Efficient nutrient removal from swine manure in a tubular biofilm photo-bioreactor using algae-bacteria consortia C. Gonza ´ lez, J. Marciniak, S. Villaverde, C. Leo ´ n, P. A. Garcı ´a and R. Mun ˜ oz ABSTRACT C. Gonza ´ lez J. Marciniak S. Villaverde C. Leo ´n P. A. Garcı ´a R. Mun ˜ oz (correspoding author) Department of Chemical Engineering and Environmental Technology, University of Valladolid, Paseo Prado de la Magdalena s/n, 47011 Valladolid, Spain E-mail: mutora@iq.uva.es Concentrated animals feeding operations (CAFOs) often pose a negative environmental impact due to the uncontrolled spreading of manure into soils that ends up in the release of organic matter and nutrients into water bodies. Conventional aerobic methods treating CAFOs wastewater require intensive oxygenation, which significantly increases the operational costs. The alternative proposed in this research is the application of micro-algae based systems by taking advantage of the cost-effective in situ oxygenation via photosynthesis. A 4.9 L enclosed tubular biofilm photo-bioreactor was inoculated with an algal–bacterial consortium formed by the micro-algae Chlorella sorokiniana and a mixed bacterial culture from an activated sludge process. C. sorokiniana delivers the O 2 necessary to accomplish both organic matter and ammoniun oxidation. The reactor was fed with diluted swine wastewater containing 180, 15 and 2,000 mg/L of NH þ 4 ZN, soluble P and total COD, respectively. The photo-bioreactor exhibited good and sustained nutrient removal efficiencies (up to 99% and 86% for NH þ 4 and PO 32 4 , respectively) while total COD was removed up to 75% when the biofilm was properly established. Liquid superficial velocities up to 0.4 m/s (achieved by culture broth recirculation) hindered the formation of a stable biofilm, while operation at velocities lower than 0.1 m/s supported stable process performance. The high shear stress imposed by the centrifugal recirculation pump disintegrated the large aggregates detached from the biofilm, which resulted in a poor settling performance and therefore poor COD removal efficiencies. Enclosed biofilm photo-bioreactors therefore offer a potentially more economical alternative to conventional tertiary treatments process. Key words | algal – bacterial consortia, biofilm, nutrient removal, photo-bioreactor, swine manure INTRODUCTION The treatment of livestock effluents is receiving increasing attention in Europe as nutrients discharge into water bodies is causing a severe eutrophication of aquatic ecosystems. The progressive application of European Directives is limiting the discharge of total nitrogen to 15 mg N/L and phosphorus to 2 mg P/L (Council Directive 91/271/EEC 1991) and this is urging industrial sectors to follow Integrated Pollution Prevention and Control practices (Council Directive 96/61/EC 1996) by integrating Best Available Techniques (BAT) in both production and wastewater treatment lines. Early studies demonstrated that the application of micro-algae systems for the treatment of livestock effluents offers the possibility of in situ oxygen production via photosynthesis and nutrients removal, thus reducing the number of treatment steps (Garrett & Allen 1976; Fallow- field & Garrett 1985). Algal–bacterial consortia are able to establish a cycle of O 2 production and usage thereof, the so-called photosynthetic oxygenation. Thus, when irra- diated with light, micro-algae produce the O 2 needed by aerobic bacteria to mineralise the organic pollutants and doi: 10.2166/wst.2008.655 95 Q IWA Publishing 2008 Water Science & Technology—WST | 58.1 | 2008 Downloaded from https://iwaponline.com/wst/article-pdf/58/1/95/437184/95.pdf by guest on 17 June 2020