The efficacy of nanobubble generator technology for microbial inactivation in urban lake water: A comparative study of contamination profiles

Abstract

The current growing situation of water contamination crisis is the pressing issue for worldwide and most prominently in Bangladesh. Requires the urgency of affordable and efficient purification systems. This research focuses on development of a multi-staged Nano-bubble (NB) technology with a promising solution by generating ultra-fine bubbles less than 250nm capable of releasing reactive oxygen species (ROS), degrading pollutants, and destroying pathogenic microbes in treating polluted surface water collected from Hatirjheel, Banani lake and Aftabnagar Lake water in Dhaka, Bangladesh. The Assembly of NanoBubble generator begins by choosing high-performing components: a water pump, air compressor, a custom made nano bubble injector, and a nanobubble diffuser (100–500 nm pores). A microcontroller is connected to the flow and water pressure to track system performance. PWM motor drivers and solenoid valves manage air and water flow. The dynamic PID control code changes dynamically control inputs for optimal bubble formation. The system is then mounted with pressure-rated piping and securely fastened. During integration, code is uploaded into the controller, and the setup is calibrated. Air-water ratios are optimized to enhance nanobubble dissolution. Polluted water (10 L) from each water sample was treated for 1 hour, and microbial analysis was performed using Luria Agar (LA), Nutrient Agar (NA), and selective media such as EMB, MacConkey, TCBS and XLD. Dynamic Light Scattering (DLS) analysis was conducted to determine bubble size distribution and stability. To check the effectiveness of the Nano-bubble generator prototype on microbial population, biological tests were conducted on both treated and untreated water samples from Hatirjhil, Dhaka. In 10 L of water, the generator ran for 1 hour, then treated and untreated samples were diluted in saline to 10⁻⁴ and 100 μL from each diluted sample were plated on Luria Agar (LA), Nutrient Agar (NA) media and with dilution at 10⁰, 100 μL was spread plated on EMB, MacConkey, and XLD media. After 24 hours of incubation, the untreated sample yielded 2.5-3.5 × 10⁶ CFU/mL in LA and 7.9-9.9 × 10⁶ CFU/mL in NA, and E. coli, Salmonella, and Shigella were identified, showing heavy to moderate growth. In comparison, the treated sample result showed a significant reduction, with 0.8-0.9 × 10⁶ CFU/mL in LA and 2.8-3.8 × 10⁶ CFU/mL in NA and in selective media, noticeably reduced or no growth of pathogens were detected. This represents a maximum 68% reduction in microbial load in LA and 71.7% reduction in NA, indicating the potential of nanobubbles inhibiting dangerous pathogens. Our findings demonstrate the high efficiency in producing nano-sized bubbles with more than 75% of bubbles under 250 nm and significantly lowering microbial contamination in polluted surface water and efficiency of this Nano bubble generator can filter polluted water better than the classic techniques used in Bangladesh.