicated that goethite biochar (GtBC) was the most effective for the adsorption of Cd among the five Fe-modified biochar. Ferrihydrite biochar (FhBC) formed more diverse complexes, coupled with the relatively stronger electrons accepting ability, thus making it more effective for As adsorption than the others. Additionally, GtBC and hematite biochar (HmBC) were found effective for the adsorption of both Cd and As, whereas MBC was not found effective for either metal. Furthermore, combined with XPS results, the adsorption of Cd by the materials was mainly governed by Cd2+-π interactions, complexation precipitation, and co-precipitation, while oxidation reactions also existed for As.

Electrocatalytic reduction of nitrate by carbon encapsulated Cu-Fe electroactive nanocatalysts on Ni foam.

Electrocatalytic denitrification is an attractive and effective method for complete elimination of nitrate (NO3-). However, its application is limited by the activity and stability of the electrocatalyst. In this work, a novel bimetallic electrode was synthesized, in which N-doped graphitized carbon sealed with Cu and Fe nanoparticles and immobilized them on nickel foam (CuFe NPs@NC/NF) without any chemical binder. The immobilized Cu-Fe nanoparticles not only facilitated the adsorption of the reactant but also enhanced the electron transfer between the cathode and NO3-, thus promoting the electrochemical reduction of NO3-. Therefore, the as-prepared electrode exhibited enhanced electrocatalytic activity for NO3- reduction. The composite electrode with the Cu/Fe molar ratio of 1:2 achieved the highest NO3- removal (79.4 %) and the lowest energy consumption (0.0023 kW h mg-1). Furthermore, the composite electrode had a robust NO3- removal capacity under various conditions. Benefitting from the electrochlorination on the anode, this electrochemical system achieved nitrogen (N2) selectivity of 94.0 %. Moreover, CuFe NPs@NC/NF exhibited good stability after 15 cycles, which should be attributed to the graphitized carbon layer. This study confirmed that CuFe NPs@NC/NF electrode is a promising and inexpensive electrode with long-term stability for electrocatalytic denitrification.

"Turn-off" photoelectrochemical aptasensor based on g-C3N4/WC/WO3 composites for tobramycin detection.

Tobramycin (TOB), as a widely used antibiotic, poses severe unpredictable risks to ecology and health. Here, a novel photoelectrochemical (PEC) aptasensor based on a "turn-off" PEC mode was constructed for TOB detection. The working electrode could be modified by g-C3N4/WC/WO3 composites and TOB aptamer probes in turn. The TOB aptamer probes could anchor on the g-C3N4/WC/WO3 through π-π stacking interaction to avoid interference from other modifications. When TOB was captured by the aptamer probes anchored on the modified fluorine-doped tin oxide (FTO) electrode, a decreased photocurrent was obtained owing to steric hindrance and hinder electron transfer. Under optimal conditions, 0.005-5 ng mL-1 of TOB could be detected with a detection limit as low as 2 pg mL-1. Meanwhile, actual samples were investigated as well. The proposed sensor shows high specificity, satisfactory detectability, great reproducibility, and may provide a new thought for detecting other pollutants.

Mechanistic insights into the effect of poly ferric sulfate on anaerobic digestion of waste activated sludge.

Poly ferric sulfate (PFS), one of the typical inorganic flocculants widely used in wastewater management and waste activated sludge (WAS) dewatering, could be accumulated in WAS and inevitably entered in anaerobic digestion system at high levels. However, knowledge about its impact on methane production is virtually absent. This study therefore aims to fill this gap and provide insights into the mechanisms involved through both batch and long-term tests using either real WAS or synthetic wastewaters as the digestion substrates. Experimental results showed that the maximum methane potential and production rate of WAS was respectively retarded by 39.0% and 66.4%, whereas the lag phase was extended by 237.0% at PFS of 40 g per kg of total solids. Mechanism explorations exhibited that PFS induced the physical enmeshment and disrupted the enzyme activity involved in anaerobic digestion, resulting in an inhibitory state of the bioprocess of hydrolysis, acidogenesis, and methanogenesis. Furthermore, PFS's inhibition to hydrogenotrophic methanogenesis was much severer than that to acetotrophic methanogenesis, which could be supported by the elevated abundances of Methanosaeta sp and the dropped abundances of Methanobacterium sp in PFS-present digester, and probably due to the severe mass transfer resistance of hydrogen between the syntrophic bacteria and methanogens, as well as the higher hydrogen appetency of PFS-induced sulfate reducing bacteria. Among the derivatives of PFS, "multinucleate and multichain-hydroxyl polymers" and sulfate were unveiled to be the major contributors to the decreased methane potential, while the "multinucleate and multichain-hydroxyl polymers" were identified to be the chief buster to the slowed methane-producing rate and the extended lag time.

