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— The cations are needed as stimulants for effective flocculation by the cation-dependent bioflocculants. Addition of metal ions (cations) can counterbalance anionic functional groups of both bioflocculant and solid particles thereby increasing the bioflocculant adsorption to suspended particles. In the present study, addition of all dose of both Ca2+ and Mg2+ stimulated the efficiency of the bioflocculant with optimum flocculation efficiency of 95% recorded with 5 mL of 1% Ca2+. While lower dose (1 – 2 mL) of Al3+ also stimulated the bioflocculant to about 94%, Na+ and Fe3+ inhibited flocculation at all doses tested. K+ slightlyenhanced the flocculation at 4 - 10mL of 1%. The present cationic bioflocculant can be suggested as a substitute for chemical flocculants.

The biodegradability and safety of the bioflocculants make them a potential alternative to non-biodegradable chemical flocculants for wastewater treatment. However, low yield and production cost has been reported to be the limiting factor for large scale bioflocculant production. Although the utilization of cheap nutrient sources is generally appealing for large scale bioproduct production, exploration to meet the demand for them is still low. Although much progress has been achieved at laboratory scale, Industrial production and application of bioflocculant is yet to be viable due to cost of the production medium and low yield. Thus, the prospects of bioflocculant application as an alternative to chemical flocculants is linked to evaluation and utilization of cheap alternative and renewable nutrient sources. This review evaluates the latest literature on the utilization of waste/wastewater as an alternative substitute for conventional expensive nutrient sources. It focuses on the mechanisms and metabolic pathways involved in microbial flocculant synthesis, culture conditions and nutrient requirements for bioflocculant production, pre-treatment, and also optimization of waste substrate for bioflocculant synthesis and bioflocculant production from waste and their efficiencies. Utilization of wastes as a microbial nutrient source drastically reduces the cost of bioflocculant production and increases the appeal of bioflocculant as a cost-effective alternative to chemical flocculants.

Organic and synthetic flocculants are conventional flocculants used in wastewater treatment and tap water purification. The challenges of toxic residue and the resultant secondary pollutants generated from organic and synthetic flocculants have attracted research efforts towards microbial extracellular polymers as nontoxic and biodegradable substitutes. However, the bioflocculants themselves have been associated with high production costs and low efficiency. To address these challenges, tremendous efforts have been made to hybridise cations with the bioflocculants. The contradictory reports on the role of cations in bioflocculation have necessitated this review. This paper reviews the relevant and recent literature on EPS-cation structuring, cationization of bioflocculants, the efficiency of the cationization of bioflocculants, the factors affecting cation induced bioflocculation, and the mechanisms of cation induced bioflocculation. Variations in experimental procedures microbial species and growth medium composition yield bioflocculants with positive or negative functional sites and may be responsible for the contradictory effect of the cations. Establishment of a standard fermentation system that could elucidate the mechanism of cation induced bioflocculation and of the standard techniques for evaluation of the cationic content of wastewater treated with cationized bioflocculants is needded for better understanding of the cation stimulated bioflocculation.

The economics of bioflocculant production is coupled with the use of a low-cost substrate at appropriate culture conditions. The use of a waste substrate for this purpose offers an additional treatment measure to mitigate environmental pollution. We investigated the growth of Aspergillus flavus and its bioflocculant yield using chicken viscera hydrolysate as the sole media. The effects of culture conditions including time, pH, shaker speed, temperature and inoculum size on bioflocculant production were all investigated and optimised through response surface method based on the central component design (CCD) package of Design Expert. Next, the purified bioflocculant was physically and chemically characterised. Under optimised culture conditions (incubation time 72 h, pH 7, shaker speed 150 rpm, temperature 35 °C and inoculum 4%), 6.75 g/L yield of crude bioflocculant was recorded. The bioflocculant activity was mostly distributed in the cell-free supernatant with optimum efficiency of 91.8% at a dose of 4 mL/100 mL Kaolin suspension. The purified bioflocculant was a glycoprotein consisting of 23.46% protein and 74.5% sugar, including 46% neutral sugar and 2.01% uronic acid. The X-ray photoelectron spectroscopy fundamental analysis of the purified bioflocculant indicated that the mass proportion of C, O and N, were 63.46%, 27.87% and 8.86%, respectively. The bioflocculant is mainly composed of carbonyl, amino, hydroxyl, and amide functional groups. This study for the first time indicates a high potential of bioflocculant yield from chicken viscera at the appropriate culture conditions.

