Composting 1000 tonnes per day? A Continuous Aerated Windrow System

John Paul, Ph.D.

CCC Conference 2010

TRANSFORMCompost Systems

How Do We Deal with Organic Waste Diversion From Very Large Cities? - some cities have 5000 tonnes + per day of organic waste!

How much organic waste is 1000 tonnes per day?

2540 tonne trailers per day!Even energy recovery processes still need to handle a lot of bulk material before and after energy recovery!

How much organic waste is 1000 tonnes per day?

325 6 yard buckets per day!

We first have to accept some basic principles of composting

Principles of Composting1.Composting is an aerobic process and hence needs aeration and/or turning

2.Composting has the potential to pollute, therefore must be protected from precipitation in wet climates

3.Composting is a biological process and requires time

4.Composting generates heat which kills pathogens, increases microbial activity to stabilize carbon, and evaporates moisture

5.Odor potential increases with increased moisture content, decreased oxygen supply, and increasing amounts of food waste

this violates most of the principles of compostingOne can say its a slightly more organized version of……

…this!

this can hardly be called composting: it is difficult to maintain control of the process in either dry or

wet season

CCC Conference 2010

Outdoor Turned Windrows

Inexpensive to begin, but will be quite difficult to maintain control of the process in either dry or wet season

With 10 m wide x 3 m high windrows – need 500 m2 per dayWith 5 m wide x 2 m high windrows – 1200 m2 day

Outdoor Turned Windrows

Inexpensive to begin, but will be quite difficult to maintain control of the process in either dry or wet season

We now have the option of working under a roof, but space requirements are significant

With 10 m wide x 3 m high windrows – need 500 m2 per dayWith 5 m wide x 2 m high windrows – 1200 m2 day

Additional challenges with turned windrow systems inside a building - not so easy for a turner operator to see

Blower offBlower on

We now want to optimize our indoor space – we need to turn more often, or provide forced aeration to speed up the process

We should now consider other technology choices as well-Aerated bunker-Covered aerated windrow-Continuous aerated bed-Agitated bed

We should also consider some rules of thumb for composting1.Composting is optimized at moisture contents of 50-65%, and bulk densities of 600 to 700 kg per cubic meter

2.Composting will result in a 30-50% volume loss depending on process conditions

3.Static aerated systems require greater porosity to prevent preferential air pathways

4.The amount of drying depends mostly on the temperature above the composting material

5.Composting is very corrosive, use appropriate building material

Rules of thumb for compostingComposting is optimized at moisture contents of 50-65%

Composting at 65% moisture – 1000 tonnes per day = 325 buckets

If we have to decrease to 55%, we have to add 700 tonnes of a 40% moisture content bulking agent = total of 566 buckets/ day

Technology choices impact capital and operating cost

65% moisture to 55% moisture – from 325 buckets to 566 buckets/day

We double the size of the facility required

If we have to handle 3 x with loader, we now have ~1500 buckets/day

At a cost of $120/hour, and 1 minute/bucket = $ 3400 per day

Rules of thumb for compostingComposting will result in 30-50% volume loss depending on conditions

Rules of thumb for compostingStatic aerated systems require greater porosity to prevent preferential air pathways

Rules of thumb for compostingThe amount of moisture removed increases with increasing air temperature above the composting mass.

Summer in New York

35% moisture after 10 days

65% moisture coming into channels

Rules of thumb for compostingComposting is very corrosive, so we should use appropriate building material

We also have to think about operations cost, and the type of material that we are processing, and

for worker health and safety, and…..

Can we start with a cost effective, corrosion resistant building structure?

Can we optimize the use of this space with a large aerated windrow, say 10 m wide by 3 m high?

We can aerate this pile with an aeration system in the floor

How are we going to turn or mix this material?

We then need a machine that is remotely controlled, and moves the entire windrow 10-12 m through the building, and can adjust for volume reduction during composting

We have a cost effective composting process that optimizes the use of space, and optimizes the process using aeration and turning – process time up to 8 weeks.

Higher moisture content material?Catch the leachate at the beginning, and put it back in after 3-4 weeks. Still have time for pathogen kill in the 8 week process

SummaryWe have to start thinking creatively if we are going to benefit from our organic waste, whether through “energy recovery” production, or composting. We have to remember that even “energy recovery” will leave a lot of organic material behind that we still need to do something with!