Houston Water Research Articles

Tapping Tomorrow: Houston's Water Prospects for the Next Century

Key TakeawaysAfter long‐term groundwater pumping increased subsidence‐related flood risk in Houston, the Texas legislature created subsidence districts to manage groundwater use.Reducing groundwater pumping requires alternative water supplies (AWSs) to meet current and future water demands.An assessment of AWS options in the Houston area determined that potential supplies should be more than ample to meet anticipated growth and demand.

Mesoscale Modeling of Distributed Water Systems Enables Policy Search

AbstractIt is widely acknowledged that distributed water systems (DWSs), which integrate distributed water supply and treatment with existing centralized infrastructure, can mitigate challenges to water security from extreme events, climate change, and aged infrastructure. However, it is unclear which are beneficial DWS configurations, i.e., where and at what scale to implement distributed water supply. We develop a mesoscale representation model that approximates DWSs with reduced backbone networks to enable efficient system emulation while preserving key physical realism. Moreover, system emulation allows us to build a multiobjective optimization model for computational policy search that addresses energy utilization and economic impacts. We demonstrate our models on a hypothetical DWS with distributed direct potable reuse (DPR) based on the City of Houston's water and wastewater infrastructure. The backbone DWS with greater than link and node reductions achieves satisfactory approximation of global flows and water pressures, to enable configuration optimization analysis. Results from the optimization model reveal case‐specific as well as general opportunities, constraints, and their interactions for DPR allocation. Implementing DPR can be beneficial in areas with high energy intensities of water distribution, considerable local water demands, and commensurate wastewater reuse capacities. The mesoscale modeling approach and the multiobjective optimization model developed in this study can serve as practical decision‐support tools for stakeholders to search for alternative DWS options in urban settings.

Digital Twin in Development for Houston Water System

Digital Twin in Development for Houston Water System

Mechanisms of Physically Irreversible Fouling during Surface Water Microfiltration and Mitigation by Aluminum Electroflotation Pretreatment

A modified poly(vinylidene fluoride) membrane was used to directly microfilter untreated Lake Houston water, which was then regenerated by surface washing and hydraulic backwashing, a process that was cycled five times. The source water was also electrochemically precoagulated using aluminum and microfiltered, and the membrane was physically regenerated for five cycles. Attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS) were used to characterize foulants on membrane surfaces and rigorously deduce their contributions to physically irreversible fouling after cycles 1 and 5. Hydrophobic molecules primarily appeared to initiate fouling during microfiltration of untreated raw water because O-H/N-H bands were attenuated while C-H bands remained relatively unchanged in FTIR-spectra of membrane surfaces after only one cycle. However, O-H/N-H and symmetric and asymmetric C(═ O)O(-) stretching bands significantly intensified with continued filtration/regeneration of untreated water, showing the importance of hydrophilic molecules and the role of complexation, respectively, to longer term irreversible fouling. Distinct C-H bands were detected in floated flocs after electrolysis, suggesting the sorption and subsequent removal of a substantial portion of the hydrophobic moieties present in Lake Houston water during pretreatment. Consequently, hydrophilic compounds appeared to contribute more to irreversible fouling in pretreated waters throughout the course of filtration as evidenced by significantly more intense O-H bands (compared with C-H bands) on the membrane surface after cycles 1 and 5. Therefore, electroflotation pretreatment reduced accumulation of hydrophobic foulants but simultaneously increased complexation of hydrophilic foulant molecules along with any carried-over aluminum hydroxide precipitates evidenced by increasing Al and O concentrations via XPS and intense C(═ O)O(-) stretching bands in IR spectra.

Surface water nanofiltration incorporating (electro) coagulation–microfiltration pretreatment: Fouling control and membrane characterization

