SCIENCE, RESEARCH & TECHNOLOGY Algae: From Resource Depletion to Resource Recovery By Barry Liner, Ph.D., P.E., and Noah Mundt ROCKY MOUNTAIN WATER MAY 2017 | 33 GENERALLY, WHEN WE THINK of algae in the context of water quality, we think of how nutrients in agricultural runoff, municipal waste-water effluent, and urban stormwater provide the conditions for algae blooms in water bodies. These algal blooms lead to eutrophication and dead zones, causing negative water quality and eco- nomic effects. The same biological processes that lead to water quality problems from nutri-ent pollution can be harnessed to treat, and recover, nitrogen and phosphorus through production of algae biomass for wastewater bioremediation. Algae can be cultivated and harvested to create biomass that can be transformed into biofuels and bioproducts. As the wastewater sector seeks to manage high energy costs while recov-ering resources to meet tighter nutrient limits, the algae bioproducts and biofu-els industry is searching for productive feedstock. The potential is being recog-nized, as demonstrated by awarding of the 2016 Paul L. Busch Award to Jeremy S. Guest, Assistant Professor in the Department of Civil & Environmental Engineering at the University of Illinois at Urbana–Champaign. This $100,000 award recognizes Guest’s work with algae treatment and resource recovery. In October 2016, WEF (Alexandria, Vir-ginia) and the Algae Biomass Organiza-tion (ABO; Preston, Minnesota) hosted the forum Algae in Wastewater Treat-ment at the Algae Biomass Summit. The forum brought together algae technolo-gy developers, leading design and engi-neering firms, municipalities, regulators, and other stakeholders to review the state of algae-based tertiary wastewater treatment systems. Forum participants also discussed opportunities and chal-lenges in deploying such systems in the context of an evolving economic, envi-ronmental and regulatory landscape. Types of algae Algae tolerate a wide range in environ-ments with respect to temperature, salinity, and water quality. The commu-nities of algae found in treatment and harvesting operations typically are mixed culture, combining both photosynthetic and heterotrophic types, as occurs in nature. Photosynthetic algae use nutri-ents from nitrogen and phosphorus in wastewater, capture carbon as carbon dioxide, use energy from sunlight, and produce oxygen as a waste product. Het-erotrophic algae use organic chemicals for carbon and energy. Blue-green algae are photosynthetic, but actually are bacteria (cyanobacteria) that contain phyocyanin, which give the blue-green color. Blue-green algae also produce microcystins, which are toxins that cause many of the negative effects of algae blooms in lakes. Other algae are eukaryotes, as opposed to bacteria, and are generally green, brown, and red. Common green algae strains are shown in Figure 1. Algae treatment The use of algae as wastewater treatment is common, as the biological processes take place in ponds and lagoons naturally. About half of the 16,000 regulated water resource recovery facilities (WRRFs) have ponds/lagoons. These features are preva-lent especially at smaller WRRFs (Bas-tian, 2016). Efforts now are focusing on how to use microalgae for wastewater treatment within conventional WRRFs. Similar to other biological wastewater treatment techniques, algae treatment can use suspended- or attached-growth methods. Suspended-growth ponds use paddles to keep microalgae suspended for sunlight, coupled with a shallow depth for light penetration. The layout of these ponds gives rise to the name raceways, as shown in Figure 2. Attached-growth techniques use a sub-stratum that rotates alternatively through wastewater (to provide nutrients) and atmosphere (to provide sunlight and carbon dioxide). Two common types of attached-growth algae treatment tech-nologies are rotating algae biofilm reac-tor and revolving algal biofilm (RAB). In pilot tests in Chicago, an RAB system has demonstrated the potential for recovering nutrients from wastewater. The RAB system is capable of produc-ing concentrated algae biomass (10 to 25 percent solids), which has value and can be used to produce a variety of products (Kumar, 2016). Figure 1. Green algae typically found in wastewater pond polycultures. CREDIT: LUNDQUIST ET AL, 2016.
RMW - May 2017
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