Algal nutrient recycle Catalytic liquefaction of algal biomass yields an organic phase which serves as the bio crude This phase is rich in carbon and hydrogen All the inorganic nutrients from the biomass get accumulated in the aqueous phase 20 These nutrients can be recycled back to the system making it a rich medium for algal growth Cultivation of microalgae Chlorella vulgaris Scenedesmus dimorphus and cyanobacteria Spirulina Platensis was attempted by Biller et al 2012 in process water obtained after hydrothermal liquefaction The resultant growth obtained after 400 times dilution of process water was comparable to control growth medium making it possible to develop a sustainable closed loop process for growing algal biomass and obtaining oil from the process 40 c Media replacement by waste streams These are commonly the effluent streams from domestic and industrial outlets These nutrient sources completely replace the algae growth medium eliminating the dependence of fertilizers as well as water fertilizer replacement by waste streams like swine feedlot dairy effluent and tannery effluent which contain high concentration of organic carbon and nitrogen have been previously attempted for the cultivation of microalgae 41 43
Abou Shanab et al 2003 have screened multiple organisms in piggery wastewater and reported an average biomass production of 0 4 g L in the effluent 43 Growth of Chlorella pyrenoidosa in dairy effluent resulted in 5 times increase in the biodiesel obtained as compared to control growth medium 41 Ruiz Marin et al 2010 observed a specific growth rate of 0 285 day 1 with 100 nitrogen and 83 phosphate removal in 48h with Scenedesmus obliquus using urban wastewater 44 Utilization of waste streams a critical need Current liquid effluent statistics around the world shows production of about 120L of sewage water per capita per day 45 Exponential rise in the number of cities around the world and the fast urbanizing lifestyles of the people makes this source of water a theoretically never ending resource to be utilized for as a source of fertilizer Metropolitan cities like Mumbai alone generate 25MLD sewage water every day 46 Comparison of this municipal liquid effluent with other types of effluents shows that India produces approximately 72 times more municipal liquid wastes MLW than the other types of effluents
The statistics of different types of effluent generation are shown in table 1 2 The figures shows the vital need to utilize this source of water for fertilizers Table 1 2 Abundance of different effluent sources in India Types of effluent Load of nutrients Indian production estimate MLD Reference Total N ppm Total P ppm Municipal sewage 85 5 40 000 Current study 47 Dairy effluent 185 30 550 41 48 Swine feedlot 1500 150 Data not available 49 Paper mill 11 0 6 2000 50 Tannery 270 20 50 51 52 Textile 90 20 300 53 Alcohol distillery 20 400 Current study 54 The MLW discharges contain organic and inorganic matter which can be potential source of nutrients for algal growth Algae utilize the nutrients from these water sources treating the water in the process 37 Major fraction of this humongous source of water is discharged into water bodies like rivers and oceans leading to the loss this potential resource and tremendous pollution of these water bodies 55 Recycling of this water for algal growth could reduce the dependence on freshwater as well as synthetic fertilizers while simultaneously alleviating the pollution issues MLW utilization for algal growth Many countries and industries around the world are taking serious cognizance to the problems encountered in sewage water treatment and putting positive expectations for sewage treatment using algae Though several plants are operational for STP using algae the biofuel aspect of the STPs is currently in very nascent stage 56 One positive step ahead in use of algae for STP is the sewage treatment plant in Chiclana de la Frontera in Spain This facility has HRAP of the area 200m2 and capable of treating the sewage water from the entire city and producing fuel for powering vehicles 57
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