Advanced bioreactors target operating costs

Paul Boughton

The next generation of bioreactors will offer improved performance for wastewater treatment. Eugene McCarthy reports.

While bioreactor treatment of wastewater is already a cost-effective solution for many process companies, the drive is now on to improve the technology, particularly in terms of process efficiency.

The latest development came in March when Envirogen Technologies and Inotec announced that they had entered into a joint technology development agreement to advance the performance of bioreactors in groundwater, mining water and a broad range of wastewater treatment applications.

The initial focus of the development activity will be on reducing the amount of substrate (electron donor) required to successfully operate anoxic bioreactors as well as on minimising the amount of solids generated during operation.

Bioreactor treatment operating costs are among the lowest of any type of water treatment technology on the market today - with electron donor and solids handling representing a significant portion of long-term project costs. Initial targets for technology development will be removal of metals and inorganics such as perchlorate, nitrate, sulphate, selenium, arsenic and mercury.

According to Dave Enegess, senior vice president for Envirogen, the potential synergies for Envirogen's fluidised bed reactor (FBR) and Inotec's electro-biochemical reactor (EBR) technologies can be a boon for companies in need of high-performance, lower cost water treatment. "We're excited at the opportunity to work with Inotec to advance the state-of-the-art of bioreactor technology. Jack Adams and his team have been at the forefront of bioreactor technology development for decades. The innovation in the EBR technology is apparent and addresses key industry concerns," he said.

"This agreement is another step in our drive to push bioreactor technology to meet new challenges for treatment efficiency and cost-effectiveness. The goal here is first to be able to develop better solutions tailored to groundwater and wastewater treatment applications in mining, power, chemical and refining facilities - and potentially to develop revolutionary, next-step bioreactor technology," he continued.

Envirogen's FBR is a fixed-film bioreactor in which biological media is suspended, or fluidised, within the reactor vessel by the upward flow of water through the system. High concentrations of biomass, its plug-flow characteristics and tall beds minimise bioreactor footprint and shorten retention times. They offer steady-state performance, without the need for backwashing and are tolerant of high feed total dissolved and suspended solids and metals.

Inotec's EBR provides electrons to microbes in reactor environments using low DC voltage potential (1-3 volts) and mA current in configurations that provide an electron density gradient or a controlled electron density. The provided electrons result in increased microbial contaminant transformation kinetics, reduced retention times, and reductions in the amount of nutrients and chemicals required for contaminant removal.

Jack Adams, president of Inotec cited Envirogen's experience in deploying over 60 FBRs for groundwater and wastewater treatment as an indication of the company's leadership in the field. "The Envirogen team are pioneers in fluidised bed bioreactor technology for water treatment. Development of hybrid bioreactors, like an electro-biochemical fluidised bed reactor technology, holds considerable potential for more economical and more effective water treatment. We look forward to working with Dave Enegess and the Envirogen team to apply the synergistic benefits of our combined technologies and to continue advancing the science and performance of bioreactor technology."

Meanwhile Siemens continues its development of membrane bioreactor (MBR) systems.

"The need to recycle wastewater and stricter environmental regulations make an MBR system a viable solution for current and future wastewater treatment. We make MBRs for large municipal wastewater applications that can be fit into concrete tanks, package plants for smaller flows, new developments and hotels as well as a system developed for the petroleum industry to meet most refinery standards," says the company.

For example, Xpress MBR package plants are designed for applications from 25,000 gallons/day(gpd) to 100,000gpd and utilise the immersed MBR process - a novel wastewater treatment process designed by Siemens specifically for municipal and industrial applications, and land developers.

At the same time, integrating biological process with membrane separation technologies is a rapidly growing area. Here Siemens offers a hybrid group of technologies combined together in order to meet the requirements of specific user applications. For example a combination of the company's Envirex biological processes, MemPulse membrane technology (Fig.1) and SmartMBR Controls automation provides a reduction in energy, biosolids and footprint.

In addition, it is not only new developments that benefit from MBR technology - existing wastewater installations can, too. For example, an MBR, paired with an Envirex Orbal or vertical loop reactor (VLR) oxidation system and aerated anoxic process, is designed for operators seeking activated sludge, advanced secondary sludge treatment, simultaneous nitrification-denitrification, biological phosphorus removal or storm water treatment and reduced energy consumption. "Reengineering biological processes with a membrane bioreactor system unit can reduce footprint requirements and meet strict effluent regulations," says the company.

GE focuses on advanced primary treatment

LEAPprimary, from GE, is an advanced primary treatment system that combines separation, thickening and dewatering of primary solids in a single compact unit. The LEAPprimary system performs the same function as a primary clarifier and fine screen in a typical MBR plant. According to the company, the performance advantages of combining its LEAPprimary and LEAPmbr technologies include: a 25 per cent reduction in energy needed for biological treatment; 20-40 per cent cost savings on primary treatment equipment needed for an MBR; and requires as little as one tenth of the footprint as a conventional system.

Proof of the benefits of the system come from a wastewater treatment plant in Southern Ontario, Canada, that replaced its conventional 2mm fine screen as a primary treatment with LEAPprimary in 2013.

The LEAPprimary system proved to have a positive impact on the membrane performance by enhancing the removal of particulate material from the wastewater prior to the MBR. Trash content (material in the mixed liquor greater than 2mm in size) was 60mg/l prior to the installation of the LEAPprimary unit. One month after the fine screen was replaced with LEAPprimary the trash content reduced to near zero, which indicates that the material that could reduce ZeeWeed membrane life had been removed from the process.

Process testing was also performed to quantify the total suspended solids (TSS) and chemical oxygen demand (COD) removal of the LEAPprimary system. Total suspended solids and chemical oxygen demand removal were measured at 50 per cent and 25 per ead SO Piccent respectively. The impact of this was a reduction in the air demand for biological process aeration in the bioreactor.

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