Landfill & Remediation

Landfill is the one sector where the gas you are detecting is also the product you are selling. Methane is a fire and explosion risk, an asphyxiation risk, a reportable greenhouse emission and a revenue stream, depending on which part of the site you are standing in.

Most of what follows comes from work our Technical Consultants have done on Australian landfill, biogas and waste sites.

Four Processes, Similar Gases, Different Problems

Organic decomposition produces broadly the same gas mix wherever it happens. What changes is the concentration, the containment and who is exposed.

Anaerobic digestion breaks down organic material using microorganisms in the absence of oxygen. Methane, carbon dioxide, hydrogen sulphide, ammonia and volatile organic compounds all accumulate, bringing explosion, asphyxiation, toxicity and respiratory irritation together in one process.

Landfill gas recovery collects what decomposing waste produces naturally, primarily methane and carbon dioxide. Methane brings the explosion risk and high carbon dioxide brings asphyxiation, particularly in low lying areas and enclosed spaces where it settles.

Sewage sludge digestion produces the same gases through the same mechanism, with hydrogen sulphide more prominent.

Biogas upgrading converts raw biogas into biomethane pure enough to inject into a natural gas pipeline or use as vehicle fuel. Pressure swing adsorption and membrane separation both operate at pressure, so methane leaks here are an explosion risk in a plant rather than a diffuse emission across a site.

Typical coverage runs fixed detection at 0 to 100 percent LEL for methane, with carbon dioxide to 5 percent by volume, oxygen to 25 percent, hydrogen sulphide and volatile organics, reporting to a controller with audible and visual alarms. Portable instruments cover spot checks, maintenance and confined space work. Temperature, humidity and dust are the environmental challenges rather than anything exotic.

The Hydrogen Sulphide Problem

Bio waste facilities produce hydrogen sulphide at concentrations that most gas detection is not built to measure.

On a large animal effluent site, waste is directed into outdoor storage that resembles dug out reservoirs holding black rubber pillows the size of football fields. The effluent decomposes through digestion, similar to microbial fermentation, using the sun as a natural heat source, and the resulting gas inflates them. The two main products are usable methane at up to 100 percent by volume and unusable hydrogen sulphide at 2,000 to 6,000 parts per million. Gas pressure in the pillows drives the mixture through pipelines to a scrubber that separates the two.

A standard portable hydrogen sulphide sensor tops out around 100 ppm. In a 6,000 ppm atmosphere it over-ranges immediately and tells you nothing about whether a space has cleared. This is the same problem as phosphine in grain fumigation: the instrument that protects the person is not the instrument that assesses the space.

Sustained exposure at those concentrations also poisons sensors, and cross sensitivity between the gases present compounds it. Practically that means a shorter sensor life than a datasheet suggests, more frequent bump testing, and where sampling is used, stainless steel accessories and attention to the sample and return path. Corrosion affects the equipment as well as the infrastructure.

There is one further hazard on these sites that is easy to miss. Spent absorption pellets from the scrubbing process can undergo a chemical reaction generating enough heat to start a fire, so the fire risk is not confined to the methane.

Certification is typically intrinsically safe for portables, with flameproof fixed detection for Zone 1 and Zone 2.

Borehole And Perimeter Monitoring

Remediation and landfill aftercare bring a different problem: monitoring points that are remote, unmanned and required to report for years.

Perimeter boreholes around a landfill or a contaminated site track gas migration into surrounding ground and adjacent property, which is both a safety question and a liability one. The practical constraints are that there is no power, no network cabling and often nobody on site.

A BW RigRat fitted with a borehole insertion probe addresses that. Readings for gas, pressure and temperature are recorded in real time with GPS location linked to mapping, and data is time and date stamped and retained on a portal for up to two years, with the reporting pages configurable to what a particular site has to demonstrate. A solar power option removes the mains requirement entirely.

