Lack of water resources for industry can severely limit growth and contribute significantly to the cost of manufacturing. Beyond the environmental and business costs for wastewater treatment, environmental restrictions are increasingly stringent, leaving facilities to identify ways to comply without breaking the budget. In fact, we spend approximately $366 billion a year on water purification and consumption alone.
Currently, over one fifth (22%) of all available freshwater is used for industrial applications. In industrialized countries, that average is even higher, with nearly two thirds (59%) of all freshwater used by industry. In many areas of the U.S., there is more water than is available from local sources. Additionally, each year, some 300 to 500 million tons of heavy metals, solvents, toxic sludge and other wastes accumulate from industry, many of which end up polluting the usable water supply if the water is not adequately treated.
Industrial wastewater can be treated at the site or at a municipal wastewater facility. However, since industrial wastewater streams are complex and difficult to treat, municipal wastewater treatment facilities are often unable to accept the load due to the consequences upon their treatment processes. Where it is available, the cost can be hundreds of thousands of dollars each year.
Another option for industrial facilities is on-site wastewater treatment, where the treated water (effluent) is either discharged to a surface water body, sent to a municipal sewage treatment plant for further treatment, or reused internally. Not only does on-site treatment enable the recovery of valuable materials that would otherwise incur a disposal cost, it is also significantly more cost effective than sending untreated water directly to a municipal treatment facility.
In order to reuse wastewater, it must be treated to a relatively high standard.Though the standard required depends upon the reuse application, there are an increasing number of sites where wastewater is treated to potable standards, enabling it to be reused for almost any application. These high levels of treatment have allowed for the concept of an "industrial zero discharge" facility where water continually circulates within a single site is becoming more common.
For two Asia-based textile Effluent Treatment Plants (ETPs) zero discharge has enabled them to meet more stringent regulations while incurring significant cost savings. Faced with the threat of closure if the quality of their wastewater was not improved within a year, the plants turned to ITT to build internal water treatment systems.The multi-tiered solution combined flow balancing, screening, dual-stage membrane bioreactor (MBR), granular activated carbon (GAC) and two-stage reverse osmosis (RO) to create high-quality treated wastewater.The in-house systems also allowed for incredible cost savings for the companies who are no longer incurring municipal charges for wastewater treatment.
The ETPs process 0.04 million gallons of water per day (1.5 million liters per day) and 1.3 MGD (5 million liters per day) respectively and all water treated on site is reused. The dry sludge is used as fuel, the salt recovered from the RO process is used for further dyeing use and the water is resold to the industrial wastewater generators at a lower than supply rate.
The dual stage MBR system detailed above is fast becoming the standard for industrial wastewater treatment and reuse. However, traditional activated sludge processes are still common. In this process, wastewater is treated through a settling tank where solids are separated and filtered out prior to water disinfection. For the highest quality water, an additional sand or carbon gravity filtration and/or micro/ultrafiltration steps may be required.
Membrane bioreactors, on the other hand combine these multiple treatment steps, using the physical barrier provided by an ultrafiltration membrane instead of a settling tank and gravity filters to separate solids from liquid.Thus the effluent is of significantly higher quality and little, if any, additional treatment is required prior to disposal or reuse.
Other options for water treatment can include reverse osmosis, nanofiltration, ion exchangers, ultraviolet and ozonation. The resulting water is extremely pure and contains low or no concentration of dissolved solids or particulates.
Who Needs It?
While on-site water reuse does not make sense for every industry, it can be a cost effective solution for most. For those with significant water needs especially due to water scarcity, high water cost, or high purity standards that are difficult to meet through municipal supplies, recycling water within the facility often provides a relatively inexpensive means to address water needs in an environmentally conscience manner. And with demand for fresh water expected to double in the next 20 years, it may be a smart way to ensure access to this critical resource well into the future.
Henry J. Driesse is president of ITT Corporation's fluid technology business one of the world's largest providers of water and wastewater treatment solutions, and a provider of pumps and related technologies for industrial, chemical and commercial customers.