By Krishnan Sadasivam
To make water safe for consumption and compliant with regulations, disinfection chemicals are a basic supply for water treatment facilities. Thanks to technological advancements and changing market and environmental trends, the choice between purchasing bulk bleach or making it on-site is getting a fresh look from many utilities.
Purchasing bulk bleach has traditionally been the more cost-effective option for securing a supply of disinfectant. Large-scale manufacturers have been able to produce it cheaply in large quantities and ship it to remote locations. Due to capital costs, installing an on-site chlorine generator just hasn’t made economic sense in most situations. However, changing environmental and market conditions have increased the costs and risks of purchasing bulk bleach while technological improvements have driven down the cost and accessibility of on-site generation. For an increasing number of water treatment facilities, on-site generation is becoming a more attractive financial choice.
The Rising Costs and Risks of Buying Bulk Bleach
The cost of generating a pound of chlorine is based only on the costs of water, salt and electricity and is a fraction of the cost of delivered bleach. Furthermore, supply shortages and increased production costs due to inflation have driven up the costs of bulk bleach, which are tied to market forces and subject to increasing volatility.
There is an array of additional bulk bleach costs and risks that can be avoided with on-site generation. These include the costs and risks of chemical transportation and logistics, safety-related costs and liability risks due to chemical storage and handling (including higher insurance premiums), the risk of service disruption due to supply shortage, the cost of environmental controls to protect chemicals from the degrading effects of warm temperatures, and greater waste in the forms of bleach lost to degradation and chemical packaging necessary for shipping.
On-site generation systems do present an up-front capital equipment cost, but most facilities experience a return on investment within one to two years – or a matter of months when replacing expensive biocides like chlorine dioxide or stabilized bromine. Once these capital costs are recouped, facilities experience significantly reduced operating costs.
How On-site Generation Works
Using electrolysis, on-site generators use salt, water and electricity to produce chlorine gas, bulk sodium hypochlorite, calcium hypochlorite, chlorine dioxide, bromine, glutaraldehyde and other biocides. During the process, an electric current is passed through saltwater, causing chloride ions from the salt solution to oxidize and form chlorine gas (at high anode potential) or hypochlorite ions (at low anode potential). Systems can generate from 250 to 3,000 kilograms per day of free chlorine and treat up to one million cubic meters per day with low power consumption and no unwanted byproducts.
A single on-site generator can produce different concentrations for operations that have more than one disinfection requirement, offering flexibility that is much harder to manage with delivered bleach. Some of these systems also have a flexible design that can increase capacity without increasing footprint.
The Advantages of On-site Chlorine Generation
In addition to the purchase cost savings available by generating bleach on-site, there are multiple other advantages.
First, on-site generation is safer. It eliminates the need for storing and transporting hazardous chemicals, reducing the risk and liability of spills and explosions at the plant and in transit. It also reduces overall traffic to a plant, because it takes more than three deliveries of bleach to equal the chlorine equivalent produced by one truckload of salt. In terms of the chemical quality, on-site generation can produce a 0.8% sodium hypochlorite solution, which is considered a non-hazardous chemical that does not present a threat to public safety or require OSHA Process Safety Management, U.S. EPA Risk-Management Planning, special personal protective equipment for operators or special containment provisions in case of leaks. Although one potentially dangerous byproduct, hydrogen, is produced during the electrolysis of brine, it is safely contained, rapidly diluted and carefully vented into the atmosphere.
Second, there is far less wasted bleach. High concentration sodium hypochlorite decomposes when stored too long or at too high a temperature, and the clock starts ticking on this decomposition as soon as the chemicals are manufactured and readied for shipping. Every minute bleach sits in a container on a truck or in plant storage adds to its loss of efficacy, and this degradation can result in the discarding of expired chemicals or the need to dose more product to achieve the desired result. An increasingly warmer climate is exacerbating this problem. With on-site generation, facilities can generate bleach on an as-needed basis, so there is no degradation and no waste. A related advantage is the reduced formation of chlorine byproducts. While degradation causes the formation of chlorine byproducts such as chlorate and perchlorate, 0.8% sodium hypochlorite produced from on-site generation decomposes at a much slower rate.
Third, on-site generation is more sustainable. Due to greatly reduced waste, lower health and environmental threats of transporting and storing bulk concentrated chlorine, less reliance on an emissions-heavy trucking network and reduced byproduct formation, on-site generation is a more sustainable practice.
Fourth, on-site generation is more reliable. By generating its own chlorine products, a plant no longer has to rely on buying from the chemical market, which is more vulnerable to price fluctuations and delivery delays than water, salt and electricity. This ensures a fresh and reliable supply of disinfectants without the need for bulk chemical transportation or long-term storage.
And finally, for some utilities, on-site generation can create a revenue stream. By establishing a small-scale bleach production operation for their own use, water and wastewater treatment facilities also can sell bleach products to local partners who need small amounts. And for wastewater plants looking to replace income from the loss of sales of biosolids due to PFAS regulations, selling bleach may offer a solution.
Why The Time Has Come for On-site Bleach Generation
The choice between purchasing bulk bleach and making it on-site typically comes down to which one offers the greater economic benefit when considering OPEX and CAPEX expenses. Increasingly, the risks of transporting and storing hazardous chemicals combined with the unreliability of the supply chain and volatility of the chemical market are outweighing the capital investment of installing on-site generation systems, which is quickly recouped and can deliver a measurable ROI in the form of life cycle cost savings and potential revenue.
Case Study: Mount Isa Wastewater Treatment Facility
Using the De Nora CECHLO system to generate 12.5% sodium hypochlorite on-site at Mount Isa’s Wastewater Treatment Facility in Mount Isa in Queensland, Australia. Mount Isa City Council is now the primary chlor-alkali production hub in north Queensland. In this decentralized arrangement, they sell locally-made chlorine compounds for use in water and wastewater treatment to partners in the surrounding municipalities. Fresh sodium hypochlorite that has not decayed has fewer disinfection by-products such as chlorates and ensures the potable water supply complies with the Australian Drinking Water Guidelines. By using chlorine that is manufactured very close to the point of use, the operation has reduced its carbon footprint and increased the resiliency of its supply chain.
These kinds of partnerships generate income from chemical sales, create local employment and stimulate sustainable growth. In this case, Mount Isa City Council has solved an operational problem while also providing valuable benefits to the community.
Krishnan Sadasivam is global business development director for CECHLO at De Nora. He is a seasoned executive with more than 30 years in the water and wastewater industry. He specializes in disinfection technologies, digital water, advanced membrane technologies and engineered equipment for water purification, wastewater treatment, ZLD and water reuse in various sectors.
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