The economy of mass bioflocculant production and its industrial application is couple with the cost of production. The growth medium is the most significant factor that accounts for the production cost. In order to find a substitute for the expensive commercial media mostly the carbon and nitrogen sources used for bioflocculant production, we use chicken viscera as a sole source of nutrient for bioflocculant production. The culture conditions for Aspergillus flavus S44-1 growth and bioflocculant yield were optimized through one factor at a time (OFAT). The use of chicken viscera as a sole source to develop a culture medium seems to be more appropriate, simple, reduce cost of bioflocculant production and in addition offers a sustainable means of managing environmental pollution by the poultry waste. In this article, we focus on detailed description of the steps involve in developing an optimized culture medium using chicken viscera as a sole source for bioflocculant production. • A new media for bioflocculant production was developed from chicken viscera. • The culture conditions for bioflocculant production were determined and optimized. • The bioflocculant yield and efficiency were parallel to mycelial weight at log phase. Method name: Synthesis of low-cost media for bioflocculant production, Keywords: Hydrolysate, Low-cost, Substrate, Bioflocculation, Efficiency

The inherent natural tendency of bacteria to adhere and form biofilm on both biotic and abiotic surfaces and the consequential resistance to antimicrobial treatments remained a major concerned to humanity. The surface roughness of the sand blasted and cleaned stainless steel (type 304) substrates were measured using 3D measuring laser microscope before biofilm were developed on different surface roughness under continuous nutrient supply. The effect of benzalkonium chloride (BKC) as antibacterial agent on the biofilms was investigated. A concentration of 5 mg/mL BKC exert no pronounced effect on the biofilm formed on the three surfaces as compared to the 10 mg/mL and 20 mg/mL that removed approximately 50% of the cells from the respective surfaces. Conversely, the overall effect of the three concentrations tested were significantly higher (p ≤ 0.05) on the stainless steel coupon with the least average surface roughness of 0.38 ± 1.5 µm. These observations support the hypothesis that surface profile is one of the factors that influence biofilm susceptibility to antibacterial agents and reinforced the wide spread observation that microorganisms living as biofilm tends to be resistance to antimicrobial treatment especially at lower concentrations of 5 mg/mL.

Sulfate-reducing bacteria are categories of bacteria and archaea that can obtain energy by oxidizing organic compounds or molecular hydrogen (H2) while reducing sulfate (SO42−) to hydrogen sulfide (H2S). By analysis, these organisms "respire" sulfate rather than oxygen, a form of anaerobic respiration, the oxidation of hydrogen by the primary genus of Sulfate Reducing Bacteria (Desulfovibrio, Desulfovibrio desulfuricans) is catalyzed by enzymes called Hydrogenases. Three basic types of hydrogenases have been widely isolated from the primary genus of sulfate-reducing bacteria Desulfobibrio which differ in their structural subunits, metal compositions, physico-chemical characteristics, amino acid sequences, immunological activities, structural gene configuration and their catalytic properties. Broadly, hydrogenases can be considered as ‘iron containing hydrogenases and nickel-containing hydrogenases. The iron-sulfur-containing hydrogenase enzyme contains two ferredoxin-type (4Fe-4S) clusters and typical iron-sulfur center believed to be involved in the activation of H2 yet it is the most sensitive domain to CO and NO2−.eventhough it is not featured in all species of genus Desulfovibrio. The nickel-(iron-sulfur)-containing hydrogenases, [NiFe] hydrogenase posses two 4Fe-4S centers and one 3Fe-xS cluster in addition to nickel and have been found in all species of Desulfovibrio with strong resistance to CO and NO2- so far investigated. The genes encoding the large and small subunits of a periplasmic and membrane-bound species of the [NiFe] hydrogenase have been cloned in Escherichia coli and sequenced, however the functional complexity of the hydrogenase system remained unexplored as a result of the metabolic diversity in Desulfovibrio spp. The [NiFe] hydrogenase plays an important role in the energy metabolism of Desulfovibrio spp. Thus, the expression of the encoded structural genes would be an excellent marker for the metabolic functionalities under specific inducible environment.

Antioxidative compounds play a vital role to inhibit the oxidation of oxidizable products and influences the body defense system against Reactive Oxygen Species (ROS), which are harmful byproducts engendered during normal aerobic cellular respiration. ROS are specialized class of highly reactive molecules that originates during oxygen metabolism, whereas extensive evidences indicate the involvement of ROS in the development of degenerative diseases in humans. Despite the fact that synthetic antioxidants such as butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT) are threat to human’s health; they are widely employed as chemical preservatives to avert potential deterioration of food products. Several toxicological findings reveal that natural antioxidants are capable of providing protection against free radical-related diseases, cancer and other cardiovascular infections. In cognizance with these facts, natural antioxidant attracts a great deal of research interest; therefore, this review provides a comprehensive and an up-to-date overview of the three most essential natural plant antioxidants; their antioxidative properties, methods of analysis and evaluation. These Polyphenols comprise: Phenolic acid, an essential polyphenol that are broadly dispersed in plants to exert positive influence on oxidative stress; Flavonoid, an ubiquitous antioxidant that functions in free radical scavenging, metal ion chelation and enzymes inhibition to suppress the synthesis of free radicals; and Tannic acid, a water soluble anti-nutrient that acts to precipitate alkaloids & proteins, reduce mineral & vitamin utilization and restrict the activities of digestive enzymes. In conclusion, a variety of plant species were characterized to indicate in vitro antioxidative properties.