Orthophosphate and Residence Time Impacts in Chloraminated Model Distribution Systems

Orthophosphate is commonly added as a corrosion inhibitor in drinking water distribution systems (DWDSs). However, there is limited understanding of the interrelationships between its addition, monochloramine decay, and biofilm growth. Further research is needed to evaluate its potential to accelerate monochloramine decay and promote biofilm development. This study examines the impact of orthophosphate doses (0 to 4 mg PO43-/L) on monochloramine decay and biofilm growth using model distribution systems (MDSs) at a 10-day residence time, fed with phosphorus-limited water. Findings showed that, in addition to expected enhanced microbial growth, biofilm formation potential, and metabolic activity (i.e., carbon utilization), orthophosphate addition also increased monochloramine decay. For instance, biofilm growth increased from 2.9 to 3.2 to 5.3-6.3 log CFU/cm2 between 1 and 4 mg PO43-/L, with the most substantial increase observed between 1 and 2 mg PO43-/L (an increase of >2 log units). Around day 52, changes in metabolic activity, biofilm formation potential, and biofilm growth in MDSs with added orthophosphate suggested a shift in the microbial community from early colonizers to bacteria thriving in biofilms. A correlation between biofilm profiles and monochloramine decay was apparent, with significant positive correlations between total chlorine decay and (i) biofilm HPC (R2 = 0.86, p < 0.001), (ii) biofilm formation potential (R2 = 0.73, p < 0.01), and (iii) metabolic activity (R2 = 0.81, p < 0.001). Higher orthophosphate concentrations (2-4 mg PO43-/L) were linked to greater biofilm growth and monochloramine demand, while 1 mg PO43-/L had minimal impact. Total chlorine decay coefficients ranged from 0.0034-0.004 h-1 (control) to 0.0050-0.0072 h-1 (4 PO43-/L) in the phase of further biofilm development. These findings emphasize that orthophosphate usage in DWDSs needs to balance corrosion control aspects with effects on water quality (e.g., biofilm growth and monochloramine stability).

