The continued high cost of fresh water and environmental concerns are causing industrial plants to expand and explore their wastewater reuse options. Many facilities are finding it more economical to reuse wastewater from specific process areas than it is to reuse wastewater from centralized wastewater treatment plants. Performing water audits can help facilities develop appropriate programs to meet their water-intake reduction and water reuse goals.
A well-performed water audit should identify water needs, uses and wastewater sources throughout a facility. The audit should characterize each of the identified streams by flow rate, type, concentrations and variability of the substances and compounds contained. After determining the facility’s water reduction and wastewater recycle and reuse goals, the various sources of wastewater then can be matched with the facility’s water needs. An economic model for wastewater recycle and reuse can be created.
Understanding Water Audits
Engineers can conduct a comprehensive, on-site water audit to gain important insight into their operations, uncover ways to ensure cost-effective operation and ensure consistent compliance with water quality standards — all while conserving water. In many cases, such an audit can help engineers improve operations and maintenance practices in a way that reduces costs and downtime.
What Does a Water Audit Include? A water audit consists of a review of all equipment that is used to treat process water and wastewater at the plant. Whoever conducts such assessments should have experience with the process units that use water and generate wastewater. For instance, many process units in petroleum and petrochemical facilities operate under variable conditions that can affect water needs and wastewater generation volume and quality. Comprehending these variables is key to understanding the available options to reducing water usage, the treatment required to recycle or reuse the wastewater, and the ability to reduce the total cost of water.
Many process units in petroleum and petrochemical facilities operate under variable conditions that can affect water needs and wastewater generation volume and quality. Comprehending these variables is key to understanding the available options to reducing water usage.
Process operators should conduct a water audit whenever they suspect a possible problem. Typical examples of when to perform an audit include when a plant is using greater than expected quantities of water, or the quantity or quality of the wastewater being generated is below expectations.
When Should a Water Audit Be Conducted? Plant operators should not wait until there is a problem before conducting a water audit. An audit could help determine if it would make sense to upgrade or replace individual components, or the whole system. A water audit also can help identify if a plant is using water in the most efficient manner to reduce operating costs and encourage recycling and reuse. Conducting an on-site water assessment can help identify equipment needing upgrade or replacement. It also can help determine whether additional equipment would enhance the economical treatment capabilities of the existing system (throughput volume- or pollutant-reduction capabilities).
A system-wide evaluation also will provide plant personnel the opportunity to evaluate whether any additional equipment should be purchased, permanently installed, handled as a build-own-operate or set up as a temporary mobile system. Such a decision will depend on site-specific operational needs and budget.
Finally, an audit should be planned before every scheduled plant outage so that any necessary work can be done during the expected facility downtime.
A well-performed water audit should identify water needs and uses as well as wastewater sources throughout a facility. The audit should characterize each of the streams by flow rate, type, concentrations and variability of the substances and compounds.
What Will the Water Audit Uncover? Some unit operations or processes are, by nature, prone to developing water-related problems. For example, reverse osmosis (RO) and microfiltration systems may develop problems if their membranes are not cleaned correctly and at appropriate intervals. Improper cleaning, or cleaning that is done too late, may cause irreversible damage to the RO and microfiltration membranes and result in compromised system flow or diminished product water quality.
What Are the Long-Term Benefits of a Water Audit? Developing a timely, comprehensive water audit can help prepare plants for a short-term or emergency water-system outage (or shortage). The plan should take into account identified weaknesses in the existing system and provide ways to address those potential component failures. Provisions also could be included for adding emergency mobile equipment, improving system redundancy or simply making sure the plant has the proper inventory for high wear spare parts. Detailed instructions such as a checklist on what is needed to minimize the impact of a water-related failure also should be included.
Conducting an on-site water assessment can help identify equipment that needs to be upgraded or replaced. An audit also can help determine whether additional equipment should be added to enhance the treatment capabilities of the existing system.
Performing the Audit
A water audit can be as inclusive as reviewing all process operations, including those related to process control, instrumentation, vessels, piping, influent and discharge water quality. It also can be as simple as reviewing one specific part of the process. In general, a full comprehensive water assessment is recommended if a system has been in service for more than five years, has been poorly maintained, is operating less efficiently or is not meeting final water-quality specifications.
Reviewing Current Conditions. A work team evaluates the facility’s water-related operation and maintenance activities. The team also reviews any seasonal variations in plant influent water quality or changes in demand for process or wastewater flows. The team reviews maintenance logs to ensure that proper maintenance has been carried out at appropriate intervals. The audit team should also review whether all systems are operating at the correct flows and pressure according to design data and associated process and instrumentation drawings (P&IDs).
Once the inspection is complete, the overall system operation should be verified against the system P&IDs. Modifications required to meet design flows or water quality can be implemented at this time.
Estimating How Much Time Is Needed for the Audit. The time it takes to do an audit will vary depending on who conducts the evaluation and the scope of the audit. If it is carried out as a full comprehensive assessment of all water-related aspects of the entire facility, it will reasonably take longer than one that reviews just a single part of the process. Assessments will proceed quickly when design drawings and other documentation are readily available from plant personnel. It may take longer when critical documentation has to be reconstructed.
A Glossary of Water Audit Terms
Build-Own-Operate. Build-own-operate service contracts allow processors to focus on their core business while a professional service company takes responsibility for the design and operation of the water or wastewater treatment system. Because many water technologies and treatment solutions are available, some processors are choosing outside firms to operate and maintain their water and wastewater treatment systems. Such companies can evaluate and provide a technological solution for the operation. This allowing the processor to focus on its core business while maintaining strategic control of their operation.