Bench-scale experiments were performed to evaluate the capability of four different advanced pretreatment processes to reduce fouling of a commercially available thin-film composite nanofiltration (NF) membrane during surface water treatment. Specifically, microfiltration (MF) alone, chemical (alum) coagulation–MF, electrocoagulation–MF, and electroflotation–MF were compared in terms of their ability to maintain specific flux during NF of Lake Houston water. It was empirically determined that NF productivity decline was best controlled by electroflotation–MF. Attenuated total reflection-Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy revealed polysaccharides and proteins as major NF foulants. Coagulation induced subtle differences in protein foulants in terms of their secondary structures as inferred from second derivative analysis of the amide I band. For example, electro- and chemical-coagulation decreased intramolecular β structures and α helices but increased 310-helices and unordered structures indicating conformational changes of protein foulants with pretreatment type. Alcian Blue staining established the presence of acidic polysaccharides in the fouling layer. Similar air–water contact angles for virgin and fouled nanofilters provided further evidence that foulants were predominantly hydrophilic in nature. Fouling caused only a slight increase in surface roughness suggesting that natural organic matter complexation with divalent cations (soft feed water) was relatively insignificant leading to the deposition of a thin foulant layer. Further, the RMS surface roughnesses of fouled nanofilters were all statistically similar suggesting negligible effect of pretreatment type on the physical morphology of NF foulant layers.

Targeted Application of Seasonal Load Duration Curves Using Multivariate Analysis in Two Watersheds Flowing Into Lake Houston1

Teague, Aarin, Philip B. Bedient, and Birnur Guven, 2011. Targeted Application of Seasonal Load Duration Curves Using Multivariate Analysis in Two Watersheds Flowing Into Lake Houston. Journal of the American Water Resources Association (JAWRA) 47(3):620-634. DOI: 10.1111/j.1752-1688.2011.00529.x Abstract: Water quality is a problem in Lake Houston, the primary source of drinking water for the City of Houston, Texas, due to pollutant loads coming from the influent watersheds, including Spring Creek and Cypress Creek. Statistical analysis of the historic water quality data was developed to understand the source characterization and seasonality of the watershed. Multivariate analysis including principal component, cluster, and discriminant analysis provided a custom seasonal assessment of the watersheds so that loading curves may be targeted for season specific pollutant source characterization. The load duration curves have been analyzed using data collected by the U.S. Geologic Survey with corresponding City of Houston water quality data at the sites to characterize the behavior of the pollutant sources and watersheds. Custom seasons were determined for Spring Creek and Cypress Creek watersheds and pollutant source characterization compared between the seasons and watersheds.

Nanofiltration of pretreated Lake Houston water: Disinfection by-product speciation, relationships, and control

Water quality results related to disinfection by products (DBPs) from a bench-scale study designed to evaluate surface water nanofiltration (NF) for the City of Houston are analyzed to provide insights into mechanisms of DBP formation and control. One contribution of this manuscript is that we report on DBP speciation following NF of Lake Houston water containing very low concentrations of the bromide ion (< ∼50 μg/L or 0.6 μM). Rejection of natural organic matter (NOM) and DBP precursors decreased with increasing recovery indicating diffusion-limited transport of these macromolecular contaminants under conditions typical of drinking water NF. Additional evidence of diffusivity effects on transport was provided by decreasing permeation coefficients of polyethylene glycols with molecular weight. Haloacetic acid (HAA) molar concentrations were higher than corresponding trihalomethane (THM) concentrations in NF permeates contrary to expectations from the DBP rule where lower mass-based maximum contaminant levels are enforced for HAAs. Similar to conventional treatment, ultraviolet absorbance at 254 nm (UV 254), dissolved organic carbon (DOC), and chlorine consumption were found to be excellent surrogates for aqueous DBP concentrations even in chlorinated nanofiltered waters. Mole fractions of mono-, di-, and trihalogenated HAA species were invariant with respect to changes in Br −/DOC molar ratio suggesting that the brominated HAAs are formed through the same mechanisms as the chlorinated ones in NF permeate waters. Additionally, bromine incorporation into both THMs and HAAs increased with increasing Br/DOC ratio suggesting that the brominated THM and HAA species form first consuming the reactive precursor sites and in the process restricting formation of the chlorinated species. Bromide utilization was observed to decrease with Br −/DOC molar ratio demonstrating that nanofilter permeate waters were substantially limited with respect to NOM and DBP precursors.

