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Published in Samuel C. Sugarman, HVAC Fundamentals, 2020
backflow: (Water Flow) The undesirable reversal of flow (downstream pressure is greater than upstream or supply pressure) of non-potable water or other substances through a cross-connection and into the piping of a public water system or consumer’s potable water system. Backflow is caused by an increase in downstream pressure, a reduction in the potable water supply pressure, or a combination of both. Increases in downstream pressure can be created by pumps, temperature increases in boilers, etc. Reductions in potable water supply pressure occur whenever the amount of water being used exceeds the amount of water being supplied, such as during water line flushing, fighting fires, or breaks in water mains. backflow preventer: (Water Flow) A mechanism to prevent backflow which provides a physical barrier to backflow. The principal types of mechanical backflow preventer are the reduced-pressure principle assembly, the pressure vacuum breaker assembly, and the double check valve assembly. A secondary type of mechanical backflow preventer is the residential dual check valve.
Plant Security
Published in Frank R. Spellman, Fundamentals of Public Utilities Management, 2020
As their name suggests, backflow prevention devices are designed to prevent backflow, which is the reversal of the normal and intended direction of water flow in a water system. Backflow is a potential problem in a water system because it can spread contaminated water back through a distribution system. For example, backflow at uncontrolled cross-connections (cross-connections are any actual or potential connection between the public water supply and a source of contamination) or pollution can allow pollutants or contaminants to enter the potable water system. More specifically, backflow from private plumbing systems, industrial areas, hospitals, and other hazardous contaminant-containing systems, into public water mains and wells poses serious public health risks and security problems. Cross-contamination from private plumbing systems can lead to biological hazards (due to bacteria or viruses) or transfer of toxic substances that can contaminate and sicken an entire population in the event of backflow. The majority of historical incidences of backflow have been accidental, but growing concern that contaminants could be intentionally backfed into a system is prompting increased awareness among private homes, businesses, industries, and areas most vulnerable to intentional strikes. Therefore, backflow prevention is a major tool for the protection of water systems.
Plant Security
Published in Frank R. Spellman, Handbook of Water and Wastewater Treatment Plant Operations, 2020
As their name suggests, backflow prevention devices are designed to prevent backflow, which is the reversal of the normal and intended direction of water flow in a water system. Backflow is a potential problem in a water system because it can spread contaminated water back through a distribution system. For example, backflow at uncontrolled cross-connections (cross-connections are any actual or potential connection between the public water supply and a source of contamination) or pollution can allow pollutants or contaminants to enter the potable water system. More specifically, backflow from private plumbing systems, industrial areas, hospitals, and other hazardous contaminant-containing systems, into public water mains and wells poses serious public health risks and security problems. Cross-contamination from private plumbing systems can contain biological hazards (such as bacteria or viruses) or toxic substances that can contaminate and sicken an entire population in the event of backflow. The majority of historical incidences of backflow have been accidental, but growing concern that contaminants could be intentionally backfed into a system is prompting increased awareness for private homes, businesses, industries, and areas most vulnerable to intentional strikes. Therefore, backflow prevention is a major tool for the protection of water systems.
The role of green stormwater infrastructure in flood mitigation (Detroit, MI USA) – case study
Published in Urban Water Journal, 2020
Jamie Steis Thorsby, Carol J. Miller, Lara Treemore-Spears
The average dry weather flow from each house was determined by dividing the average flow during dry weather going into one of the flow meters by the total number of houses whose sanitary flow is contributing to that meter. For each subcatchment area, the total number of houses was multiplied by the average dry weather flow for each house. The resulting average dry weather flow was approximately 1,665 liters per day per house, which is substantially higher than the design sanitary flow rate, which comes out to approximately 946 liters per day per house. This could be due to infiltration into the pipes from the groundwater (because, due to the amount of rain during this period, the groundwater level was likely higher) or could be due to downstream backflow in the sewer system. Backflow is defined as water flowing in the opposite of the usual (i.e. intended or engineered) direction and is due to too much stormwater runoff entering the sewer system. For this model, there is particular concern about backflow that occurs on properties when water from the sewer system is backing up into basements through drains or toilets, or it could occur in catch basins, when water from the sewer system is either backing up onto the street surface or too much rainwater is entering the catch basin at once.
Simulation and vulnerability assessment of water distribution networks under deliberate contamination attacks
Published in Urban Water Journal, 2021
N. Pelekanos, D. Nikolopoulos, C. Makropoulos
Different methods of approaching these emerging challenges have been introduced, such as backflow prevention (Allmann and Carlson 2005), installing water-quality sensors (Hart and Murray 2010), introducing the concept of ‘self-cleaning’ pipes (Abraham, Blokker, and Stoianov 2017; Buchberger, Blokker, and Vreeburg 2009; Vreeburg et al. 2009) and booster disinfection optimization techniques (Ohar and Ostfeld 2014; Islam, Sadiq, and Rodriguez 2013; Isovitsch Parks and VanBriesen 2009). Backflow prevention devices are often installed by water utilities as a first barrier in order to prevent contaminant from reaching the main service lines. This defense tends to reduce the number of viable points of access for deliberate or accidental contamination, but is still not effective for attacks in the main transmission (Allmann and Carlson 2005). Also, sensor deployment methods can be applied to enable real-time pollution detection in critical points across the pipes of a network aiming in localizing quickly and accurately a contamination threat (Sankary and Ostfeld 2019; Krause et al. 2008). Nonetheless, this promising approach to risk identification and management has its weaknesses: deployment and maintenance costs for large number of sensors are very high for most utilities, current sensor technology is not very reliable and requires continuous re-calibration, and the sensors themselves are necessarily generic and cannot possibly monitor every compound an attacker may inject (Lambrou et al. 2014). As a consequence, and in parallel to improving the sensor development, placement, and optimization approach, emphasis must also be given in the understanding of the susceptibilities of WDSs as a precaution in case of a contamination event. Engineering analyses and pragmatic dynamic water simulations can help to identify the points of the system that are most susceptible to contamination and estimate the consequences from various contamination events to prioritize emergency response plans and mitigation measures.
A Review of sewerage and drainage systems typologies with case study in Abidjan, Côte d'Ivoire: failures, policy and management techniques perspectives
Published in Cogent Engineering, 2023
Zié Adama Ouattara, Amos T. Kabo-Bah, Kouassi Dongo, Komlavi Akpoti
Backflow is identified as a situation in which the free flow capacity in a downstream section of a collection system has been fully reached (Figure 7) and acts as a disruption to further flow (Irwin et al., 2018). The phenomenon of backflow in wastewater and rain water systems is mostly due to blockages in the network (Ouattara et al., 2021).