Reverse Osmosis (RO). Reverse osmosis uses a semi-permeable membrane to remove minerals and dissolved solids from water. Normally, RO can be considered economically attractive on water chemistries with greater than 250 ppm total dissolved solids (TDS) but less than 2,000 ppm. Between 150 and 250 ppm TDS, local considerations and water chemistry will determine whether RO is a viable option. Typically on waters with less than 150 ppm TDS, ion exchange without RO is feasible for TDS reduction.
A single pass reverse osmosis system typically removes 97 percent of the total dissolved solids and 95 percent of naturally occurring organics. The water recovery and average membrane flux usually ranges from 65 to 80 percent recovery and 14 to 18 gfd, respectively, with both being dependent on the water chemistry.
Microfiltration Systems. Microfiltration systems are skid mounted and factory assembled to ease reassembly and installation. The tubular membranes are designed for high solids loadings. The membrane provides for an absolute barrier to the passage of solids. This results in the removal of most colloids; therefore, it provides a filtrate that exhibits a low silt density index (SDI). A microfiltration system often is a good option to place immediately before a reverse osmosis unit or other polishing technology.
Third-party service providers typically take 30 to 60 days to conduct an audit from start to finish. This includes developing the scope of the assessment, performing the equipment review and creating a report. The latter verifies the project scope, details the current and desired condition of the system, and outlines the remedial steps needed to reach the desired outcomes.
Assessing Cost. Time spent by internal plant personnel or external third-party service providers to conduct the assessment is factored into the cost of a water audit. As the need for upgrades or repairs will likely be identified, costs associated to repair or replace any equipment also need to be considered.
Inlet water and wastewater are essential parts of most process unit operations. The ability to treat water so that it meets process specifications and regulatory thresholds is of critical importance to the facility’s smooth operation.
Upgrading an older system that still produces water of sufficient quality could help prevent water-related failures from occurring. In deciding whether or not to repair or upgrade the system, the cost of the repair must be weighed against the long-term potential gains in efficiency or improvements in system performance. It also should be weighed against the costs associated with unscheduled interruptions in process water availability or insufficient water and wastewater treatment capabilities.
Getting Outside Help
When a facility decides to hire an outside water audit team, plant personnel should assemble the following types of plant documentation and data to help facilitate the assessment:
- System operating manuals.
- P&IDs for the water treatment system.
- Schedule of preventive maintenance done on the system.
- Water consumption and wastewater produced by process area. (Compare actual performance with system design and analyze any excursions.)
- System acid/caustic and other chemical consumption.
- Replacement history for cartridge filters, resin, membranes and media.
- Makeup water and product water quality measurements.
- Operating schedule (hours/days/week/year).
In conclusion, inlet water and wastewater are essential parts of most process unit operations. The ability to treat water so that it meets process specifications and regulatory thresholds is of critical importance to the facility’s smooth operation.
By conducting timely water assessments, operators can identify opportunities for improvement. They can take steps to rectify subpar performance in the most orderly and cost-effective manner. Most importantly, by conducting timely water assessments, a plant can help minimize the risk of system failures or unscheduled downtime. PC
What Is Industrial Water Reuse and Recycling?
Industrial water reuse and recycling is the process by which wastewater produced from one source (such as municipal wastewater) is treated so it can be used in an industrial process. Sometimes, the source wastewater may be produced by the same industrial facility that treats it and reuses it. Industrial wastewater can be recycled on or off site, depending on space constraints and budgetary considerations.
Recycling wastewater is important for the natural environment because it avoids straining drought-stricken areas and natural habitats such as wetlands.
Common Industrial Water Reuse Opportunities. Industrial water may be reused in many different ways. Before determining how to reuse waters, you should consider where potential water reuse opportunities exist. Some opportunities for water reuse in an industrial plant may include:
- Wastewater recycling.
- Cooling tower blowdown.
- Boiler blowdown.
- Once-through cooling water.
- Collected rain waters.
The Need for Water Recycling and Reuse. Whatever is behind your need to recycle and reuse wastewater, decreasing the plant’s water footprint is beneficial your company and community. The need for industrial water recycling and reuse has many drivers.
Industrial and Population Growth. A growing population increased the need for power generation, for example, which placed greater demands on water use.
Fresh Water Costs. The cost of clean, fresh water is continually increasing and is impacting all regions.
Regulatory Requirements. Many industrial sites have wastewater discharge permits that include flow and quality restrictions. Moreover, Environmental Protection Agency (EPA) industrial effluent guidelines often are revised.
Social Responsibility. Protecting the world’s resources is a global concern, and the public is paying attention. Negative publicity around a company’s water use can have an impact on the company’s sales and growth.
Discharge Costs. Sewer and wastewater costs have increased at a higher rate than fresh water costs.
Water Scarcity. Many regions in North America are susceptible to drought. Additionally, some industrial plants have limited access to clean and fresh water.
Wastewater Processing Limitations. In many industries, plant wastewater treatment capacities have not increased proportionally with plant production. Plants are challenged to meet higher flows and have limited operational resources.
Sustainability Efforts. Many companies strive towards sustainability by using economically sound programs that help minimize a plant’s negative environmental impact while conserving energy and natural resources.