Separating useful fiber from contaminants has historically been a persistent operational bottleneck for institutions in the paper sector, and it’s through such prevalent problems that intuitive solutions have emerged.

What Counts as Contamination in Secondary Fiber

Contamination covers anything that isn’t usable cellulose fiber. A major offender here is plastic. Film wrap, shrink wrap and plastic-coated packaging often slip through single-stream collection systems. Wet or moisture-damaged packaging is another issue, since soggy paper mats together and resist proper pulping, often creating the ideal environment for mold growth.

Metals, such as staples and paper clips, also end up in a mixed bale, damaging screening equipment. Food residue, particularly grease from takeout containers, interferes with the pulping chemistry in ways that are hard to reverse once fiber is already in the slurry.

Recovered fiber degrades every time it’s processed, resulting in a loss of structural integrity and bonding capacity through a natural mechanical breakdown called hornification.

Paper fibers can typically only be recycled between five and seven times before their structural quality falls below what’s usable for papermaking. Contamination accelerates that clock by degrading and weakening the fiber structures and forcing mills to run harsher cleaning cycles, which further stress the fiber and shorten usable life.

Why Contamination Costs Mills More Than Time

Given the inevitability of contamination in paper recycling, mills typically tolerate a certain amount of it as a cost of doing business. However, there’s a threshold beyond which the economics become unreasonable. Foreign materials, such as wet-strength additives or plastic films, can jam or wear down pulpers, screens and cleaners, leading to unplanned downtime and expensive repairs.

Firms that process every grade of secondary fiber, from mixed paper to bleached board grades, exist largely because mills need dependable, pre-screened sources. This specialized service involves an intuitive process of collecting secondary fiber, chopping and baling it, before reselling it to paper mills. Such provisions reduce the need for mills to clean raw curbside material themselves.

Quality issues also travel downstream in ways that are hard to fix later. Components like ink residues and mineral fillers left behind by coatings affect the strength and printability of the finished sheet. A mill running high-value grades such as printing paper can’t absorb much of this variability before product quality deteriorates and customers start rejecting shipments. That’s part of why contamination is treated as a direct line item on a mill’s cost sheet, affecting yield loss, energy use, institutional reputation and equipment maintenance considerations.

Catching Contaminants Before They Reach the Pulper

Recycling facilities rely on a layered approach to catching contamination before fibers reach the mill. Optical sorters can help identify and eject plastics and other non-paper materials from a moving belt. Magnets and eddy current separators pull out ferrous and nonferrous metals. Screens and trommels remove larger debris by size, while manual quality control stations still play a role, especially for catching irregular contaminants that automated systems can miss.

Even with all of that in place, one category of contaminants remains difficult to remove entirely. The industry term for this categorization is stickies, representing coatings, adhesive residues and tacky polymer fragments that survive pulping. Mill-collected wastepaper typically contains only 3% to 5% stickies by weight, while material pulled from residential collection runs closer to 15%.

The smallest of these are known as microstickies, and they make up the bulk of the problem, being notoriously difficult to filter out because conventional screening is built to catch larger particles. Once stickies deposit on the machine felt and rollers, they cause sheet defects and runnability problems that ripple through the entire production line.

Keeping Contamination Out From the Start

While sorting technology has become highly advanced, it is inherently limited. One of the most practical ways to manage contamination is to prevent it before it ever enters the collection stream, which means education and protocols matter as much as equipment. Waste generators, whether a retailer or a household recycling bin, benefit from clear guidance on what belongs in paper recycling and what doesn’t. Considering that every ton of paper recycled saves an estimated 17 trees, such efforts have a tangible impact on the environment.

On the facility side, protocols for bale inspection and rejection thresholds give recycling operations leverage to push quality upstream. Facilities can also track contamination rates by supplier and communicate problems directly, giving waste generators clearer feedback on what needs to change.

This is reminiscent of a challenge familiar to anyone managing feedstock or anaerobic digestion, where contamination from film plastics or nonorganic material in a seemingly clean organic stream can cause similarly disproportionate downstream damage relative to its volume.

Source variability is also important. Recovered fiber quality varies with the origin material itself, rather than with contamination alone.

Research on secondary fibers derived from fibreboard manufacturing residues and post-consumer wood waste shows that fiber properties can vary by source. This reinforces the idea that contamination management should not be separated from a clear understanding of the feedstock’s origin. The same logic applies broadly across recycling industries. It’s always important to know where material comes from, as it’s a first step toward truly understanding what’s likely to be wrong with it.

The Immense Environmental Value of Secondary Fiber

Contamination management in paper recycling is foundational to whether secondary fiber can compete with virgin pulp on cost and quality. The industry has gotten reasonably good at catching contaminants after the fact, but the more durable gains come from reducing what enters the stream in the first place.

Paper recycling offers a useful case study of the operational discipline required to turn waste into a dependable resource. It represents both the significant strides the recycling sector has made and what still needs to be done.

The post Contamination in Paper Recycling: Identifying, Managing and Minimizing Quality Issues first appeared on BioEnergy Consult.

Understanding Landfill Gas and RNG

Landfill gas (LFG) is produced through the natural decomposition of organic materials such as food scraps, paper products, yard waste and other biodegradable materials. A typical landfill gas stream contains approximately 50% to 55% methane and 45% to 50% carbon dioxide.

While methane is a valuable energy source, it is also a potent greenhouse gas with a significantly higher warming potential than carbon dioxide over a shorter time horizon. In fact, one-third of the food produced globally reaches the landfill instead of the consumer’s table, creating about 8% of total global greenhouse emissions.