Challenges to achieve biological stability in drinking water distribution systems Drinking water is distributed from the treatment facility to consumers through extended man-made piping systems. The World Health Organization drinking water guidelines (2006) stated that “Water entering the distribution system must be microbiologically safe and ideally should also be biologically stable”. The biological stability criterion refers to maintaining the microbial drinking water quality in time and distance from the point of drinking water production up to the point of consumption. However, uncontrolled growth of indigenous bacteria during water transport can result in the deterioration of aesthetic aspects of water, such as taste, colour, and odour, in exceeding of guideline values, and/or in technical problems. Controlling bacterial growth in piping systems and premise plumbings is very challenging (Chapter 2), and changes in drinking water microbial characteristics are often measured in networks distributing water with or without residual disinfectant such as chlorine, monochloramine or chlorine dioxide. In the Netherlands, drinking water is distributed without detectable residual disinfectant. Quantitative and qualitative knowledge on the indigenous bacterial communities and microbiological processes taking place during drinking water distribution is limited and in-depth investigations are required. New opportunities with novel analytical methods One reason for the lack of knowledge on bacterial growth controlling factors in drinking water distribution systems is that methods for characterizing drinking water bacterial communities are still relying heavily on culture-based techniques such as plate counts, developed more than 130 years ago. The conventional cultivation-based methods have major limitations: only a minute fraction (<0.1 %) of drinking water bacteria is detected, which is not representative of the drinking water bacterial community, and results are obtained only after a minimum of two days. During the last decade, new cultivation-independent techniques have emerged for the characterization of water bacterial communities. Among them, flow cytometry (FCM) enables the rapid detection and counting of all bacterial cells in water (within 15 minutes), and provides information on bacterial cell properties such as viability. Besides, high-throughput sequencing methods (e.g. 454-pyrosequencing or Illumina) enable characterization of the total bacterial community composition and structure at various taxonomic levels. FCM and high-throughput sequencing methods offer new perspectives for better and faster water microbiology monitoring and for increased understanding of the complex bacterial dynamics occurring during drinking water distribution up to the point of consumption (Chapter 2). Method development The primary goal of this study was to develop a methodological approach, based on advanced analytical methods, for the assessment of biological stability in drinking water distribution systems. A standardized, rapid and simple FCM method was shown to be highly reproducible and sensitive for total and intact bacterial cell enumeration. Changes in bacterial community characteristics could be detected based on bacterial cell concentrations and FCM fluorescence fingerprints, which are characteristic of each water sample (Chapter 3). Changes in fluorescence fingerprints were proven to be a rapid indication for changes in bacterial community composition, by comparing FCM and 16S rRNA gene pyrosequencing data obtained from the same drinking water samples. Combining the two methods enabled both quantitative and qualitative characterization of water bacterial communities (Chapter 4). An integrated approach was proposed for the assessment of bacterial growth-controlling factors in drinking water and for the evaluation of the impact of full-scale distribution conditions on bacterial growth extent. The approach combines (i) characterization of autochthonous bacterial communities in water samples collected at several locations in full-scale drinking water distribution systems, using FCM and high-throughput sequencing methods, (ii) comparison of changes in bacterial abundance recorded during water distribution and during controlled laboratory bacterial growth tests, and (iii) stepwise assessment of bacterial growth limitations in drinking water using straightforward bacterial growth potential tests (Chapter 5). Application of developed methodological approach to a full-scale drinking water system The developed methodological approach was applied to a Dutch full-scale drinking water treatment and distribution system operated without detectable disinfectant residual. Spatial and temporal variations were studied on short-term (hour, day, week) and long-term (seasonal) time-scales, and bacterial growth-limiting factors were investigated. Bacterial growth in the produced drinking water was limited both by organic carbon and inorganic nutrients (Chapter 5). Large seasonal variations in bacterial cell concentrations were recorded at the treatment effluent, which were congruent with water temperature fluctuations. Changes in bacterial community characteristics in the distribution system were minor compared to temporal variations in the treatment effluent (Chapter 6). However, all studies univocally showed that changes in bacterial community abundance, viability and/or community composition occurred during water distribution in the well-maintained network (Chapters 4, 5, 6 and 7). Changes were not detected with conventional bacterial detection methods. In-depth analysis of bacterial community composition in water samples, using pyrosequencing, showed that the core bacterial community did not change during water distribution, whereas high dynamicity was found in rare taxa (Chapter 7). Different bacterial cell concentrations were measured in the full-scale system and after incubation of the same water under controlled conditions, highlighting the effect of distribution conditions (e.g. temperature, pipe material, residence time) on drinking water microbial quality (Chapter 5). The results suggest that the extent of bacterial growth at one specifically studied location in the distribution system was not determined by the concentration of assimilable organic carbon in the treatment effluent. Likely not only one single parameter can be considered as controlling factor of microbial growth in drinking water distribution systems (Chapter 6). Recommendations From these observations, it is recommended to study microbial dynamics in drinking water distribution systems using a combination of controlled laboratory growth potential tests and in-situ characterization of the drinking water bacterial communities in the distribution network, which includes both spatial and temporal investigations. Applying such an approach to individual systems would provide better understanding of microbial dynamics during drinking water production and distribution, enabling (i) rapid and sensitive drinking water monitoring, (ii) effective corrective and maintenance actions and (iii) funded decisions for the optimization of water treatment production and/or distribution conditions to control bacterial growth in drinking water distribution systems. In this regard, the recent emergence of on-line flow cytometers will promote flow cytometry as an ideal monitoring method, for the rapid detection of system failure and targeted maintenance management.

Orthophosphate is a common corrosion inhibitor used to control lead release in drinking water distribution systems (DWDSs). It may enhance monochloramine decay and promote biofilm growth. This study assessed the impact of two monochloramine dosages on biofilm growth and monochloramine decay in model distribution systems (MDSs), with/without orthophosphate, at a 10-day residence time. Four bench-scale MDSs were run for 15 weeks: two tested a low monochloramine dose (2 mg Cl2/L), with or without orthophosphate, and two a higher dose (3 mg Cl2/L), with and without orthophosphate. The feedwater was phosphorus-limited, which may have amplified microbial response to orthophosphate addition. At both monochloramine dosages tested, orthophosphate addition increased viable cell count, biofilm reformation potential, and metabolic activity, while biofilm genetic diversity was influenced by both orthophosphate and monochloramine dose. Communities subjected to high monochloramine without orthophosphate were the least diverse, whereas those exposed to low monochloramine with orthophosphate showed the greatest diversity. These findings suggest that high monochloramine exerts selective pressure, reducing diversity, while orthophosphate enhances it. First-order total chlorine decay coefficients were higher in MDSs with lower monochloramine doses, and at the same dose, MDSs with orthophosphate showed slightly higher monochloramine decay than those without orthophosphate.

HI-Light: A Glass-Waveguide-Based "Shell-and-Tube" Photothermal Reactor Platform for Converting CO2 to Fuels.