Solute rejection by porous thin film composite nanofiltration membranes at high feed water recoveries

The authors developed a rigorous framework to model nanofiltration (NF) membrane selectivity at high feed water recoveries and verify it experimentally. The phenomenological model and the Donnan steric partitioning pore model (DSPM) were incorporated into a differential element approach for predicting removal of a variety of solutes from single salt solutions and natural water by NF membranes up to 90% feed water recovery in the temperature range 5–41 °C. In this approach, the entire membrane ensemble was divided into numerous sub-elements analogous to real-world full-scale NF installations, where concentrate (or reject) from one element feeds into the next element. Fundamental membrane properties (average pore radius, surface charge density, and ratio of thickness to porosity) and the reflection coefficient and permeability coefficient were first independently obtained for each solute–membrane–temperature combination using separate low recovery experiments with negligible concentration polarization and later used as model inputs to calculate solute removal in a purely predictive fashion for 5–90% recovery. This modeling approach accurately predicted removals from single salt solutions of NaCl and MgSO 4 as well as natural organic matter, disinfection by-product precursors, and several ions from pretreated Lake Houston water in a wide range of operating conditions demonstrating its use to simulate NF permeate water quality under real-world conditions of high feed water recovery.

Managing an Urban Watershed

As a result of instances in the early 1980s of high densities of fecal coliform being detected in Lake Houston, concerns were raised about the continued use of the lake as a major drinking water supply for the city of Houston, Texas. Effluent from several wastewater treatment plants in the watershed was suspected as the primary source of indicator organisms, and public health officials implemented a management plan to ensure proper operation of the plants. A study to assess the effectiveness of the plan, which called for strict enforcement of chlorine residual requirements, showed it to be working successfully. The study also showed, however, that other point and nonpoint sources of pollution were contributing indicator organisms to the lake. Also, although total coliform density in the forebay water at the Houston water treatment plant increased after rainstorms, no deterioration of finished drinking water quality occurred.

Health significance of chlorination byproducts in drinking water: the Houston experience.

In 1954, following the construction of Lake Houston, a change from lightly chlorinated ground sources to a heavily chlorinated surface source of drinking water took place for a sizable part of the population in the city of Houston, Texas. This has provided the opportunity to compare the incidence of urinary tract cancer mortality in populations exposed to heavily chlorinated and lightly chlorinated drinking water. The spatial, diurnal, and seasonal concentrations of chlorination byproducts (trihalomethanes) in Houston water were assessed. The range of concentrations varied from below the limits of detection in treated ground water, to more than 200 mg/l (twice the level allowed by US drinking water standards) in treated lake water. The mortality experience by gender, by race, and by age cohorts for the period 1940 to 1970 from urinary tract cancers and three comparison causes was determined for 56 of Houston's census tracts classified by the duration of exposure to the surface water. By the 1970's 20 years following the switch to surface water, an increase was detected in urinary cancer mortality rates for white females without a corresponding increase observed for white males. No clear-cut trends were found for the non-white population. On balance, a detrimental urinary cancer effect associated with a switch to chlorinated surface water has not been demonstrated yet.

Evaluation of the relationship of sodium in drinking water and toxemia of pregnancy.

This study is a retrospective case comparison analysis of the relationship of water-borne Na+ and toxemia of pregnancy as a part of a continuous investigation at our facility on the role of various water constituents in human chronic disease. Five hundred thirty-seven toxemic pregnant women delivered at Jefferson Davis Hospital, Houston, Texas, during 1976 were matched by age, race, obstetrical history, and month of delivery to 537 non-toxemic controls. Sodium concentration in each patient's drinking water was derived, based on her address, from earlier prepared maps of sodium distribution in Houston's water supplies. Paired t-tests were performed to compare the Na+ levels, which varied from 19 to 250 mg/l in water supplies of cases and controls. Odds ratio analysis was used to test for the presence of a gradient in occurrence of toxemia in parallel with the gradient of Na+. No significant impact of water-borne Na+ in the indicated range was observed. Further studies incorporating still higher ranges are contemplated.

Central Surveillance and Control of the City of Houston's Water System

For a city the size of Houston, Tex., the central surveillance of its water system is necessarily becoming dependent upon computer technology. Through a combination of computer technology and the human element, the Houston Water Div. has initiated a surveillance program that could prove to be fail‐safe, economical, and dependable.

Development of Houston's Water Supply

Development of Houston's Water Supply

Limitation of Actions. What Prevents Bar of Statute. Phoenix Lumber Co. v. Houston Water Co., 59 S. W. 552 (Tex.)

Limitation of Actions. What Prevents Bar of Statute. Phoenix Lumber Co. v. Houston Water Co., 59 S. W. 552 (Tex.)