Without adequate water supplies and an understanding of the true value of water, many businesses would be incapable of operating. Defining the true value of water helps businesses make intelligent decisions regarding how they source, use, reuse and dispose of water in order to maintain profitable economics of operation.
Determining this value can be accomplished through development and implementation of an intelligent water management strategy. The strategy is comprised of a series of audits, evaluations and analysis to identify and control the risk associated with various water sources, the cost of using this water supply in production facilities, and evaluate appropriate uses and re-use opportunities for each process. This course of action is supported by analytical data obtained by the smart deployment of instrumentation such as flow meters and water quality monitoring devices that allow facilities to record and make full use of each drop of water that is delivered and used at the site.
Water use by industry has come under increasing scrutiny on many locales over the past few years. Unrelenting drought in the western United States, India and Africa, along with deterioration of water sources globally combined and increasing concerns over water contamination from industrial wastewater discharges have pushed water practices to the forefront of facility utility managers’ lists of potential operational risks. These risks, although real and potentially incapacitating to businesses, are often difficult to quantify in a manner that allows facilities to determine the potential cost to operations.
The risks presented by water supply and treatment can be quantified and managed cost effectively, but first facilities must understand the true cost of water to operations. Generally, when facility operations personnel are asked to quantify the cost of water to their operations, the first response is to consult the water bill, where the raw cost of water is provided. When prodded, many will also volunteer their wastewater discharge bill. However, the true cost of water encompasses so much more.
The true cost of water is a sum of the cost of procuring, conditioning the water for facility usage, conveying, treating, and disposing of water. It can include all of the following costs that a business will incur as it uses water, such as:
• Licensing • Equipment maintenance • Chemical addition • Analytical costs • Pumping costs (including power and maintenance of pump systems) • Pre-treatment • Effluent treatment costs • Sludge treatment and disposal • Softening chemicals • Brackish water or RO reject water effluent treatment or disposal costs • Water associated labour • Water and wastewater treatment costs • Cooling tower bacterial controls • Borehole abstraction • Power
The ability to quantify and describe the costs associated with these items allows improvements in the decisions associated with water management at a site, but how can a facility begin to quantify the water associated costs and risks in an operation?
In order to understand the risks and costs associated with water usage at a facility, the first key is to understand the quantity of water used and discharged within the facility, along with the water quality needs for consumption/production and discharge. Generally, facilities will have the gross measurement of water available to them from the water meter and from a discharge point, but the discrete analysis of water in individual processes allows facilities to make better decisions on how to use the water. This requires facilities to submeter water consumption within areas of the facility and even within individual processes.
Submetering involves the use of multiple water meters in a facility, allowing identification of water consumption in individual processes. It is better to measure the water entering process units to identify water consumption than to look at the effluent of a process, since there can be significant consumption and transfer of water from various processes.
Meters can be installed permanently or can be placed into service temporarily. Facilities can often get by with periodic examination of water consumption using temporary meters rather than permanent monitoring, since production processes will generally follow preset patterns, making temporary meters, such as strap-on ultrasonic flow meters (Figure 1), more cost effective for short term use. Permanent meters, on the other hand, allow facilities to track usage per process and capture changes in facilities over the longer term and will also allow facilities to quickly identify the risk of excessive water usage in processes.
The best strategy is a combination of online permanent meters for major process areas and periodic spot checking of individual processes using temporary metering. This approach allows facilities to examine practices associated with individual processes and to determine if change is necessary using the temporary meters. It also allows the longer-term monitoring of changes to the facility operation and identification of excessive water usage that may be the result of equipment failures.
One example we have of this strategy of using permanent and temporary meters working is a facility that we audited that was using permanent flow meters to quantify facility water consumption. They noticed several periods of excessive water consumption and wanted to determine the source of this excessive consumption. Using temporary flow meters, we were able to identify that a stuck valve in the cooling tower system was sending excessive water to the cooling towers and causing that water to be wasted. The facility was able to correct the valve issue and add an additional flow meter to this susceptible system to prevent future recurrence of this excessive water waste. In this instance, by adding up the various submeters, more than 1.2 million gallons of excess flow for these periods of stuck valves were identified and were saved by making appropriate system modifications.
Additionally, consistent monitoring of effluent flows allows facilities to rapidly respond to adverse facility conditions. While facilities generally monitor the total flow to the sewer system, this instrument is typically not incorporated into the remainder of plant operations. By monitoring the effluent discharge volumes, facilities can rapidly identify excessive discharges that may be the result of broken pipes, stuck valves, or operator error. With these discharges closely monitored, facilities can reduce the waste associated with excessive discharge volumes.
In addition to flow measurement, companies can find great value in continuous monitoring of water quality. Many facilities are required to continuously monitor wastewater effluent parameters, such as pH, to maintain compliance with wastewater permits. Online instrumentation for other water and wastewater quality parameters, however, can reduce operation costs for facilities.
