Even minor alterations in the surfactants
Even minor alterations in the surfactants structure could have consequences on their physico-chemical characteristics; mono-RLs have less solubility, stronger surfaces sorb, and stronger cationic metals binding than homologue di-RLs (Zhang et al., 1997).
The HPLC separation of RLs structure is based on their polarity. Purified biosurfactant that produced from the different diesel sources, in the current study, was eluted using HPLC. HPLC was recommended as an excellent tool for rhamnolipids separation (Aguilar, 2004). RLs could also be detected with various tools; the UV absorbance and chromatography on a C-18 column were applied for detecting the structure of crude RLs, dissolved in 30% methanol (Gueldner et al., 2003), whereas Romero et al. (2007) could analyze the RLs using TLC method than by analytical C-18 column in the RP-HPLC.
Data obtained from MALDI-TOF-MS analysis of produced RLs, from biodiesel S, showed well-resolved peaks groups at m/z values of 527.281, 673.290, 761.310 and 717.269. The mass peaks at 527.281, 673.290 and 717.269 indicated structural homogenous RLs (Rha C10-C10), while structural RLs in a mass peak at 673.290 and 717.269 m/z could be attributed to non-homogenous RLs (Rha C10-C12). In addition, the mass peaks at m/z 717.269 indicated rhamnolipids with a mixture of structural analogs such as (Rha C14-C16) and the unique and new structure homogenous rhamnolipids Rha C16-C16. While the RLs (Rha C12-C14) was detected at 673.290. Mass spectrometry confirmed isomers of rhamnolipids in purified fractions containing a β-hydroxy fatty Irinotecan with Rha-Rha-C12-C12 and Rha-Rha-C12-C14 at the same peak 761.310.
Conclusions Rhamnolipid production by Burkholderia sp. C3 could be successfully achieved from basal minimal medium supplemented with hydrocarbons raw materials, e.g. petro-diesel, biodiesel S and BP diesel B20. The supplementation with diesel and biodiesel greatly enhanced RLs production. The specific analysis of produced RLs indicated their containments of different rhamnolipidic congeners’ mixture (mono-rhamno-mono-lipidic, mono-rhamno-di-lipidic and di-rhamno-di-lipidic). Burkholderia sp. C3 could be promisingly recommended for the biodegradation of hydrocarbon wastes for the production of the valuable RL mixtures.
Introduction Most of agricultural countries produce large amount of rice, as a result, large amount of rice husk is disposed to the environment as waste. World rice production is 637 million tons in 2006 , 704.4 million tons in 2010  749.8 million tons in 2015  and expected to increase in future. By weight, 10% of the rice grain is husk , which are accumulated near-by rice-mills creating environmental issues. In most of agricultural areas, rice husk is open dumped, while in a few of industrial areas, rice husk is used as a fuel. For example, in Sri Lanka, the handmade brick producers use rice husk to fire clay bricks. In Nigeria, rice husk is used to produce energy for rice drying oven and the resulting RHA is rich in silica . In Malaysia, rice husk is used for steam boilers, where rice husk has undergone self-burning process at maximum of 1000 °C . The use of rice husk on energy production is a one of the sustainable energy practices, however, the RHA a by-product from burning as a fuel has not been effectively utilised. In previous studies, attempts have been given to investigate possible ways of making waste rice husk ash for bricks manufacturing. Sultana et al.  produced rice husk ash (burning 750 °C for 2 h in furnaces) and used for test specimens. The specimens were fired from 800 °C to 1100 °C temperature, in an electric furnace and tested for mechanical strength. Increasing percentage of RHA did not improve the compressive strength. No improvement of strength properties was observed, probably, because the rice husk ash used in the study was in black colour, mostly consisting with unburnt carbon; available SiO2 was found to be 74.2%.