Sediment microbial fuel cell coupled floating treatment wetland for enhancing non-reactive phosphorus removal.

The presence of non-reactive phosphorus (NRP) in environmental waters presents a potential risk of eutrophication and poses challenges for the removal of all phosphorus (P) fractions. This study presents the first investigation on the removal performance and mechanism of three model NRP compounds, sodium tripolyphosphate (STPP), adenosine 5'-monophosphate (AMP) and 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTC), in the sediment microbial fuel cell-floating treatment wetland (SMFC-FTW). Coupling SMFC with plants proved to be effective at removing NRP via electrochemical oxidation and plant uptake, particularly the challenging-to-degrade phosphonates that contain C-P bonds. Compared with the control group, the removal efficiencies of the model NRP in SMFC were observed to increase by 11.9%-20.8%. SMFC promoted the conversion of NRP to soluble reactive phosphorus (sRP) and the transfer of P to sediment. Furthermore, the electrochemical process enhanced both plant growth and P uptake, and increased P assimilation by 72.6%. The presence of plants in the bioelectrochemical system influenced the occurrence and fate of P by efficiently assimilating sRP and supporting microbial transformation of NRP. Consequently, plants enhanced the removal efficiencies of all P fractions in the overlying water. This study demonstrated that SMFC-FTW is a promising technology to remove various NRP species in environmental waters.

Transformation and fate of non-reactive phosphorus (NRP) in enhanced biological phosphorus removal process with sidestream phosphorus recovery.

Recovery of phosphorus (P) from wastewater can help establish a new P cycle. However, there are many P forms in wastewater, not always in reactive forms, which are the most suitable for direct recovery. The enhanced biological phosphorus removal process with sidestream phosphorus recovery (EBPR-SPR) is an effective way to remove and recover P resources in wastewater, but there is a lack of research on the transformation and fate of non-reactive phosphorus (NRP) in it. This study selected four model NRP to investigate their transformation and fate in an EBPR-SPR process. The transformation of NRP in pure water and activated sludge under anaerobic and aerobic conditions were compared. The effects of Ca/P ratio and pH on NRP recovery were studied, and the recovery products of NRP were characterized. It was found that NRP containing phosphoanhydride and phosphoester bonds were more easily hydrolyzed to reactive P (RP) than that containing PC bonds. NRP will be adsorbed and accumulated by activated sludge, and activated sludge will accelerate the conversion of NRP to RP. Tripolyphosphate can form complex precipitation with Ca2+. When multiform P co-existed, Ca2+ preferably complexed with polyphosphate, which harmed RP recovery. The conversion of NRP should be strengthened to recover more P in wastewater. The effect of NRP should be considered when recovering P from wastewater.

Modelling of self-sustainable microbial fuel cell type oil sensors based on restricted oxygen transfer and two-population competition.

Oil leaks during oil industrial chain pose threats to the ecosystem. The microbial fuel cell-type oil sensor has been developed for early warning of such issues. Oil contacting with the sensor restricts oxygen availability and triggers correlative signal anomaly which serves as indicative of the oil presence. To extend its application for the real world, modelling of the sensor is required to pre-describe the signal behavior under unknown conditions. Therefore, by integrating Butler-Volmer, restricted oxygen transfer (ROT) and Monod equations, a dynamic ROT-MFC model with sufficient substrate precondition was developed. The ROT-MFC model was trained on the experimental single-oil-shock test (R 2 = 0.996) and validated by the experimental sequential-shocktest (R 2 = 0.998). Numerical analysis of the trained ROT-MFC model indicates that the single-shock detection has higher sensitivity (≥40.6 mV/detection) and the sequential-shocks detection spends a shorter response time (≤2.2 h). Besides, the sequential-shocks detection with proper strategy is more applicable due to flexible options on detection limit and working range. The model was further evolved into the TPC-ROT-MFC model by introducing a two-population competition (TPC) theory to describe performance under limited substrate conditions. Results indicate a critical substrate concentration range (42.1 to 62.8 mg-COD/L) for dividing baseline steadiness, and that the impact of substrate concentration on anodic charge transfer coefficient soars when the substrate concentration lessens furtherly. This sensor model is relatively easy to implement and may enhance practical use for design and operation.

On-line monitoring of minor oil spills in natural waters using sediment microbial fuel cell sensors equipped with vertical floating cathodes.

