SciCombinator

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Concept: Environmental engineering

202

Artificial sweeteners have been widely incorporated in human food products for aid in weight loss regimes, dental health protection and dietary control of diabetes. Some of these widely used compounds can pass non-degraded through wastewater treatment systems and are subsequently discharged to groundwater and surface waters. Measurements of artificial sweeteners in rivers used for drinking water production are scarce. In order to determine the riverine concentrations of artificial sweeteners and their usefulness as a tracer of wastewater at the scale of an entire watershed, we analyzed samples from 23 sites along the entire length of the Grand River, a large river in Southern Ontario, Canada, that is impacted by agricultural activities and urban centres. Municipal water from household taps was also sampled from several cities within the Grand River Watershed. Cyclamate, saccharin, sucralose, and acesulfame were found in elevated concentrations despite high rates of biological activity, large daily cycles in dissolved oxygen and shallow river depth. The maximum concentrations that we measured for sucralose (21 µg/L), cyclamate (0.88 µg/L), and saccharin (7.2 µg/L) are the highest reported concentrations of these compounds in surface waters to date anywhere in the world. Acesulfame persists at concentrations that are up to several orders of magnitude above the detection limit over a distance of 300 km and it behaves conservatively in the river, recording the wastewater contribution from the cumulative population in the basin. Acesulfame is a reliable wastewater effluent tracer in rivers. Furthermore, it can be used to assess rates of nutrient assimilation, track wastewater plume dilution, separate human and animal waste contributions and determine the relative persistence of emerging contaminants in impacted watersheds where multiple sources confound the usefulness of other tracers. The effects of artificial sweeteners on aquatic biota in rivers and in the downstream Great Lakes are largely unknown.

Concepts: Water, Water pollution, Sewage treatment, Wastewater, Environmental engineering, Effluent, Sweeteners, Sucralose

144

The biotransformation of diclofenac during wastewater treatment was investigated. Attached growth biomass from a carrier-filled compartment of a hybrid-MBBR at the wastewater treatment plant (WWTP) in Bad Ragaz, Switzerland was used to test the biotransformation. Laboratory-scale incubation experiments were performed with diclofenac and carriers and high-resolution LC-QTof-MS was implemented to monitor the biotransformation. Up to 20 diclofenac transformation products (TPs) were detected. Tentative structures were proposed for 16 of the TPs after characterization by MS(2) fragmentation and/or inferring the structure from the transformation pathway and the molecular formula given by the high resolution ionic mass. The remaining four TPs were unambiguously identified via analytical reference standards. The postulated reactions forming the TPs were: hydroxylation, decarboxylation, oxidation, amide formation, ring-opening and reductive dechlorination. Incubation experiments of individual TPs, those which were available as reference standards, provided a deeper look into the transformation pathways. It was found that the transformation consists of four main pathways but no pathway accounted for a clear majority of the transformation. A 10-day monitoring campaign of the full-scale plant confirmed an 88% removal of diclofenac (from approximately 1.6 μg/L in WWTP influent) and the formation of TPs as found in the laboratory was observed. One of the TPs, N-(2,6-dichlorophenyl)-2-indolinone detected at concentrations of around 0.25 μg/L in WWTP effluent, accounting for 16% of the influent diclofenac concentration. The biotransformation of carriers was compared to a second WWTP not utilising carriers. It was found that in contact with activated sludge, similar hydroxylation and decarboxylation reactions occurred but at much slower rates, whereas some reactions, e.g. reductive dechlorination, were not detected at all. Finally, incubation experiments were performed with attached growth biomass from a third WWTP with a similar process configuration to Bad Ragaz WWTP. A similarly effective removal of diclofenac was found with a similar presence of TPs.

Concepts: Water pollution, Sewage treatment, Sewage, Wastewater, Industrial wastewater treatment, Sewerage, Environmental engineering, Reductive dechlorination

32

Linking fecal indicator bacteria concentrations in large mixed-use watersheds back to diffuse human sources, such as septic systems, has met limited success. In this study, 64 rivers that drain 84% of Michigan’s Lower Peninsula were sampled under baseflow conditions for Escherichia coli, Bacteroides thetaiotaomicron (a human source-tracking marker), landscape characteristics, and geochemical and hydrologic variables. E. coli and B. thetaiotaomicron were routinely detected in sampled rivers and an E. coli reference level was defined (1.4 log10 most probable number⋅100 mL(-1)). Using classification and regression tree analysis and demographic estimates of wastewater treatments per watershed, septic systems seem to be the primary driver of fecal bacteria levels. In particular, watersheds with more than 1,621 septic systems exhibited significantly higher concentrations of B. thetaiotaomicron. This information is vital for evaluating water quality and health implications, determining the impacts of septic systems on watersheds, and improving management decisions for locating, constructing, and maintaining on-site wastewater treatment systems.

