Geopolymer composites are an attractive alternative to those based on ordinary Portland cement, owing to their lower carbon footprint and higher mechanical performance. However, brittleness is one of the major barriers limiting their use in construction applications. In this work, cellulose nanocrystal (CNC), a cost-effective and eco-friendly nanoparticle, was exploited in polyvinyl alcohol (PVA)-reinforced metakaolin-based geopolymer composite to further increase its mechanical performance. To this end, PVA-reinforced geopolymer composites were prepared by varying the CNC concentration from 0 wt% to 0.15 wt%. Three-point bending and fracture testing, combined with digital image correlation (DIC) and scanning electron microscopy (SEM), were performed to evaluate the bending and fracture behavior of samples containing CNC and reveal various toughening mechanisms. Composites with 0.15 wt% CNC recorded an increase of 190% in flexural strength and a 325 time of increase in fracture energy, compared to the control geopolymer (i.e. without PVA fibers and CNC). Isothermal calorimetry, Fourier transform infrared (FTIR) spectroscopy, and x-ray diffraction (XRD) were also utilized to characterize the heat flow, chemical bonds, and crystalline phases of the samples. These analyses revealed that CNC incorporation increased the amount of formed geopolymer gel with no significant changes in the crystalline structure and chemical bonding. In addition, stronger interfacial bonding between the PVA-geopolymer matrix was achieved, resulting in substantial improvements in flexural strength and fracture energy.

Geopolymer cement is a promising alternative to ordinary Portland cement as it offers comparable mechanical properties and greater durability with lower carbon emissions. Despite its advantages, the brittleness of geopolymer hinders its application as a structural material. In this work, a bioinspired brick-and-mortar structure is explored as a design paradigm to overcome this brittleness and to further augment geopolymer mechanical performance. To this end, composites were prepared with geopolymer as the brick phase and 3D-printed polymers as the mortar phase, with focus on the influence of the mortar phase stiffness. Bending and fracture results reveal strong and tough geopolymer composites can be achieved through a bioinspired brick-and-mortar structure. The geopolymer based composites showed up to 830 times greater toughness with simultaneous gains of 48% in strength compared to the bulk geopolymer. This composite exceeds bending strength and toughness of both its constituents. Stiffer soft phases generate tougher composites compared to more compliant soft phases. Various toughening mechanisms, including brick interlocking, crack bridging and crack deflection, triggered by the bioinspired design, were revealed through Digital Image Correlation, indentation, and microscopy.

Three distinct septic systems designed for onsite removal of nitrogen (N) from residential wastewater were installed at the Massachusetts Alternative Septic System Test Center (MASSTC) and at homes across Suffolk County (SC), New York. All configurations featured nitrifying sand beds coupled with denitrifying biofilters composed of 1) a lined, saturated sand and woodchip layer, 2) a saturated box filled with woodchips, or 3) an unlined, unsaturated sand and woodchip layer. Total N (TN) in final effluent discharge from the three systems at MASSTC over more than two years were 7.1 +/- 7.8, 4.3 +/- 4.2, and 6.9 +/- 8.4 mg N L-1, respectively representing TN reductions of 83%, 87%, and 84% from influent TN. Systems at MASSTC also removed on average 90.0-99.9% of 10 of 11 organic contaminants in pharmaceutical and personal care products, microbes indicative of pathogens, and biochemical oxygen demand. Over periods up to 16 months from start-up, effluent from three lined, one woodchip box, and three unlined systems in SC averaged 8.3 +/- 9.2, 5.3 +/- 3.7, and 8.7 +/- 4.9 mg-TN L-1 representing removal rates of 90%, 94%, and 88%, respectively. For all systems, wastewater N was effectively nitrified year-round; N removal varied seasonally as denitrification attenuated in winter. Substantial quantities of TN were removed in the sand beds, likely due to denitrification in anoxic micro-zones. While elevated levels of carbon leached from the wood-based biofilters installed at MASSTC during the first 60 days of operation, no substantial decline in dissolved organic carbon or N removal was observed between the first 15 months of operation and the following 12 months. Collectively, the performance of these non-proprietary, passive systems suggest they may be a useful alternative septic system for protection of groundwater from elevated levels of N, organic contaminants, and pathogens.

