By Lior Eshed
Water scarcity and population growth create increasing pressure on natural water sources and require the development of new, sustainable water sources. As technologies gradually improve, reusing effluent from municipal wastewater plants is becoming more popular as an alternative renewable source and wastewater reuse is proving to be an effective sustainable method for ensuring a drought-proof, safe, reliable, locally controlled water supply.
The conventional water reuse process (and more so the RO part of it) hasn’t changed much over the years. It normally includes two to three stages operating at continuous and fixed hydraulic conditions and is accompanied by continuous chloramine dosing to protect membranes from biofouling. Chloramine should be carefully dosed and monitored in order to avoid overdose, because if the dosage values are too high it may end up as free chlorine, a stronger oxidizing agent than chloramine that can oxidize RO membrane surfaces very quickly. In addition, chloramine dosage is associated with the production of DBPs such as N-Nitrosodimethylamine (NDMA), trihalomethane (THM) and haloacetic acids (HAA), all of which are organic contaminants. NDMA is even suspected as carcinogenic and is therefore limited to a value as low as 10 ng/L. Another drawback of chloramine usage is its negative impact on the UV Transmittance (UVT) value of the RO permeate. UVT is a measure of the amount of UV light that passes through a water sample compared to the amount of light that passes through a pure-water sample. In other words, it is a measure of the water’s purity level. Higher UVT value translates to higher energy and chemical demand in the subsequent ultraviolet/advanced oxidation process (UV/AOP) stage. Operation without chloramine results in energy savings of 30-40 percent, as well as savings on the equipment size (CAPEX) and chemical demand (OPEX).
Demonstration facilities, such as one that recently operated in the Pismo Beach Wastewater Treatment Plant (WWTP) in California (as part of Central Coast Blue, a regional recycled water project) have proven that chloramine-free, indirect potable reuse can be both cost effective and highly efficient. The demo facility, which operated from October 2018 until September 2019, leveraged a technology where the water source was the secondary effluent of a municipal wastewater plant. This technology enabled higher recovery and flux without chloramine dosage, while avoiding the formation of DBPs and reduction of permeate UVT value.
The unit operated with an average flux of 16.5 gallons per ft2 of membrane/day (GFD) (28 L/hr/m2), which is 50-percent higher than the standard design of 11 GFD (18-19 LMH). Specific flux was 0.12 GFD/psi, which is about 25-percent higher than most well-operated wastewater reuse facilities, operating at the same recovery, with specific flux of 0.09-0.1 GFD/psi. The unit operated at 86-percent recovery in a single RO stage. No chloramine was dosed, meaning no DBPs (such as NDMA) were formed.
Chloramine-free operation generated permeate with a UVT value of about 100 percent, thereby saving 30-40 percent on capital expenditure (CAPEX) and operational expenditure (OPEX) in the final stage of UV/AOP. The overall cost of water from this process was 14-28 percent lower than a similar standard fully advanced treatment (FAT) water reuse process.
Wastewater reuse for industrial applications
The main industrial sectors that are utilizing wastewater reuse are power plants, food and beverage industries, chemical manufacturing, hydraulic fracking, oil and gas, and petrochemicals. Industrial cooling towers have long been seen as an ideal repository for wastewater, because of the large volumes of water necessary for the evaporative cooling process.
What are the main factors driving the need for better and more advanced industrial water reuse technologies? In most cases, these are water scarcity and the ability to reduce costs by maximizing water recovery, as well as increased awareness of corporate social responsibility (CSR). Some industries, however, are still hesitant to adopt reuse solutions on a wider scale. Industrial users typically think of water management issues at their facility from two perspectives: securing water supplies for operations (including supply and discharge) and complying with quality standards for wastewater discharge.
On the one hand, putting in place a smart reuse management plan helps facilities reduce their freshwater demand and generated wastewater volume, minimize subsequent discharge permits, reduce the costs of freshwater acquisition and effluent treatment and, in some cases, even provide recycling opportunities for certain industrial byproducts. On the flip side, properly managed reuse requires knowledge, financial investment and, understandably, modification of current operations for both direct and indirect potable reuse applications. Weighing the pros against the cons, implementing a reuse management plan often proves to be the most sustainable, resource-efficient, cost-effective and environmentally conscious alternative.