Concepts: Bacteria, Gut flora, Escherichia coli, Water pollution, Sewage treatment, Wastewater, Environmental engineering, Septic tank

28

This study was conducted at a centralized wastewater treatment plant that receives discharges from nearly 160 industries. The chemical oxygen demand (COD) was fractionated for two objectives: delineation of the limits of the activated sludge process being used at the plant, and evaluation of the potential environmental impact of the treated effluent. Physico-chemical analyses, respirometric and biodegradation tests, as well as COD fractionation were carried out. Molasses-wastewaters were determined to be the major contribution to the plant. The influent was dark brown in color, with a relatively high content of both organics (2503 mg/L COD) and salts (5459 μS/cm conductivity), but a low biochemical oxygen demand (568 mg/L BOD(5)) and BOD(5)/COD ratio (0.24). The degradability of the organics was limited by the high content of inert soluble COD (S(I)). The COD fractionation pattern was 40-20-40% for S(I), X(I) (inerts) and S(H) (soluble hydrolyzable), respectively. More than 90% BOD(5) removal was obtained, which was sufficient for the plant to meet the national Standards. However, the effluent discharged into the river was intensely colored and polluted (>1000 mg/L COD, >5000 μS/cm), emphasizing the need for legislation regulating COD, color and salinity, and for upgraded treatment methods worldwide for molasses wastewaters.

Concepts: Water pollution, Sewage treatment, Anaerobic digestion, Wastewater, Chemical oxygen demand, Activated sludge, Environmental engineering, Biochemical oxygen demand

28

Anaerobic digestibility of the waste activated sludge (WAS) discharged from large-scale membrane bioreactors (MBRs) and conventional activated sludge processes (CASs) were compared using batch trials. Four wastewater treatment plants were sampled. Results showed that the sludge from MBRs had poor anaerobic digestibility as it had lower volatile solid (VS) reduction rate and lower maximum biogas production rate. The partial sludge stabilization during the long sludge retention time (SRT) typically applied in MBRs was the possible reason. On the other hand, the difference in wastewater composition had a great impact on the properties of activated sludge and the downstream sludge digestion. Inorganic matter accumulation in the WAS may hinder the access of microorganisms to substrate. The humic-like substances accumulating in the activated sludge was expected to contribute to the worse digestibility and these substances were observed to be released during anaerobic digestion through three-dimensional excitation-emission matrix (EEM) fluorescence spectra.

Concepts: Sewage treatment, Anaerobic digestion, Waste management, Biogas, Sewage, Activated sludge, Sewerage, Environmental engineering

28

The formation of thick stable brown foams within the activated sludge process has become a familiar operational problem. Despite much research having already been carried out into establishing the causes of activated sludge foaming there is still no general consensus on the mechanisms involved. Historically investigation into activated sludge foaming has involved either measuring, under aeration conditions, the propensity of mixed liquor samples to foam, or evaluating different physico-chemical properties of the sludge which have previously been linked to activated sludge foaming. Both approaches do not present a means to quantify the risk posed to the treatment plants once foams have started to develop on the surface of aeration basins and final clarifiers. The Foaming Scum Index (FSI) is designed to offer a means to quantify risk on the basis of different foam characteristics which can easily be measured. For example, foam stability, foam coverage, foam suspended solids content and biological composition. The FSI was developed by measuring foam samples taken from several different domestic and municipal wastewater treatment sites located in Greater Dublin area (South-East Ireland). Path analysis was used to predict co-dependencies among the different sets of variables following a number of separate hypotheses. The standardized beta coefficients (β) produced from the multivariate correlation analysis (providing a measure of the contribution of each variable in the structural equation model) was used to finalise the weighting of each parameter in the index accordingly. According to this principal, foam coverage exerted the greatest influence on the overall FSI (β = 0.33), whilst the filamentous bacterial composition in terms of the filament index of foam, provided the least (β = 0.03). From this work it is proposed that the index can be readily applied as a standard tool in the coordination of research into the phenomenon of activated sludge foaming.

Concepts: Measurement, Sewage treatment, Sewage, Wastewater, Activated sludge, Sewerage, Environmental engineering, Foam

28

Tannery operations consist of converting raw animal skins into leather through a series of complex water- and chemically-intensive batch processes. Even when conventional primary treatment is supplemented with chemicals, the wastewater requires some form of biological treatment to enable the safe disposal to the natural environment. Thus, there is a need for the adoption of low cost, reliable, and easy-to-operate alternative secondary treatment processes. This paper reports the findings of two pilot-scale wetlands for the secondary treatment of primary effluents from a full tannery operation in terms of resilience (i.e., ability to produce consistent effluent quality in spite of variable influent loads) and reliability (i.e., ability to cope with sporadic shock loads) when treating this hazardous effluent. Areal mass removal rates of 77.1g COD/m(2)/d, 11g TSS/m(2)/d, and 53mg Cr/m(2)/d were achieved with a simple gravity-flow horizontal subsurface flow unit operating at hydraulic loading rates of as much as 10cm/d. Based on the findings, a full-scale wetland was sized to treat all the effluent from the tannery requiring 68% more land than would have been assumed based on literature values. Constructed wetlands can offer treatment plant resilience for minimum operational input and reliable effluent quality when biologically treating primary effluents from tannery operations.