Enhanced biological nutrient removal in sequencing batch reactors operated as static/oxic/anoxic (SOA) process.

An innovative static/oxic/anoxic (SOA) activated sludge process characterized by static phase as a substitute for conventional anaerobic stage was developed to enhance biological nutrient removal (BNR) with influent ammonia of 20 and 40 mg/L in R1 and R2 reactors, respectively. The results demonstrated that static phase could function as conventional anaerobic stage. In R1 lower influent ammonia concentration facilitated more polyphosphate accumulating organisms (PAOs) growth, but secondary phosphorus release occurred due to NOx(-) depletion during post-anoxic period. In R2, however, denitrifying phosphorus removal proceeded with sufficient NOx(-). Both R1 and R2 saw simultaneous nitrification-denitrification. Glycogen was utilized to drive post-denitrification with denitrification rates in excess of typical endogenous decay rates. The anoxic stirring duration could be shortened from 3 to 1.5h to avoid secondary phosphorus release in R1 and little adverse impact was found on nutrients removal in R2.

Microbial community analysis involved in the aerobic/extended-idle process performing biological phosphorus removal.

Recently, it has been found that biological phosphorus removal can be achieved in an aerobic/extended-idle (AEI) process using both glucose and acetate as the sole substrate. However, the microbial consortiums involved in glucose-fed and acetate-fed systems have not yet been characterized. Thus the aims of this paper were to investigate the diversities and dynamics of bacterial communities during the acclimation period, and to quantify polyphosphate-accumulating organisms (PAOs) and glycogen-accumulating organisms (GAOs) in the systems. The phylogenetic analysis showed that the microbial communities were mainly composed of phylum Proteobacteria, Bacteroidetes, Chlorobi and another six kinds of unclassified bacteria. Fluorescence in-situ hybridization (FISH) analysis revealed that PAOs and GAOs accounted for 43 ± 7 and 16 ± 3% of all bacteria in the glucose-fed system, and 19 ± 4 and 35 ± 5% of total bacteria in the acetate-fed system, respectively. The results showed that the conventional PAOs could thrive in the AEI process, and a defined anaerobic zone was not necessarily required for putative PAOs growth.

Improved biological phosphorus removal performance driven by the aerobic/extended-idle regime with propionate as the sole carbon source.

Our previous studies proved that biological phosphorus removal (BPR) could be achieved in an aerobic/extended-idle (AEI) process employing two typical substrates of glucose and acetate as the carbon sources. This paper further evaluated the feasibility of another important substrate, propionate, serving as the carbon source for BPR in the AEI process, and compared the BPR performance between the AEI and anaerobic/oxic (A/O) processes. Two sequencing batch reactors (SBRs) were operated, respectively, as the AEI and A/O regimes for BPR using propionate as the sole substrate. The results showed that the AEI-reactor removed 2.98 ± 0.04-4.06 ± 0.06 mg of phosphorus per g of total suspended solids during the course of the steady operational trial, and the phosphorus content of the dried sludge was reached 8.0 ± 0.4% after 56-day operation, demonstrating the good performance of phosphorus removal. Then, the efficiencies of BPR and the transformations of the intracellular storages were compared between two SBRs. It was observed that the phosphorus removal efficiency was maintained around 95% in the AEI-reactor, and about 83% in the A/O-reactor, although the latter showed much greater transformations of both polyhydroxyalkanoates and glycogen. The facts clearly showed that BPR could be enhanced by the AEI regime using propionate as the carbon source. Finally, the mechanisms for the propionate fed AEI-reactor improving BPR were investigated. It was found that the sludge cultured by the AEI regime had more polyphosphate containing cells than that by the A/O regime. Further investigation revealed that the residual nitrate generated in the last aerobic period was readily deteriorated BPR in the A/O-SBR, but a slight deterioration was observed in the AEI-SBR. Moreover, the lower glycogen transformation measured in the AEI-SBR indicated that the biomass cultured by the AEI regime contained less glycogen accumulating organisms activities than that by the A/O regime.

[Comparison study on phosphorus removal between single-stage oxic process and anaerobic/aerobic process].

