Agro-industrial waste materials and wastewater as growth media for microbial bioflocculants production: A review

Abstract

Various microbial strains (bacteria, fungi, and microalgae) produced polymers variable in composition (protein, cellulose, polysaccharide, etc) with interesting flocculation properties such as the ability to remove large spectrum of pollutants (organic and inorganic materials, etc) from wastewater and the stability over a wide range of temperature, pHs and salt concentrations. These bioflocculants have been characterized and successfully tested in wastewater treatment and sludge dewatering. The production of microbial bioflocculants involves the culture step of the bioflocculant-producing microorganism in an appropriate medium, followed by polymer extraction. The production processing is mostly controlled by the microbial growth medium cost. Agro-industrial wastes including agricultural by-products (rice hull, rice stover potato by-products, peanut hull, corn cob, wheat bran, etc), sugar processing wastes and fermentation liquors contain nutrients such as nitrogen and carbon, which can sustain the microbial growth and bioflocculant production. Recently, the potential use of wastewater and sludge as growth media for various bioflocculant-producing microorganisms has been demonstrated. Interestingly, waste pre-treatments may be essential to enhance the microbial growth and the bioflocculant production. Bioflocculant properties (polymer yield, polymer composition, flocculating activity, etc) are controlled by the growth conditions. Moreover, the produced materials showed acceptable results for wastewater treatment and sludge dewatering. This new strategy reported in this review can decrease to some extent the environmental problems related to the disposal of agro-industrial wastes and wastewater sludges. At the same time, this could reduce the cost of microbial bioflocculant production.