Two years of continuous time stamped data is the part that matters for an aftercare obligation. Reconstructing a monitoring history from spot readings taken monthly is considerably harder than downloading it.

Where multiple points need covering across a large site, wireless fixed detection avoids cabling to each one, and open path detection covers a boundary line rather than a series of points. Methane is lighter than air, which suits open path well, since the beam can be mounted above obstructions in the path of a rising plume.

Methane Is Also Revenue

Worth stating because it changes who inside an organisation cares about the measurement.

Many large Australian landfills capture methane rich landfill gas and use its energy value, usually by combustion to generate electricity sold to the grid. Beyond the energy, landfill gas capture projects can earn Australian Carbon Credit Units under the ACCU Scheme, administered by the Clean Energy Regulator, using a dedicated method for reducing methane emissions from landfill gas.

That makes methane measurement a commercial function as well as a safety one, and it means the accuracy and traceability of the measurement is of interest to the finance side of the business as well as the safety side. Where a monitoring programme has to support a credit claim, calibration records stop being a compliance formality.

Composting And Organics Processing

Composting facilities present the acute end of the same chemistry, because material is processed in enclosed volumes rather than spread across a site.

In-vessel systems, composting tunnels, pits and the areas beneath piles all concentrate oxygen depletion and hydrogen sulphide, and the risk peaks during turning and movement when trapped gas is released. Detection is needed both on the people doing that work and fixed at the spaces they enter.

Composting is also a licensed activity in its own right in some jurisdictions, so the monitoring may be a licence condition rather than only a safety control.

Confined Space

Digesters, tanks, pits, wet wells, culverts and access chambers are confined spaces, and this sector has a lot of them.

Entry requires pre-entry testing and continuous monitoring during occupancy, and there is a specific problem with catalytic bead LEL sensors that anyone doing this work should know about, covered on our confined space page.

Storm water and drainage assets deserve a particular mention. They are assumed to contain decomposition gases, and they frequently contain something else entirely, since fuel spillages, dumped chemicals and solvents, fertilisers and factory waste all find their way into drainage networks. The flammable risk there is routinely underestimated.

Who Regulates It

This sector answers to three separate frameworks, which is more than any other industry we supply.

Environmental licensing is the first and it is state based. In Western Australia landfill operations are licensed by the Department of Water and Environmental Regulation, with licence conditions covering monitoring and annual environmental reporting. In New South Wales the EPA is the primary environmental regulator, issuing Environment Protection Licences under the Protection of the Environment Operations Act and setting climate change requirements for landfill licensees. In Queensland landfill and composting are Environmentally Relevant Activities requiring approval under the Environmental Protection Act 1994.

Worker safety is the second, and falls under general work health and safety law. The regulator is WorkSafe WA, SafeWork NSW or Workplace Health and Safety Queensland depending on location.

Emissions and carbon are the third. Landfill methane is reported under the National Greenhouse and Energy Reporting scheme, and gas capture projects are administered by the Clean Energy Regulator under the ACCU Scheme.

Standards relevant to detection include AS 2865:2009 for confined space entry and AS/NZS 60079.29.2 for gas detector selection, installation, use and maintenance.

What Gastech Supplies

Fixed gas detection for digesters, gas holders, upgrading plant, pump stations, scrubbers and enclosed processing areas, in flameproof form for classified areas.

Wireless fixed detection and open path detection for large sites, boundaries and points where cabling is impractical.

Area monitors including borehole configurations with solar power and long term data logging for perimeter and aftercare monitoring.

Portable multi-gas and single gas instruments for spot checks, confined space entry and maintenance work.

Controllers with the relay capacity to drive ventilation, isolation and alarms.

Behind them sit project engineering, NATA calibration and service, field service, fleet management and hire, from WA, NSW and QLD.

If you are setting up perimeter monitoring, or dealing with hydrogen sulphide at concentrations your instruments cannot read, talk to our Technical Consultants.