Biofiltration of Groundwater Andrew Stevenson, Manager SK/MB/ON - - PowerPoint PPT Presentation

November 21, 2019

Andrew Stevenson, Manager SK/MB/ON

Biofiltration of Groundwater

New Challenges - New Solutions: Innovative Technologies

Overview

• Biofiltration concepts
• Example of a small groundwater system
• What we learned

What is Biological Filtration?

Biofiltration

• Exploiting naturally occurring bacterial growth to purify drinking water
• Given proper environmental conditions, bacteria can use undesirable

compounds in the raw water to gain energy or nutrients

• Usage by bacteria = removal or conversion of compounds
• Encourage growth of bacteria on filter media

Change in Philosophy - Membranes

• Traditional philosophy of membrane technology (esp. RO) was that it

could solve any water treatment problem

• Communities experienced fouling and clogging of membranes with

difficult source water that left membrane plants wanting

• Membrane plants treat many problems, but it is not a sustainable

method to treat all waters

• Excessive backwashing, fouling of membranes and membrane

replacement is costly

Biofiltration Benefits

• Reduced chemicals usage
• Simple treatment – operator friendly
• No biological fouling of water treatment equipment, such as

membranes (less waste)

• Production of biologically stable water, which means low bacteria re-

growth potential in distribution systems

• Low chlorine demand of finished water very little chlorine residual

decay in distribution systems (ammonia, organics reduction)

Biological Treatment Feasibility

• Inorganics: nitrate, ammonia, perchlorate, bromate, arsenic, sulfide,

iron, & manganese

• Organics: dissolved organic carbon, taste & odour, trace organics

Bugs Need a Home

• Provides a ‘hotel’ for bacteria
• A combination of biological and

physical-chemical processes occur

• Provides the right conditions (food

source, environmental)

Backwash

• Most facilities use non-chlorinated water in a dedicated backwash tank
• Air scour is helpful in removing debris and film from media
• Simultaneous air and water scour followed by fluidization of media is preferred
• backwash is maintained at ~15 L/s until water is clear
• take samples of backwash waste to check for lost media
• filter to waste, if required

Backwash

Instrumentation

• Conductivity
• pH
• Flow
• Pressure (differential)

Record Keeping

• Daily log sheets
• Chemicals usage
• Water quality
• Pump runs
• Plant flows
• Minor and major upsets

RO Prefilters

Eagles Lake - SK

Eagles Lake WTP

Biological Treatment Feasibility

• Groundwater source ~180 cu. m/day capacity
• Existing Process: Greensand Filtration + Sodium Hypochlorite

Disinfection

• High ammonia ~3.5 mg/L
• High Iron ~3 mg/L
• Manganese ~ 0.350 mg/L
• Free chlorination not practiced due to high ammonia levels

Existing WTP Performance

Parameter Raw (mg/L) Treated (mg/L) GCDWQ Ammonia 3.1 2.4

• Arsenic

0.041 0.002 0.01 Iron 3.66 0.07 0.3 Manganese 0.11 0.048 0.1/0.02 Hardness 443 429

• TDS

938 956 500 DOC 5.2

Performance Issues

• High chlorine demand >30 mg/L by ammonia
• Exceeds NSF application limit for sodium hypochlorite and gas chlorination
• Disinfection Concerns - 4-log Virus inactivation needed
• Chloramination cannot provide 4-log virus disinfection
• UV disinfection if not feasible (UVT<70%)
• Ammonia removal necessary

Biological Filtration Plus Membranes (typical)

• Air and oxygen injection
• Staged biofilters – Iron

Ammonia/Manganese

• NF/RO Membranes -

Demineralization

• pH correction – caustic or

pH contactor

• Disinfection - chlorine

Biological Filtration Piloting Goal

• Reduce ammonia below 1 mg/L to enable breakpoint chlorination &

disinfection compliance

• Reduce iron to less than 0.3 mg/L
• Assess effect of natural biofiltration on arsenic, manganese and
• rganics removal
• Greensand filter for Mn

Biological Filtration Piloting

Eagles Lake Treatment Scheme

Biological Filtration Media Configuration

Media Description Purpose Filter Dia. (m) Media Depth (m) Anthracite Biological Iron Removal 0.2 0.8 Activated Carbon Biological Ammonia Removal 0.1 0.8 Anthracite Biological Ammonia Removal 0.1 0.8 Ceramic Clay Biological Ammonia Removal 0.1 0.8 Natural Zeolite Ion Exchange Ammonia Removal 0.1 0.8 Anthracite/Greensand (partial Operations) Physical/ chemical Mn Removal 0.2 0.5 / 0.3

Chlorine Demand – Before/After Ammonia BF

Manganese Removal Performance

Full-scale data - 2015-2018

• Raw water Ammonia = 3.2 - 3.5 mg/L
• Iron: Biofilter effluent = 0.0 – 0.05 mg/L
• Ammonia: Biofilter effluent = 0.0 – 0.1 mg/L
• Manganese: Greensand filter effluent = 0.001 – 0.002 mg/L
• Over 4 years in service
• No issues noted by the operator

Iron & Ammonia Biological filters

Findings

Key Learnings – Iron & Manganese

• Environmental conditions (pH, ORP, etc.) are important in iron &

manganese biofiltration

• Separate processes may be required for iron & manganese removal
• Primary biofilter reduced iron & arsenic to acceptable levels
• No organics reduction seen across biofilters tested

Key Learnings - Ammonia

• Anthracite & GAC media appear to be better suited than the tested

ceramic media

• Ion exchange did not perform as well as GAC or anthracite biofilter
• Converting Ion exchange media into biofiltration, ammonia removals

were comparable to GAC & anthracite media

Key Learnings

• Importance of piloting
• Experienced operational support
• Single consultant:
• Design
• Piloting
• Construction
• Commissioning
• Many RO/biological examples over 15 years

Questions?

Contact Andrew Stevenson, stevensona@ae.ca