Wastewater, Algae, and the New Pathway to Resource Recovery

Rotating Algae Biofilm Reactor project

Once considered to be ordinary and mundane, wastewater treatment is becoming a recognized contributor to the green technology movement. It’s a rising star in the resource recovery world with the adoption of one key ingredient – algae. With the use of algae to treat wastewater, focus has shifted from simply removing constituents in wastewater toward the recovery of valuable products, such as nutrients and energy, through the processing of algae biomass.

In this way, algae systems can synchronously solve environmental and sanitary problems and provide economic benefit.

Algae Provides a New Path

A nationwide trend to reduce the allowable nutrient levels in wastewater treatment plant (WWTP) discharge is causing facility owners to consider new treatment options, such as algae. The nutrient loading allowed downstream is currently contingent upon the determined sensitivity of local water bodies.

Algae can play a crucial role in helping facilities reduce their total effluent nutrients, manage their sidestream treatment to meet stringent downstream requirements, and lower overall plant operating costs.

Once considered a nuisance for WWTPs, algae may now play a key role in nutrient management and resource recovery. There are many advantages to using algae for wastewater treatment.

Algae is readily available, and it is extremely adaptable and capable of significant nutrient uptake. As photosynthesis is key for microalgae cultivation, the system is especially ideal for high sunlight and high temperature regions, with little maintenance required. Algae use results in high quality treated water.

Major barriers to large scale use of algae in wastewater treatment include the need for large footprints and the high cost/energy associated with algae harvesting. However, a university/industry research partnership is drawing attention for its innovative approach to growing and harvesting the algae in a wastewater application with a smaller footprint.

WesTech at the Forefront

WesTech Engineering fabricated a pilot unit for algae use in wastewater treatment that is based on a process design developed by Utah State University. The pilot demonstrates the effectiveness of algae-based resource recovery on a larger scale at an operating wastewater treatment and resource recovery facility.

The central piece to the project is the innovative RABR – Rotating Algae Biofilm Reactor – a rotating drum with attached discs that facilitate robust algae biofilm growth on the surfaces. The algae is harvested when it is scraped off the discs.

RABR Rotating Algae Biofilm Reactor bench scale
Utah State University’s RABR lab testing.

At the nationally-recognized Algae Biomass Summit in 2017, attendees can tour a commercial installation of the WesTech RABR at the Central Valley Water Reclamation Facility in Salt Lake City, where it will be demonstrating ammonia and phosphorus removal from concentrated digestate sidestreams.

The site, the largest municipal wastewater reclamation facility in Utah, showcases the algal biofilm technology of the RABR and byproduct. The valuable products from the algae process include enhanced biomethane generation for heat and power, and microalgae additions that can enhance the current composting operations at the facility.

WesTech expertise at the conference includes engineer Kirsten Sims’ presentation, titled Striving to Close the Cycle: Role of Algae in the Fossil Fuel and Mining Industry, based on WesTech-sponsored research projects taking place at Utah State University.

The topic of the session is expanding the use of algae in waste streams beyond municipal wastewater. In the fossil fuel and mining industries, algae can help decrease the footprint of operations and improve a site’s economics by utilizing the industry’s low value waste streams to cultivate and process algae.

RABR Is a Proven Technology

Work with the RABR has found the following advantages over conventional nutrient removal technologies:

  1. Increases microalgal yield: areal (footprint) microalgal productivities as high as 40 g m-2 d-1 have been attained, which is twice what is observed for raceway ponds (20 g m-2 d-1)
  2. Harvesting using simple mechanical scraping rather than centrifugation
  3. Reduces atmospheric CO2: 1.3 kg CO2 sequestered per kg microalgae
  4. Does not add chemicals (flocculants or coagulants) for harvesting
  5. Treats turbid and/or highly-colored wastewater (fossil fuel, produced water, dairy, and swine)
  6. Recycles nutrients, N and P, that go into the biomass that can then be used to produce bioproducts (bioplastics, fertilizer, biofuel as bio-oil, and methane)

Reusing leftover N and P is a key value in the algae process. Biofuel has been a marketable byproduct of the recovery of algae from wastewater for some time. It reduces the electrical energy demands from aeration at the wastewater treatment plant, which can be more than 50 percent of the total energy used at the plant.

Another byproduct, biopolymers, can be converted into renewable packaging materials. In addition, the resulting high N and P algae biomass contributes to a high-value animal feed and fertilizer byproduct.

The RABR capitalizes on the benefits of biofilm technology – including high biomass efficiency, reduced light requirements, and high algae biomass yields – to comprehensively treat wastewater and produce valuable byproducts. Further, the RABR marks a crucial advancement in algae harvesting ease and cost. Instead of having to separate suspended algae particles from water, dense algae biomass can simply be “scraped” or pulled off a surface.

The rotational speed of the RABR allows the biomass to undergo a degree of drying as it is rotated out of the water, resulting in reduced water handling, separation, and drying requirements.

A RABR pilot project, a collaboration between Utah State University and WesTech, was successful for seven years. It was located on an open-pond lagoon system that treats municipal wastewater for Logan, Utah. Operating between April and October, the system had enough nutrients to produce 27.2 metric tons dry weight of algae per day. The algae growth was harvested daily for university research.

Research studies at Utah State demonstrate that algal biofilms grown using the RABR are very effective for waters with turbidity, color, and high salinity, said Professor Ronald Sims, Ph.D., Co-Director of the Sustainable Waste-to-Bioproducts Engineering Center at Utah State University.

The opportunities for commercial installation are currently being evaluated for municipal water resource recovery facilities, dairy farms, oil and gas extraction, mining, and petroleum refining industries. The partnership with WesTech is critical to the scale up of the technology.

Algae’s Emergence in Resource Recovery Opportunities

Wastewater has historically been expensive to treat and a threat to human health. But in the last few years, it has become apparent that wastewater can be a resource to embrace, providing energy and a source of water for reuse.

Global population growth, drought, and increasing water demands make it vital to remove the concept of waste in wastewater. It’s time to look at the water from the 15,000 municipal wastewater facilities nationwide as a precious resource to recover, not waste, and to consider engaging algae systems to make that happen. Algae technology is emerging as the next horizon for wastewater treatment.

Related Articles:

Converting Wastewater Algae Into High-Value Resources

Trends in the Design of Wastewater Collection and Treatment Systems

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