Modular interdependency analysis for water distribution systems.

Complexity in water distribution systems (WDSs) poses a challenge for analysis and management of the systems. To reduce the complexity, the recent development of complex network science provides a system decomposition technique that converts a complex WDS with a large number of components into a simple system with a set of interconnected modules. Each module is a subsystem with stronger internal connections than external connections. Thus far, the topological features of the modular structure in WDS have been extensively studied but not the behavioural features, e.g. the hydraulic interdependencies among modules. Therefore, this paper aims to quantitatively measure and graphically visualize the module interdependency in WDSs, which helps understanding the behavioural complexity of WDSs and thus various WDS analyses, such as pipe maintenance, model calibration, rehabilitation, and District Metered Areas planning. Specifically, this study first identifies the WDS's modular structure then measures how changes in the state of one module (i.e. any single pipe failure or perturbed demand within each module) affect the state of another module. Modular interdependencies are summarized in an interdependency matrix and visualized by the digraph. Four real-world systems are analysed, and three of them shows low interdependencies among most of the modules and there are only a few critical modules whose status changes will substantially affect a number of other modules. Hence, highly interconnected topologies may not result in strong and complex module interdependency, which is a fact that simplifies several WDS analysis for practical applications as discussed in this paper.

A dynamic simulation based water resources education tool.

Educational tools to assist the public in recognizing impacts of water policy in a realistic context are not generally available. This project developed systems with modeling-based educational decision support simulation tools to satisfy this need. The goal of this model is to teach undergraduate students and the general public about the implications of common water management alternatives so that they can better understand or become involved in water policy and make more knowledgeable personal or community decisions. The model is based on Powersim, a dynamic simulation software package capable of producing web-accessible, intuitive, graphic, user-friendly interfaces. Modules are included to represent residential, agricultural, industrial, and turf uses, as well as non-market values, water quality, reservoir, flow, and climate conditions. Supplementary materials emphasize important concepts and lead learners through the model, culminating in an open-ended water management project. The model is used in a University of Arizona undergraduate class and within the Arizona Master Watershed Stewards Program. Evaluation results demonstrated improved understanding of concepts and system interactions, fulfilling the project's objectives.

Boron isotopes as an artificial tracer.

A field study was conducted using a combination of intrinsic and artificial tracers to estimate travel times and dilution during transport of infiltrate from a reclaimed water infiltration basin to nearby monitoring wells. A major study objective was to validate boric acid enriched in (10)B as an artificial tracer. Basin 10E at the Rio Hondo Spreading Grounds in Whittier, California, was the site of the test. The basin normally receives a mixture of treated municipal waste water, purchased State Project water, and local runoff from the San Gabriel River. Approximately 3.5 kg of (10)B-enriched boric acid was dispersed among 2.05 x 10(5) m(3) of basin water to initiate the experiment. The resultant median delta(11)B in the infiltration basin was -71 per thousand. Prior to tracer addition, the basin water had an intrinsic delta(11)B of +2 per thousand. Local monitoring wells that were used to assess travel times had delta(11)B values of +5 per thousand and +8 per thousand at the time of tracer addition. Analytic results supported an assumption that boron is conserved during ground water transport and that boron enriched in (10)B is a useful artificial tracer. Several intrinsic tracers were used to reinforce the boric acid tracer findings. These included stable isotopes of oxygen (delta(18)O) and hydrogen (deltaD), sulfate concentration, and the boron to chloride ratio. Xenon isotopes, (136)Xe and (124)Xe, also supported boron isotope results. Xenon isotopes were added to the recharge basin as dissolved gases by investigators from the Lawrence Livermore National Laboratory.

Fate of wastewater effluent hER-agonists and hER-antagonists during soil aquifer treatment.

Estrogen activity was measured in wastewater effluent before and after polishing via soil-aquifer treatment (SAT) using both a (hER-beta) competitive binding assay and a transcriptional activation (yeast estrogen screen, YES) assay. From the competitive binding assay, the equivalent 17alpha-ethinylestradiol (EE2) concentration in secondary effluent was 4.7 nM but decreased to 0.22 nM following SAT. The YES assay indicated that the equivalent EE2 concentration in the same effluent sample was below the method-detection limit (<2.5 x 10(-3) nM) but increased to 0.68 nM in effluent polished via SAT processes. It was hypothesized thattest-dependent differences arose because the competitive binding assay responds positively to both estrogen mimics and anti-estrogens; the YES assay responds to estrogen mimics, but test response is inhibited by anti-estrogens. The hypothesis was supported when organics extracted from wastewater effluent inhibited the YES test response to EE2 (anti-estrogenic effect). A similar extract prepared from SAT-polished effluent augmented the EE2 curve (agonist response). When hydrophobic organics in secondary effluent were fractionated, assay results indicated that several physically distinct anti-estrogens were present in the sample. From this work, it is evident that transcription-activation bioassays alone should not be relied upon to measure estrogenic activity in complex environmental samples because the simultaneous presence of both agonists and antagonist compounds can yield false negatives. Multiple in vitro bioassays, sample fractionation or tests designed to measure anti-estrogenic activity can be used to overcome this problem. It is also clear that there are circumstances under which SAT does not completely remove estrogenic activity during municipal wastewater effluent polishing.