The filtration performance, fouling and flux recovery efficiency of a novel thin film nanofibrous compositecellulose nanofiber (TFNC-CNF) coated membrane was studied and compared with polyvinylidene fluoride (PVDF) membranes treating domestic wastewater. The enhanced anti-fouling property of the TFNC-CNF membrane was associated with the super-hydrophilic nature and negative charge on the membrane surface. The deadend cell filtration tests demonstrated the TFNC-CNF membrane recovered more than 90% of the initial flux after mechanical cleaning, compared with 26-43% recovery by PVDF membranes. Continuous wastewater ultrafiltration tests with mechanical air scouring confirmed the outstanding permeability (71.3-138.9 LMH/bar) and the superior anti-fouling characteristics (59.2-86.8% recovery of the initial flux) of the TFNC-CNF membrane. Furthermore, higher total organic carbon rejection rates were also observed in the TFNC-CNF membrane (>83.2%) than the PVDF membrane (<69.8%). Collectively, the superior flux recovery and high permeability makes the TFNC-CNF membrane a promising material for membrane bioreactors.

Advanced oxidation processes (AOPs) such as UV/hydrogen peroxide (H2O2) systems are typically paired with a polishing granular activated carbon (GAC) filter to remove degradation byproducts from AOP effluent. In this study, the impact of residual H2O2 on the removal of five frequently detected AOP byproducts (formic acid: FA, acetic acid: AA, oxalic acid: OA, formaldehyde, and glyoxal) by two types of GACs (Filtrasorb-600/F-600 and Centaur) was investigated in batch experiments. The presence of byproducts significantly inhibited the decomposition of H2O2 on Centaur, but no inhibition was observed on F-600. In multi-component systems, byproduct removal kinetics and capacity of both GACs decreased due to competition. Centaur showed a sequential removal of byproducts following OA >FA/AA >aldehydes in mixtures. The presence of 10 mg/L H2O2 showed a temporary inhibition (0-72 h) on the removal efficiency of FA and AA by F-600, respectively. However, in multicomponent tests the presence of H2O2 had little impact on the removal efficiency of byproducts. Abiotic control experiments suggested the mechanism of byproduct removal by GACs was likely a combination of adsorption, biodegradation, and catalytical decomposition.

Bench-scale columns were used to test the impact of depth, alkalinity, and nitrogen/hydraulic loading on nitrification performance and microbial community abundance in a sand filter treating onsite wastewater. The extent of nitrification was independent of the column depth at the test hydraulic loading rate (20.5 L m- 2 d-1), as full nitrification was observed at 15 cm of the column. The nitrification performance was less sensitive to nitrogen loading increase (0.15 to 0.53 mg N cm-2 d-1), while increased hydraulic loading (from 20.5 L m- 2 d-1 to 32.8 L m- 2 d-1) and insufficient alkalinity caused reduced nitrification at shallow column depth. Microbial analysis suggested the majority of biomass and functional species were present at the top 15 cm, with several orders of magnitude lower microbial density was observed at 45 cm depth. In addition, the microbial community present in the aged sand matrix could sustain efficient nitrification when treating synthetic wastewater. Collectively, these findings reveal the precise conditions for optimizing for complete nitrification of wastewater by sand filters.

The application of membrane bioreactor (MBR) processes for conventional, municipal and industrial wastewater treatment [e.g., biological oxygen demand (BOD) reduction] is well established. The research and development of MBR processes for nitrogen removal is more recent. To date, no thorough review of MBR technology for nitrogen removal from wastewater has been carried out. The review presented here provides an overview of MBR process configurations for the removal of nitrogen based on conventional nitrogen-removal pathways (i.e., nitrification/denitrification) as well as alternative nitrogen-removal pathways, such as anaerobic ammonium oxidation (ANAMMOX). A wide range of system configurations have been explored for the application of MBR for nitrogen removal, including immersed or side-stream membrane configurations, single or multichamber processes, and the application of fixed and moving bed biofilms. Operating variables play an important role in controlling nitrogen removal and fouling, especially feed composition (particularly the carbon : nitrogen ratio), membrane characteristics, solids retention time, and hydraulic retention time. Modeling approaches for predicting nitrogen removal using MBR are evolving and are better able to represent key process differences in MBRs compared to conventional activated sludge. Although several challenges remain (e.g., membrane fouling, cost, and energy consumption), a number of opportunities exist (such as new reactor configurations, new microbial pathways, and development of a better understanding of process function through metaomic approaches) that may lead to the broader application of MBR processes for nitrogen removal from municipal wastewater in the future.

AbstractTo investigate spatial variability, regulation, and mass balances of N transformations in nitrogen-removing biofilters (NRBs), N2─N production and NO3−─N consumption were measured in suboxi...