Concepts: Biology, Water pollution, Wetland, Sewage treatment, Wastewater, Environmental engineering, Effluent, Constructed wetland

27

Aerobic granulation is a promising process for wastewater treatment, but this granulation process is very complicated and is affected by many factors. Thus, a mathematical model to quantitatively describe such a granulation process is highly desired. In this work, by taking into account all of key steps including biomass growth, increase in particle size and density, detachment, breakage and sedimentation, an one-dimensional mathematic model was developed to simulate the granulation process of activated sludge in a sequencing batch reactor (SBR). Discretization methodology was applied by dividing operational time, sedimentation process, size fractions and slices into discretized calculation elements. Model verification and prediction for aerobic granulation process were conducted under four different conditions. Four parameters indicative of granulation progression, including mean radius, biomass discharge ratio, total number and bioparticle size distribution, were predicted well with the model. An optimum controlling strategy, automatically-adjusted of settling time, was also proposed based on this model. Moreover, aerobic granules with a density higher than 120 g VSS/L and radius in a range of 0.4-1.0 mm were predicted to have both high settling velocity and substrate utilization rate, and the corresponding optimum operating conditions were be determined. Experimental results demonstrate that the developed model is appropriate for simulating the formation of aerobic granules in SBRs. These results are useful for designing and optimizing the cultivation and operation of aerobic granule process. Biotechnol. Bioeng. © 2012 Wiley Periodicals, Inc.

Concepts: Scientific method, Mathematics, Operations research, Mathematical model, Activated sludge, Sewerage, Environmental engineering, Aerobic granulation

26

Due to the nature of the phosphorus (P) removal mechanisms associated with constructed wetlands, the sustainability of P treatment is usually of high interest. As a result, a 4-year dataset from a typical multi-celled integrated constructed wetland (ICW) located at Glaslough in Co. Monaghan, Ireland was evaluated to determine the effects of long-term P loadings and hydrological inputs on P treatment. The ICW was intensively monitored year-round from February 2008 through March 2012 for total P and molybdate reactive phosphate (MRP). Domestic wastewater was loaded at 16.4 ± 0.96 g m(2) year(-1) for total P and 11.2 ± 0.74 g m(2) year(-1) for MRP. Average mass reductions over the monitoring period were 91.4 and 90.1 %, respectively. The area-based kinetic coefficients (K (20)) of 11.8 for total P and 15.6 m year(-1) for MRP indicated a high area-specific retention rate. The ICW appeared to have a sustained capacity for P adsorption and retention, but the treatment was influenced mainly by external hydrological inputs and fluctuations in wastewater loadings. Linear regression analyses showed a reduction in mass retention of both total P and MRP with increased effluent flow volumes. Monthly mass reductions exceeded 90 % when the effluent flow volumes were less than 200 m(3) day(-1). When monthly effluent flow volumes exceeded 200 m(3) day(-1), nonetheless, mass reductions became highly variable. Designs and management of ICW systems should adopt measures to limit external hydrological loadings in order to maintain sufficient P treatment.

Concepts: Regression analysis, Water pollution, Marsh, Wetland, Sewage treatment, Wastewater, Environmental engineering, Constructed wetland

25

Dark fermentation is a bioprocess driven by anaerobic bacteria that can produce hydrogen (H2) from organic waste and wastewater. This review analyses a relevant number of recent studies that have investigated dark fermentative H2 production from wastewater using two different types of anaerobic biofilm reactors: anaerobic packed bed reactor (APBR) and anaerobic fluidized bed reactor (AFBR). The effect of various parameters, including temperature, pH, carrier material, inoculum pretreatment, hydraulic retention time, substrate type and concentration, on reactor performances was investigated by a critical discussion of the results published in the literature. Also, this review presents an in-depth study on the influence of the main operating parameters on the metabolic pathways. The aim of this review is to provide to researchers and practitioners in the field of H2 production key elements for the best operation of the reactors. Finally, some perspectives and technical challenges to improve H2 production were proposed.

Concepts: Enzyme, Fermentation, Environmental engineering, Fermentative hydrogen production, Hydrogen production, Dark fermentation, Photofermentation, Fluidized bed reactor