Microbial Lipid production from potato processing waste water and simultaneous nutrient removal using oleaginous fungi

Abstract

Microbial lipids can be used as a feedstock for biodiesel production, and use of biowastes as the substrate for microbial lipid production can reduce its production cost. The aims of this research include: (i) isolation and identification of local oleaginous species from Irish soils; (ii) feasibility of oleaginous fungi for microbial lipid production from potato processing wastewater, in addition with nutrient removals from wastewater; and (iii) microbial lipid production using pure carbon sources for comparison. Local oleaginous fungi were isolated from Irish soils with the aim of producing microbial lipids with low cost starch substrates. 30 cultures were oleaginous with glucose as the carbon substrate; the maximum lipid content in biomass (44.3%) was observed in the isolate I16-3. When the isolates were grown on starch medium, 19 cultures among 30 cultures were able to accumulate lipids. The maximum lipid content (39%) was observed in I16-3. The isolate was identified as Aspergillus flavus. This study also explored the amylase secretion capability of isolated cultures and the maximum yield (34 IU/mL) was observed in the isolate I16-3. Identification of isolated fungi with molecular techniques revealed a number of non mucaraceous fungi including Aspergillus sp., Penicillum sp., Tricoderma sp., and Aceremonium sp. along with mucaraceous fungi zygomycetes sp., Mortierella sp. and Umbliopsis sp. These non mucaraceous oleaginous fungi would be of future interest in generation of the second generation biodiesel. Potential use of potato processing wastewater for microbial lipid production was studied under various conditions. Using Aspergillus oryzae, diluting the wastewater by adding 25% of tap water achieved the maximum lipid yield of 3.5 g/L. It was observed that phosphate limitation may be the mechanism to stimulate microbial lipid production. At this dilution ratio, total soluble starch was utilized by 99% and the fungi secreted amylase of 53.5 IU/mL. Nutrient removal from potato processing wastewater was examined; at this dilution ratio, removals of chemical oxygen demand, total soluble nitrogen, total soluble phosphorus, ammonium nitrogen, orthophosphate and sulphate of 91%, 98%, 97%, 100%, 100% and 30% were achieved. Lipids of A.oryzae contained major fatty acids like palmitic acid (12.6%), palmitolic acid (4.3%), stearic acid (14.5%), oleic acid (22.5%), linolenic acid (5.5%), and linoleic acid (6.5%). When external nutrients were added to raw potato processing wastewater for lipids and gamma - linolenic acid (GLA) production using two oleaginous fungi, Aspergillus flavus I16-3 and Mucor rouxii, the lipid and GLA yields were enhanced; 3.5 and 4.2 g/L of lipids, and 100 and 140 mg/L of GLA were produced by Aspergillus flavus I16-3 and Mucor rouxii, respectively. In addition, the wastewater was efficiently treated, when external nutrients were added to raw wastewater, with total soluble chemical oxygen demand removals of 60% and 90%, total soluble nitrogen removals of 100% and 98%, total soluble phosphorus removals of 92% and 81% by Aspergillus oryzae I16-3 and Mucor rouxii, respectively.

In the study with pure glucose, starch and cellulose as the carbon substrate, Mucor rouxii was cultured at an initial C/N ratio of 60. The highest lipids yield of 4.9 g/L was found with glucose as the carbon substrate. The lipid content in biomass for starch was less than for glucose. The maximum lipid yield was increased when the starch concentration was increased to 60 g/L and 5.8 g/L of lipids was produced. Cellulose supported M.rouxii biomass growth but did not support the lipid production. Significant quantities of a-Amylase (0.5 and 1.2 IU/mL) and cellulase (0.19 IU/mL) were produced by M.rouxii to hydrolyze the complex carbon sources. Microbial lipids comprised oleic, palmitic, stearic, linolenic and GLA fatty acids. On the whole, this research has found non mucaraceous oleaginous fungi for low cost lipid production on starchy wastes. Isolated indigenous fungi have been proven to be efficient in microbial lipid production from potato processing wastewater. Our research also demonstrates the potential use of potato processing wastewater for microbial lipid production with simultaneous wastewater treatment.