Xiaodi Hao

Degradation of soil-sorbed trichloroethylene by stabilized zero valent iron nanoparticles: Effects of sorption, surfactants, and natural organic matter

Zero valent iron (ZVI) nanoparticles have been studied extensively for degradation of chlorinated solvents in the aqueous phase, and have been tested for in-situ remediation of contaminated soil and groundwater. However, little is known about its effectiveness for degrading soil-sorbed contaminants. This work studied reductive dechlorination of trichloroethylene (TCE) sorbed in two model soils (a potting soil and Smith Farm soil) using carboxymethyl cellulose (CMC) stabilized Fe-Pd bimetallic nanoparticles. Effects of sorption, surfactants and dissolved organic matter (DOC) were determined through batch kinetic experiments. While the nanoparticles can effectively degrade soil-sorbed TCE, the TCE degradation rate was strongly limited by desorption kinetics, especially for the potting soil which has a higher organic matter content of 8.2%. Under otherwise identical conditions, ∼ 44% of TCE sorbed in the potting soil was degraded in 30 h, compared to ∼ 82% for Smith Farm soil (organic matter content = 0.7%). DOC from the potting soil was found to inhibit TCE degradation. The presence of the extracted SOM at 40 ppm and 350 ppm as TOC reduced the degradation rate by 34% and 67%, respectively. Four prototype surfactants were tested for their effects on TCE desorption and degradation rates, including two anionic surfactants known as SDS (sodium dodecyl sulfate) and SDBS (sodium dodecyl benzene sulfonate), a cationic surfactant hexadecyltrimethylammonium (HDTMA) bromide, and a non-ionic surfactant Tween 80. All four surfactants were observed to enhance TCE desorption at concentrations below or above the critical micelle concentration (cmc), with the anionic surfactant SDS being most effective. Based on the pseudo-first-order reaction rate law, the presence of 1 × cmc SDS increased the reaction rate by a factor of 2.5 when the nanoparticles were used for degrading TCE in a water solution. SDS was effective for enhancing degradation of TCE sorbed in Smith Farm soil, the presence of SDS at sub-cmc increased TCE degraded by ∼ 10%. However, effect of SDS on degradation of TCE in the potting soil was more complex. The presence of SDS at sub-cmc decreased TCE degradation by 5%, but increased degradation by 5% when SDS dosage was raised to 5 × cmc. The opposing effects were attributed to combined effects of SDS on TCE desorption and degradation, release of soil organic matter and nanoparticle aggregation. The findings strongly suggest that effect of soil sorption on the effectiveness of Fe-Pd nanoparticles must be taken into account in process design, and soil organic content plays an important role in the overall degradation rate and in the effectiveness of surfactant uses.

Looking Beyond Struvite for P-Recovery

) and could potentially be used asa slow-release fertilizer. If the economic and life cycle costs aretaken into account, however, it becomes clear that phosphaterecovery as struvite is likely not the best approach, for thefollowing reasons: (1) production of P-mineral with a highcontent of struvite from real wastewater is a difficult and costlyprocess; and (2) struvite is not superior to other phosphate-based compounds in fertilization efficiency, nor is it an exclusiveform of raw materials favored by the fertilizer industry.In literature and practice, struvite precipitation is usuallyperformed under alkaline conditions, which are created bydosing alkalinity or CO

Struvite formation, analytical methods and effects of pH and Ca2+.

Struvite formation is mainly controlled by concentrations of Mg2+, NH4+ and PO4 3+, pH, temperature, and other ions like Ca2+. Experiments evaluating the effects of pH and Ca2+ on struvite formation indicated that XRD is only a qualitative method to analyze the struvite content in precipitating compounds, which was also reflected in microscopic images. The element analyses preceded by a dissolution method were introduced to quantitatively determine the struvite content and were shown to be an efficient enough method. Based on element analyses, the struvite content could be calculated according to the N content in the precipitations, based on the molar ratios (1:1:1) of Mg, N and P in pure struvite (MgNH4PO4 x 6H2O). It was found that the optimal pH ranges for the struvite content >90% were respectively at 7.5 approximately 9.0 with ultra pure water as solute and at 7.0 approximately 7.5 with tap water (mainly consisting of ground water) as solute. Applying a pH > 8.0 in real wastewater containing Ca2+ might result in impure struvite contents in the precipitate due to the effect of Ca2+.

Experimental evaluation of decrease in bacterial activity due to cell death and activity decay in activated sludge

Decrease in bacterial activity (cell decay) in activated sludge can be attributed to cell death (reduction in the amount of active bacteria) and activity decay (reduction in the specific activity of active bacteria). The aim of this study was to experimentally differentiate between cell death and activity decay as a source of decrease in microbial activity. By means of measuring maximal oxygen uptake rates, verifying membrane integrity by live/dead staining and verifying presence of 16S rRNA with fluorescence in-situ hybridization, the decay rates and the death rates of ammonium oxidizing bacteria (AOB), nitrite oxidizing bacteria (NOB) and ordinary heterotrophic organisms (OHOs) were determined respectively in a nitrifying sequencing batch reactor (SBR) and a heterotrophic SBR. The experiments revealed that in the nitrifying system activity decay contributed 47% and 82% to the decreased activities of AOB and NOB and that cell death was responsible for 53% and 18% of decreases in their respective activities. In the heterotrophic system, activity decay took a share of 78% in the decreased activity of OHOs, and cell death was only responsible for 22% of decrease in their activity. The difference between the importance of cell death on the decreased activities of AOB and OHOs might be caused by the mechanisms of substrate storage and/or cryptic growth/death-regeneration of OHOs. The different nutrient sources for AOB and NOB might be the reason for a relatively smaller fraction of cell death in NOB.

