Agricultural nutrient surpluses as potential input sources to grow third generation biomass (microalgae): A review

Biofuel consumption is increasing and in order to meet EU targets, alternatives to first and second generation biofuels are being examined. The use of micro-algal biomass in the production of biofuel is an area of research which has received attention in recent years. Traditionally, microalgae are commercially grown using synthetic fertilisers, the price of which is linked with rising oil prices. An alternative to the use of inorganic fertiliser is to use surplus agricultural manures in their raw state, bi-products of anaerobic digestion, or runoff and artificial drainage waters, all of which have variable nutrient contents within and across source types. Many studies have shown that manures containing a high nutrient content e.g. pig and poultry manures, or bi-products from anaerobic digestion, are potentially viable sources of nutrients to grow algae. Feasibility issues prevail such as variable nutrient contents amongst and across source types, transparency issues and early and sustained nutrient losses during the storage phase. Agitation and efficient nutrient testing before use are important. In Ireland, pig and poultry manures, dairy dirty water, artificial drainage or runoff waters where coupled with agitation during storage to prevent P precipitation and a CO2 source, all have potential to be used in the future.