As such, capturing and utilizing methane before it escapes into the atmosphere offers substantial environmental benefits. LFG is converted to renewable natural gas (RNG) by removing carbon dioxide and other contaminants, resulting in a methane-rich fuel that meets pipeline quality standards. Once upgraded, RNG can be injected into existing natural gas infrastructure and used for heating, electricity generation, industrial processes or transportation.

Unlike conventional natural gas extracted from fossil reserves, RNG originates from renewable waste streams, making it an attractive option for organizations seeking lower-carbon energy solutions. In fact, forecasts indicate that LFG-to-RNG production could reach 2.2 billion cubic feet per day (bcfd) by 2050 — up from 0.3 bcfd today.

Why Upgrading Matters

Although landfill gas contains methane, it cannot be directly injected into natural gas pipelines in its raw form. Utilities maintain strict gas quality specifications to ensure pipeline safety, equipment compatibility, and reliable performance.

To meet these standards, landfill gas must undergo a series of treatment and upgrading steps. The process typically begins with contaminant removal, including moisture, particulates, sulfur compounds and siloxanes. After pretreatment, advanced upgrading systems separate methane from carbon dioxide and other remaining gases.

The result is a high-purity methane product that closely resembles conventional natural gas. This transformation is what allows landfill-derived gas to become a marketable renewable fuel rather than simply a waste by-product. RNG can be used in place of fossil natural gas, as pipeline-quality gas, compressed natural gas or liquefied natural gas, with about 20% of operating LFG energy projects creating RNG.

Membrane Separation

A widely adopted upgrading technology is membrane separation. This approach uses specially engineered membranes that selectively allow certain gas molecules — particularly carbon dioxide — to pass through while retaining methane.

As landfill gas passes through multiple membrane stages, the methane concentration steadily increases until it reaches 98% purity, producing biomethane that meets strict pipeline standards. Modern membrane systems offer several advantages that have accelerated their commercial adoption.

First, they feature relatively compact footprints, making them suitable for landfills with space constraints. Second, modular system designs allow operators to expand capacity as gas production grows. Third, membrane technologies generally require fewer moving parts than some alternative systems, reducing maintenance requirements and operational complexity.

Continuous improvements in membrane materials have also increased methane recovery rates and system efficiency, making the technology increasingly attractive for large-scale RNG projects.

Pressure Swing Adsorption

Pressure swing adsorption (PSA) is another established technology helping drive RNG commercialization. PSA systems use adsorbent materials that selectively capture carbon dioxide and other unwanted gases under high pressure.

The process operates in cycles. During the adsorption phase, contaminants adhere to the adsorbent material while methane continues through the system. When the adsorbent reaches capacity, pressure is reduced, releasing the captured gases and regenerating the material for reuse.

PSA technology has gained popularity for its ability to achieve high methane purity while maintaining reliable performance across varying gas compositions. Landfill gas quality can fluctuate depending on factors such as waste composition, weather conditions and landfill age. While PSA systems can often accommodate these variations effectively, making them suitable for many RNG applications.

The Economics of Commercial Scale

Historically, RNG projects faced challenges related to equipment costs, methane recovery efficiency, and operational complexity. As such, many landfill operators found it difficult to justify the investment required for gas upgrading systems. However, several factors have changed that equation.

Technology costs have gradually declined as equipment manufacturers gain experience and production volumes increase. At the same time, system performance has improved, enabling greater methane recovery and more reliable operation. In fact, in 2023, biomass accounted for about 5% of the U.S.’s total energy consumption, showing its growing role in the renewable energy sector.

There is also a growing demand for low-carbon fuels, which has strengthened project economics. Utilities, transportation fleets and industrial users are increasingly seeking renewable fuel alternatives to support emissions reduction commitments. Regulatory programs and renewable fuel incentives in various markets further enhance revenue opportunities for RNG producers.

Additionally, landfill operators are recognize that RNG production can transform an environmental liability into a long-term revenue-generating asset. Rather than simply flaring excess gas, operators can monetize captured methane while supporting sustainability objectives.

The Environmental Benefits Beyond Energy Production

The environmental value of landfill RNG extends beyond replacing fossil fuels, as methane capture itself delivers substantial climate benefits.

Landfills are the third-largest human-generated source of methane emissions in the United States, releasing an estimated 100.9 million metric tons of carbon dioxide equivalent to the atmosphere in 2022 alone. Capturing it before it enters the atmosphere can significantly reduce the overall climate impact of waste management operations.

Additionally, producing RNG also supports circular economy principles by extracting value from materials that would otherwise be discarded. Organic waste effectively becomes a feedstock for renewable energy production, extending the usefulness of resources that have reached the end of their original life cycle.

Lastly, because RNG can utilize existing natural gas infrastructure, it provides a practical pathway for decarbonization without requiring extensive new distribution networks. This compatibility allows renewable fuel adoption to scale more rapidly than some alternative energy solutions.

Looking Ahead

The RNG industry is entering a period of accelerated growth. Advances in membrane separation and pressure swing adsorption technologies have significantly improved project feasibility, enabling landfill operators to produce pipeline-quality gas at larger scales than ever before.

As climate policies become more ambitious and demand for renewable fuels continues to rise, landfill gas is increasingly being recognize as a valuable energy resource rather than a waste by-product. As such, RNG represents a compelling combination of waste management, renewable energy and emissions reduction, that turns landfill gas into a reliable source of renewable energy for years to come.

The post Landfill Gas to Pipeline-Quality RNG: How Upgrading Technologies Are Finally Commercializing at Scale first appeared on BioEnergy Consult.