Water sector applications: Microbubble applications: wastewater aeration, dispersed air flotation, ozone dosing, algal growth/carbon capture. Fluidic electricity generation Will Zimmerman Professor of Biochemical Dynamical Systems Chemical and Process Engineering, University of Sheffield

Outline Why microbubbles: mass transfer and flotation Wastewater aeration Potential for replacing dissolved air flotation Algal growth / carbon capture / wastewater plant integration => target energy positive and CO2 neutral Ozone Fluidic electricity generator

Why microbubbles? Steep mass transfer enhancement. Faster mass transfer -- roughly proportional to the inverse of the diameter Flotation separations -- small bubbles attach to particle / droplet and the whole floc rises

Fluidic oscillator makes microbubbles Concept for microbubble generation No moving parts switching Fluidic oscillator 60 micron bubbles from a microchip diffuser 600 micron nozzle bank

Pilot scale: Experimental design Master-slave amplifier system for fluidic oscillator Suprafilt layout for 30m^3/h

Energetics: Power consumption Oscillatory flow draws less power than steady flow at the same throughput!

With Oscillator Visualization study and Frequency analysis Without Oscillator With Oscillator, Master (small) shut completely

Frequency of oscillation depends on feedback loop and air throughput

Aeration: DO profiles, clear water Blow-up

Delay time and dosage

Summarized findings: 7-1-09 Visualization study Oscillation frequency power consumption: with maximum value of 18% reduction at the best aeration configuration. Clear water dissolved oxygen study: 3-4 fold better dosage at 83% of the design volumetric flow rate. Mixed liquor dissolved oxygen study which showed markedly higher dissolved oxygen levels achieved in highly oscillatory dynamics for the control over the best oscillatory flow configuration. Indeterminate without BOD / metabolic activity assessment.

Update / plan Mixed liquor second set of pilot trials nearly ready to report Second set of clear water trials reproduced 2008 results Currently changed over to Aquaconsult strip diffusers / awaiting thaw Planning sequencing batch reactor trials with Aecom Design Build Planning continuous flow mixed liquor trials with YW / Aecom at Leeds South YW funding for plans, Aecom knowledge transfer partnership “in the works” Stages of commercial projects envisaged Retrofit above ground “plumbing” of blowers with oscillators – saves ~18% electricity immediately + tuning for taking advantage of faster mass transfer with existing diffusers and submillimetre bubbles. PERMOX diffusers (180micron pores and non-biofouling) could decrease bubble size by factor of five so ~80% electricity reduction possible by tuning operating conditions. Microporous ceramic diffusers (20 microns) – potential for 98-99% electricity cost removal, but mixing issue.

Potential for dissolved air flotation (DAF) plant Potentially eliminate recycle flow and saturator load (90-95% electricity cost) Uses blowers not compressors/saturators (much lower capital) Cheap materials for retrofit with fluidic oscillators introduced in the plumbing and manifolds to diffuser bank for dispersal.

Microporous diffusers Original nickel-based microporous membrane ~£2k /m2 Now works with microporous ceramic ~£200-300 / m2 Suprafilt and HP Technical Ceramics are collaborating with UoS on fabrication

Field trial campaign Microporous diffuser Growing algae with microbubbles Agreed with Northern Ireland Water and AECOM Design Build (Brenda Franklin) to trial the technology in a single DAF cell at Carmoney WTW which is undergoing refurbishment Trial to be conducted March – June 2010. 12m2 of surface area available for microporous diffuser insertion for retrofit. Unit instrumented to measure performance and to be outfitted with visualization equipment. Tune performance in operating parameters – chiefly air throughput rates, water flow rate (~cm/s) and oscillation frequencies. Model data from performance studies for engineering design parameters (number of plate diffusers, placement, flow rates). Gain operational experience – identify potential problems, risks, failure modes -- to plan maintenance regime. Assess CAPEX and OPEX requirements

Ozone plasma microreactors: A proposition for commercial development for water and waste water treatment. How ozone disinfects in water solutions. The ozone plasma microreactor in the lab Components Achievements How to get the ozone off the chip? Microbubbles! Prototype conceptual design Field trial campaign

Ozone Kills! One ozone molecule kills one bacterium in water! Ozone dissolves in water to produce hydroxyl radicals One ozone molecule kills one bacterium in water! Hydroxyl radical attacks bacterial cell wall, damages it by ionisation, lyses the cell (death) and finally mineralises the contents.

