Pilot-scale Distribution System Research Articles

Water quality deterioration of reclaimed water produced by reverse osmosis process in large pilot-scale distribution systems of different pipe materials

Abstract This work reports the effects of five pipe materials on reverse osmosis (RO)-reclaimed water quality in a large pilot-scale distribution system. These materials includes cast iron (CI), cast iron with cement-mortar lining (CML), stainless steel (SS), PVC, and PE. Long-term running tests for 96 hours are conducted with water quality parameters monitored online and analyzed offline. The results showed that red water appeared in CI pipe due to iron corrosion. The pH and TDS increased during the long-term test. Alkali–silica reaction in CML pipe led to a high increase of pH from 6.3 to 11.4, and TDS from 51 to 230 mg/L. Water quality deterioration was not observed in SS, PVC, and PE pipes. Residual chlorine decay occurred in all the five material pipes with the decay rate order of CI ≫ CML > SS ≈ PVC ≈ PE. Ion concentration variation was also followed during the tests. Fe and Mn ions were detected in CI pipe and Ca, Si, Al, and S were detected in CML pipe. No detectable ion release was found in SS, PVC, and PE pipes. A kinetic model was postulated for the detected ion release with the mechanisms discussed in-depth.

Field based pilot-scale drinking water distribution system: Simulation of long hydraulic retention times and microbiological mediated monochloramine decay

Drinking water distribution systems with long hydraulic retention times (HRTs) commonly encounter rapid microbiological-mediated monochloramine decay that results in microbial regrowth and nitrification with reduction in alkalinity. In this paper, we report the design and operation of a field-based pilot-scale distribution system (PDS) operated at flows that simulate long HRTs (~10 days) to promote rapid microbiological monochloramine decay over long periods. The PDS is designed to enable the testing of chemical treatment for the control of nitrification and monochloramine decay. The PDS has two identical cylindrical polyethylene tanks (DS1 & DS2), each of 1?m diameter and 1.8?m height (~1?kL) holding 900?m of polyethylene (PE) tubing with sampling points every 300?m intervals. Microbial mediated decay (determined by the Fm test) of monochloramine occurred as treated (alum coagulated and flocculated) and chloraminated water passed through the DSs. In this manuscript we report:•An inexpensive, flexible and compact system that can be readily set-up at a full-scale water treatment plant, requiring minimal supervision for operation.•A ‘draw & fill’ system for achieving control on HRT’s through the pipes.

Investigating the role of biofilms in trihalomethane formation in water distribution systems with a multicomponent model

Biofilms are ubiquitous in the pipes of drinking water distribution systems (DWDSs), and recent experimental studies revealed that the chlorination of the microbial carbon associated with the biofilm contributes to the total disinfection by-products (DBPs) formation with distinct mechanisms from those formed from precursors derived from natural organic matter (NOM). A multiple species reactive-transport model was developed to explain the role of biofilms in DBPs formation by accounting for the simultaneous transport and interactions of disinfectants, organic compounds, and biomass. Using parameter values from experimental studies in the literature, the model equations were solved to predict chlorine decay and microbial regrowth dynamics in an actual DWDS, and trihalomethanes (THMs) formation in a pilot-scale distribution system simulator. The model's capability of reproducing the measured concentrations of free chlorine, suspended biomass, and THMs under different hydrodynamic and temperature conditions was demonstrated. The contribution of bacteria-derived precursors to the total THMs production was found to have a significant dependence on the system's hydraulics, seasonal variables, and the quality of the treated drinking water. Under system conditions that promoted fast bacterial re-growth, the transformation of non-microbial into microbial carbon DBP precursors by the biofilms showed a noticeable effect on the kinetics of THMs formation, especially when a high initial chlorine dose was applied. These conditions included elevated water temperature and high concentrations of nutrients in the influent water. The fraction of THMs formed from microbial sources was found to reach a peak of 12% of the total produced THMs under the investigated scenarios. The results demonstrated the importance of integrating bacterial regrowth dynamics in predictive DBPs formation models.

Distribution water quality anomaly detection from UV optical sensor monitoring data by integrating principal component analysis with chi-square distribution.

