Bioremediation of Domestic Wastewater and Production of Bioproducts from Microalgae Using Waste Stabilization Ponds

Asif Rahman; Joshua T Ellis; Charles D. Miller

doi:10.4172/2155-6199.1000e113

ISSN: 2155-6199

Journal of Bioremediation & Biodegradation

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Bioremediation of Domestic Wastewater and Production of Bioproducts from Microalgae Using Waste Stabilization Ponds

Asif Rahman, Joshua T Ellis and Charles D. Miller^*
Department of Biological Engineering, Utah State University, USA
Corresponding Author :	Charles D Miller Department of Biological Engineering Utah State University, 4105 Old Main Hill Logan, UT 84322-4105, USA Tel: 435- 797-2593 Fax: 435-797-1248 E-mail: Charles.miller@usu.edu
Received May 22, 2012; Accepted May 24, 2012; Published May 26, 2012
Citation: Rahman A, Ellis JT, Miller CD (2012) Bioremediation of Domestic Wastewater and Production of Bioproducts from Microalgae Using Waste Stabilization Ponds. J Bioremed Biodeg 3:e113. doi: 10.4172/2155-6199.1000e113
Copyright: © 2012 Rahman A, et al. This is an open-a ccess article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
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Domestic wastewater treatment and remediation is an expensive process due to significant time and planning needed for successful treatment. Modern wastewater treatment plants are highly mechanized and expensive to build and maintain. In less economically developed parts of the world alternative methods of wastewater treatment are required. Waste stabilization ponds, or lagoons, provide an ideal solution for wastewater treatment in developing countries and rural areas. These ponds facilitate the oxidation of organic matter through complex symbiotic relationships between bacterial consortiums and assimiliation of wastewater nutrients by photoautorophic microalgae [1]. In the United States more than 7,000 lagoon systems are used to treat domestic wastewater (U.S. EPA, 2002, Report No. EPA 832-F02- 014) [2]. Most domestic wastewater is considered weak or medium in strength with nitrogen levels between 20-40 mg/L and phosphorus levels between 4-8 mg/L [3]. These concentrations of nitrogen and phosphorus are undesirable as they can lead to considerable pollution and eutrophication of downstream waterways [1].

Open pond lagoon systems have many advantages over mechanicalized methods and are able to remove nitrogen and phosphorus to required EPA levels. Interestingly, nitrogen and phosphorus found in weak domestic wastewater are at an ideal level for microalgae cultivation and growth. Microalgae can grow to high densities by assimilating nitrogen and phosphorus, thus removing these inorganic nutrients from the wastewater. In addition, open pond lagoon systems also allow ideal mixing and adequate light exposure for microalgae growth. Microalgae play a vital role in recycling carbon in the biosphere by converting carbon dioxide into organic compounds through photosynthesis [2], while also producing oxygen via the oxidation of water. Metal compounds such as Cr, Cu, Pb, Cd, Mn, As, Fe, Ni, Hg, and Zn can also be bioremediated by microalgae. Microalgae such as Chlorella and Scenedesmus have shown tolerance and bioremediation capabilities to certain heavy metals [4]. Additionally, microalgae have been used for the bioremediation of textile dyes in wastewater from industrial textile processes. These bioremediation capabilities of microalgae are useful for environmental sustainability and algal biomass can be used as feedstock for the production of high energy compounds [5,6].

Algal biomass can be processed chemically and biologically to produce high value products such as bioacetone, biobutanol, biodiesel, and biomethane. Microalgae as feedstocks provide high densities of carbohydrates (typically comprising glucose units), triacylglycerides and free fatty acids that can be used to produce biofuels and biodiesel. It has been demonstrated that microalgae can be a promising feedstock and will play a vital role in the future production of clean and renewable energy [1,5].

The disadvantages to an open pond lagoon system are that the microalgae nutrient requirement may not match the stoichiometric ratio of the microalgae biomass, where the optimum nitrogen to phosphorus ratio for microalgae growth is 16:1. Thus, photoautotrophic bioremediation of inorganic compounds might not be carried out to adequate levels. To meet nutrient requirements for microalgae growth, additional chemicals (usually nitrogen rich sources) may need to be supplemented to the wastewater, which is undesirable.

Microalgae grown in open pond lagoon systems are at low densities and specialized harvesting technologies need to be implemented in order obtain suitable biomass yields. Harvesting techniques such as a Rotating Algal Biofilm Reactor (RABR) [2], filtration, sedimentation, and dissolved air flotation (DAF) units can be employed to harvest the microalgae from open pond lagoon systems. There are advantages and disadvantages to each method, but the cost of harvesting is currently high and more efficient technologies need to be created [1].

To summarize, waste stabilization ponds provide an active bioremediation system to clean domestic wastewater, and they can also produce microalgal feedstocks for the production of high value bioproducts. Interest in the use of microalgae will continue to grow as rural cities and developing countries look for sustainable and affordable ways to clean domestic wastewater. Processes where wastewater is bioremediated through heterotrophic and photoautotrophic organisms, and in turn high value bioproducts are generated have great potential to stimulate regional and local economic development [1].