The provision of safe drinking requires high quality water sources, treatment of the water, and its distribution. However, the first distribution systems in cities were designed for fire protection. In time they were extended to commercial and then to residential properties but their design then was the responsibility of the National Board of Fire Underwriters. Today, it is the Insurance Services Office, Inc., whose regulations are the text of AWWA's Manual M31, Distribution System Requirements for Fire Protection. Not one word relates to drinking water quality. Its only purpose is to assure adequate pressure and flows for fire protection. Apparently, drinking water quality is of no importance. Recent AWWA Water Quality Technology Conferences have had hundreds of papers on the degradation of water quality in distribution systems. Last year, AWWA compiled a 1,083-page volume, Water Quality in the Distribution System. The problems arise from defects in distribution systems designed for fire protection. Pipes and storage tanks need to be larger than necessary for drinking water systems, resulting in residence times that range to months. Long residence makes many water quality problems. Difficulties in maintaining disinfection, demanding higher doses of disinfectant, in turn result in excessive levels of disinfection by-products (DBPs), which are the most serious water quality health problems extant today. Another problem created by long residence times is the growth of biofilm on the insides of the pipes. The biofilms react with the disinfectants ,reducing their and creating growths that harbor the pathogens This leads to tuberculation that in time reduces the hydraulic capacity of the pipes. Still another problem created by the minimum 6- and 8-inch diameter pipes, which make up the larger lengths of pipes in the systems, are heavy pipes laid on soil with some 350 joints per mile, many of which, in time, leak. Loss of water may not be serious, but the frequent negative transient pressures that occur in the pipes have been found to suck contaminated groundwater into the pipe. One solution is a distribution system that carries only drinking water. It would not have hydrants and in most of the city, the pipes would be less than one inch, and laid with few joints. It would be a drinking water distribution system with none of the problems we face today. What about fire protection? In the last half-century, dual water systems have spread over the country. They were created to conserve drinking water by using reclaimed wastewater for the many nonpotable demands, including water for fire protection. More than 2,000 cities and towns have dual systems and more are being created every day. Most conventional water treatment plants are far short of being adequate despite statements that they meet EPA regulations. If only drinking water needs to be treated, the far lower cost would permit the adoption of membrane treatment, assuring drinking water of high quality Without question, new communities adopting such dual systems would deliver much higher quality water at lower cost. For existing communities, distribution systems would need to be introduced gradually when retrofitting for growth and as funds are available.

In the present work, the effect of residence time on the production of biochar by the pyrolysis process of Pinus spp. was investigated. Biochar was produced at three different residence times in the reactor (30, 60, and 240 min). The effect of residence time on the load in the pyrolysis process was evaluated based on the rheometric, physical and mechanical properties of the elastomeric compounds. The shortest residence time, 30 min, produced a biochar with a graphitic structure (turbostratic) that was ideal for the interaction between load and elastomer and caused the least possible disturbance to the crystallization process by stretching the natural rubber, which was observed from the tensile strength, while maintaining the mechanical properties. As the residence time increased, it was observed that the more crystalline structure interfered with the crystallization process of the natural rubber when stretched, causing a decrease in tensile strength and decreasing the interaction between the load- elastomer, thus increasing the vulcanization time of the rubber. The compound was prepared using the filler with the longest residence time (NR/BIO240min).

Fibrinogen adsorbed to polymeric surfaces and then allowed to reside on the surface while it is kept in a buffer solution for a period of time (the 'residence time') undergoes postadsorptive changes that decrease its SDS elutability, displaceability by plasma, polyclonal antifibrinogen binding, and ability to support platelet adhesion (summarized in Chinn et al. J. Biomed. Mater. Res. 26, 757 (1992)). In order to better understand the nature of the changes in adsorbed fibrinogen, the binding of ten different monoclonal antifibrinogen molecules to fibrinogen adsorbed from plasma to Biomer and several other surfaces has been measured after increasing residence time in buffer. Three of the monoclonal antibodies used bind to sequences that have been implicated in platelet binding to fibrinogen. One of these (M1) binds to the C-terminal region of the gamma chain (402-411), another (R1) binds to the N-terminal region of the A alpha chain containing an RGDF sequence (95-98), and the third (R2) binds to the C-terminal region of the A alpha chain containing an RGDS sequence (572-575). Two other antibodies (P1 and K4) also bind to the C-terminal region of the gamma chain (373-385 and 392-406, respectively). Five other antibodies that bind to other regions in fibrinogen were also used. Two of the antibodies (K4 and P1) are also known to be sensitive to conformational changes in the fibrinogen molecule. The binding of the various antibodies changed with residence time in ways that were highly dependent on the particular antibody. The binding of some antibodies was very stable with respect to residence time, others rose with time, some declined with residence time and one appears to pass through a maximum. However, none of the changes in antibody binding were nearly as fast as has been observed for the changes in platelet binding reported previously. Binding to the platelet binding region near the gamma chain C-terminal region either did not change with residence time (M1), increased with residence time (K4), or else decreased more slowly than observed for platelets (P1). Binding of the antibodies to the RGD sequences near the N-terminus of the A alpha chain (95-98) was very low initially but increased with residence time, while the binding to the RGD sequence near the C-terminus of the A alpha chain (572-575) increased slightly at short residence times but then declined substantially after longer residence times. Thus, the changes in the expression of the putative platelet binding domains do not correlate with the declines in platelet binding to plasma preadsorbed Biomer.(ABSTRACT TRUNCATED AT 400 WORDS)

Hydrothermal carbonisation of poultry litter: Effects of treatment temperature and residence time on yields and chemical properties of hydrochars

The influence of residence time on the anodic oxidation of phenol

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.

