Abstract
A collection of lipase-producing microorganisms was isolated from sludge derived from an urban wastewater treatment plant. The microorganisms with the highest levels of lipase activity were selected in order to use triglycerides present in the sludge effectively and were then transformed with pdc:adhB genes for the production of ethanol. The transgenic strains showed high growth rates in diluted sludge and produced lipase protein in order to utilize fat present in the sludge, which provides an abundant source of carbon. Using sludge derived from treated wastewater as nutrient source, ethanol was produced by certain transgenic species belonging to the genera Proteus. Different forms of sludge were tested for maximal ethanol production, with dehydrated sludge being found to produce the best performance.
Highlights
Wastewater treatment generates large quantities of sewage sludge, which is estimated to account for ∼1–2% of the total volume of treated wastewater
The term microdiesel was coined by Kalscheuer et al (2006) to describe diesel produced in the form of fatty acid methyl esters (FAMEs) and fatty acid ethyl esters (FAEEs) by Escherichia coli from glucose and oleic acid
As fat is regarded as the most energetic fraction of wastewater sludge for biofuel production, we decided to isolate lipase-producing microorganisms from four different types of sludge produced by the wastewater treatment plant in Granada (Spain) depending on their capacity to use fat as carbon source
Summary
Wastewater treatment generates large quantities of sewage sludge, which is estimated to account for ∼1–2% of the total volume of treated wastewater. Sludge composition depends on the type of wastewater treatment used, organic materials generally account for up to 50% of the total, of which 17–30% of dry weight is in the form of fat (Martinez-Toledo et al, 2012) This fat is produced by direct absorption of lipids present in the wastewater by sludge particles and phospholipids released by the cell membranes of microbiota (mainly bacteria); in addition, fat comes from metabolites and cell lysis by-products (Jarde et al, 2005). The term microdiesel was coined by Kalscheuer et al (2006) to describe diesel produced in the form of fatty acid methyl esters (FAMEs) and fatty acid ethyl esters (FAEEs) by Escherichia coli from glucose and oleic acid This is caused by the insertion of genes coding for ethanolic enzymes pyruvate decarboxylase (Pdc) and alcohol dehydrogenase (AdhB) from Zymomonas mobilis, as well as unspecific acyltransferase WS/DGAT from Acinetobacter baylyi strain ADP1. We propose a new way of using this type of residue to reduce the negative impact of sludge derived from treated wastewater
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