The issue of distribution water quality security ensuring is recently attracting global attention due to the potential threat from harmful contaminants. The real-time monitoring based on ultraviolet optical sensors is a promising technique. This method is of reagent-free, low maintenance cost, rapid analysis and wide cover range. However, the ultraviolet absorption spectra are of large size and easily interfered. While within the on-site application, there is almost no prior knowledge like spectral characteristics of potential contaminants before determined. Meanwhile, the concept of normal water quality is also varying due to the operating condition. In this paper, a procedure based on multivariate statistical analysis is proposed to detect distribution water quality anomaly based on ultraviolet optical sensors. Firstly, the principal component analysis is employed to capture the main variety features from the spectral matrix and reduce the dimensionality. A new statistical variable is then constructed and used for evaluating the local outlying degree according to the chi-square distribution in the principal component subspace. The possibility of anomaly of the latest observation is calculated by the accumulation of the outlying degrees from the adjacent previous observations. To develop a more reliable anomaly detection procedure, several key parameters are discussed. By utilizing the proposed methods, the distribution water quality anomalies and the optical abnormal changes can be detected. The contaminants intrusion experiment is conducted in a pilot-scale distribution system by injecting phenol solution. The effectiveness of the proposed procedure is finally testified using the experimental spectral data.

Accumulation and Fate of Microorganisms and Microspheres in Biofilms Formed in a Pilot-Scale Water Distribution System

The accumulation and fate of model microbial "pathogens" within a drinking-water distribution system was investigated in naturally grown biofilms formed in a novel pilot-scale water distribution system provided with chlorinated and UV-treated water. Biofilms were exposed to 1-mum hydrophilic and hydrophobic microspheres, Salmonella bacteriophages 28B, and Legionella pneumophila bacteria, and their fate was monitored over a 38-day period. The accumulation of model pathogens was generally independent of the biofilm cell density and was shown to be dependent on particle surface properties, where hydrophilic spheres accumulated to a larger extent than hydrophobic ones. A higher accumulation of culturable legionellae was measured in the chlorinated system compared to the UV-treated system with increasing residence time. The fate of spheres and fluorescence in situ hybridization-positive legionellae was similar and independent of the primary disinfectant applied and water residence time. The more rapid loss of culturable legionellae compared to the fluorescence in situ hybridization-positive legionellae was attributed to a loss in culturability rather than physical desorption. Loss of bacteriophage 28B plaque-forming ability together with erosion may have affected their fate within biofilms in the pilot-scale distribution system. The current study has demonstrated that desorption was one of the primary mechanisms affecting the loss of microspheres, legionellae, and bacteriophage from biofilms within a pilot-scale distribution system as well as disinfection and biological grazing. In general, two primary disinfection regimens (chlorination and UV treatment) were not shown to have a measurable impact on the accumulation and fate of model microbial pathogens within a water distribution system.

A framework for the implementation and design of pilot-scale distribution systems

In recent years, model distribution systems have become valuable tools for understanding physical, chemical and microbiological processes that occur in full-scale distribution systems. These systems enable numerous treatment strategies to be examined in controlled conditions and without adversely affecting the water quality at a customer9s tap. Many model reactors have been developed for obtaining water quality data for evaluating very specific processes that occur in the distribution system (e.g. trihalomethane formation). The simulated distribution system (SDS) test is used to predict the formation of trihalomethanes in the distribution system, annular reactors (AR) are commonly used for biofilm studies and pipe rig systems can be used for a variety of studies including corrosion and biofilm. Of the three model reactors, pipe rig systems provide the most flexibility, however relatively few standard or de facto testing procedures have been developed in comparison to the other laboratory-based model systems (e.g. SDS test protocol). There are several hydraulic configurations that can be modelled along with various lengths and diameters of different pipe materials. However, this flexibility and the lack of standard pipe rig designs cause difficulties in making broad comparisons among research projects. This paper outlines the important design variables of a pipe rig system and provides examples of different options for each variable. Based on a thorough review of previous pipe rig studies, a framework was developed to assist in the design and selection of pipe rig configurations. It is recommended that the framework provides a method for selecting the physical and hydraulic configuration for future pipe rig investigations. Ultimately, the framework would provide the water industry with potential designs that would allow for improvement in data evaluation and strategies for minimizing water quality degradation in distribution systems.