Grafting polymerization by reactive small molecules involves the formation of graft copolymers from a reaction between polymers and monomers. Monomer units can be propagated onto the polymer backbone to form a graft structure. In the polymer processing industry, the internal mixer is the most important piece of machinery. The study used the internal mixer as a reactor to make a reactive process with the interest in residence time,as the residence time is importance in the chemical reaction. By increase the residence time, the optimum degree of grafting may be occurred. The objectives of this study are to increase the knowledge and understanding of the internal mixer process, determine optimum residence time process variables for grafting LLDPE and study the effect of the residence time toward the LLDPE grafting process. Several residence times was choosing for the specified sample, to study the effect of the residence time which were 60 s, 120 s, 180 s, 240 s, 300 s and 600 s. Degree of grafting (DOG) was calculated to determine the grafting of LLDPE grafted copolymers and a series of samples in which degrees of grafting had been determined by chemical titration. Residence time at 300 s produces the optimum DOG of monomer onto polymer. Longer residence time will produce high degree of grafting but will cause other issues such as increasing in gel content and lower the mechanical properties of the grafted polymer.

Biomass from agriculture is a promising alternative fuel due to its carbon-neutral feature. However, raw biomass does not have properties required for its direct utilization for energy generation. Torrefaction is considered as a pretreatment method to improve the properties of biomass for energy applications. This study was aimed at investigating the effects of torrefaction temperature and residence time on some physical and chemical properties of torrefied corncobs. Therefore, a fixed-bed torrefaction reactor was developed and used in the torrefaction of corncobs. The torrefaction process parameters investigated were the torrefaction temperature (200, 240, and 280 °C) and the residence time (30, 60, and 90 min). The effects of these parameters on the mass loss, grindability, chemical composition, and calorific value of biomass were investigated. It was shown that the mass loss increased with increasing torrefaction temperature and residence time. The grinding throughput of the biomass was improved by increasing both the torrefaction temperature and the residence time. Torrefaction at higher temperatures and longer residence times had greater effects on the reduction in particle size of the milled corncobs. The calorific value was highest at a torrefaction temperature of 280 °C and a residence time of 90 min. The energy yield for all treatments ranged between 92.8 and 99.2%. The results obtained in this study could be useful in the operation and design of torrefaction reactors. They also provided insight into parameters to be investigated for optimization of the torrefaction reactor.

Due to the rapid growth of the global economy, energy consumption has been steadily increasing, leading to increasing issues such as energy shortages and environmental concerns. Biomass energy, a critical renewable energy source, plays a vital role in advancing low-carbon energy development and resource sustainability. In this study, experiments were conducted to study the migration of C, H, and N elements of corn straw during the microwave heating process, and the effects of residence time, heating temperature, and microwave power were also investigated. The results showed that when the temperature rose, both the proportion of C and H elements fluctuated slightly. Specifically, when the temperature rose from 75 °C to 275 °C, there was a 1.02% increase in the proportion of the C element and a 0.25% decrease in the proportion of the H element. Residence time appeared to be a significant factor influencing the changes in C, H, and N elements. For a 40 min residence time, the proportion of the C element increased from 31.77% to 35.36%, while the proportion of the H element decreased from 4.50% to 3.83%. When there was an increase in the microwave power between 160 W and 200 W, higher temperatures were reached in the samples, leading to the carbonization process of corn straw being more complete. Consequently, the proportion of the C element rose with extended residence time, whereas the proportion of the H element decreased as the residence time increased.

Effects of temperature and residence time on continuous torrefaction of spruce wood

Hydrothermal carbonization is a promising technique for conversion of industrial waste into valuable products. Producing hydrochar from corn cob residual (CCR) in a cost-effective way is key, from an economic standpoint. For this purpose, the effect of residence time in the range of 0.5 to 6 h was studied under the optimal temperature of 250 °C. Results showed that the higher heating value (HHV) of hydrochar increased approximately 40% in comparison to that of the raw material; however, prolonging the residence time beyond 0.5 h had a negligible effect on the HHV increase. Chemical compositions and H/C and O/C ratios of hydrochars revealed a minimal effect of longer residence time. Furthermore, thermogravimetric and derivative thermogravimetric analysis (TG/DTG), Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD) analysis of hydrochars also verified that the pyrolysis behavior and chemical structure of hydrochars with various residence times were similar.