Water conditioning systems for production facilities have inherent operating costs, often include expensive chemicals, and can produce wastes either as sludge or through regeneration cycles. Making these systems more efficient will result in reduced operations costs, but it is important to carefully make adjustments to these systems, since the water that they produce needs to be fit for the processes in which it is used. Careful examination of the requirements of the process will allow facilities to reduce water consumption and thereby reduce the cost of water treatment.
One common example is associated with water softening systems. The water produced by a water softening system can be used in many different processes, but is commonly associated with boiler loops or cooling towers. A key parameter for these systems is total dissolved solids (TDS), components of which can result in scaling and reduced efficiency. While it is difficult to directly measure TDS, conductivity can be closely correlated to TDS in water. By monitoring the conductivity of water in a recycle loop for a boiler or cooling tower, facilities can minimise the makeup water required for these loops, ultimately reducing the cost of water treatment.
Additionally, water treatment systems themselves can be monitored for optimal performance. The simplest method of initiating backwash, regeneration or cleaning cycles in treatment systems involves the use of either timers or flow meters. After a preset time or flow, the regeneration or backwash cycle commences. In order to prevent poor quality water from entering the process systems, these cycles are typically set to occur well before the facility water would approach quality guidelines. By monitoring parameters such as turbidity or conductivity, however, facilities can identify the point at which water quality begins to approach their process needs, allowing facilities to initiate these regeneration or backwash cycles based on the water quality, rather than the conservative timing.
For one recent client, frequent regeneration of ion exchange systems was a cause of major issues. The facility in question had a discharge limit on TDS that could be exceeded by excessive regeneration of ion exchange columns. As a result, the facility was collecting the brine spent during regeneration and hauling it offsite. By examining the quality of the water leaving the ion exchange system, this facility was able to drastically reduce ion exchange regeneration and the consequent costs of brine disposal.
Online effluent monitoring
One area where online instrumentation has not been fully developed is in the area of online effluent monitoring. As mentioned earlier, many facilities use online monitors to track effluent pH and flow. These parameters are monitored largely for compliance, however, and do little to help facilities reduce operating expenses. By carefully monitoring facility effluent, product losses can be identified and hopefully minimised. Additionally, treatment strategies can be optimised to reduce the potential for non-compliance with operating permits.
Facilities can use online chemical oxygen demand (COD) analysis to help maintain compliance with discharge regulations, helping to avoid expensive fines or surcharges. The standard method for discharging from a facility involves sampling and sending the samples to a lab for analysis, which will provide sample results anywhere from one day to two weeks from the date of the sample. If wastewater is above either the discharge limit or the surcharge threshold, the facility operators will not be aware of the problem until it is too late to make facility changes that could reduce the magnitude of the problem. With online COD analysis, facility operators can discontinue discharges or make proper adjustments to prevent exceeding the appropriate discharge criteria.
Online COD analysis can be performed in a number of different manners. While online COD analysers are available on the market, the use of reagents may make them unappealing to some facility operators. Alternatively, total organic carbon (TOC) analysers or ultraviolet absorption spectrometry (UVAS) can be used for reagent free online COD analysis. These alternatives require additional time for initial calibration and also require follow up testing, but they can provide much faster analytical results than some of the online COD analysers. There are, however, new analysers that provide nearly real-time analytical results.
One issue with some of this online instrumentation is that it may require some sample conditioning prior to analysis. This is necessary when instrumentation cannot fit in a probe, which is a common issue with online COD analysers. Generally, instruments that are not probe based will have a small water line feeding the instrument. These lines can foul if there are excessive solids in the flow as the instruments are typically more sensitive to high solids content than probe based instrumentation.
Online instrumentation comes in a variety of packages and can monitor many different parameters, helping to ensure the quality of process water and wastewater. The instrumentation used to measure flow and various water quality parameters is well understood and can provide the information necessary for operators to react quickly to changes in water quality parameters resulting from facility spills, changes in operation, and even routine operations.
The overall goal of using online instrumentation is to help facilities reduce the total cost of water, improving overall operating efficiency. While water is often viewed as an inexpensive commodity, the expense associated with treatment of water to ready it for facility processes and treatment for disposal can often be extremely expensive, once all the costs of operation are accounted for. By reducing the overall water consumption and optimising treatment process efficiency, online instruments can rapidly pay for themselves by helping operators identify sources of facility waste, improving facility compliance with discharge parameters, and reducing the cost of treatment.
Effective deployment of this instrumentation will help facilities become more reliable as well, reducing the potential for downtime associated with improper maintenance and allowing operators to identify long-term facility trends, permitting correction of issues before they reach a critical phase. Overall, improvements in water and wastewater instrumentation at industrial sites allow improvements to facility operations while reducing operating costs, which is something that every facility can surely appreciate.
Published: 27th May 2015 in AWE International