Pioneering methane reduction: ELOVAC®-P’s role in the water sector’s net zero journey

The global water industry plays a pivotal role in achieving net zero carbon emissions. Wastewater treatment processes are a significant source of greenhouse gases particularly methane, which has a warming potential 84 times greater than carbon dioxide over 20 years.

These processes have historically posed a significant climate challenge but have also become critical focal points for innovation. Technologies that can mitigate these emissions offer an opportunity to accelerate progress toward climate targets.

Thames Water, aiming for carbon neutrality by 2030, recently trialled the ELOVAC®-P vacuum degassing system at Riverside Sewage Treatment Works (STW). Designed to reduce methane emissions, improve sludge dewatering efficiency, and cut operational costs, the 8-week trial demonstrated the system’s potential to transform sludge management.

Background and Goals

The wastewater treatment and bioresource sector contributes significantly to methane emissions, particularly from the anaerobic digestion processes. Although biogas is typically captured for energy recovery, residual methane often escapes during downstream sludge handling post-digestion. This leakage exacerbates greenhouse gas emissions and the carbon footprint of WWTPs with anaerobic digestion. Methane emissions exceeding 4% of total biogas production could negate the environmental benefits of green energy generation and fail to meet the Green Gas Support Scheme (GGSS) compliance criteria.

Riverside STW processes thermally hydrolysed sludge, which is known for its high biogas yield. However, this efficiency also leads to greater entrapped and dissolved methane in the sludge. In addition, the site’s high phosphorus levels contribute to operational challenges such as struvite scaling, inefficient dewatering, and high polymer consumption.

The ELOVAC®-P system, developed by ELIQUO Technologies, was trialled to address these issues. Its dual benefits of capturing both entrapped and dissolved methane aligns with Thames Water’s net zero ambitions and the broader industry’s goals to reduce emissions.

The ELOVAC®-P Technology

The ELOVAC®-P system employs vacuum degassing to remove entrapped and dissolved gas, including methane, from digested sludge. By reducing dissolved gas and microbubbles, it prevents methane emissions during subsequent sludge processing and storage. Additionally, the system doses MgCl₂ to facilitate phosphate precipitation, improving sludge dewatering and reducing struvite formation in downstream equipment.

Implementation at Riverside

The ELOVAC®-P trial at Riverside STW included three key phases:

1. Initial Setup: The system was connected downstream from aerated sludge buffer tanks. While this configuration allowed for an easy start, most methane had already escaped during aeration, limiting capture efficiency.
2. Optimised Configuration: Sludge was redirected directly from the digesters to the ELOVAC® unit, bypassing aeration tanks to maximise methane capture.
3. Cross-Site Validation: In a sophisticated logistics operation Sludge from Crossness STW was processed at ELOVAC in Riverside and transported back for dewatering, allowing performance comparisons between different sludge types and dewatering technologies.

Key Results

1. Methane Capture and Climate Benefits

The ELOVAC®-P system captured an average of 545 litres of gas per cubic meter of sludge, with methane comprising approximately 25%. Over a 20-year timeframe, this represents a reduction of 2,704 metric tons of CO₂ equivalent annually at Riverside. These avoided emissions are equivalent to the annual impact of driving over 62,000 times from Riverside to ELIQUO Hydrok’s facility in Cornwall.

Reducing methane emissions offers an immediate and powerful climate benefit, aligning with global initiatives like the COP26 Global Methane Pledge, which targets a 30% reduction in methane emissions by 2030.

2. Phosphate Precipitation

By combining vacuum degassing with MgCl₂ dosing, the system achieved phosphate removal efficiencies of up to 90%, reducing phosphorus concentrations in sludge to below 50 mg/L. This reduction mitigates struvite scaling and improves sludge dewaterability, enhancing operational reliability.

3. Dewatering Efficiency

ELOVAC®-treated sludge demonstrated clear improvements in dewatering:

• Higher Cake Solids: Treated sludge achieved up to 32% dry solids compared to 24-27% for ‘Un-ELOVAC’d’ sludge.
• Reduced Polymer Use: Polymer requirements dropped by 39%, from 18 kg/TDS to 11 kg/TDS, reducing chemical costs.
• Better Filtrate Quality: Lower suspended solids in filtrate were observed, improving overall sludge handling.
• Reduced Phosphorus Load in Return Liquors: ELOVAC®-P significantly reduced phosphorus (PO₄-P) concentrations in the filtrate, cutting the phosphorus load returned to the head of the treatment works. This alleviates the burden on biological and chemical phosphorus removal processes, lowering treatment costs. For plants with high phosphorus loads, this could lead to savings on chemical dosing, reduced sludge generation, and improved overall performance.

4. Cross-Site Validation

Tests with sludge imported from Crossness STW validated ELOVAC®-P’s benefits across different sludge types and dewatering technologies (Belt press vs Bucher press). The trial demonstrated equally strong results, highlighting the system’s adaptability and reliability in varied settings.

These results not only reinforced the versatility of the ELOVAC®-P system, but also demonstrated its ability to deliver consistent performance improvements at different facilities with varying setups. By confirming its efficacy at multiple sites, the trial highlighted the potential for Thames Water to replicate these benefits across its wider network.

Implications for Net Zero Goals

The ELOVAC®-P trial represents a critical step forward for the water industry’s net zero agenda. By specifically targeting methane, the technology offers a rapid pathway to emissions reductions. Key benefits include:

1. Emission Reductions: Capturing entrapped methane prevents its release into the atmosphere, directly improving the carbon footprint of wastewater treatment processes.
2. Operational Savings: Enhanced dewatering efficiency reduces polymer costs, improves sludge quality, and minimizes maintenance related to struvite scaling.
3. Versatility: The system adapts seamlessly to different sludge types and process configurations, making it a viable option across diverse facilities.

The success at Riverside and Crossness underscores the potential for broader adoption of ELOVAC®-P to meet the water industry’s ambitious climate targets.

Conclusion

As the water sector grapples with its role in mitigating climate change, technologies like ELOVAC®-P offer a clear path to reducing emissions and improving operational sustainability. The Riverside trial demonstrated the system’s ability to capture significant methane volumes, enhance dewatering performance, and cut chemical use, aligning with Thames Water’s goal of achieving carbon neutrality by 2030.

The success of this trial was made possible through the strong collaboration with Thames Water, whose expertise and commitment ensured the tests were conducted under real-world conditions.

Methane’s significant impact on global warming makes its reduction an urgent priority. By incorporating innovative solutions like ELOVAC®-P, the water industry can significantly advance its net zero targets while driving cost-effective and sustainable operations.

In an era where every fraction of a degree in warming matters, embracing these technologies is not just a choice, but a responsibility for the sector.