A review of a recently emerged technology: constructed wetland - microbial fuel cells.

Constructed wetlands (CWs) and microbial fuel cells (MFCs) are compatible technologies since both are reliant on the actions of bacteria to remove contaminants from wastewater. MFCs require the anode to remain anaerobic with the cathode exposed to oxygen while these redox conditions can develop naturally in CWs. For this reason, research into combining the two technologies (termed as CW-MFC) has emerged in recent years with the aim of improving the wastewater treatment capacity of wetlands while simultaneously producing electrical power. Based on the published work (although limited), this review aims to provide a timely, current state-of-the-art in CW-MFC while exploring future challenges and research directions.

The integrated processes for wastewater treatment based on the principle of microbial fuel cells: A review

abstract Microbial fuel cell (MFC) technology offers the dual advantages of wastewater treatment and electricity generation. Research efforts have been made to improve its power output. However, MFC seems limited at pilot scale and power outputs appear to have plateaued. As such, some integrated technologies have emerged based on MFC. These hybrid technologies have the larger potential for scaling up and practical application compared with the pure MFC. Therefore, in their review the authors present these emerged technologies and discuss the development tendency and the challenges. The review can hopefully provide a framework to identify priorities for further research on this area.

Microbiological Endogenous Processes in Biological Wastewater Treatment Systems

Microbiological endogenous processes in biological wastewater treatment systems (BWTSs) refer to combinations of biological and ecological mechanisms and processes, including endogenous respiration/cell maintenance, cell decay, death-regeneration/cryptic growth, predation on bacteria by higher microorganisms, and cell lysis due to viral attack or adverse environmental conditions (pH, toxic substances, temperature and others), which have significant effects on almost all aspects of BWTSs. However, the current state of knowledge about endogenous processes is very limited. With this review article, the definition of endogenous processes is identified and summarized. Based on a review of the relevant literature, the endogenous processes in BWTSs are classified at two microbial levels, a cell level and a community level. At the cell level, each living microbial cell needs a certain amount of energy to satisfy cell maintenance; the community level reveals interactions between microorganisms and operating parameters. Processes such as uncoupling, programmed cell death (PCD), starvation, viral infection, and predation are reviewed, and state-of-the-art information about these processes is summarized. The development of determining maintenance energy and decay rate of bacteria in BWTSs is also outlined. Based on these reviews, further research aspects related to endogenous processes are proposed.

Evaluation of the potential for operating carbon neutral WWTPs in China.

Carbon neutrality is starting to become a hot topic for wastewater treatment plants (WWTPs) all over the world, and carbon neutral operations have emerged in some WWTPs. Although China is still struggling to control its water pollution, carbon neutrality will definitely become a top priority for WWTPs in the near future. In this review, the potential for operating carbon neutral WWTPs in China is technically evaluated. Based on the A(2)/O process of a typical municipal WWTP, an evaluation model is first configured, which couples the COD/nutrient removals (mass balance) with the energy consumption/recovery (energy balance). This model is then applied to evaluate the potential of the organic (COD) energy with regards to carbon neutrality. The models calculations reveal that anaerobic digestion of excess sludge can only provide some 50% of the total amount of energy consumption. Water source heat pumps (WSHP) can effectively convert the thermal energy contained in wastewater to heat WWTPs and neighbourhood buildings, which can supply a net electrical equivalency of 0.26 kWh when 1 m(3) of the effluent is cooled down by 1 °C. Photovoltaic (PV) technology can generate a limited amount of electricity, barely 10% of the total energy consumption. Moreover, the complexity of installing solar panels on top of tanks makes PV technology almost not worth the effort. Overall, therefore, organic and thermal energy sources can effectively supply enough electrical equivalency for China to approach to its target with regards to carbon neutral operations.

Enhancing the CH4 yield of anaerobic digestion via endogenous CO2 fixation by exogenous H2

A large amount (25-60%) of degraded organics is converted directly to CO2 during anaerobic digestion (AD) process, which substantially lowers the energy (methane, CH4) yield. In this study, endogenous CO2 fixation by H2 from in-situ iron corrosion was explored to enhancing the CH4 yield. The results demonstrated that a substantial enhancement (up to 61%) in the CH4 yield could be achieved with both nano-scale zero-valent iron (NZVI) and waste iron scraps (WIS) being the added iron. Additionally, the added iron could also achieve effective phosphorus removal from the AD supernatant.

Evaluating sludge minimization caused by predation and viral infection based on the extended activated sludge model No. 2d

The Activated Sludge Model No. 2d (ASM2d) was extended to incorporate the processes of both predation and viral infection. The extended model was used to evaluate the contributions of predation and viral infection to sludge minimization in a sequencing batch reactor (SBR) system enriching polyphosphate-accumulating organisms (PAOs). Three individual decay processes formulated according to the general model rules were used in the extended model. The model was firstly calibrated and validated by different experimental results. It was used to evaluate the potential extent of predation and viral infection on sludge minimization. Simulations indicate that predation contributes roughly two times more to sludge minimization than viral infection in the SBR system enriching PAOs. The sensitivity analyses of the selected key parameters reveal that there are thresholds on both predation and viral infection rates, if they are too large a minimal sludge retention time is obtained and the effluent quality is deteriorating. Due to the thresholds, the contributions of predation and viral infection to sludge minimization are limited to a maximal extent of about 21% and 9%, respectively. However, it should be noted that the parameters concerning predation and viral infection were not calibrated separately by independent experiment in our study due to the lack of an effective method, especially for the parameters regarding viral infection. Therefore, it is essential to better evaluate these parameters in the future.