Evolving regulation supports more rapid reuse market growth and encouragement at a legislative level and is also a key factor contributing to market readiness. Therefore, despite minimal push-back, all predictions indicate a much broader adoption of water-reuse management plans in industrial facilities across the globe.
Water reuse in the power sector
Electricity utilities are challenged by a competitive use of water in water-scarce regions and therefore need to rely on alternative water sources. Water-use applications in electricity utilities include cooling tower make-up, boiler feed, sanitation and irrigation of landscape. The day-to-day operation of a thermoelectric power plant, for example, is especially water-intensive and requires a large quantity of freshwater to sustain its ongoing activities.
To address this pressing need for water in such large-scale quantities without exhausting freshwater supplies or competing with municipalities over local water resources, reused municipal wastewater can offer a feasible alternative water supply for the power sector. Degraded or non-traditional water supplies are constantly being considered by the power sector to offset water consumption. Although reclaimed wastewater appears an obvious choice due to geographic accessibility and unlimited availability, only 60 of 5,000 power plants across 16 states in the US currently use municipal reclaimed water.
One of these rare examples for a reuse-centric plant is Palo Verde Generating Station in Arizona, the largest power generator in the US with a total output of 4,030 net MW, which meets the electricity needs of approximately four million people around the clock (source: WateReuse, https://watereuse.org/wp-content/uploads/2015/10/S3B2_WRA-FLagstaff-Industrial-Water-Reuse-2015hd.pdf)). Because of its desert location, Palo Verde is the only nuclear power facility that uses 100-percent reclaimed water for cooling. The facility is a 409-K-m3/day tertiary treatment plant that reclaims treated secondary effluent from local valley cities and, unlike other nuclear plants, it maintains zero-discharge, meaning no wastewater is released to rivers, streams or oceans.
The Koyambedu case study
The Chennai area has very challenging water circumstances, due to heavy industrial activity in the area and highly polluted water sources in the city’s vicinity. To tackle this issue, a major industry player has recently completed the erection phase of the tertiary treatment reverse osmosis (TTRO) plant for Chennai Metropolitan Water Supply & Sewage Board (CMWSSB) at the facility’s location in Koyembedu, City of Chennai, province of Tamil Nadu, India. The TTRO plant, which includes a capacity of 45K m3/day, was initially executed in 2018, in order to produce non-potable-use water (NPU) for industrial use. The NPU product helps to relieve some of the extensive water demand generated by the industrial activity in the area and allows a larger portion of the local potable water sources to be allocated for municipal use.
CMWSSB was in need of a partner to design, build and operate (DBO) the plant at Koyambedu, including supplying and laying of pipeline transmission for conveying product water to various industries situated at Irungattukottai, Sriperumbudur and Oragadam. Leveraging technologies, including gravity sand filters, ultrafiltration (UF) and reuse RO treatment, the plant is equipped to successfully treat the intensely poor quality of the sewage treatment plant effluent. Additionally, the DBO project was a key priority for local authorities seeking to improve the difficult water conditions in the area. It even included a 15-year O&M period, funded by the Jawaharlal Nehru National Urban Renewal Mission (JNNURM), the Government of India (GOI) and the Tamil Nadu Investment Promotion Program (TNIPP).
Images source: Shutterstock
Conclusion
As more regions around the world face increasing water crises, it will be paramount for more local governments and authorities to get involved. The technologies outlined in this article will go far to advance progress for all entities to offset the dire consequences of having done little until crises occur.
About the author
Lior Eshed graduated from Technion Israel Institute of Technology with B.Sc. and M.Sc. Degrees in environmental engineering. He started at IDE Technologies in 2015 as a process engineer focused primarily on advanced reuse technologies R&D. Eshed is in charge of IDE new products development and has several water treatment patents. Previously, he was an R&D manager at Emefcy (now Fluence), a startup that develops membrane-aerated biofilm reactors and microbial fuel cells.
About the company
IDE Technologies specializes in the development, engineering, construction and operation of desalination and industrial water treatment plants. They provide small to large cost-effective desalination solutions and have an especially well-proven track record in large-scale membrane and thermal desalination, including some of the largest plants worldwide. IDE has proven experience in providing plants that deliver reliable, sustainable and economical solutions across industries.