In collaboration with
De-risking and Deploying a UK-First Soil Steaming Innovation for Invasive-Impacted Brownfield Soil
Shortlisted for Best Research or Application in the Advancement of Science, Technology or Digital Innovation in the Brownfield Sector
1. Introduction and Sector Context
Invasive non-native plant species are a pervasive and increasingly costly constraint across the UK brownfield, infrastructure and utilities sectors. Japanese knotweed (Fallopia japonica) presents a unique combination of biological resilience, regulatory sensitivity, programme disruption and reputational risk. Despite decades of guidance and research, the dominant remediation responses on development sites remain prolonged herbicide-based management, volume reduction through screening with residuals still requiring herbicide or excavation and disposal to landfill.
The fastest and most certain approach (for the site of origin and often necessitated by development programmes) of off-site disposal is increasingly misaligned with modern brownfield objectives. Multi‑year chemical treatment introduces delays and uncertainty into construction programmes and relies on repeated herbicide application within sensitive receiving environments. Excavation and off-site disposal offer immediacy but incur high financial cost, embedded carbon, dependence on diminishing landfill capacity and permanent loss of soil as a recoverable resource. As sustainability expectations increase, these limitations are becoming more acute.
This submission presents a substantive advancement in brownfield science, technology and digital practice: the UK‑first deployment of a mobile, ex‑situ soil steaming solution for invasive‑impacted soils. It demonstrates how GGG identified, de‑risked, independently validated and commercially applied an overseas-proven but UK‑unproven technology, converting invasive species impacted soils from waste liability into certified, reusable materials.
2. Origin of the Innovation
The innovation originated within GGG ID’s wider research programme exploring sustainable applications for residual mineral fractions from soil washing. Initial investigations focused on sterilisation of filter cakes to create growing media, where steam treatment is a recognised agricultural and industrial technique. During this work, GGG ID identified emerging Nordic research demonstrating that controlled ex‑situ soil steaming could destroy invasive plant propagules, including knotweed rhizomes.
While compelling, this research and associated technology did not appear to have been applied within UK brownfield practice. The concept was unfamiliar to regulators and clients, and no UK case studies existed. GGG ID recognised a strategic opportunity: if the technology could be validated under UK conditions and integrated into brownfield delivery models, it could bridge the gap between slow chemical control and rapid carbon‑intensive disposal.
Importantly, this was not a low‑risk adoption exercise. The technology required significant capital investment, operator training, process adaptation and regulatory engagement. GGG ID therefore formalised the workstream into an Innovation Plan, aligned with Welsh Government* policy on landfill reduction, circular economy and net zero ambitions, and committed over £600,000 of capital expenditure to progress the innovation from concept to live deployment. *Whilst Welsh Government Innovation Specialists were supportive of the project and innovation plan, the technology adoption was self-funded by GGG as potential funding options did not match the timing of the opportunity.
3. Technology Overview: Mobile Ex‑Situ Soil Steaming using SoilSaver Technology
The selected system, the Soilsteam SoilSaver 20™, is a purpose‑built mobile soil‑steaming plant designed for treatment of excavated soils, substrates and sludges. The process applies controlled steam heat directly to the soil matrix within an enclosed system, raising temperatures sufficiently to denature plant tissues and destroy viable propagules without the use of chemical additives.
Although soil steaming has been used in agriculture since the nineteenth century, the SoilSaver system represents a modern engineering reinterpretation of a proven physical principle, specifically adapted for large scale infrastructure and brownfield use.
Scientific basis; Steam has a uniquely high energy density and heat transfer capability. When injected into soil, wet steam rapidly transfers thermal energy through pore spaces, raising soil temperature and denaturing plant tissues. Academic research has demonstrated that invasive plant seeds and rhizomes are highly sensitive to short duration exposure at elevated temperatures, with mortality governed by the interaction between peak temperature and exposure duration, rather than prolonged heating alone.
Unlike chemical treatments, steam has no residual effects. Once the soil cools, it can be immediately reused, avoiding the long waiting periods often associated with fumigants or herbicide programmes.
Machine design and operation; The SoilSaver system is a mobile, continuous feed ex situ treatment unit. Excavated soils are introduced via a feed hopper and conveyed into an enclosed rotating treatment chamber. Steam is injected to raise soil temperatures uniformly, while mechanical agitation ensures consistent exposure across all particles. Key technical features include; continuous feed operation, throughput of up to 30 tonnes per hour, enclosed treatment chambers and integration with standard earthmoving plant. Unlike in‑situ thermal techniques, ex‑situ processing ensures direct thermal exposure of rhizomes embedded within soil aggregates, addressing historical challenges associated with uneven heat distribution. An illustration of the machine is presented below.
Digital quality assurance; A critical differentiator is the system’s cloud-linked digital monitoring. Temperature and throughput data are continuously logged during operation, creating a robust audit trail. This provides objective evidence of treatment performance, supporting regulatory confidence, defensible reuse decisions, and alignment with materials management plans.
In contrast to traditional invasive species remediation — which often relies on prescriptive assumptions rather than measured outcomes — soil steaming introduces a verifiable, data-driven process, consistent with requirements in modern brownfield practice.
4. Independent Pilot Study and Scientific Validation
The deployment of mobile soil steaming in the UK was deliberately preceded by an independently designed and executed validation study, commissioned with Advanced Invasives Ltd, led by Dr Daniel Jones. Dr Jones is one of the UK’s leading invasive plant specialists, with over a decade of peer reviewed academic research and long term field trials informing UK guidance on Japanese knotweed management. The objective of the study was the evaluation of the Soilsteam SoilSaver 20™ system and confirm the lethality of ex situ soil steaming against viable knotweed rhizomes.