To compare the efficiency of phosphorus removal between anaerobic/aerobic process (SBR1) and single-stage oxic process (SBR2), two SBRs were conducted using acetate as the sole carbon source which is the most extensive substrate in municipal wastewater. The results obtained from three months experiment showed that the phosphorus removal efficiency and the TP removed on a unit MLSS were 91.72%, 3.23 mg x g(-1) (SBR1)and 71.70%, 2.91 mg x g(-1) (SBR2) respectively during steady operation. The further study found that a significant increase of PHA associated with an decrease of glycogen in SBR1 while a significant synthesis of PHA increased with the accumulation of glycogen in SBR2, indicating glycogen was not essential for the synthesis of PHA in single-stage oxic process. Furthermore, obvious phosphorus release was observed in both SBRs during idle period, but the content of phosphorus released in SBR2 (13.28 mg x L(-1)) was significantly higher than that in SBR1 (2.6 mg x L(-1)). The possible reason for SBR1 and SBR2 exhibited different phosphorus removal efficiencies was that microorganisms in both SBRs had different cyclic storage and consumption process of energy storages during metabolic process.

Effects of earthworms on surface clogging characteristics of intermittent sand filters.

Intermittent sand filters (ISFs) are effective and economical in treating wastewater, but they are easy to clog up. To explore a feasible and simple method to alleviate clogging, two pilot-scale ISFs were constructed, one of which contained earthworms and the other did not. During the operation, the effects of earthworms on the hydraulic behaviour of ISFs were investigated. The results showed that both ISFs exhibited good performance in wastewater treatment. However, they showed different hydraulic characteristics although operated at the same organic loading rate (approximately 300 g m(-2) d(-1)). The ISF without earthworms clogged only after 53 d operation, and was partially recovered after 7 d resting, but after that, clogging occurred again, and more rapidly than the initial clogging event (40 d). However, water on the medium surface of the ISF with earthworms was not observed during the whole experiments. In addition, 11-13% of effective porosity and 0.015-0.026 cm s(-1) of infiltration rate were measured in the upper 20 cm of the ISF at the end of the experiments. The facts demonstrated that earthworms played a positive role in alleviating clogging and earthworms fed filter could alleviate surface clogging effectively.

[Effects of two typical substrates as the sole carbon source on biological phosphorus removal with a single-stage oxic process].

To investigate the performances of phosphorus removal in a sequencing batch reactor (SBR) with single-stage oxic process using synthetical wastewater, glucose (R1) and acetate (R2) were fed to two SBRs as the sole carbon source, respectively. The operation run mode was determined to be: influent --> aeration (4 h) --> settling (8 h) --> effluent. The results showed that the performance of phosphorus removal in R1 was higher than that in R2 after steady-operation. Total phosphorus (TP) removed per MLVSS in R1 and R2 were 7.2-7.7 and 3.8-4.6 mg x g(-1) during aeration, respectively, but the rate of phosphorus release at the two reactors were 3.6-3.8 and 2.7-3.1 mg x g(-1) during the idle zone, respectively. The energy storage of poly-beta-hydroxyalkanoates (PHA) was constant nearly in R1 during the whole period, but glycogen was accumulated to the maximum value at 30 minutes of aeration, and then was decreased to the initial level. However in R2, PHA and glycogen were both accumulated at about 45 minutes of aeration. This phenomenon suggested that glycogen is the main energy source for metabolism during aerobic period in R1, and the main energy resource come from the decomposition of PHA and the hydrolysis of glycogen in R2. The facts showed that glycogen could replace PHAs to supply energy for phosphate uptake and polyphosphate accumulation in such a single-stage oxic process. Since glycogen accumulated in R1 was more than that in R2, the efficiency of phosphorus removal in R1 was higher than that in R2.

Nitrogen and phosphorus recovery from wastewater and the supernate of dewatered sludge.

Excessive nitrogen and phosphorus supply to freshwater negatively affects water quality and ecosystem balance through a process known as eutrophication. This can lead to increased wastewater treatment costs, a reduction in the biological diversity and recreational value of natural water bodies. Besides, algal blooms can result in loss of livestock and human health issues. Therefore, efficient and reliable nitrogen and phosphorus removal methods are required. In wastewater containing relatively high concentrations of nitrogen and phosphorus (e.g. wastewater from chemical fertilizer plant, the supernate of dewatered sludge, etc.), these elements are difficult to remove economically to reach the appropriate compliance limits by biological methods. On the other hand, both nitrogen and phosphorus are nutrients for the plants, and recently, nitrogen and phosphorus recovery by precipitation (e.g. struvite) has drawn much attention, because nitrogen and phosphorus precipitates can be utilized as a fertilizer and both phosphorus and ammonium can be simultaneously removed. Thus, this review summarized nitrogen and phosphorus recovery methods, during which nitrogen and phosphorus compounds can be used as a raw material for the fertilizer industry, including the options of struvite and hydroxyapatite formation and other feasible using options. In this article most important patents are also discussed.