Mass murder! Plasma needle treatment: 1 bar @ 1000’s 0C Results Plasma needle: Comparison Autoclave treatment of E Coli: 2 bar @ 121°C for 20 min Some survive Plasma needle treatment: 1 bar @ 1000’s 0C for few seconds No survivors

Ozone plasma microreactor in the lab. Upper plate Electrical connection Electrodes Fibre optics Chipholder construct Lower plate

Microfluidic onchip ozone generation Emission UV-Vis spectrum of exit gas with clear O3 signature. Analysis suggests 30% conversion at temperature 350K. Our new chip design and associated electronics produce ozone  from O2 with two key economic features: 1. Low power.  Our estimates are a ten-fold reduction over conventional ozone generators. 2. High conversion.  The selectivity is double that of conventional reactors (30% rather than 15% single pass). Additionally, it works at atmospheric pressure, at room temperature, and at low voltage (170V, can be mains powered).

Modular integrated microchip concept for water treatment Essential electronics Schematic microchip Microfluidic device: Ozone plasma reactor + microbubble generator to be submerged (with shroud Protecting connections) Power source and matching network in printed circuit board above water. Two wires and one air feed line Connecting to microfluidic device. Note: conventional plasma sources cost ~£12000. Our low power, bespoke and tuned electronics cost about £100 in materials.

Plasma disks 25 plasma reactors each with treble throughput over first microchip

Dosing lance assembly The top view of the lance (8 reactors above, 8 reactors below), separate oscillator branches Axial view of the lance

Corporation cock assembly Valve control to toggle for flow/no flow External assembly. Ball valve

WTW tests on raw water Raw water inlet Upstream sample point for benchmarking water quality and corporation cock to be fitted Downstream sample point for turbidity measurements. Sufficient for water quality study.

Potential markets Water purification (municipal) Waste water – organics removal Waste water – disinfection before release Sterilization (medical, biotech, pharmaceutical) Distributed / remote / portable water purification Ventilation system sterilization Gas analysis (ozonolysis) and sensors

Air lift loop bioreactor design Schematic diagram of an internal ALB with draught tube configured with a tailor made grooved nozzle bank fed from the two outlets of the fluidic oscillator. The microbubble generator is expected to achieve nearly monodisperse, uniformly spaced, non-coalescent small bubbles of the scale of the drilled apertures. Journal article has won the 2009 IChemE Moulton Medal for best publication in all their journals. Designed for biofuels production First use: microalgae growth Current TSB / Corus / Suprafilt grant on carbon sequestration feasibility study on steel stack gas feed to produce microalgae.

Construction Top with lid Inner view: Heat transfer coils separating riser /downcomer. Folded perforated Plate m-bubble generator. Replaced by Suprafilt 9inch diffuser Body / side view

ALB for algae growth

With Fluidic Oscillator Without Fluidic Oscillator Results CHLOROPHYLL CONTENT (μg/ml) DAYS With Fluidic Oscillator Without Fluidic Oscillator 1 0.53 0.58 2 0.86 0.61 3 0.98 0.66 4 1.36 1.45 5 1.34 1.7 7 1.90 2.33 8 2.23 2.72 9 2.80 3.04 10 3.10 2.39 11 3.43 2.83 Rapid pH drop Potential licensee for carbon Sequestration organic chemistry Best poster 6th Annual bioProcessUK Conference, Nov 2009, York. 30% higher relative growth rate with only 60 minutes per day dosing TSB / Corus / Suprafilt project for continurous dosing.

Prospects for process integration / intensification for WWTW flowsheet re-design Anaerobic digestor: CO2 dosing and CO2/CH4 stripping Accelerates biochemistry CHP provides CO2 for algal growth Key concept: Microbubble dosing will be cheap, but allow access to all process gases. Anammox process Stage 1 Aerobic (air dosing) Stage 2 Anaerobic CO2 dosing and CO2/N2 stripping Result: Accelerate biochemistry of all processes by reactive extraction. Influence production by nutrient dosing rate. Grow algae for biomass / biofuel. Sequester CO2. Provide O2.

Remote fluidic electricity generator Concept: Fluidic oscillator provides “AC” fluidic power. Piezoharvester converts to AC electricity. Need: remote pipelines for parasitic electricity generation from flow energy. No moving parts, fit and forget, power sensors and telemetry, potentially actuators. German group published results in December 2008. Found 150microWatts from flows rates typical of tap water. We have a similar approach but with our key feature have been able to achieve 1.5mW with same flow rates and can apply standard approach for another factor of 5-10 increase.

Potential microbubble markets Dispersed air flotation for solids removal in water and wastewater (achieved target bubble size, 20 microns) Wastewater aeration (partner YW, 18% energy reduction, 3-fold higher dosing rates on retrofit) Algal biomass / bioenergy production (partner Corus, >30% extra biomass from CO2 microbubble dosing) Wastewater treatment processes integration and intensification: aeration, digestion, de/nitrification, algal growth. Targets: smaller footprint; carbon and energy neutral! Ozone dosing from a plasma microreactor dosing lance Air lift loop bioreactor development for biofuels Heterogeneous chemical and bioreactor engineering, gas-lift oil recovery, oil-water separations, heat transfer