Oil spills near natural water bodies pose considerable threats to aquatic ecosystem and drinking water system. Various detection techniques have been developed to identify the oil pollution in natural waters. These techniques mainly focus on large and major oil spills involving significant changes in environmental characteristics. However, monitoring of minor oil spills (from seepage and dripping) in waters remains a bottleneck, allowing inconspicuous and persistent oil contamination. To overcome this drawback, a sediment microbial fuel cell (SMFC) sensor equipped with a vertical floating cathode is developed for on-line and in-situ monitoring of minor oil spills in natural waters. The vertical floating cathode was intended for recognizing oil on water surface. Oil on the cathode will trigger current drop. Two kinds of natural sediments were adopted in two sensors (SMFC1 from a lake and SMFC2 from an urban stream) for comparison. Both showed linear relationship between net steady-state current decrease and oil dose (30.78 and 27.29 µA/mL of sensitivity, respectively). The current change process was fitted well to a pseudo-first order kinetic equation. A one-point/two-point dynamic identification methods were derived from the kinetic equation. Therefore, the detection time was shortened from 10 h to 10/30 min. The triggered current decrease was mainly attributed to the increase in internal resistance related to charge and mass transfer. Despite the power loss after oil contamination, results implied SMFC sensor could still achieve self-sustainability. This study shows that the SMFC sensor with vertical floating cathodes is applicable to monitoring the unnoticeable minor oil pollutions in natural waters.

An integrative model to assess water quality in China's Lake Taihu: Comparing single-factor and multifactor assessments.

To determine the differences between single-factor assessment (SFA) and multifactor assessment (MFA) of the water quality in Lake Taihu Basin in China, a software program was developed to perform absolute distance (AD) computations between SFAs and MFAs that refer to the Nemerow comprehensive index (NCI) and fuzzy comprehensive assessment (FCA). Symbolic models were established to describe the computation types and sequences that are involved in the models above. Water data that were obtained weekly from 7 monitoring sites (MSs) in the basin over 10 years were tested to generate water quality grades and ADs. Our results corroborated that the MFAs would approximate the SFA when each water quality indicator (WQI) is in its worst or best state. In addition to supporting that SFA ≥ NCI ≥ FCA, the ADs illustrated that FCA was inappropriate for process integration unless all WQIs had the same grading standards. The annual water quality grades of most MSs of Lake Taihu Basin and time could be fitted to quintic polynomials with relative average deviations (RADs) of below 5%. Integr Environ Assess Manag 2019;15:135-141. © 2018 SETAC.

Start-up performance and granular sludge features of an improved external circulating anaerobic reactor for algae-laden water treatment.

The microbial characteristics of granular sludge during the rapid start of an enhanced external circulating anaerobic reactor were studied to improve algae-laden water treatment efficiency. Results showed that algae laden water was effectively removed after about 35 d, and the removal rates of chemical oxygen demand (COD) and algal toxin were around 85% and 92%, respectively. Simultaneously, the gas generation rate was around 380 mL/gCOD. The microbial community structure in the granular sludge of the reactor was complicated, and dominated by coccus and filamentous bacteria. Methanosphaera, Methanolinea, Thermogymnomonas, Methanoregula, Methanomethylovorans, and Methanosaeta were the major microorganisms in the granular sludge. The activities of protease and coenzyme F420 were high in the granular sludge. The intermittent stirring device and the reverse-flow system were further found to overcome the disadvantage of the floating and crusting of cyanobacteria inside the reactor. Meanwhile, the effect of mass transfer inside the reactor can be accelerated to help give the reactor a rapid start.

Characterization of microorganisms responsible for phosphorus removal linking operation performance with microbial community structure at low temperature.

Two enhanced biological phosphorus removal (EBPR) reactors were started up at low temperatures to obtain microorganisms responsible for aerobic and anoxic phosphorus removal, namely polyphosphate-accumulating organisms (PAO) and denitrifying PAO (DPAO), and their operational performance and microbial community were together investigated in the hope of assessment of the effectiveness of the EBPR process at low temperature by combining chemical analysis and microbial community structure evolution based on polymerase chain reaction-denaturing gradient gel electrophoresis. When two reactors reached the steady state after 40 and 80 days for the anaerobic-aerobic (AO) and anaerobic-anoxic (AA) reactor operation in AO and AA modes, respectively, a good ability of anaerobic phosphorus release and aerobic or anoxic phosphorus uptake was present both in these two reactors. During this start-up process, a total of 22 bands were detected in seed, AA and AO sludge samples, including Alpha-, Beta-, Gamma- and Deltaproteobacteria, as well as Chlorobi, Firmicutes, Bacteroidetes and Actinobacteria. Of all the bands, only four bands were present in all the lanes, suggesting that shift in microbial community occurred greatly depending on the electron acceptors in this study. From evolutionary tree, it was found that microorganisms related to DPAO mostly belong to the phylum Betaproteobacteria, while microbes corresponding to PAO were present in several phyla. Overall, the new strategy proposed here was shown to be feasible for the enrichment of PAO and DPAO at low temperature, and may be regarded as a new guidance for the application of EBPR technology to practice, especially in winter.