In this study, a semi-batch, bench-scale UV/hydrogen peroxide (UV/H2O2) advanced oxidation process system was used to investigate how typical groundwater quality parameters (pH, alkalinity, natural organic matter (NOM), nitrate, and iron) influence the treatment of 1,4-dioxane. Deionized (DI) water spiked with 1,4-dioxane (100 μg L-1), treated using H2O2 (10 mg L-1) in a commercially available UV system (40 W low-pressure lamp) showed an UV fluence-based first-order rate constant (k') and electrical energy-per-order (EEO) of 4.32✕10-3 cm2-mJ-1 and 0.15 kWh-m-3-order-1, respectively. The most abundant byproduct generated in spiked-DI water was oxalic acid (up to 55 μg L-1), followed by formic and acetic acids. The k' showed no significant difference at pH ranging from 5 to 7 and at low alkalinity concentrations (<20 mg-CaCO3 L-1), typical of sandy aquifers. The k' declined by up to 85% with increasing NOM concentration. Elevated production (up to ∼400% increase) of aldehydes and organic acids was observed in NOM-spiked water, implying that NOM is a significant byproduct precursor during UV/H2O2 treatment. High NO3- concentration (10 mg-N L-1) in source water reduced the k' by 25%, while no significant impact was observed at lower concentrations (<2 mg-N L-1). Addition of Fe(II) at 0.5 mg-L-1 resulted in an instantaneous Fenton-reaction-assisted removal of ∼10% 1,4-dioxane in the presence of H2O2, but did not enhance the performance of UV/H2O2 treatment over time. In contrast, both Fe(II) and Fe(III) addition lowered the k' by 15-27%. The decline of k' observed in these experiments was attributed to reduced UVT (Fe), .OH radical scavenging (pH), or both (NO3-, NOM). Treatment of groundwater samples collected from three 1,4-dioxane-contaminated wells located in Long Island, NY, showed k' values of 13-40% lower than what was observed for DI water due to radical scavenging from a combination of high NO3- and NOM in the samples. A multiple linear-regression model, developed using water quality data as model input, showed good agreement with field observations (paired t-test: p > 0.05) in predicting k' for the removal of 1,4-dioxane from groundwater. This study provides the first systematic evaluation of the impacts of groundwater quality on UV/H2O2 process to remove environmentally relevant levels of 1,4-dioxane and reports standardized performance-related parameters to aid in the design and evaluation of full-scale systems.

On-site wastewater treatment systems can contribute to the oversupply of phosphorus (P) to aquatic systems which represents a key factor for the development of eutrophic conditions and associated environmental issues, such as harmful algae blooms. This study provides novel insight into the biogeochemical processes that control P sequestration in a nitrogen-removing biofilter, a saturated two-layer lignocellulose-based soil treatment system. The concentrations of dissolved phosphorus pools at different depths within the system were investigated. Low effluent total dissolved phosphorus (TDP; 0.02-0.06 mg P L-1) and dissolved inorganic phosphorus concentrations (DIP; <0.008 mg P L-1) were observed suggesting efficient P attenuation. Analyses of different sequentially extracted solid-phase P pools revealed that P adsorption only played a minor role (<1% of total DIP removal). In the nitrification layer, P was likely sequestered into Fe and Al (hydr)oxides through deep deposition and recrystallization reactions, and by dissimilatory iron reduction followed by authigenic iron-phosphorus mineral precipitation. Organic matter P uptake also occurred in this zone. In the underlying denitrification layer, P removal by calcium phosphate precipitation was likely the dominated process.

In the United States, 24% of single-family homes have on-site wastewater treatment systems (OWTS). Not only is the proportion much higher in some areas, but also most of the OWTS provide no nitrogen removal. An innovative alternative to such OWTS are nitrogen-removing biofilters (NRBs), passive two-layer systems designed to select nitrifying (top layer) and denitrifying (bottom layer) microbial assemblages from incoming microorganisms to remove nitrogen from household wastewater by sequential nitrification-denitrification. Little is known about the microbial ecology of NRBs, or even about best practices for investigating NRB microbiology. This study characterized microbial communities of wastewater passing through three NRBs that differed in construction and nitrogen-removal efficiency by sampling nondestructively at four times over 1 year. Microbial assemblages collected from pan lysimeters buried within NRBs and from final effluent were distinct from the influent community, indicating environmental conditions in NRBs were selecting specific microbial communities. Principal coordinate analysis (weighted UniFrac) showed extensive overlap of microbial communities from different systems, layers, and times, as well as significant relationships between microbial community structure and NRB function (nitrogen transformation and removal). Genus-level analysis revealed differences between systems in dominant nitrifiers and that denitrification is likely driven by different bacteria than typically dominate in wastewater treatment plants. Replicated experiments and alternative sampling approaches will be necessary to elucidate whether differences in microbial communities between systems reflected environmental selection due to differences in NRB design, and how much stochastic processes affect NRB microbial community structure.

