Usually algae is sensitive for removal of hazardous pollutants hence it is important to select fast growing and high resistant strains of algae Muñoz and Guieysse 2006 The biological treatment of wastewater with algae to remove nutrients such as nitrogen and phosphorus and to provide oxygen for aerobic bacteria was proposed over 50 years ago by Oswald and Gotaas 1957 Algae culture offers an elegant solution to tertiary treatments due to their ability to use inorganic nitrogen Oswald 1988b c Richmond 1986 In reported papers Lau et al 1996 studied the ability of Chlorella vulgaris in the removal of nutrients They found that the results indicated in a nutrient removal efficiency of 86 inorganic N In earlier study Colak and Kaya 1988 reported an elimination of nitrogen 50 2 in industrial wastewater treatment Mohamed 1994 pointed out that Scenedesmus sp is very common in all kinds of freshwater bodies which play an important role as primary producers and contributes to the purification of eutrophic waters The author indicated that the presence or absence of certain species of Scenedesmus can be used for the evaluation of water quality Abdel Raouf et al 2012 Palmer 1974 surveyed microalgal genera from a wide distribution of waste stabilization ponds In order of abundance and frequency of occurrence the algae found were Chlorella Ankistrodesmus Scenedesmus Euglena Chlamydomonas Oscillatoria Micractinium and Golenkinia
Pandi et al 2009 Lima et al 2004 reported p nitrophenol removal of 50mgl_1 d_1 by a consortium of Chlorella vulgaris and Chlorella pyrenoidosa under non optimized conditions which was close to the 100mgl_1 d_1 achieved with Pseudomonas sp by Kulkarni and Chaudhari 2006 However heterotrophic microalgae can be out competed by heterotrophic bacteria in continuous open systems because microalgae often exhibit lower specific growth rates than bacteria Semple et al 1999 ii Factors affecting algae growth Algal growth and efficiency is not only influenced by availability of nutrients but also due to other physical parameters such as pH light intensity temperature dissolved oxygen DO and some biotic factors Abdel Raouf et al 2012 The various physical parameters affecting the algae efficiency in nutrient removal from wastewater are defined below pH CO2 uptake by microalgae increases the pH in the range of 10 11 Munoz Raul and Benoit Guieysse 2003 The pH also influences nitrogen removal via NH3 volatilization Gordon and Seckbach 2012 Fortunately it is easy to maintain the level of pH in biological treatment systems Temperature
Other biotic factors Infections by parasitic fungi like Chytridium sp or the development of food chains in the photo bioreactor can cause unexpected process failure Abeliovich and Dikbuck 1977 Fortunately these potential problems can easily be avoided by daily operating the process at low O2 levels for a short period of time 1 h in order to suppress the growth of higher aerobic organisms Bux 2013 iii Algae based wastewater treatment Algae can be used in wastewater treatment but care should be taken to ensure that the algae developed in sewage and manure are used in which mixed culture of bacteria and algae are active La Noue and Pauw 1988 Figure 2 The role of algae in purification of wastewater by biological recycling La Noue and Pauw 1988 Algal ponds have been utilized for several decades for the treatment of municipal and other wastewaters with the algae mainly providing dissolved oxygen for bacterial decomposition of the organic wastes Algae and bacteria exist in a classic symbiotic relationship Bacteria metabolize organic waste for growth and energy producing new bacterial biomass and releasing carbon dioxide and inorganic nutrients Algae then utilize the CO2 through photosynthesis assimilating the nutrients into algal biomass and releasing O2 concentration in turn supports the aerobic bacterial activity Use of Chlorella seems to be one of the feasible methods to reduce the amount of nitrogen and phosphorus entering the nearby coastal water thus preventing the eutrophication problem which results in depletion of oxygen in water followed by fish death Oilgae 2010
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