How Can STP Plants Maximize Biogas Production and Energy Recovery?
Sewage treatment plant is an energy-intensive process, but it also presents an opportunity to recover valuable biogas resources that can offset energy costs. Many sewage treatment plants are taking steps to optimise their anaerobic digesters to produce more biogas that can be used for renewable energy generation on-site. Maximising biogas production and energy recovery offers economic and environmental benefits.
We'll explore strategies sewage treatment plants can use to get the most out of their biogas systems.
Pretreatment for Improving Biogas Potential
One of the most effective ways to increase biogas production is by pretreating the sludge to make it more bioavailable before sending it to the anaerobic digesters. Various pretreatment methods help break down complex organic matter into simpler compounds that are easier for microorganisms to convert into methane biogas.
Thermal Hydrolysis: Heating the sludge to high temperatures (around 160°C) combined with rapid decompression causes cell lysis, solubilising organic matter. This thermal hydrolysis process has been shown to increase biogas yields by 50% or more.
Microwave Pretreatment: Exposing sludge to microwave irradiation can achieve similar solubilisation effects as thermal hydrolysis using less energy.
Ultrasonic Pretreatment: Ultrasonication generates cavitation bubbles that collapse violently, disrupting sludge particles and increasing their bioavailability.
Mechanical Pretreatment: Technologies like high-pressure homogenisation shear sludge disrupt cells and improve biodegradability.
Optimising Anaerobic Digester Performance
In addition to pretreatment, maintaining optimal operating conditions and digester mixing is critical for maximising biogas yields from the anaerobic digestion of sewage sludge.
Temperature Control: Maintaining the proper temperature range (around 35-37°C for mesophilic or 50-57°C for thermophilic) ensures peak metabolic activity of methanogenic microbes.
pH Monitoring and Adjustment: Holding digester pH between 6.8 - 7.2 maintains an ideal environment for methanogens while preventing inhibition from acidic conditions.
Balanced C:N Ratios: Monitoring the carbon to nitrogen ratio (typically 20:1 to 30:1) and adjusting feedstock to achieve this balance maximises biogas production.
Proper Mixing: Adequate mixing of digesters prevents stratification, ensures even distribution of microbes/substrates, and prevents the buildup of potentially toxic compounds.
New Digester Designs: Anaerobic membrane bioreactors, up-flow anaerobic sludge blanket digesters, and other emerging digester configurations aim to improve biogas yields while minimising footprint.
Co-Digestion of Other Organic Wastes
Many sewage treatment plants are pursuing co-digestion by combining sewage sludge with other organic waste streams in their anaerobic digesters. The complementary mix of substrates can significantly boost biogas production compared to digesting sewage alone. Common co-digestion feedstocks include:
Food Wastes: Food processing residuals, fats/oils/grease from restaurants, spoiled food from grocery stores, etc.
Agricultural Residues: Crop residues from farms, herbaceous energy crops, manures from livestock operations, etc.
Organic Fraction of Municipal Solid Waste (OFMSW)
Fats, Oils and Grease (FOG) from grease traps
Appropriate co-digestion ratios and feedstock preparation must be established to maintain the proper nutritional balance and prevent inhibition from compounds like ammonia or sulfides.
Upgrading and Utilizing Biogas
Once produced, sewage-derived biogas (comprising 55-65% methane) can either be combusted in combined heat and power (CHP) engines and boilers to generate electricity and heat or upgraded to renewable natural gas (RNG).
CHP Systems: On-site CHP taking advantage of the heat allows sewage treatment facilities to reduce energy costs and improve overall energy efficiency compared to grid electricity and natural gas usage.
Biogas Upgrading: Using technologies like amine/water scrubbing, pressure swing adsorption or membrane separation, raw biogas can be purified into pipeline-quality biomethane that meets standards for injection into natural gas pipelines or used as vehicle fuel.
Conclusion:
By implementing strategies to maximise biogas production, from sludge pretreatment to optimised digester operation and co-digestion, sewage treatment plants can dramatically boost their renewable energy generation from biogas. With continued innovation, these biogas energy recovery systems will play an increasingly important role in the future of energy-positive wastewater treatment infrastructure.
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
