Solid-state fermentation to produce myco-coagulant for water treatment

Abstract

Chemical coagulants have been widely used in water treatment. However, their potential negative impacts on human health and the environment keep motivating researchers to develop commercially available natural coagulants. Microbial coagulants are widely recognized for their safety and water treatment capabilities, but their high production costs pose a significant challenge to their widespread use. Therefore, this study aims to develop a solid-state fermentation system to produce a myco-coagulant for water treatment. In an attempt to reduce the production, low-cost lignocellulosic biomasses were screened in this study among them coco peat was a suitable lignocellulolytic substrate for producing an efficient myco-coagulant with a high flocculating activity of 84.6 % without any optimization. Low nutritional condition is also an effective strategy to reduce the production cost; fermentation process parameters were optimized in this study in order to maximize myco-coagulant production, which was achieved after 5 days of incubation at 25º C and moisture content of 70 %, the highest flocculating activity of 93.06 % was obtained under the conditions: 3 % (w/w) malt extract, 2.5 % (w/w) glucose, and pH 7. The potential fungal strain used in this study was identified as Phanerochaete concrescens. Characterization of the produced myco-coagulant revealed that it was primarily a polysaccharide-like substance mainly composed of 189.6 (mg/L) protein, a total carbohydrate of 170.5 (mg/L), and a total sugar of 4.20 (g/L). Myco-coagulant displayed an irregular structure of a compact nature and the elemental composition of oxygen (40.9 %), carbon (30.5 %), and a low percentage of N (5.2 %), H (6 %), P (5.0 %), Ca (2.0 %), K (4.7 %), Na (3.2 %) and Mg (2.5 %). FTIR and GC/MS analysis further indicated the produced myco-coagulant containing several compounds from varying chemical groups, including phenol, 2,4-bis (1,1- dimethyl ethyl), hydroxyl −OH, amine NH2, and ester groups as the important functional groups. Zeta potential revealed that the produced myco-coagulant was an anionic group. The produced myco-coagulant was cation-independent and pH tolerant. Based on One Factor at Time (OFAT) obtained results, optimization of the most influential parameters was carried out by applying FCCCD under RSM to develop a second-order regression model for successful improvement in flocculation. The optimum flocculation was 96 % under 200 rpm rapid mixing speed during 2 min and 90 rpm slow mixing speed during 22 min; the appropriate myco-coagulant dosage and settling time for initial turbidity of 600 NTU were 12 ml and 30 mins, respectively. TSS, COD, NH3-N, and TN removal of the purified water were 90 %, 44 %, 56 %, and 81 %, respectively. Since commercialization and industrial applications of microbial coagulants are still lacking, this study was the first attempt to scale up the production by applying different models; myco-coagulant successfully achieved a maximum flocculating rate of 92 % in foil tray under moisture content, pH value, and thickness of the substrate of 70 %, 7 and 3 cm, respectively. However, the large-scale production in an agitated bioreactor drum (ABD) was an attempt, and results show poor flocculability due to poor fungal growth in the presence of agitation rate at the vessel. The study reveals the potential of a safe, environmentally friendly myco-coagulant for sustainable water treatment, aligning with global environmental awareness and green technology for scaling-up purposes through solid-state fermentation.