Sustainable Generation and the options for aerated static pile composting

static pile composting

Capital and operational costs, along with stormwater and leachate control, are critical in organic waste processing. Sustainable Generation’s Chief Executive Officer Scott Woods discusses the options for aerated static pile composting.

The introduction of a food organics and garden organics (FOGO) collection service to every Australian household underpins a National Waste Plan target to halve organic and food waste going to landfill by 2030.

Recycling facilities and councils are developing and implementing plans now to ensure there’s the infrastructure needed to process organic waste.

Scott Woods, Chief Executive Officer Sustainable Generation, says the organics management industry faces many challenges including costs and complexity of composting, site constraints, process time, energy consumption and community acceptance.

One paramount consideration of any FOGO plan is the evaluation of the total cost of ownership of the facility over its useful life which is typically 20-plus years. 

A Net Present Valuation (NPV) of the facility, which includes all upfront capital costs, ongoing capital reserves, and operational costs are evaluated to determine in today’s dollars what is the total cost of ownership over the facility lifetime. The lower the NPV while meeting all environmental and operational requirements is the desired outcome.  

Physical structures such as concrete tunnels or buildings with a negative air biofilter have high capital and operational costs due to the physical infrastructure cost, ongoing maintenance of the biofilter and ongoing energy cost of running the biofilter fan 24 hours a day, seven days a week, 365 days a year.  

ASP’s that are not enclosed in a tunnel or building such as positive air, negative air, or reversing air require at a minimum a roof structure to provide clear separation from stormwater from leachate and have high capital costs of the roof and ongoing operational costs similar to tunnels and building with biofilters. 

Scott says an exception to this is the SG Advanced Composting Technology System which uses the GORE Cover to eliminate the need for tunnels, buildings, roofs, and biofilters, thereby lowering both the capital and ongoing operational costs.

Another critical aspect is the management of stormwater and leachate to prevent potential environmental contamination. 

“It’s important that facility operators understand the strengths and limitations of the options available to separate stormwater and leachate so they can make informed decisions about composting infrastructure that prioritise environmental protection,” Scott says.

A cross-section of an SG/GORE System showing how temperature, oxygen, and moisture are managed through the compost process. Image: Sustainable Generation

Sustainable Generation provides advanced composting technology to help global operations accelerate the natural composting process and make what is best for the environment. The team has experience as owners and operators of organic waste processing facilities and understand the challenges.

When it comes to Aerated Static Pile (ASP) composting, one of the most efficient and cost-effective approaches to organic waste processing, there are several options to separate stormwater and leachate. These include with a biofilter (negative or reversing air), with biolayer cap (positive air), in-building or a tunnel system with biofilter, and GORE Cover.

Tunnel system with biofilter

Tunnel systems are designed and operate according to a different composting approach. The object is not only to degrade the organic material but also to reduce its temperature and thus accelerate the process. 

This is done by continuous high throughput aeration providing convective cooling, driving off moisture and removing the latent heat of evaporation in the vapour. 

Scott says this requires a powerful and costly aeration system, a biofilter or scrubbing system, an irrigation system to replace the water vapour driven off, a process-water collection and recirculating system, a water filtration and/or water treatment system and a sophisticated control system monitoring and operating these activities to achieve the desired composting environment. 

“So, while the tunnel keeps rainwater and stormwater outside, the process water inside is part of a much more expensive system both in its construction and operation.”

ASP with biofilter 

The ASP composting method with a biofilter uses a negative or reversing air system to aerate the compost piles. 

Stormwater is generally managed through a combination of strategies, including proper site design and implementation of drainage systems. However, Scott says the efficiency of leachate separation in this system can vary, as it relies on a separation system or the biofilter’s ability to capture and treat any excess liquid generated during composting. 

The biofilter’s organic material helps to filter out particulates and organic compounds but is not a reliable mechanism to reduce the potential for leachate contamination.

In contrast to the biofilter method, ASP composting with a biolayer cap employs a positive air system to aerate the compost piles. This system generally exhibits better stormwater management due to enhanced aeration and more controlled moisture levels within the compost. 

The positive airflow helps to minimise excess moisture build-up, reducing the likelihood of excess leachate formation. However, the efficacy of leachate separation still relies on the overall design of the composting site and the incorporation of appropriate stormwater drainage measures. 

In-building with biofilter

The in-building system with a biofilter provides an enclosed composting environment that is isolated from all rainfall and external stormwater. Stormwater infiltration is prevented. 

To keep the environment within the building suitable for human entry and mitigate corrosion of metal roofing components, a large and continuously operating biofilter system is required. This is a significant cost. Additionally, regular monitoring and maintenance of the biofilter and air extraction system are crucial to ensure its continued effectiveness. 

“The additional construction cost of the building, along with the added maintenance requirements, typically result in a solution that is much more expensive than the other open ASP composting facility options,” Scott says.

ASP with GORE Cover

Scott says the Sustainable Generation ASP composting system with GORE Cover offers an innovative, and reliable, approach to stormwater and leachate separation. 

The GORE Cover, a breathable membrane that is impermeable to water, prevents rainwater from infiltrating the compost piles while allowing thorough aeration. This characteristic reduces stormwater management requirements and eliminates contact between stormwater and organic material. 

“By containing and controlling moisture levels with efficacy superior to in-tunnel or in-building system, the GORE Cover contributes to a robust stormwater and leachate separation system at reduced costs,” Scott says.

The scoring system: 1 = Can Achieve. 2 = Highly Likely to Achieve. 3 = Definitely Achieve. Image: Sustainable Generation

He says that using a simple, integer-based scoring system that compares three basic sets of standards of composting technology – enhanced stormwater control, effective leachate separation and reduced environmental impact – Sustainable Generation’s Advanced Composting Technology with GORE Cover comes out on top.

“The GORE Cover’s impermeability to liquid water ensures superior stormwater control compared to traditional ASP composting methods. By preventing rainwater from entering the compost piles, it reduces the risk of stormwater runoff carrying nutrients and contaminants into surrounding areas, safeguarding local surface water from pollution,” Scott says.

“Sustainable Generation’s Advanced Composting Technology with GORE Cover can collect leachate and divert it for treatment or reuse during the composting process. This system offers clear separation between stormwater and leachate, contributing to a safer and more environmentally friendly composting process.

“With better stormwater and leachate separation, the system helps minimise the environmental impact of composting operations. By preventing the escape of nutrients and contaminants, it promotes sustainable waste management practices that protect surrounding ecosystems.”

Suitable for all types of feedstock including food waste, green waste, biosolids and source separated organics, the GORE Cover delivers a few other environmental advantages for ASP composting systems.

Volatile organic compounds (VOCs) are emitted as gases from organic and liquid waste and can cause odours. Scott says the GORE Cover can sequester VOCs to meet or exceed local regulations through the reduction of emissions by more than 90 per cent during the initial covered phases of the process. It also helps to maintaining the proper pile temperature to produce Class A or AA compost at 55 degrees Celsius (131oF) or higher for a minimum of three continuous days.

Reusing process water and/or leachate within the system helps maintain optimal levels of moisture and the cover ensures optimum free air space (FAS) in the pile to promote the growth of oxygen-consuming bacteria. Scott says optimal process management shortens the time to  inished compost from several months in windrow composting, to as little as six to eight weeks in the SG/GORE System. 

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