Flocculation properties of xanthan produced by Xanthomonas campestris

Microbial flocculation by Bacillus mucilaginosus: Applications and mechanisms

Microbiological flocculation in wastewater by a strain of Bacillus mucilaginosus was examined and the flocculation mechanism was investigated using Coomassie brilliant blue reaction, Anthrone reaction, thin-layer chromatography (TLC), scanning electronic microscope, and infrared spectroscopy. The GY03 strain, isolated from farmland soil, was identified as B. mucilaginosus by its morphology and 16S rDNA sequence. Cultivated in a nitrogen-free medium, the flocculation material (bacterium-mineral complex) was used to treat domestic, brewage, and pharmaceutical wastewater. On the basis of one-way experimental results, orthogonal experiments were carried out and the optimum processing conditions of the microbial flocculants were obtained. In the optimal conditions, the maximal removal ratio of COD in domestic, brewage, and pharmaceutical wastewater reached 74.6%, 70.5%, and 66.2%, respectively; the maximal removal ratio of BOD was 42.3%, 77.4%, and 41.7%, respectively; and the maximal removal of SS amounted 93.3%, 93.6%, and 88.4%, respectively. The treatment to kaolin suspended liquid by the GY03 strain may act as a model of studying microbial flocculation mechanisms in which bridging and charge neutralization hypothesis were proposed as the critical reasons based upon the experimental observations.

Characterization of a bioflocculant produced by Citrobacter sp. TKF04 from acetic and propionic acids

A bacterial strain, TKF04, capable of producing a bioflocculant from acetic and/or propionic acids was isolated from a biofilm formed in inside a kitchen drain. It was identified as a Citrobacter based on its morphological and physiological characteristics and the partial sequences of its 16S rRNA. TKF04 produced the bioflocculant during the logarithmic phase of growth, and the optimum temperature and pH for the bioflocculant production were 30 degrees C and 7.2-10.0, respectively. It could utilize some organic acids and sugars for its growth as the sole carbon sources when yeast extract was supplemented; however, only acetate and propionate were found to be good substrates for the bioflocculant production. The crude bioflocculant could be recovered from the supernatant of the culture broth by ethanol precipitation and dialysis against deionized water. It was found to be effective for flocculation of a kaolin suspension, when added at a final concentration of 1-10 mg/l, over a wide range of pHs (2-8) and temperatures (approximately 3-95 degrees C), while the co-presence of cations (Na+, K+, Ca2+, Mg2+, Fe2+, Al3+ or Fe3+) did not enhance the flocculating activity. It could efficiently flocculate a variety of inorganic and organic suspended particles, including kaolin, diatomite, bentonite, activated carbon, soil and activated sludge. It contained glucosamine as the major component, and the molecular weight was estimated to be between 232 and 440 kDa by gel filtration. The observation that the flocculating activity was completely lost following chitinase treatment and its analysis with a Fourier transform infrared spectrometer suggested that the bioflocculant is a biopolymer structurally-similar to chitin or chitosan.