Windrow Composting: Difference between revisions

Latest revision as of 15:04, 20 May 2022

Windrow Composting, also referred to as Open Air Windrow Composting (OAW) and Open Windrow Composting (OWC), is a means of treating Green Waste and uses naturally occurring microbes which feed on organic material and require oxygen. Open Air Windrow Composting is therefore a form of Aerobic Digestion and by processing the organic material the treatment process produces a compost material.

Overview

OAW is a relatively inexpensive way of treating Green Waste e.g. twigs, leaves, glass cuttings and branch prunings etc. and is generally not suitable for Food Waste because of the legislative requirements to deal with Animal By-product Material - which generally requires management in In Vessel Composting or Anaerobic Digestion treatment processes. The process to turn the original material into the compost type material through processing in windrows takes around 12 to 16 weeks. OAW sites typically process 20,000 to 30,000 tonnes per year, but can operate at smaller and larger scale.

The Process

For the process to produce a soil conditioner to be used by farmers and others it must meet End of Waste Criteria and, in the majority of the UK, this is demonstrated by meeting the Quality Protocol for compost and the associated Quality Standard PAS100. The statutory guidance can be found here^[1]^[2].

Stage 1

Green Waste is delivered to the site (which has to have an Environmental Permit) and large items of contamination such as plastic, metal etc. are removed. The material is then shredded to produce a uniform particle size which has a structure to allow air to pass through it during the treatment process.

Stage 2

The shredded material is then placed into piles in long rows known as ‘windrows’, in the open air. The composting process is kick-started by naturally occurring micro-organisms already in the waste. They break down the material, releasing nutrients (and producing heat and some steam) and in doing so they increase the temperature up to around 65^oC needed to kill pathogens and weed seeds and meet the criteria for the final product quality specification. There are three discreet phases in the overall process^[3] which is set out in more detail in PAS100 but which is typically:

Sanitation - temperature must be held above 65°C, for at least 7 days, and turned at least twice
Stabilisation - temperature maintained above 55°C, managed for 10 weeks, and turned at least 6 times
Maturation - Post-screening (stage 4 below) the product is generally stored for at least 4 weeks before it can be used

Stage 3

Each windrow is individually monitored and when the required temperature has been reached and held for the required time at each stages it is then turned to mix the material and ensure an even distribution of the composting process and to introduce sufficient oxygen to ensure the process does not turn anaerobic. The turning of the windrows may occur up to 8 times or more before a stabilised compost is produced. The turning process can be done with simple tractor/shovel type machines, or dedicated turning machines that introduce some additional mechanical breakdown of the material.

Turning windrow with shovel source linkedin.com	windrow turning with dedicated plant source bizjournals.com

Stage 4

Stabilised material is screened, and any remaining contaminants removed, to produce a range of product grades for various end uses such as soil conditioning/a soil improvement material providing it meets the Quality Standard PAS100 which dictates the process standard to ensure that it meets End of Waste Criteria. Any large materials that have not fully broken down in the process (such as larger branches) are taken from the screening process and re-introduced back into the process as outlined above.

Screening compost source growingagreenerworld.com

The different grades of compost can be used for different purposes. Some grades are used as agricultural soil conditioners, others as mulches and others are suitable for landscape gardening or finer grades can be used on golf courses. In some cases the material is blended with other material to produce other products for horticultural use (for example sand)^[4].

References

[1] SR2021 No.1: composting in open systems - installations

[2] SR2021 No.2: composting in open systems - waste recovery operation

[3] The Compost Shop Website

[4] Freeland Horticulture Website

[1]

[2]

[3]

[4]

