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Biogas from dairy farm
ponds Stephan Heubeck & Rupert Craggs
Hamiltion
22. April 2015
National Institute of Water & Atmospheric Research Ltd, New Zealand
Why bother with pond biogas systems?
Because we can address more
than one problem at once!
Why bother with pond biogas systems?
“Look deep into nature, and then you will
understand everything better”
Albert Einstein
NIWA pond monitoring programs
Obtaining methane production data in the field
Storage pond sites 2013 • Monitoring sites in Northland, Waikato and
Southland
• Farms of high and low intensity
o (use of feed pads, stocking rate)
• Pond biogas production + quality
• Raw effluent quantity
• Raw effluent quality:
o Solids - TS/VS, COD
o Nitrogen - TN
o Phosphorus - TP
2013 storage pond monitoring Pond temperature shows seasonal variation:
• Minimum pond bottom: ~ 7oC
• Minimum pond water: ~ 3oC
2013 storage pond CH4 Southland storage pond:
• Correlates with number of cows milked
• Autumn reduction due to single milking
2013 storage pond CH4 Waikato storage pond:
• Milk throughout winter – more constant load
• Greater correlation of CH4 production with
solids load than temperature
Per cow solids loading:
• Southland: 0.29 kgTS/0.18kgVS /cow/day
• Waikato: 1.13 kgTS/0.82kgVS /cow/day
feed pad
Methane productivity:
• Southland: 0.21 m3CH4/kgVS
• Waikato: 0.22 m3CH4/kgVS
2013 storage pond summary
2013 storage pond methane emissions:
• Southland: 6.7 kgCH4/cow/year
• Northland: 8.3 kgCH4/cow/year
• Waikato: 34.1 kgCH4/cow/year
feed pad – more solids
2012 anaerobic pond methane emissions:
• Southland: 14.37 kgCH4/cow/year
• Northland: 14.45 kgCH4/cow/year
• Waikato: 7.68 kgCH4/cow/year
Methane GHG Emissions
Pond monitoring summary Dairy farm effluent ponds minus side:
• Release much more GHG emissions (methane)
than previously assumed
• Emissions will increase with farm intensification
Dairy farm effluent ponds plus side :
• Conversion of VS to CH4 similar to engineered
digesters
• Very good at removing (coarse) solids
• Simple to build
• Simple to operate
• Can cover to capture odour and GHG
• Biogas energy potential
Basics:
o For flush manures and dilute wastes only
o Solids concentrations up to ~5%
o Different retention times for solids and liquids
o Loading rates <0.5 kgVS/m3/day
o Retrofits possible
NIWA Covered Anaerobic Pond Design
Custom designed covered anaerobic pond: o Deep, narrow and long pond
o Dedicated pond often better than retrofit
o Covering (shallow) storage pond often uneconomic
o Liner depending on regulation (plastic, clay)
NIWA Covered Anaerobic Pond Design
NIWA Covered Anaerobic Pond Design
Simple cover: o Common cover materials (LLDPE)
o Flexible, UV resistant, cost effective
o Weight pipes for rainwater guidance
o Electric rainwater draw off pump
o Ring pipeline for efficient biogas draw-off
o No floatation underneath cover
Biogas is the most versatile renewable
energy resource - usage options include:
o Flaring – GHG and odour control
o Combined heat and power (CHP) – generator
o Heat – boiler use
o Transport fuel – purification and compression
There is no size
that fits all!
Biogas use options
Biogas flaring
Biogas flaring: o Low maintenance
o Odour and GHG control
o No local heat demand
o Small electricity demand
o Not big enough for advanced biogas use options like vehicle fuel etc.
Biogas CHP Motor-generators:
o Spark ignition
o Gas purification for generator longevity
o Grid synchronisation or stand alone
o Radiator heat recovery
o Exhaust heat recovery
o Renewable 3-phase electricity on call
o With biogas storage back-up function for grid outages
Biogas CHP
Waste heat use: o 80-90 C hot water
o 2 kWh hot water for every 1 kWh electricity
o Hot water for washing and heating
o Hot water can be stored independently to decouple electric and thermal load
Biogas as boiler fuel
The “overlooked” option: o Far simpler to operate than CHP
o Little (no) biogas purification required
o Highly efficient biogas use: 90 – 102% efficiency
o Doable at small scale
o Financial attractiveness can be good as well
Biogas transport fuel
Biogas as transport fuel:
o Purified and compressed biogas (bio-methane)
can be used in any CNG vehicle
o The size of the biogas resource on NZ farms may
be often too small to justify the high investment
o Further increases in the cost of petroleum fuels
may however make this option attractive in the
future
So how much does a covered anaerobic
pond based biogas system cost, and
does it make financial sense?
Biogas from covered
anaerobic ponds
The answer depends, because:
o Every farm is different
(size, soil, existing gear)
o A lot of covered
anaerobic ponds will be
built without biogas use
As solids removal technology:
o Dry matter (DM) reduction higher than with
mechanical solids separator or weeping wall
o Cost less than mechanical solids separator and
about equal to weeping wall
o No odour or GHG emissions
o Maintenance more flexible
Covered Anaerobic Ponds
Covered Anaerobic Pond pre-treatment prior to storage pond:
Covered Anaerobic Ponds
Covered Anaerobic Pond treated effluent
ready for:
o Recycling as wash water, i.e. through backing
gate
o Injection into low application sprinkler system (K-
line) or centre pivot irrigator
Covered Anaerobic Ponds
Covered Anaerobic Ponds As compliance tool:
o Reduce effluent odour see pig industry
o Reduce GHG emissions the dairy industry’s
chance to reduce the GHG foot-print by 10 –
20% with here and now technology without
curtailing production
Indicative costs Assuming a 600 cow dairy farm with feed pad. Covered Anaerobic Pond added to existing storage pond system for pre-treatment: Earth works: $15k – $25k$ (cut and fill or import?)
Plastic: $15k - $35k (bottom liner required?)
Pond pipe work: $5k - $10k
Consents, Planning, Supervision: ????
Biogas piping and conditioning: $5k - $15k
Biogas boiler: $3k - $6k
Biogas CHP: $30k - $80k (longevity, only ~2,500 h/y!)
Installation and connections: $5 - $30k (lines company decides)
Biogas value Assuming a 600 cow dairy farm with feed pad:
Annual electricity consumption: 80k – 120k kWh/y
Thereof hot water (heat): 25k – 30k kWh/y
Annual usable electricity generation: 50k – 70k kWh/y
Annual usable hot water generation: 25k – 30k kWh/y
Gross earnings biogas boiler: $3k/y - $7k/y (D/N tariff!)
Gross earnings biogas CHP: $15k/y - $30k/y (lines charging structure and / or islanding of generation will have a big impact on net result)
Biogas use The early (mass) adopters for covered anaerobic pond based biogas technology will therefore be piggy-backed schemes where the pond is in place for other reasons:
o Biogas system payback = payback of gas user
o Can be economic for small (gas boiler) and large schemes (CHP)
o Economic threshold of <3 years doable
Covered anaerobic pond based biogas
systems will likely be installed for their multiple
benefits: Solids removal; effluent reuse;
odour/GHG emission reduction
Biogas energy will be the icing on the cake
Conclusion
