How can STP Plants Implement Greenhouse Gas Capture and Reuse?

As the world seeks solutions to combat climate change and reduce greenhouse gas emissions, an unlikely industry is stepping up with innovative approaches - municipal sewage treatment plants. While these facilities have traditionally been regarded as sources of emissions like carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O), they are now pioneering greenhouse gas capture and utilisation technologies.Sewage treatment processes like anaerobic digestion, sludge dewatering, and effluent treatment naturally release greenhouse gases that would typically be vented or flared into the atmosphere. However, these gases actually represent a potential resource if properly captured and purified. Emerging systems allow treatment plants to reuse greenhouse gas streams for renewable energy production, industrial applications, and even nutrient recovery.

We'll explore the various technologies enabling sewage treatment plant greenhouse gas reuse and the significant economic, environmental, and operational benefits these solutions provide.

Biogas Upgrading to Renewable Natural Gas (RNG)

One of the most widespread greenhouse gas reuse practices at sewage treatment plants revolves around their anaerobic digesters that treat sewage sludge. During anaerobic digestion, microbes break down organic matter and release a constant stream of biogas comprised primarily of methane and carbon dioxide.Rather than simply combusting this biogas in combined heat and power (CHP) systems, many plants are now implementing biogas upgrading equipment to purify the biogas into renewable natural gas (RNG) that meets pipeline quality standards.

Common biogas upgrading technologies include:

• Water/Amine Scrubbing: Scrubbers using water or amine solutions absorb CO₂ and other contaminants to purify the methane stream. 

• Pressure Swing Adsorption: Utilizing cycling pressure changes to preferentially adsorb CO₂ and other gases onto a molecular sieve or activated carbon media.

• Membrane Separation: Employing semi-permeable membranes to separate CO₂ and other gases from methane based on molecular size and diffusion rates.

The resulting RNG stream consists primarily of biomethane with energy content and properties equivalent to conventional natural gas. This RNG can be directly injected into natural gas utility pipelines for distribution as renewable vehicle fuel or heat/power generation. Or it can fuel boilers, turbines and CHP equipment onsite.By monetising biogas as pipeline-quality RNG instead of just combusting it, treatment plants gain a valuable revenue stream while offsetting fossil natural gas usage and preventing greenhouse gas emissions.

Carbon Dioxide Utilization

There are also emerging applications for harvesting and utilizing the carbon dioxide byproduct from anaerobic digestion and biogas upgrading processes at sewage treatment plants.

Carbon Capture and Reuse: CO₂ captured from biogas can be purified and liquefied or solidified into dry ice. These CO₂ products can then be sold for applications like carbonated beverages, greenhouses, water treatment, food processing, and more.

Algae Cultivation: Bubbling the CO₂ stream into algae bioreactors provides the carbon source to cultivate algae crops for biofuels, nutraceuticals, aquaculture feed and other products. Algae cultivation also captures and utilizes the CO₂.

Enhanced Nutrient Recovery: Sewage-derived CO2 can be sparged into wastewater treatment streams to strip out nutrients like phosphorus and nitrogen as stable precipitated solids for beneficial reuse as fertilisers. 

These carbon dioxide utilisation strategies help offset operational costs for treatment plants while deriving value from an abundant greenhouse gas byproduct.

Nitrous Oxide Capture

In addition to the more widespread CO₂ and CH₄ capture efforts, some sewage plants are also starting to address their emissions of nitrous oxide (N2O) - a greenhouse gas almost 300 times more potent than CO₂.N₂O is produced naturally during the nitrogen removal processes of wastewater treatment like nitrification and denitrification. While typical venting levels may seem negligible, the warming impact of these N2O emissions is significant for sewage plants.

These greenhouse gas reuse and mitigation approaches transform sewage treatment plants from emissions sources to emissions solution providers. Key benefits include:

• Revenue generation from RNG, CO2 and other greenhouse gas products

• Operational cost savings from energy recovery, nutrient recovery, etc.

• Reduced carbon footprint and environmental compliance 

• Environmental stewardship and enhanced public image

As carbon taxes, emissions regulations, renewable fuel standards and other climate policies continue advancing, adopting greenhouse gas capture and utilisation allows sewage treatment facilities to get ahead of regulatory and market pressures.

Conclusion:

Municipal sewage plants were once viewed strictly as industrial facilities for basic treatment and discharge of wastewater. However, with rising sustainability goals and the drive toward more resource recovery models, these plants are ideal environments to extract value from waste greenhouse gas streams - including biogas, carbon dioxide, and even nitrous oxide.Capturing and productively reusing these gases creates new economic opportunities for sewage plants through diverse revenue streams from renewable natural gas to industrial CO₂ products and nutrient recovery. At the same time, plants can drastically reduce emissions, environmental impact and operating costs through improved energy efficiency.While widespread implementation of greenhouse gas capture systems is still in relatively early stages, the technologies have been validated at numerous pilot and full-scale installations around the world. As momentum grows, it's clear that these new solutions will be very important in changing sewage treatment plants into places where we can get more resources in a way that's better for the environment.

To explore customised commercial RO plants, Industrial RO plants, ETP or STP solutions for your needs in your areas and nearby regions, contact Netsol Water at:

Phone: +91-965-060-8473, Email: enquiry@netsolwater.com