Transformation of effluent organic matter during subsurface wetland treatment in the Sonoran Desert.

The fate of dissolved organic matter (DOM) during subsurface wetland treatment of wastewater effluent in a hot, semi-arid environment was examined. The study objectives were to (1) discern changes in the character of dissolved organics as consequence of wetland treatment (2) establish the nature of wetland-derived organic matter, and (3) investigate the impact of wetland treatment on the formation potential of trihalomethanes (THMs). Subsurface wetland treatment produced little change in DOM polarity (hydrophobic-hydrophilic) distribution. Biodegradation of labile effluent organic matter (EfOM) and internal loading of wetland-derived natural organic matter (NOM) together produced only minor changes in the distribution of carbon moieties in hydrophobic acid (HPO-A) and transphilic acid (TPI-A) isolates of wetland effluent. Aliphatic carbon decreased as a percentage of total carbon during wetland treatment. The ratio of atomic C:N in wetland-derived NOM suggests that its character is determined by microbial activity. Formation of THMs upon chlorination of HPO-A and TPI-A isolates increased as a consequence of wetland treatment. Wetland-derived NOM was more reactive in forming THMs and less biodegradable than EfOM. For both HPO-A and TPI-A fractions, relationships between biodegradability and THM formation potential were similar among EfOM and NOM isolates; the less biodegradable isolates exhibited greater THM formation potential.

Fate of organics during soil-aquifer treatment: sustainability of removals in the field.

A 5-year program of study was conducted at the Sweetwater Recharge Facilities (SRF) to assess the performance of surface spreading operations for organics attenuation during field-scale soil-aquifer treatment (SAT) of municipal wastewater. Studies were conducted utilizing both mature (approximately 10 yr old) and new infiltration basins. Removals of dissolved organic carbon (DOC) were robust, averaging >90 percent during percolation through the local 37-m vadose zone. The hydrophilic (most polar) fraction of DOC was preferentially removed during SAT; removals were attributed primarily to biodegradation. Reductions in trihalomethane formation potential (THMFP) averaged 91 percent across the vadose zone profile. The reactivity (specific THMFP) of post-SAT organic residuals with chlorine decreased slightly from pre-SAT levels (60 vs. 72 microg THM per mg DOC, respectively). Variations in the duration of wetting/drying periods did not significantly impact organic removal efficiencies.

Fate of effluent organic matter during soil aquifer treatment: biodegradability, chlorine reactivity and genotoxicity.

Hydrophobic acid (HPO-A) and transphilic acid (TPI-A) fractions of dissolved organic matter (DOM) were isolated from a domestic secondary wastewater effluent that was polished via soil aquifer treatment (SAT). Fractions were isolated using XAD resin adsorption chromatography from samples obtained along the vadose zone flowpath at a full-scale basin recharge facility in Tucson, Arizona. Changes in isolate character during SAT were established via biodegradability (batch test), specific ultraviolet light absorbance (SUVA), trihalomethane formation potential (THMFP), and Ames mutagenicity assays. The dissolved organic carbon (DOC) concentration decreased by >90% during SAT. A significant fraction (up to 20%) of isolated post-SAT HPO-A was biodegradable. The (apparent) refractory nature of DOM that survives SAT may be a consequence of low DOC concentration in groundwater as well as the nature of the compounds themselves. Specific THMFP (microg THM per mg DOC) of HPO-A and TPI-A varied little as a consequence of SAT, averaging 52 and 49 microg THM per mg DOC, respectively. The nonbiodegradable fractions of HPO-A and TPI-A exhibited higher reactivities: 89 and 95 microg THM per mg DOC, respectively. Genotoxicity of HPO-A (on a per mass basis) increased after SAT, suggesting that responsible compounds are removed less efficiently than bulk organics during vadose zone transport.