Development of locally isolated microbial coagulant for removal of river water turbidity

Abstract

Many rivers are affected by high sediment and turbidity due to land erosion and industrial pollution. Chemical coagulants are frequently used to clarify the water. However, it is proven that chemical coagulants are to some extent harmful to the environment. As such, the researchers are still working for safe, biodegradable and efficient flocculants. The potential of microbial flocculant for turbidity reduction from water was conducted by several approaches. In this study, six types of river water fungi (RWF), RWF-1 to RWF-6 were isolated from river water. The fungi showed good potential in terms of turbidity reduction in the shake flask method by entrapping particles from river water and kaolin suspension. The supernatant produced by fungi was applied to reduce turbidity from kaolin suspension and river water. The supernatants produced by the RWF-5 and RWF-6 showed good turbidity removal of 95% and 75% from kaolin suspension and 25% and 23% from river water, respectively. The growth conditions were optimized and showed that 96% turbidity removal was obtained with 0.1% (w/v) malt extract, 3% (v/v) inoculum dose and initial pH 7.0 at 6-day fermentation by the fungus strain RWF-5. The fungal strain RWF-5 was identified as the species of Lentinus squarrosulus RWF-5. The chemical composition of the extracellular myco-flocculant was 5.17 g/L total sugar; 237 mg/L total carbohydrate; 295.4 mg/L protein and 1.15 mg/L glucosamine. The cellulase and laccase activity were 20 U/L & 6.22 U/L, respectively. Fourier transform infrared spectroscopy (FITR) revealed the presence of hydroxyl, carbonyl, amide and amine groups as the main functional groups. The elemental analysis showed that the weight fractions of C, H, O, N and S were 40.9%, 6.0%, 49.8%, 1.7% and 1.4%, respectively. SEM images of the myco-flocculant showed an irregular structure with netted texture and zeta potential value of the myco-flocculant was recorded at -7.0 mV which may be responsible for the myco-flocculation activity. The effect of cations and pH results showed that cations addition did not significantly enhance the flocculation rate indicating a cation independent flocculant more than 95% of turbidity removal occurred at pH 7.0 to 8.0. The myco-flocculant stability showed the ranges pH 4-8 and temperature 25-65⁰C and can be stored at room temperature (28±2⁰C) for minimum of 12 days. The optimum flocculation process showed that the agitation speed and mixing time were 250 rpm and 7 mins for rapid mixing process while 90 rpm and 22 mins for slow mixing, respectively. Under optimum agitation and mixing time, the optimum myco-flocculant dose and settling time for initial turbidity of 600 NTU was 1% (v/v) and 5 mins. Settling column test was also conducted to determine the detention time and overflow rate of the particles which can be used to design sedimentation basin. The detention time and overflow rate of kaolin suspension and river water were 59.5 minutes and 41.6 m/day for 80% turbidity removal and 63 mins and 29.25 m/day for 65% turbidity removal, respectively. The optimization exercise in the channel revealed that the maximum efficiency of 82% turbidity removal was achieved at velocity of 0.75 m/sec, myco-flocculant dose of 2.5 % (v/v). The removal of TSS, COD, NH3-N and TN of the treated river water were 93%, 50%, 76% and 91%, respectively. The new myco-flocculant is very potential for reducing river water turbidity that is non-toxic as well as biodegradable, and therefore may be encouraging to water treatment plant in future applications.