Water conservation is becoming a major focal point, both in the public and private sector whether it is due to cost of water, availability of water, or environmental concerns.

In the private sector, the petroleum and petrochemical industries are one of the largest users of water.   The uses of water can vary considerably in these facilities based on the manufacturing processes.  But in general, most of these facilities use a large amount of water for a variety of purposes including steam generation, cooling water, and utility water.   In addition, a significant amount of this water is returned to the environment in various water and wastewater streams which are treated to meet environmental discharge standards.  In those areas where renewable water resources are limited, and/or in regions where there are significant environmental concerns/costs associated with wastewater discharges, reuse of wastewater may be a valid option to conserve valuable water resources and to reduce overall water treatment costs.

While there is a significant amount of interest in the reuse of water from petroleum and petrochemical facilities, the number of facilities at the present time actually reusing wastewater from centralized wastewater treatment plants is somewhat limited.   Reuse of wastewater from specific process areas, or reuse of wastewater from sources outside the petroleum or petrochemical facility, are more common.   As the costs and availability of fresh water becomes more prohibitive, more and more petroleum and petrochemical plant are looking to internal reuse of wastewater as a solution to their water needs.

Map Water Needs to Specific Waste Sources

Whenever considering wastewater recycle/reuse, a water audit is a good idea.   A well performed water audit will identify the sources of wastewater throughout a facility and will characterize each of the identified wastewater streams not only for flowrate, but the type, concentrations and variability of the substances and compounds in each wastewater stream.   Additionally, the areas in the facility where fresh water, or make-up water, is used are also mapped.   Based on the water intake reduction goals (or wastewater recycle/reuse goals) the various sources of wastewater can then be matched with the water needs in the facility, and an economic model for wastewater recycle/reuse can be developed.

When investigating ways to recycle/reuse wastewater from a petroleum or petrochemical facility, many times the first thing considered is the recycling/reusing the wastewater from the facilities central wastewater treatment plant.   Often, this should be the last place considered for wastewater recycle/reuse.

Wastewater flowing to a centralized wastewater treatment plant in a petroleum or petrochemical facility typically comes from many sources.   Each of these sources generates a wastewater with different characteristics.   Some can be very high in organic compounds, salts, metals, or suspended solids.  If a facility’s goal is 10%, 30% or even  50% recycle/reuse of wastewater generated in the facility, it may be relatively easy to identify specific wastewater streams in a facility that have relatively low concentrations of pollutants, or pollutants that are easier to remove, for very economic recycle/reuse of the wastewater.  In comparison, treating the wastewater in the facilities centralized wastewater treatment plant will typically contain a wide variety of wastes and pollutants from process areas throughout the facility.

For example, the condensate, stormwater, coker cutting water or cooling water blow down waste streams are many times easier to treat for reuse.  They do not contain the number and level of contaminants contained in combined wastewater streams from petroleum and petrochemical facilities.  Unless significant quantities of water are required for reuse, isolating those waste streams that contain a minimal amount of contaminants can significantly reduce treatment costs.

Also, understand all the points of water use in a facility.   You will find that not all water uses in a facility require the same level of water quality.   Some water needs require relatively low quality water, such as fire water or utility water, while some uses require much higher water quality, such as cooling tower make-up or boiler feed water.   Attempting to match a specific wastewater stream in the facility to a specific water need in the facility can result in a very inexpensive way to recycle/reuse wastewater.  

Finally, don’t limit the search for wastewater to be reused just to the wastewater generated within the facility.   There may be other industries, or even large municipal (sanitary) wastewater treatment plants that are nearby that generate a wastewater that may be much easier to treat for reuse.   While there may be increased costs for pumping systems and pipelines to bring this wastewater to the petroleum or petrochemical facility for reuse, the wastewater may also be significantly less expensive to treat, more than off-setting the costs of the pump stations and pipeline.