Membrane fouling is a major issue in wastewater treatment. In this study, a unique class of low fouling nanocellulose-enabled thin film nanofibrous composite (TFNC) ultrafiltration (UF) membranes was fabricated by coating of negatively charged TEMPO-oxidized cellulose nanofibers (CNF) on the porous electrospun polyacrylonitrile (ePAN) substrate. The surface charge density of the nanocellulose barrier layer was controlled by using CNF with different degree of oxidation (DO) and coating area density (AD, g/m(2)). The morphology, pore size distribution, hydrophilicity and zeta potential of these CNF-TFNC membranes were characterized, all of which exhibited excellent permeation flux (15-61 L m(-2)h(-1) at 0.5 psi), high rejection ratio (>98%), and good antifouling tendency against bovine serum albumin (BSA). The practical antifouling and self-cleaning characteristics of CNF-TFNC membranes were further evaluated using biotreated municipal wastewater. The best performing membrane (CNF with 0.40 AD and 1.80 DO) achieved a near total flux recovery ratio (98 +/- 2%) using simple hydraulic flushing. This could be attributed to the strong electrostatic repulsions between the CNF layer and foulants, both of which were negatively charged. Conversely, the commercial polyvinylidene difluoride (PVDF) UF membrane suffered severe fouling decay and very low flux recovery ratio (33 +/- 3%). The results indicated the practicality of using charged CNF as a barrier layer for antifouling ultrafiltration membranes in wastewater treatment.

This study examined whether the accumulation of nitrogen (legacy nitrogen) within and surrounding leaching pools for onsite wastewater treatment may act as a source of nitrogen contamination to groundwater upon changes to the quantity and/or composition of the influent to the pool. In this study, one concrete leaching pool with neutral pH (A, pH 6.9) and one leaching pool after acid washing (B, pH 3.7) were selected to examine the quantity and composition of legacy nitrogen in the surrounding soil, as well as evaluate the potential release of this nitrogen under two environmentally relevant leaching scenarios: (i) the concrete leaching pool serves as the final discharge unit for aerobic treatment unit (ATU) effluent; (ii) extreme weather events (flash flood/heavy rains) act to increase the quantity and dilute the composition of flow to the pool. Core sample analysis showed that organic nitrogen accounts for the majority (97.3-99.7%) of the total nitrogen (TN) at site A (4.1 +/- 0.6 mg N/g soil) and site B (3.0 +/- 0.4 mg N/g soil); while ammonium was the major form of inorganic nitrogen present at the sites. The TN accumulated under the two leaching pools was equivalent to approximately 17-39 days of nitrogen loading to the system. pH had a significant impact on the mass of TN leached from the soil, while no significant difference in leached TN was observed for the two leaching scenarios. The amount of TN leached from the soil matrix was not affected by the flow rate (18.6 mL/d in scenario i vs. 547.2 mL/d in scenario ii) or flow pattern (intermittent dosing vs. continuous flow). The quantity of TN leached from soils in both scenario (i) and (ii) was low and accounted for 2.6-8.9% of the total nitrogen in the soil. (C) 2019 Elsevier Ltd. All rights reserved.

In this study, microcystin-LR (MCLR) interactions with three representative silicate clays were studied using equilibrium batch experiments in order to provide insight into the role of clays on determining MCLR fate. The three tested clay minerals (kaolinite, montmorillonite and illite), saturated with sodium or calcium ions, were equilibrated with MCLR across a range of toxin concentrations at pH 5, 7 or 9. The results were fit to Freundlich and linear isotherm models, with the linear isotherm fits deemed most appropriate. In general, adsorption of MCLR was greater in the systems with Ca than in those with Na, however, regardless of the cation present, montmorillonite had the highest adsorption affinity for MCLR. Furthermore, except for Ca-montmorillonite, MCLR adsorption decreased with increasing pH. The pH-dependence of adsorption suggests the polar groups of MCLR, carboxylate associated with the glutamic acid and methylaspartic acid groups and amine associated with the arginine group, were more important in determining MCLR interactions with clays than the nonpolar ADDA group. Increased adsorption in systems enriched with calcium suggests Ca modified the clay interfacial properties and the availability of MCLR groups in a manner that increased MCLR affinity. Overall, the results suggest clays are capable of adsorbing MCLR from the aqueous phase, particularly at low pH and when saturated with Ca2+.