@@ Line 1: / Line 1: @@
 [[Category:Technologies & Solutions]]
-Open Air Windrow Composting (OAW) uses naturally occurring microbes which feed on organic material (garden waste) and require oxygen. By feeding on the garden waste, the microbes break down the material and turn it into compost.
+[[Windrow Composting]], also referred to as '''Open Air Windrow Composting''' ([[OAW]]) and '''Open Windrow Composting''' ([[OWC]]), is a means of treating [[Green Waste]] and uses naturally occurring microbes which feed on organic material and require oxygen. Open Air Windrow Composting is therefore a form of [[Aerobic Digestion]] and by processing the organic material the treatment process produces a compost material.
+[[File:Windrow composting pic.jpg|300px|left|Windrows of compost in a processing plant source Suffolk recycling]]__TOC__
+<br clear='left'/>
+==Overview==
+OAW is a relatively inexpensive way of treating [[Green Waste]] e.g. twigs, leaves, glass cuttings and branch prunings etc. and is generally not suitable for [[Food Waste]] because of the legislative requirements to deal with [[Animal By-product Material]] - which generally requires management in [[In Vessel Composting]] or [[Anaerobic Digestion]] treatment processes. The process to turn the original material into the compost type material through processing in windrows takes around 12 to 16 weeks. OAW sites typically process 20,000 to 30,000 tonnes per year, but can operate at smaller and larger scale.
-OAW is not suitable for [[Food Waste]] because the process needed to deal with [[Food Waste]] has not been performed in an enclosed vessel and in the open air. The [[Animal By-Products Regulations]] ([[ABPR]]) prevent food waste being treated in this manner in order to protect animal and human health<ref name="wc">https://www.zerowastescotland.org.uk/sites/default/files/Open%20air%20windrow%20composting%20factsheet.pdf</ref>.
+==The Process==
+For the process to produce a soil conditioner to be used by farmers and others it must meet [[End of Waste Criteria]] and, in the majority of the UK, this is demonstrated by meeting the [[PAS100|Quality Protocol]] for compost and the associated Quality Standard [[PAS100]]. The statutory guidance can be found here<ref>[https://www.gov.uk/government/publications/sr2021-no-1-composting-in-open-systems-installations?utm_medium=email&utm_campaign=govuk-notifications-topic&utm_source=cbdf5521-4cce-43f9-a94d-21490357a1b8&utm_content=daily SR2021 No.1: composting in open systems - installations]</ref><ref>[https://www.gov.uk/government/publications/sr2021-no-2-composting-in-open-systems-waste-recovery-operation?utm_medium=email&utm_campaign=govuk-notifications-topic&utm_source=ef959613-acc5-4a9b-b692-54b2ff2322fd&utm_content=daily SR2021 No.2: composting in open systems - waste recovery operation]</ref>.
-What is OAW used to treat?
+===Stage 1===
+[[Green Waste]] is delivered to the site (which has to have an [[Environmental Permit]]) and large items of contamination such as plastic, metal etc. are removed. The material is then shredded to produce a uniform particle size which has a structure to allow air to pass through it during the treatment process.
+[[File:Compost shredding pic.jpg|400px|left|Shreeding green waste source kps-UK.com]]__TOC__
+<br clear='left/>
-OAW is a relatively inexpensive way of treating [[Waste Collection Authority]] [[Green Waste]] e.g. twigs, leaves, glass cuttings and branch prunings etc.
+===Stage 2===
+The shredded material is then placed into piles in long rows known as ‘windrows’, in the open air. The composting process is kick-started by naturally occurring micro-organisms already in the waste. They break down the material, releasing nutrients (and producing heat and some steam) and in doing so they increase the temperature up to around 65<sup>o</sup>C needed to kill pathogens and weed seeds and meet the criteria for the final product quality specification.
+There are three discreet phases in the overall process<ref>[https://www.thecompostshop.co.uk/how-organic-compost-is-made The Compost Shop Website]</ref> which is set out in more detail in [[PAS100]] but which is typically:
+* '''Sanitation''' - temperature must be held above 65°C, for at least 7 days, and turned at least twice
+* '''Stabilisation''' - temperature maintained above 55°C, managed for 10 weeks, and turned at least 6 times
+* '''Maturation''' - Post-screening (stage 4 below) the product is generally stored for at least 4 weeks before it can be used
-The Process<ref name="wc" />:
+===Stage 3===
-# The material is delivered to an OAW composting licensed site and sorted to remove any contamination, plastics, metals etc. The material is then shredded.
+Each windrow is individually monitored and when the required temperature has been reached and held for the required time at each stages it is then turned to mix the material and ensure an even distribution of the composting process and to introduce sufficient oxygen to ensure the process does not turn anaerobic. The turning of the windrows may occur up to 8 times or more before a stabilised compost is produced. The turning process can be done with simple tractor/shovel type machines, or dedicated turning machines that introduce some additional mechanical breakdown of the material.
-# The shredded material is then placed into piles in long rows known as ‘windrows’, in the open air.
+{| class="wikitable"
-# Naturally occurring microbes feed on the materials. This creates heat and windrows will often give off steam.
+|-
-# The windrows are regularly turned to make sure that there is enough oxygen for the microbes to work.
+| [[File:Windfrwo turning pic.jpg|300px|left|Turning windrow with shovel source linkedin.com]] || [[File:Windrow turner pic.jpg|360px|left|windrow turning with dedicated plant source bizjournals.com]]
-# The process to turn the original material into compost takes around 12 – 16 weeks.
+|}
-The compost is checked to make sure that it meets the [PAS 100] Quality Standard regularly. Any contaminants which were missed in the first stage are removed and the compost is graded. The grading also removes any pieces of material which have not completely broken down. This can include items like small tree branches which are often too thick to fully compost. These items are then put back through the process outlined above.<ref name="wc" />
+===Stage 4===
+Stabilised material is screened, and any remaining contaminants removed, to produce a range of product grades for various end uses such as soil conditioning/a soil improvement material providing it meets the Quality Standard [[PAS100]] which dictates the process standard to ensure that it meets [[End of Waste Criteria]]. Any large materials that have not fully broken down in the process (such as larger branches) are taken from the screening process and re-introduced back into the process as outlined above.
-The different grades of compost can be used for different purposes. Some grades are used as agricultural soil conditioners, others as mulches and others are suitable for landscape gardening or finer grades can be used on golf courses.
+[[File:Screening compost pic.jpg|300px|left|Screening compost source growingagreenerworld.com]]__TOC__
+<br clear='left/>
+The different grades of compost can be used for different purposes. Some grades are used as agricultural soil conditioners, others as mulches and others are suitable for landscape gardening or finer grades can be used on golf courses. In some cases the material is blended with other material to produce other products for horticultural use (for example sand)<ref>[http://www.freelandhorticulture.co.uk/products-and-services/composting.html Freeland Horticulture Website]</ref>.
 ==References==
 <references />