Proper Plant Design, Equipment Selection Critical for Effective Wastewater Reuse

These treatment systems are well understood and are common throughout the industry.   Reuse technologies are normally added to these systems to provide the water quality required for various reuse purposes.  However, even in the best operated facilities, there are still compounds and substances which may be present in the treated wastewater from these systems, which can provide significant negative impact on reuse technologies, if the technologies are not properly selected.   Experience shows the effectiveness of each wastewater treatment technology is only as good as the prior treatment step.  This is particularly true in wastewater reuse systems where the reuse technologies are significantly more sensitive to the upset conditions and pollutants commonly found in petroleum/petrochemical wastewater streams.   Selection of the wrong reuse technology can have serious implications.

Due to the wide variety of organic chemicals, crude oil, organic acids and other pollutants which are present in petroleum/petrochemical facility wastewater, studies have shown significant challenges with reusing some wastewater streams generated in these facilities.  Problems which have been encountered include scaling of membrane system, biological fouling of microfiltration and RO membranes, and chemical deterioration of membrane and demineralization system.   Our experience has shown that when considering reuse of wastewater from petroleum refineries, pilot studies are recommended to ensure proper selection and design of the treatment technologies.

Petroleum refineries present the biggest challenges to reusing water due to the wide variety of pollutants which can be present in the wastewater.   While the number of petroleum refineries that reuse wastewater at the present time is fairly small, reuse of wastewater in petrochemical facilities is more common due to the nature and limited number of pollutants in the wastewater.   Other applications where wastewater has been reused includes oil production, gas-to-liquids, petrochemicals and chemicals.   But by far, petroleum refining presents the biggest challenges to wastewater reuse.

Robust Treatment System Required

The higher the water quality need is, the more complicated the wastewater reuse system can become.  For most facilities that discharge their wastewater to the environment (fresh or salt water discharge), the typical treatment steps found in a centralized wastewater treatment facility normally include screening, oil/water separation, biological treatment and possibly a tertiary treatment step such as media filters to meet the discharge requirements.  

The process units in these facilities operate under many variable conditions.   These operating conditions also affect the quantity and quality of the wastewater generated at each unit.   So, designing and operating a wastewater treatment system can be a challenge at times, as can meeting effluent treatment requirements.   The first step in the wastewater treatment plant is the most important, because if that step does not work, it affects every treatment step downstream of it.

Not meeting wastewater discharge requirements from a petroleum or petrochemical wastewater treatment plant can have serious consequences for a facility and should be avoided at all costs.   A robust wastewater treatment plant design is essential to ensure adequate treatment even when the treatment plant is experiencing unusually poor raw wastewater quality.   In the event there is an upset, and one or more of the treatment processes do not meet the treatment requirements, they normally recover relatively quickly, once the influent wastewater returns to normally/design quality.  The exception to this might be biological treatment systems, but even here, there are methods to minimize recovery time, with minimal costs.   However, when we start to add additional treatment steps to meet water quality requirements for recycle/reuse, the consequences of sending a wastewater which does not have sufficient pretreatment to recycle/reuse technologies can be significant. 

Don’t Forget Final Waste Disposal

When recycling and reusing wastewater, it is critical to understand reuse simply concentrates wastewater into a smaller stream making disposal potentially problematic.

When you consider wastewater reuse in the petroleum and petrochemical industry, consider all the substances present in the waste stream.   These can be minor concentrations of organics, salts, metals and other compounds.   In the process of recovering the wastewater for reuse, in most cases water is extracted from the waste stream, leaving behind the metal, organic substances, salts and other compounds, in a much smaller volume of water, thereby increasing their concentration.   By recovering 90+ percent of the water in the waste stream, these metals, while in a much small volume of waste, may now be in parts per million (ppm) concentrations, and depending on regulatory disposal requirements, these higher metal concentrations may now present a disposal challenge and may significantly increase the cost of disposal of this smaller, but more concentrated, waste stream. 

While reusing wastewater can be an economical alternative to internal or external fresh water supplies, there are many factors that must be addressed which can impact the reliability of the reuse system and the associated cost of wastewater reuse.    Doing a proper evaluation of these factors can insure a well operating water reuse system, as well as a continuous and economic stream of high quality water is available for the facility. 

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