Trial design and methodology; The trial was undertaken at GGG’s Cwmgwili Recycling Facility under controlled field conditions. Healthy, untreated Japanese knotweed plants were collected (from the site), and
rhizome material was prepared into sections of approximately 50 mm length and variable diameter (10–40 mm). Each rhizome section contained one or more viable buds (apical meristems), representing a conservative test of survival potential.
Eighty rhizome sections, shown in the plate to the right, were prepared in total and divided equally between treated and untreated control samples. All samples were embedded within uncontaminated topsoil to replicate bulk soil conditions encountered during development works, rather than testing isolated plant material.
The SoilSaver system, shown above, was operated by GGG staff following commissioning and training by Soilsteam and under the supervision of Advanced Invasives. Prior to treatment, a full decontamination run using clean soil was undertaken, ensuring no risk of cross contamination. Treated soil was retained in piles for 24 hours post processing to allow residual thermal exposure, consistent with anticipated field operations.
Results and interpretation; Post treatment, soils were conditioned to promote emergence, with rhizome sections placed at shallow depth and monitored over time. Assessments were undertaken at 23 days and 46 days after treatment (DAT). Untreated control soils produced 32 emergent Japanese knotweed plants at 23 DAT and 35 emergent plants at 46 DAT, confirming high rhizome viability and the robustness of the experimental design. In contrast, no emergent growth was observed from any steam treated rhizome sections at either monitoring point.
The independent report concluded that the SoilSaver process demonstrated effective destruction of Japanese knotweed rhizomes within bulk soil matrices. Importantly, the findings align closely with a substantial body of peer reviewed research from the Norwegian Institute of Bioeconomy Research (NIBIO) and associated universities. This prior research had demonstrated near complete mortality of invasive plant propagules at soil temperatures in the range of 75–98°C with short exposure durations, including for rhizomatous species closely related to Japanese knotweed (such as Reynoutria bohemica).
The treated and control soils were retained on site and are illustrated in plates below taken 6 months after steam treatment. Untreated soil is shown to the left and treated soils in right hand plate.
This validation bridges a critical gap between controlled academic research and real-world brownfield application, providing UK specific evidence that ex situ steaming could reliably destroy invasive propagules without chemicals and without reliance on extended treatment times.
5. Transition from Research to Full‑Scale Application
The next challenge was proving that the technology could operate reliably at infrastructure scale, under real programme, health and safety and commercial constraints. At this stage GGG started to search for imminent or active projects with Japanese knotweed impact within the client base and the first opportunity arose through Morgan Sindall (MS) Infrastructure who were delivering works at Dŵr Cymru Welsh Water’s Trebanos wastewater treatment site.
This project represents the first full-scale UK application of mobile soil steaming for invasive species remediation within a regulated construction setting.
Site context and constraints; South Wales is recognised as a hotspot for Japanese knotweed infestation. At Trebanos, construction of new process infrastructure required the removal of a substantial soil bund within the treatment works. Detailed surveys identified approximately 6,292 tonnes of material, of which an estimated 35–40% was impacted by Japanese knotweed and Himalayan balsam.
Integration of soil steaming into the remediation strategy; the project already had an approved knotweed management strategy with segregation, burial and spraying but being proactive on innovative technologies MS re-designed the works and a proportion of the overall management strategy was allocated for treatment using mobile soil steaming. GGG ID worked collaboratively with Morgan Sindall to design the logistics, sequencing and verification approach suitable for a fully operational site.
Approximately 1,780 m³ of impacted soil were treated onsite using the SoilSaver system. Japanese knotweed impacted soils were carefully excavated and transferred directly to the SoilSaver unit, minimising handling and preventing secondary spread.
Soil and stone fractions below 60 mm were processed through the SoilSaver unit at a minimum verified soil temperature of ~74°C, ensuring lethal exposure across the treated matrix. Oversized materials were segregated and sent for appropriate recycling routes, maintaining a circular management approach.
Quantified outcomes; In total, approximately 1,780 m³ of invasive impacted soil was treated on site. All treated material was verified as free of viable invasive propagules and subsequently reused within the project for landscaping and earthworks. Following delivery, the project attracted interest from Welsh Government representatives, who visited the site to understand the technology and its potential wider application within Wales’ circular economy and net zero objectives.
9. Conclusion - Leadership, Risk and Industry Impact
Through independent research, technological adaptation, digital verification and full‑scale application, GGG has delivered a genuine advancement in UK brownfield science, technology and digital practice. The project demonstrates how invasive‑impacted soils can be transitioned from waste to resource, providing the sector with a sustainable, defensible alternative to landfill and long‑term chemical management aligned with circular economy and net zero objectives. This materially improves how brownfield risks are managed, how soils are valued, and how sustainability outcomes are delivered within constrained programmes.
GGG role extended beyond technology adoption into market creation, taking on first‑mover risk by investing capital, commissioning independent science, engaging regulators and integrating the process into live delivery. This leadership bridged the gap between academic research and UK brownfield implementation and directly enabled the UK brownfield sector to access a proven but previously unavailable solution.
The innovation demonstrates broad potential impact and transferability and while the Trebanos case study focused on Japanese knotweed, the platform is applicable across brownfield redevelopment, infrastructure, utilities and land restoration projects where other invasive flora or biological contaminants/ pathogens constrain progress. Its scalability, digital verification and chemical free operation position it as a genuinely transformative option for future brownfield delivery.